Physicians' understanding of radiation risks: a systematic review
Radiation exposure during CT examinations continues to be a much discussed topic in the medical
literature. An important element in the attempt to limit the population's exposure is awareness of
risks among prescribing physicians. On this topic, numerous studies have been carried out in
different geographical and clinical settings. Researchers from Mainz and Bremen conducted a
systematic review of the literature to get an overall picture of physicians' knowledge in this area
[
1].
The authors searched PubMed and seven other literature databases for papers describing
surveys of healthcare personnel for their knowledge of radiation issues. Papers were scored
subjectively for quality, considering study group size, response rate, reproducibility,
completeness of the methods, and absence of selection bias and interview effects.
The literature search identified 14 studies that had surveyed between 68 and 313 physicians.
Two were published in the period 1996-1997, while the remaining 12 were published between 2004 and
2009. Six had “very good” quality (the highest level possible), five were “good” and 3 were “weak”;
none was rated as “flawed”. The response rates ranged from 20% to 96%, although 4 papers failed to
indicate the percentage of invited persons who actually provided answers, an essential piece of
information for reporting surveys. All 14 studies asked participants to estimate radiation doses
for different types of imaging examinations, but the actual questions varied widely and thus made
meta-analysis impossible; nonetheless, certain trends emerged. Overall, a minority of physicians
was able to correctly state the radiation dose of plain chest radiography or chest CT; there was a
tendency to underestimate rather than overestimate. Surprisingly, up to about one-quarter of
participants thought incorrectly that ultrasonography and magnetic resonance imaging also exposed
patients to ionizing radiation. The surveys revealed a generally low rate of physicians who
discussed radiation exposure and related risks with their patients. No aspect of education,
specialization, years of service or work environment seemed to influence their knowledge of the
health effects of radiation, except for the fact of having attended a course on radiation
protection.
The study pointed out a low level of knowledge about radiation exposure from imaging
examinations, although the small sample sizes of these surveys makes generalization difficult. It
also revealed a lack of research into temporal trends in physicians' knowledge, as only 2 of 14
studies were conducted in the same population in different years; follow-up studies would reveal if
radiation awareness is growing as a result of greater media attention to this issue. The authors
stressed that simply testing physicians' ability to estimate radiation dose does not provide
insight into their prescribing practices; future studies should also characterize physicians'
decisions to refer patients for these examinations, to see if the referrals are medically
justified.
Selected literature update
Imaging osteoporosis: recent literature
Two papers recently added to MDCT.net's literature database examined the use of X-ray imaging
methods, including MDCT, in the clinical setting of osteoporosis.
Authors from Greece, Italy, the UK and USA reviewed standard and state-of-the-art techniques
for assessing bone quantity and structure and for diagnosing low-energy bone fractures typical of
osteoporotic subjects [
1]. They discussed vertebral fracture assessment by dual-energy X-ray
absorptiometry (DXA), which provides data on bone mineral density (BMD) with a low radiation dose
(<0.03 mSv). With quantitative CT, inclusion of a bone phantom scanned with the patient permits
the conversion of CT data into BMD values; this can be done using either single-slice scanners to
produce two-dimensional images or MDCT scanners for volumetric images, for hip, spine or
appendicular bones. Characterization of trabecular bone and monitoring of its changes during
treatment for osteoporosis require high-resolution CT. The quantitative MDCT and high-resolution CT
methods deliver effective radiation doses up to 3 mSv. The authors commented that low dose
protocols are required even for bone imaging applications.
Researchers from China and the USA tested the ability of 16-slice quantitative MDCT to
provide useful information on bone mineral content and density as well as on bone volume and
strength in a group of 237 hospitalized elderly women [
2]. The women were divided into three groups according to their bone status
as revealed by DXA: normal, osteoporotic, or osteoporotic with atraumatic vertebral fractures. For
10 of 12 MDCT parameters considered, ANOVA showed significant differences in bone quality among the
three groups, although significance was reported only according to cutoffs and not with precise p
values. The authors concluded that quantitative MDCT can discriminate among women with and without
osteoporotic vertebral fractures.
MDCT of the spine: a review in
Insights into Imaging
A technical review of spinal CT has recently been published in the new journal
Insights into Imaging [
1]. The first section of the review focuses on patient positioning, scanning
parameters and radiation exposure. Typical settings are summarized for cervical spine and
thoracic-lumbar spine, depending on the type of CT scanner. The second section, dedicated to data
elaboration, begins by attempting to clarify differences in meaning between the terms “image
reconstruction” and “image reformating” and then describes common display options. The last section
discusses clinical uses of spinal CT, often in comparison to spinal MRI. Approaches to reducing
radiation exposure and artifacts from metal implants are also discussed.
The Asian Society of Cardiovascular Imaging (ASCI) was founded in 2006 in Seoul, Korea, by a
group of radiologists representing 10 Asian nations. ASCI is an independent non-profit association
that aims to promote knowledge, research and teaching in the field of cardiovascular imaging across
Asia. Since its establishment, the association has organized annual conferences in Seoul,
Singapore, Tokyo and Taipei, with over 1000 delegates attending the most recent meeting; the
society will meet again in June 2011 in Hong Kong. Although ASCI does not yet produce its own
research journal, it has organized the publication of special issues focusing on Asian research in
the
International Journal of Cardiovascular Imaging. In particular, the December supplement
included ASCI appropriateness criteria for cardiac imaging, an ASCI standardized practice protocol,
and ASCI contrast media guidelines, all prepared by the association's CCT and CMR Guideline Working
Group.
TIn the first December issue of
JAMA, University of Toronto physicians Baerlocher and Detsky argued for the need to obtain
informed consent for procedures involving ionizing radiation. They expressed concern that, despite
attention to the greatly increased use of medical imaging – not all of which is necessary, there
remains a lack of awareness of radiation risk among both healthcare operators and patients.
Approaches to reduce radiation exposure have been developed on all fronts: industry (e.g. dose
reduction technology), government (national data registries), and the medical profession (Image
Gently campaign). But, they argued, one “critical component” is lacking, namely the “mandatory
dissemination of radiation risk information to patients”.
The commentary pointed out issues that the medical community should resolve before mandating
informed consent for radiation exposure: Should the responsibility for obtaining informed consent
lie with the ordering physician or the radiologist? What is the exposure threshold for a
significant risk? If radiation risk is discussed, will patients deny needed examinations? In
closing, the authors suggested that such a form of self-regulation will help the medical community
not only meet its professional duty towards patients but also curb the number of clinically
unnecessary imaging examinations.
Selected literature update
Latest research on CT colonography
Two papers reported new research on CT colonography. Both were published in the October issue of
Abdominal Imaging.
Researchers from Saitama, Japan began with the observation that the diagnostic accuracy of CT
colonography has been calculated thus far using optical colonoscopy as reference test, despite the
fact that colonoscopy can lead to misdiagnoses, especially for small polyps. They therefore
compared both tests to a true gold standard, namely analysis of surgical specimens. Over a 5-year
period, 152 patients had both tests within a 1-month period prior to surgical resection of a 20-cm
colorectal segment. In 40 specimens, besides the main tumor there were additional polyps: 16 of the
specimens came from patients in whom colonoscopy was incomplete due to tumoral obstruction, while
for the remaining 24 specimens (47 polyps) both tests were completed. Considering these 47 lesions,
CT colonography had an 81% sensitivity and a 90% positive predictive value; these values for
colonoscopy were 66% and 100%, respectively. Higher values were obtained for both techniques when
the analysis was limited to the 22 lesions >5 mm. The authors concluded that CT colonography is
not inferior to colonoscopy. Moreover, they suggested that earlier accuracy data for CT
colonography were underestimated due to an improper choice of reference test.
The second study, contributed by researchers from Pisa, compared the radiation exposure from a
CT colonography screening examination (in 20 adults) to that from double-contrast barium enema (in
15 adults) [
2]. Mean effective doses were 2.17 mSv for CT colonography and 4.12 mSv for
barium enema; this almost 2-fold difference was significant. The authors concluded that CT
colonography can be considered a definite substitute for barium enema.
Vasospasm diagnosis by CT angiography or CT perfusion: a meta-analysis
The diagnosis of cerebral vasospasm, a potentially fatal complication of aneurysmal subarachnoid
hemorrhage, usually involves transcranial Doppler ultrasonography and digital subtraction
angiography (DSA). In the past 10 years, several studies have investigated the use of either CT
angiography or CT perfusion to diagnose vasospasm. Researchers from New York and Munich analyzed
the diagnostic performances of these two techniques, each compared to DSA, in a meta-analysis
recently published in the
American Journal of Neuroradiology [
1].
The researchers searched the English language literature for original studies that compared one
of the CT methods to DSA in patients with subarachnoid hemorrhage; all CT scanner configurations
were included. They identified 10 studies on CT angiography and 10 on CT perfusion, but several of
these did not report appropriate data for inclusion in the meta-analysis. Therefore, statistical
analysis was done on 6 CT angiography studies (representing a total of 141 patients and 1936
arterial segments) and on 3 CT perfusion studies (64 patients).
Methodological quality of the studies was assessed using the QUADAS checklist [
2], which investigates aspects of study design (including sample size), test
execution and interpretation (looking for various forms of bias), and study limitations (such as
withdrawals). Although the published meta-analysis did not report quality scores, the authors found
numerous studies with disease-progression bias (i.e. the interval between the two tests was too
long) and review bias (i.e. reviewers who interpreted the results of one test were not blinded to
the results of the other).
Analysis of pooled data, for the few studies for which this was possible, indicated that CT
angiography had a specificity of 93.1% and a sensitivity of 79.6%; accuracy estimated from the area
under the SROC curve was 98.0%. CT perfusion had a specificity of 93.0%, a sensitivity of 74.1% and
an accuracy of 97.0%. However, considering the few patients included in the CT perfusion studies,
these latter results are preliminary. The authors concluded that the imaging modalities have high
diagnostic accuracy, which makes them “potentially valuable” in the clinical workup of patients
with aneurysmal subarachnoid hemorrhage. However, as the studies tended to be small and inadequate
- both methodologically and in terms of reporting, the authors called for higher quality research
on this topic. In particular, they stressed that researcher-authors adhere to the guideline
Standards for the Reporting of Diagnostic Accuracy Studies (STARD, www.stard-statement.org).
Researchers planning such studies should also be familiar with QUADAS, so they will know in advance
how their work will be methodologically scored.
CONFIRM: a data registry to help improve the evidence base for coronary CT
angiography
Earlier this year, the American College of Cardiology Foundation published an expert consensus
document on coronary CT angiography for patients with coronary artery disease (CAD); reviewed in
June on MDCT.net. As the
authors noted in their preamble [
1], they were limited to preparing an expert statement because of
insufficient evidence for a rigorous clinical practice guideline.
Criticism of the evidence base for coronary CT angiography was felt strongly by the
international radiological community. In response, 12 radiological centers came together to produce
a large database to support statistically powerful studies. The resulting registry, called Coronary
CT Angiography Evaluation for Clinical Outcomes International Multicenter (CONFIRM), contains data
from published studies on 27 000 patients followed on average for 2 years. Principal investigator
of the project is James Min from Weill Medical College; he is also President-Elect of the Society
of Cardiovascular Computed Tomography (SCCT). Participating centers are at 3 European universities
(Erlangen, Munich, Zurich), Yonsei University in South Korea, Ottawa Heart Institute in Canada, and
7 public and private institutions across the United States.
The first study based on a preliminary CONFIRM dataset, presented earlier this year at the SCCT
meeting, examined the prognostic value of 64-slice coronary CT angiography. Five additional studies
were presented at the American Heart Association's 2010 Scientific Sessions. These studies
investigated: use of the Diamond-Forrester classification to estimate obstructive CAD (abstract no.
12100); use of the Framingham risk score to predict stenosis (no. 12152); prognostic methods for
scoring CAD (no. 12199); all-cause mortality (no. 14571); and mortality in the diabetic population
(no. 14581). Until these studies are published in peer-reviewed journals, readers can consult the
abstracts (with graphs) by searching the abstract numbers at
http://circ.ahajournals.org/content/vol122/21_MeetingAbstracts/.
The 96
th annual scientific meeting of the Radiological Society of North America (RSNA) will
open on 28 November, as always, in Chicago. Technological advances and new clinical applications of
MDCT will be the focus of discussion in about 250 sessions during the 6-day event. In an
RSNA News issue [ 1 ] dedicated to the upcoming meeting, many MDCT topics were
highlighted as newsworthy by chairpersons of the scientific program and educational exhibits
subcommittees, representing 16 areas of medicine. Here below are some of the state-of-the-art MDCT
topics to be presented at this year's meeting.
In the area of cardiac radiology, the primary hot topic will be the development of dose- and
noise-reduction algorithms for CT angiography, as well as the use of CT in the study of arterial
plaques and lesions. Also in chest radiology will there be great attention to methods of radiation
dose reduction, especially by iterative reconstruction. New this year in chest radiology are
presentations on the use of dual-energy CT for functional pulmonary (ventilation) imaging as well
as CT-guided ablation of lung tumors. For emergency medicine, the key imaging topic will be
controlling radiation exposure while optimizing the diagnostic yield of CT procedures, in
particular regarding CT pulmonary angiography. In the area of medical physics, a new method called
time-of-flight CT angiography will be presented, while educational sessions will focus on radiation
dose management. Other topics highlighted by subcommittee chairpersons include cone beam breast CT,
dual-energy CT for detecting renal stones, and enteric CT for the study of pancreatobiliary
diseases.
Selected literature update
Interpreting patterns of pulmonary abnormalities on MDCT
Two new retrospective studies that shed light on the relationship between the pattern of
pulmonary abnormalities seen with MDCT and the severity of lung disease have been added to the full
text literature database of MDCT.net.
Researchers in Taiwan [ 1 ] looked for patterns of pulmonary lesions that could predict
which patients with tuberculosis would test positive for acid-fast bacili in sputum. They were
motivated by the fact that microbiological tests took too long, delaying the decision to place
these highly infectious individuals in isolation. Clinical and imaging findings were reviewed for
124 patients with active tuberculosis, of which 84 had positive results on smear tests for
acid-fast bacilli. Results from 64-slice MDCT revealed that smear-positive patients tended to have
clusters of nodules, cavitation, and consolidation in multiple lobes, whereas smear-negative
patients more often had centrilobar nodules. Using multiple regression, the authors developed a
model to predict clinical status from imaging findings. This tool may help triage patients with
newly diagnosed tuberculosis and consequently reduce the incidence of nosocomial infections.
Radiologists from the United States [ 2 ] sought evidence for their hypothesis that small, peripheral
pulmonary emboli are normal findings without clinical significance. They reviewed clinical and
imaging records for 50 adults with pulmonary embolism diagnosed on the basis of 16- or 64-slice
contrast-enhanced MDCT findings. Based on the size and location of low-attenuation areas in the
pulmonary vasculature, the patients were distinguished into two groups: 33 had large clots in
central pulmonary arteries, while 17 had small, dot-like filling defects in peripheral arteries.
Deep vein thrombosis was subsequently diagnosed in 58% of the patients with clots but in none of
the patients with “dots”. The authors argued that small peripheral emboli may be physiological
findings not associated with a risk of lower extremity clots, and called for further research in
this area to determine which patients require anticoagulation treatment and which can safely go
untreated.
ACR guidance regarding incidental findings on abdominal CT
Since the US National Library of Medicine introduced the medical subject heading (MeSH) term “
incidental finding” in 2003, there has been a steady growth in the number of reports on “
unanticipated information discovered in the course of testing or medical care”. This phenomenon is
particularly obvious in papers on computed tomography, especially in the last few years concomitant
with advances in MDCT technology. Incidental findings may be fortunate discoveries permitting the
early diagnosis of developing disease, but most often they represent benign structures which, after
additional tests, are found to lack clinical significance.
Recognizing that unexpected diagnostic information poses deontological and practical
challenges to radiologists and referring physicians, the American College of Radiology (ACR)
established the Incidental Findings Committee in 2006. Composed of 17 mostly academic radiologists
working in the US, the committee set three primary objectives: to establish a consensus on
identifying incidental findings in the abdomen, to develop approaches for the clinical work-up of
affected patients, and to understand how these findings are influenced by CT scanning parameters,
such as radiation dosage and use of contrast medium. The results of their efforts have recently
been published as an ACR white paper in the
Journal of the American College of Radiology [ 1 ].
An ACR white paper differs from a practice guideline in that it does not represent official
policy nor has it been developed with a formal consensus-building method. Instead, it represents “
collective experience” and aims to provide “general guidance”. To this aim, the document was
structured into four sections representing the main abdominal organ systems, namely kidney, liver,
adrenal glands and pancreas. Each section begins with a literature review describing common lesions
in each organ system and then discusses how to detect, characterize and clinically manage each
tumor type. Of particular value in the white paper are flow charts describing the work-up of
incidental findings in each organ system, considering factors such as size, morphology, growth
pattern and clinical findings. A final section addresses the problem of incidental findings seen
with low-dose, unenhanced CT scanning, such as that used for CT colonography (this topic was
specifically addressed in 2009 [ 2 ] by Berland, lead author on the ACR white paper and chairman
of the Incidental Findings Committee). The authors hope that this new white paper will facilitate
consistent reporting on incidental findings and stimulate research in this area, which will assist
the committee in its long-term goal of developing evidence-based guidelines.
A wiki, from the Hawaiian word for quick, is a website that uses particular software to
facilitate collaborative creation and editing of web pages. While the largest and most known wiki
is Wikipaedia, a general encyclopedia, specialist wikis also exist. Of interest for radiologists is
Radiopaedia.org, a wiki created in 2005 by Australian radiologist Frank Gaillard that has grown
into an international educational resource written by and for radiologists. In the wiki spirit, any
one can register and become a collaborator. However, to guarantee quality and guide content
development, Radiopaedia has a board of editors who oversee different subject areas such as
pediatrics and musculoskeletal radiology (openings for other section editors are still available).
Resources offered by the site include a radiology encyclopedia, cases, quizzes and iPad/iPhone
apps. One limit to this online resource is that content is organized by organ system and medical
category, but not by imaging modality.
MDCT angiography for carotid artery stenosis: cost-effectiveness analysis
Several imaging modalities can be used in the diagnosis of carotid artery stenosis. The choice
among them depends on their effectiveness, regarding both clinical outcomes and costs. Studies that
compare the different diagnostic approaches, using data from real-world practice, fall into the
realm of comparative effectiveness research (CER) [ 1 ]. For diagnosing carotid artery stenosis, several CER studies
have been been conducted in the past 15 years, but none has considered today's state-of-the-art
modalities, especially MDCT angiography.
Researchers in The Netherlands therefore evaluated and compared MDCT angiography, contrast–e
nhanced MR angiography and duplex ultrasonography (DUS), singly or in combination. Two definitions
of a positive test result – 50% and 70% stenosis – were adopted, for a total of 12 imaging
strategies evaluated. Decision-analytical software was used to elaborate data from a meta-analysis
published in 2006, additional published reports, and a cross-sectional diagnostic study conducted
ad hoc. In the diagnostic study, 351 consecutive patients with transient ischemic attack or minor
stroke were assessed for stenosis by DUS followed by MDCT angiography (scanner configuration not
indicated); patients with >50% stenosis had digital subtraction angiography for further work-up
and were treated, when necessary, with carotid endarterectomy. A decision tree permitted evaluation
of short-term diagnostic yield while a Markov model assessed long-term outcomes regarding treatment
decisions, patients' quality of life and health care costs.
To determine cost-effectiveness, the researchers calculated the net health benefit (NHB) of
each imaging strategy. NHB was defined as the difference between the clinical benefits (measured in
quality-adjusted life-years [QALYs] gained) and the cost ratio (total costs divided by a
predetermined value of society's “willingness to pay” [WTP] per QALY). Thus, the formula was NHB =
QALY – (costs/WTP), and the most cost-effective modality had the largest NHB.
The modelling showed that QALYs varied slightly among the 12 imaging strategies, from 14.30
to 14.39 for men and from 16.34 to 16.46 for women. Costs varied more, from €39 500 to €42 500 for
men and from €46 000 to €49 500 for women. In both genders, DUS alone was least beneficial and most
costly, while MDCT angiography (alone or with DUS) had the best profile. A combined imaging
strategy of DUS plus MDCT angiography with a 70% stenosis threshold was the most cost-effective for
both men and women, assuming a willingness to pay (WTP) of €50 000. If WTP were €80 000, MDCT
angiography alone would be most cost-effective for men (no change for women). However, MDCT
angiography alone with a 50% stenosis threshold was the best strategy for patients at greater risk
and for those in whom the interval between symptoms onset and treatment is brief. The authors noted
that these results show how the diagnostic strategy can be adapted to the expected benefits of
treatment.
Selected literature update
MDCT as preoperative support in cases of abdominal adenocarcinoma: new research
The value of MDCT in the preoperative assessment of patients with critical abdominal disease has
been addressed by two papers recently added to MDCT.net's fulltext literature database.
Researchers from Bari retrospectively reviewed data from 27 patients with adenocarcinoma of
the colon who had 16-slice contrast-enhanced MDCT in the emergency evaluation of suspected bowel
occlusion. They aimed to understand if preoperative MDCT findings could predict the postoperative
prognosis for this life-threatening condition. MDCT images permitted measurement of the colonic
diameter, determination of the obstruction site, definition of the intestinal contents (air or
fluid), identification of an air-fluid interface, and diagnosis of pneumatosis intestinalis. A poor
prognosis was associated with pneumatosis intestinalis, a colonic diameter ≥10 cm or the presence
of an air-fluid interface; prognosis was better when the intestine contained either air or fluid
but not both. The study was published in
La Radiologia Medica [ 1 ].
Researchers from Pisa reported on 64 patients with ductal adenocarcinoma of the pancreatic
head who had contrast-enhanced MDCT presurgically. The scope of the study was to determine if CT
permitted an accurate diagnosis of tumoral infiltration of the retroperitoneal fat, needed
information for planning the extent of resection. Using histological analysis for the definitive
diagnosis, the researchers found a sensitivity of 80% and a specificity of 84% for the CT
identification of infiltration. The study was published in
Abdominal Imaging [ 2 ].
The September issue of Insights into Imaging, the new journal of the European Society of
Radiology, is now online. Computed tomography is addressed in this issue in two pictorial reviews.
The first review offers 27 multipanel figures to discuss clinical applications of cardiac CT [ 1 ]. The paper focuses on CT angiography – especially for the
evaluation of suspected coronary artery disease in symptomatic patients – but also touches on some
non-coronary applications such as perfusion imaging. Approaches for reducing radiation exposure are
also discussed.
The second paper is instead dedicated to pulmonary lesions that have high attenuation on
chest CT [ 2 ]. A classification scheme for these lesions is proposed,
based on the pattern and distribution of the CT findings. Five main categories of pulmonary lesions
are defined and illustrated: small hyperdense nodules, large calcified nodules, lesions generating
linear or reticular patterns, lesions causing lung consolidation, and extraparenchymal lesions.
New nano-CT technology for high-resolution 3D bone imaging
While current CT technology is based on the measurement of X-ray beam attenuation, a new method
that also considers beam diffraction promises to permit 3D bone imaging with nanometer resolution.
Researchers in Germany and Switzerland invented a novel nano-CT technology that uses a coherent
diffractive imaging technique called ptychography, already employed in electron microscopy. They
developed an image reconstruction algorithm that elaborates both attenuation and phase shift data
and creates high-resolution phase-contrast CT images. As reported in Nature [ 1 ], the nano-CT system can reveal the microstructure of bones
and precisely measure bone density. It is expected that this technology will help advance research
on bone diseases like osteoporosis, for its ability to detect structural changes on the nanoscale.
CT colonography for cancer screening: insight into the CMS-Medicare decision against
coverage
In 2009, the US Centers for Medicare and Medicaid Services (CMS) decided against covering costs
for colorectal cancer screening by CT colonography. This meant that it will not pay outpatient
clinics for performing this test on persons with Medicare, the national medical insurance for the
elderly. CMS's decision-making process had been guided by the Cochrane-Holland framework for
evaluating screening methods (which considers simplicity, acceptability, accuracy, cost, precision,
sensitivity and specificity), together with the impact on health outcomes. As detailed in a “
decision memo” [ 1 ], the CMS found that the “evidence [was] inadequate to
conclude that CT colonography is an appropriate colorectal cancer screening test”. The evidence
supporting this decision, including independent and ad hoc commissioned technology assessments,
practice guidelines, consensus statements and public comments, is summarized in the memo.
One of the technology assessments commissioned by the CMS was a study to identify the
threshold cost below which CT colonography could be considered cost-effective to currently covered
tests, namely fecal occult blood test, sigmoidoscopy and colonoscopy (although barium enema is also
covered, it was not included in the study). The study was done by the Cancer Intervention and
Surveillance Modeling Network (CISNET), involving researchers across the US and in The Netherlands.
Although research findings were available to the CMS last year, only this month has the study been
published in the Journal of the National Cancer Institute [ 2 ].
Briefly, the newly published study used three different microsimulation models to describe
the risk of colorectal cancer in the Medicare population and to assess the impact of screening; all
three models used standardized data regarding each test's accuracy, complications profile and
costs. The researchers evaluated the life-time costs and health effects (both risks and benefits)
of each method, assuming that the screening population undergoes programmed testing from age 65 to
80 years with full compliance. They found that CT colonography every 5 years would afford 143-178
life-years gained per 1000 persons (depending on the simulation model), similar to that gained with
5-yearly sigmoidoscopy plus annual fecal testing but less than that of 10-yearly colonoscopy
(affording 152-185 life-years). To be cost-effective, CT colonography would have to be billed at US
$108-$205, a price less than half of that estimated from abdominopelvic CT examinations. This
threshold cost would increase, however, if CT colonography improved compliance, but so far these
data are lacking.
As noted in the accompanying editorial [ 3 ] by Harris, a former member of the US Preventive Services
Task Force, this cost-effectiveness study is an important contribution to the colorectal cancer
screening debate. At the same time, it illustrates the uncertainties in our understanding of the
benefits and harms of both CT colonography and colonoscopy, and leaves one hoping for the emergence
of a new technology that is simpler, safer and cheaper.
Among the articles made available to MDCT.net users this month are two new and widely diverse
studies pertinent to colorectal cancer screening.
Pickhardt et al. [ 1 ] focused on the positive predictive value (PPV) of CT
colonography. As they noted, in a screening program, it is not possible to calculate sensitivity
and specificity, since only positive results are further evaluated with second-line tests. Thus,
important “quality metrics” for screening programs are the false-positive rate and PPV. To
illustrate how this is done, they retrospectively evaluated data from over 5000 adults who had CT
colonography for screening purposes; 639 persons were found to have at least one polyp ≥6 mm, and
479 of them (with 739 lesions) chose to have colonoscopy for follow-up. Colonoscopy confirmed 677
lesions, giving an overall per-lesion PPV of 91.6% and a per-patient PPV of 92.3%. Similarly high
rates were obtained for small and large lesions and for sessile, pedunculated and mass-like
lesions, but flat lesions had a PPV of 77.7%. The authors compared their excellent single-center
results with published data and discussed how this type of analysis can be used for quality
assessment.
In a completely different approach, Imaeda and colleagues [ 2 ] developed a tool to help patients understand the
characteristics of colorectal screening tests and to choose the test that best matches their
personal needs. They used the maximum differences scaling method to help patients prioritize their
concerns about the advantages and disadvantages of fecal occult blood testing, sigmoidoscopy,
colonoscopy, CT colonography and colon capsule endoscopy. In a pilot study, 92 adults ranked
sensitivity, risk of colonic perforation, and need for a second test to remove polyps as the most
important attributes to consider when choosing a screening method. They then expressed their
preference for a screening method, choosing colonoscopy in 62% of cases (mostly for its reported
sensitivity) and CT colonography in 10%. The authors suggested that this tool will facilitate
shared, informed decision-making involving patients and their physicians.
Automatic exposure control: one cause of accidental radiation overdose
One year after cases of accidental radiation overexposure during CT examinations were reported
in the United States, still the scientific literature lacks a clear explanation of the causes. For
this reason, a recent article in the New York Times [ 1 ] may be interesting to radiologists and clinicians who wish
to avoid similar errors.
Through interviews with patients, hospital staff and state officials, investigative
journalists uncovered a complex story of multiple human errors due to poor judgement and unskilled
use of CT scanners. For example, technicians made mistakes due to inadequate training and, at one
hospital, excessive doses were intentionally used to get better images. Another worrisome cause was
attributed to improper use of the automatic exposure control (AEC) feature during brain perfusion
CT, resulting in up to 8-times more radiation than necessary. Although one of the manufacturers, GE
Healthcare, told reporters that AEC had limited value for perfusion CT, staff at two California
hospitals were unaware that this feature would actually raise radiation dose when used with certain
scanner settings. These serious medical errors can be avoided by better training, standardized dose
reporting, and implementation of additional safety features on scanners.
Pediatric chest and heart imaging: a course in Florence
The European Society of Paediatric Radiology will hold its 19th “European course” this coming
November in Florence, Italy. The course, in English, will be directed by Claudio Fonda, head of the
pediatric radiology department at Meyer Children's Hospital of Florence. The 3-day event will
address both fetal and child pathologies, and will discuss applications of plain radiography, MDCT,
ultrasonography and MRI. The program offers numerous lectures in chest and lung imaging followed by
a panel discussion, additional lectures in cardiac imaging, short workshops, manufacturers'
symposia, and a social dinner. The course is to be accredited as a continuing medical education
event by the European Union of Medical Specialists. A detailed program and registration information
are available at the course's website,
www.aimgroup.it/2010/ecpr/index.html.
Recently published in
Clinical Radiology, a journal of the UK Royal College of Radiologists, is a contribution
by the International Collaboration for CT Colonography Standards [
1 ]. The group comprises 28 radiologists and radiographers based
primarily in the UK and Canada, but with single members representing Europe, Australasia, Korea and
Japan. Working since mid-2008, this group assessed the scientific evidence on CT colonography and
reported their findings and recommendations in a set of standards, approved by all parties in
January 2010. The Canadian Association of Radiologists has made these recommendations publicly
available [
2 ].
The detailed 44-page paper deals with all possible aspects of running a CT colonography
service, from informing patients about the procedure and choosing scanner settings to interpreting
images and monitoring the performance of the CT colonography team. An interesting feature of the
document is that, for each of the dozen different sections, descriptive text is accompanied by a
list of performance standards—both those minimally accepted and those considered “best practice”.
An added value is found in the appendices, two of which consist of information sheets for patients
that can be adapted for use by any medical center. In particular, one appendix provides general
procedural information in simple terms while another gives detailed instructions on bowel
preparation with tagging. Adaptation of this second tool for use in non-Anglophone countries will
require localization regarding commonly available foods for a low-residue diet.
References
Burling D.; International Collaboration for CT Colonography Standards (2010) CT colonography standards. Clin Radiol 65(6):474-480
Safety of imaging debated in leading general medical journals
This summer, numerous editorials and commentaries have appeared in specialist and general
medical journals alike on the safe and appropriate use of medical imaging procedures involving
ionizing radiation. Many of these articles refer to radiological practices in the USA, where
hundreds of cases of accidental radiation overdose during CT have been reported.
In a “perspective” published in the
New England Journal of Medicine [
1 ], Smith-Bindman from the University of California at San Francisco
criticized the lack of a nation-wide body to monitor patients' radiation exposure as well as the
absence of guidelines as to what doses “are reasonable or achievable” for various CT examinations.
Acknowledging the great clinical value of CT (as well as its risks), she offered four strategies
for guaranteeing CT safety: lower the radiation dose associated with each type of examination,
monitor actual exposures, educate referring physicians and radiological technicians about dose
control, and reduce the number of referrals for CT.
Similar issues were raised by Brenner and Hricak, based in New York and writing on the pages
of
JAMA [
2 ]. Noting the paradox in which occupational exposure to ionizing
radiation is strictly regulated but medical exposure is not, these authors contemplated the
advantages of governmental legislation to ensure quality and safety. Currently, in the USA,
standardized, coast-to-coast use of X-ray machines has only been implemented for mammography
(whereas across Europe a single 1997 EU directive regulates medical radiation exposure). Federal
rules could establish parameters for quality control, guide educational programs for physicians who
prescribe radiographic studies, and provide decision-making tools to help abate the problem of
overprescribed CT examinations. The authors nonetheless acknowledged that legislating on clinical
practice is a delicate issue that must be done with care and sensitivity to the continual advances
in the medical evidence-base.
Selected literature update
Cardiothoracic MDCT: two new books from Springer
Springer recently published two books on cardiothoracic CT.
The first volume, called
Integrated Cardiothoracic Imaging with MDCT, was edited by Martine Rémy-Jardin and Jacques
Rémy. Published in 2009, the book is an international effort with contributions from across Europe,
North America and China. This book integrates knowledge from two distinct fields, namely thoracic
radiology and cardiac radiology. It considers heart-lung interplay in physiological and
pathological situations and discusses imaging applications and findings when cardiac pathology has
thoracic complications, and vice versa. Selected for MDCT.net's literature archive are the chapters
on technological issues.
The second volume,
Cardiac CT Imaging, will be available in print later this year. Now in its second edition,
the book was edited by Matthew J. Budoff and Jerold S. Shinbane and contains contributions from
radiologists working in the USA and Germany. It addresses CT assessment of coronary calcium, CT
angiography of the coronaries, great vessels and peripheral vasculature, the use of CT angiography
to study heart pathology, and the integration of CT with other imaging and interventional
procedures for cardiovascular disease. Of the two chapters in MDCT.net, one describes technical
aspects of CT scanners relative to cardiac imaging and the other reviews radiation dosimetry and
current protocols for dose reduction.
by V. Matarese
A new International Society for Computed Tomography
After years of success as an annual CME event, the International Symposium on Multidetector Row
CT has now grown into a distinct professional association. The decision to separate from its
sponsor, Stanford University, reflects both the need for an independent organization, due to the
size and complexity of the meeting, and the current climate in the US against industry sponsorship
of medical education.
The new association, called International Society for Computed Tomography (ISCT), represents
the first medical society dedicated to this imaging modality in all its clinical aspects. ISCT is
guided by the course's directors, namely Geoffry Rubin and Gary Glazer, both at Stanford University
in Palo Alto, USA, and Maximilian Reiser from Ludwig-Maximilians University in Munich, Germany. It
will continue to hold the International Symposium each year in California and will also begin
running a similar biannual program in Garmisch, Germany, called Internationales Symposium
Mehrschicht CT, previously sponsored by the Institute for Clinical Radiology, University of Munich.
Information about these programs is available at
www.isct.org.org.
Expert statement on coronary CT angiography from eight North American medical and
radiological societies
tIn the past several years, coronary CT angiography has been the subject of numerous systematic
reviews and expert statements but, given the rapid advances in technology and clinical insight in
this field, new overviews are always welcome. This month, three journals –
Circulation [
1 ],
Journal of the American College of Cardiology, and Catheterization and Cardiovascular
Interventions – jointly published an expert consensus document written by a task force of the
American College of Cardiology Foundation (ACCF) and sponsored by the American Heart Association
(AHA) and six other, mostly American societies of radiology and cardiovascular medicine.
As indicated in the preamble of the text, expert consensus statements are prepared when
there is not enough evidence for writing a clinical practice guideline according to the rigorous
ACCF-AHA criteria. This new statement was prepared by a panel of experts representing the
eight societies involved; additional members of these societies served as peer reviewers before the
text was approved in November 2009.
The document, addressed to practicing physicians, reviews current and developing
applications for coronary CT angiography in patients with diagnosed or suspected coronary artery
disease. The emphasis is on 64-slice MDCT, as earlier CT scanners are inadequate for cardiac
imaging while, for the newest models, there is limited evidence on which to base a consensus. The
36-page document begins with an executive summary, a technological review, and an overview of
fundamental concepts of cardiac imaging. Then follow three sections on clinical applications that
summarize established uses, emerging methods, and applications for which no consensus could be
reached; this latter part deals with extracardiac findings, the use of CT angiography in high-risk
patients, and the “triple-rule out” protocol for emergency room use. The last three sections focus
on safety (radiation and contrast medium), costs, and quality in diagnostic images.
As usual for any ACCF-AHA document, after an abundant list of references we find details of
the corporate and institutional relationships of authors and peer reviewers. Roles such as
consultant, speaker, share holder, expert witness and board member are indicated, as is the receipt
of funding for research.
Contrast-enhanced MDCT in the diagnostic workup of patients with embolic disease
Two single-center studies, recently added to MDCT.net's full text archive, examined the utility
of contrast-enhanced MDCT in diagnosing embolic disease.
Researchers at Malmö University Hospital, Sweden, focused on patients hospitalized for acute
thromboembolic occlusion of the superior mesenteric artery [
1 ]. Of the 67 patients retrospectively studied, 36 had undergone
16-slice MDCT with intravenous administration of contrast medium, 10 had had non-enhanced MDCT, and
21 had no CT examination. Revascularization procedures were performed more frequently in patients
who had contrast-enhanced MDCT, and this was associated with improved survival: the in-hospital
mortality rate in this group was 42%, while it was 90% among patients who had non-enhanced MDCT and
71% among patients who did not have CT. The authors concluded that contrast-enhanced MDCT should be
performed in all patients with acute abdomen to help vascular surgeons prepare adequate treatment.
A study from Seoul National University Bundang Hospital, Korea, focused on patients with
acute ischemic stroke in whom an embolic cause was suspected but not documented [
2 ]. They identified 50 such patients who had also undergone
contrast-enhanced 64-slice cardiac MDCT, and retrospectively examined the prevalence of signs of
atherosclerotic disease in the ascending aorta and aortic arch. Compared to a group of 106 patients
diagnosed with non-embolic stroke, patients with “possibly embolic” stroke had higher rates of
thrombus and ulcerated plaque, had thicker plaque, and were more frequently classified as having
high-risk aortic atherosclerotic disease. The authors concluded that MDCT can reveal cardioembolic
sources in stroke patients and reduce the rate of diagnoses of stroke of undetermined etiology,
thereby facilitating the implementation of specific treatments.
Clinical risks and benefits of cardiac imaging with ionizing radiation: a discussion on the
pages of iJACC
The May 2010 issue of
JACC: Cardiovascular Imaging (iJACC) includes a series of papers that discuss the health
risks from radiation exposure during cardiac CT in light of the clinical benefits provided by this
procedure. The lead paper in the series is a state-of-the-art review on cancer risk, contributed by
Laskey et al. from the US and Germany [
1 ]. The paper explains how low levels of radiation can induce cancer,
according to the linear no-threshold theory, but also stimulate bodily defences against cancer
induction, according to the process of adaptive protection (radiation hormesis). This review is
accompanied by two invited editorials on the risk-benefit balance in cardiac CT and the importance
of proper clinical decision-making [
2, 3 ].
The series is introduced on the “editor's page” by a passionate commentary by ten
cardiologists and radiologists from the US and Germany [
4 ], who point out “critical deficiencies ... in the quality of the
evidence” regarding the use of radiation in cardiac imaging. Shaw and colleagues deplore the “lack
of progress on dose measurement and cancer risk estimation and the lack of standards for evaluating
the risks and benefits of cardiac imaging.” They therefore call for “considerably more research” to
permit the development of new or better methods to measure radiation dose, categorize dose on
scales that correspond to risk and typical exposures during imaging, extrapolate from high- to
low-dose exposures, and estimate cancer risk in particular clinical groups. Research is also needed
to compare the relative effectiveness of ionizing and nonionizing procedures in different clinical
situations. Finally, they recommend the production of new practice guidelines to ensure proper
clinical decision-making as well as websites to educate patients about cardiac CT. Altogether, this
iJACC series stimulates much reflection on current cardiac CT practices and future directions.
Give a Scan: a public database of CT, MR and US images and clinical data, populated by
patients with lung cancer
In a unique step of empowering patients to drive clinical research, the Lung Cancer Alliance
(LCA) launched an online database of lung cancer images and related clinical data, voluntarily
provided by patients themselves. The database, called Give a Scan
(www.giveascan.org) , is
designed to provide researchers with a large dataset useful for retrospective study of lung cancer
screening and staging, treatment evaluation, and development of computer-assisted methods of
diagnosis.
The database will collect anonymized CT, MR and US images and videoclips from patients, who
will be protagonists in terms of deciding to participate, obtaining electronic image data (in DICOM
format) from their healthcare providers, and submitting this material and other clinical data to
the LCA for online posting. The direct involvement of patients frees researchers from tedious tasks
of data management, simplifies issues related to privacy, and guarantees creation of a
population-wide database not limited to one hospital or clinical subgroup.
The database went live in June 2010 and is just being populated. Researchers can access the
data at no cost, but are asked to acknowledge the source of the data in any resulting publications.
Contrast-induced nephropathy in the emergency room
Latest data from the US indicate that, in 2006, iodinated contrast medium was used 179 thousand
times in patients seen in outpatient and emergency departments, corresponding to about 0.1% of all
ambulatory visits [
1 ]. In this heterogeneous population, the incidence of contrast-induced
nephropathy (CIN) had previously been estimated from retrospective studies involving subgroups of
patients at risk. Therefore, researchers from the USA prospectively assessed CIN incidence and
clinical impact in an unselected urban population seen in the emergency department.
The study, published in the
Clinical Journal of the American Society of Nephrology [
2 ], enrolled 633 adults who received intravenous contrast medium for
64-slice MDCT for any emergency evaluation; patients with known kidney disease and the critically
ill were excluded from study. CIN was defined as an increase in serum creatinine ≥0.5 mg/dl or ≥25%
in the 2-7 days after receiving contrast medium.
CIN developed in 70 cases (11%; 95% CI, 9%-14%) and led to severe renal failure in 6
patients. Renal failure resulted in death in 4 cases, and 2 other patients with CIN also died, for
an all-cause mortality rate of 9%. In contrast, mortality among patients without CIN was 2%.
Compared to the non-CIN group, patients with CIN had higher rates of congestive heart failure,
diabetes and vascular disease but similar rates of baseline renal insufficiency.
The authors concluded that, in an urban emergency room setting, the rate of CIN is higher
than previously estimated. In this relatively young, heterogeneous population, CIN can lead to
severe renal failure and death, even after several days. They expressed concern that, in this
setting, traditional CIN risk factors may not be sufficient for screening patients, who may have
undiagnosed kidney pathology due to untreated diseases such as hypertension and hyperglycemia.
Selected literature update
Focus on pancreatic imaging
In stark contrast to the liver, in which diagnostic imaging has clearly delineated the dual
vasculature and segmental anatomy, the imaging appearance of the pancreas is poorly characterized.
Thus, the Chinese character for pancreas, “organ of remote region or unexplored territory”, aptly
applies to current knowledge of the pancreatic vasculature and lymphatic network [
1 ]. With this comment, Prof. H. Mori of the Department of Radiology,
Oita University (Oita, Japan) opened the Feature Section in the latest issue of
Abdominal Imaging.
The special section comprises seven articles contributed by Mori and colleagues; three
articles involving MDCT technology have been selected for inclusion in the literature archive of
MDCT.net. One study characterized the anatomy of intra- and peripancreatic veins in 42 patients,
using triple-phase 16-slice MDCT [
2 ]. Another used 16- or 32-slice MDCT to characterize peripancreatic
lymphatics in healthy subjects and in patients with pancreatic carcinoma [
3 ]. In healthy persons lymphatics appeared as thin lines contiguous
with the lymph nodes, but in carcinoma patients they were described as tubular, reticular or like a
soft tissue mass. These two imaging studies provide the first CT descriptions of pancreatic veins
and lymphatics and, together with other articles in this issue, make a step forward in defining the
normal and pathological imaging appearances of this organ. This knowledge is essential for an early
diagnosis and accurate staging of pancreatic cancer, to support treatment decisions and to
ultimately reduce the high mortality from this disease.
SharpView CT: a tool for enhancing CT datasets that may facilitate low-radiation
imaging
There is currently great interest in developing effective low-radiation CT imaging protocols.
Since a reduction in X-ray tube current or voltage is accompanied by an increase in noise,
additional steps must be taken to obtain diagnostic-quality images. This might involve, for
example, an increase in the iodine concentration of the contrast medium [
1 ] or the use of image elaboration software after data acquisition.
SharpView CT is one such software tool for image enhancement that may find clinical application in
low-radiation CT.
Produced by SharpView, a company based in Linköping, Sweden, the software SharpView CT is an
independent application that can be installed on any computer and that automatically elaborates CT
images without manual intervention. The software works by applying general operatore process (GOP)
technology. GOP is a 2D adaptive, non-linear filter that eliminates random noise by examining
different-sized areas around each pixel to identify pixels that belong to the structure imaged.
This filtering approach, developed by the Swedish company Context Vision, mimics human vision in
searching for patterns. The software then suppresses noise and enhances edges, thereby improving
image quality.
The first clinical experiences using SharpView CT for low-radiation imaging are now being
published. One retrospective study evaluated the quality of 16-slice abdominal CT images obtained
at high and low current, without and with filtering [
2 ]. SharpView CT substantially reduced noise but gave mixed results in
image quality, suggesting the need for optimization. A prospective study, presented this May at the
American Roentgen Ray Society meeting, found that SharpView CT reduced noise and increased
diagnostic confidence of both low- and standard-dose CT of the abdomen and chest [
3 ]. In the coming future, the radiological literature should offer
additional reports on the possibility of using image enhancement tools like SharpView CT to
facilitate low-radiation CT imaging.
The 110th annual meeting of the radiology society named after the discoverer of X-rays, Nobel
Laureate Wilhelm Röentgen, was held in San Diego last May. The American Roentgen Ray Society
(ARRS), the oldest US radiology society, serves a mission of advancing “medicine through the
science of radiology and its allied sciences”. These goals are reached by publication of the
monthly
American Journal of Roentgenology and its quarterly supplement
AJR Integrative Imaging, as well as through the annual scientific and educational meeting.
The ARRS annual meeting is presented as a CME event comprising a three-day categorical
course, a case-based imaging review course, instructional courses, symposia, scientific
presentations and exhibits. Compared to the large meetings of the European Society of Radiology and
the Radiological Society of North America, this is an intimate meeting hosting 2000 radiologists.
This year's meeting theme was the “appropriate use of imaging in the wide spectrum of diseases”,
emphasizing the evidence base of decision making. Thus, the categorical course theme was “Practical
approaches to common clinical conditions: efficient imaging (PAC3E) – setting the PAC3E of imaging”.
More information about the ARRS and its next annual meeting is available online at
www.arrs.org.
Insights into Imaging (I3), the new journal of the European Society of Radiology (ESR), was
created as a platform for distributing society documents, guidelines and educational reviews. The
first issue of I3 has already mets its editorial objectives with the publication of a trio of
statements signed by the ESR itself.
One paper assessed the changing role of radiology in today's healthcare system and offered
recommendations for the training of radiologists and for the optimization of relationships among
radiologists, clinicians and patients [
1 ]. This descriptive paper was accompanied by a more technical one [
2 ] on the ideal organization of diagnostic imaging and interventional
radiology units; this second paper was based on the arguments already expressed by G.P. Krestin of
the University Medical Center Rotterdam [
3 ]. A third paper continued the thread on the organization of
radiology departments by describing procedures for clinical audit, i.e. internal evaluation of the
quality of care in order to guide efforts for improvement [
4 ].
Other titles published in this first issue include an ESR position paper on ultrasonography
and a joint ESR-European Association of Nuclear Medicine survey on the practice of multimodal
imaging across Europe. Already the first papers for the second issue of
I
3 have been published “ online first” by Springer.
Selected literature update
CT colonography: recent research
The latest issue of
European Radiology contains two research reports on CT colonography protocols and
applications, both selected for inclusion in MDCT.net's full text archive.
Researchers from Sweden investigated differences in image quality achieved with standard and
low-dose imaging protocols [
1 ]. In the study, 48 consecutive patients at risk of colorectal
cancer underwent 64-slice CT colonography with both standard settings (40-160 mA) and automatic
dose modulation (10-50 mA), followed by optical colonoscopy the same day. CT images were viewed in
filet view, in which the colonic turns are virtually unrolled to permit flat viewing of the lumenal
surface. Low-dose images were assessed with and without manipulation of opacity levels to remove “
snow” artifacts. Therefore, for each patient, three sets of images (standard, modified low dose,
original low dose) were scored for noise artifacts and quality. The low-dose protocol achieved a
73% reduction in radiation exposure, but this was accompanied by an equivalent increase in total
image noise. Both sets of low-dose images had more cobblestone and snow artifacts as well as more
irregularly delineated folds, resulting in a significant loss in sensitivity for small polyps (from
82.4% for standard images, to 67.2% and 62.4% for the modified and original low-dose images,
respectively). However, for larger polyps (≥6 mm), the loss in sensitivity was not significant
(from 86.7% to 81.9% and 77.1%, respectively).
In the second report [
2 ], researchers from the United Kingdom investigated the value of CT
colonography in detecting synchronous lesions, i.e. additional colonic lesions in patients already
diagnosed with colorectal cancer. The researchers retrospectively evaluated CT images from 165
patients in whom data from sigmoidoscopy, colonoscopy or histology were also available. Of the 41
synchronous lesions (≥6 mm) identified by the gold standard examination, 33 were found with CT
colonography (per-polyp sensitivity, 80.5%). CT colonography identified 3 additional lesions but
also gave 6 false positives (per-patient specificity, 95.5%). The authors suggested that this
imaging modality could be useful in the pre-operative workup, not only to stage known disease but
also to search for additional lesions that could be simultaneously removed.
Monitoring radiation exposure with an iPhone applet
The population's exposure to ionizing radiation from diagnostic and interventional imaging
procedures has increased over the past few decades, and this has stimulated a recent increase in
interest in monitoring total exposure and understanding the related cancer risk. For this reason,
M.O. Baerlocher, a radiologist at the University of Toronto, and Tidal Pool Software (Victoria,
Canada) developed a novel applet (a software module, or small application) for iPhone and iPod
Touch devices.
The applet, called Radiation Passport, permits patients to record the type and date of every
medical imaging examination they undergo. For each examination, the application assigns a dose of
radiation taken from a database of procedures and typical exposures; the patient can alternatively
insert a custom dose value. The application also estimates cancer risk for individual procedures as
well as for the cumulative exposure. A German language version is available as well.
Radiation Passport is designed to promote awareness among patients about the association
between radiation and cancer risk and to help them decide whether to undergo imaging examinations
proposed by physicians. Access to such detailed information may confuse some patients and lead them
to refuse needed examinations, and radiologists may be frustrated by patients who are armed with
information they do not fully understand. Nonetheless, in the long term, the availability of tools
of this sort should result in greater appreciation of the risks and benefits of medical imaging.
The tool may also help radiologists explain the value of particular procedures to patients.
The developers of Radiation Passport have recently described the radiological and clinical
aspects of their applet in the
Journal of the American College of Radiology. Commercial information is available from
www.tidalpool.ca.
by V. Matarese
Clinical and cost benefits of coronary CT angiography: state of the art review
Last year, the Society of Cardiovascular Computed Tomography published practice guidelines on
performing, interpreting and reporting the results of coronary CT angiography (CTA) (reviewed in
MDCT.news of
May and
June 2009; [
1, 2 ]). Nonetheless, in this new and rapidly expanding field, there
is still debate as to the best clinical use and cost effectiveness of coronary CTA in the diagnosis
of coronary artery disease (CAD). Therefore, Min and colleagues from three US cities reviewed the
literature to assess the clinical and cost benefits of 64-slice CTA in evaluating patients with
suspected CAD [
3 ].
This traditional review, published in the
Journal of the American College of Cardiology, summarized recent studies on the accuracy
of coronary CTA for diagnosing obstructive CAD and myocardial ischemia, its use in the evaluation
of patients with acute chest pain and in the stratification of those with stable pain, and its cost
effectiveness. The authors noted that both opponents and advocates of a wider adoption of this
imaging modality use the same data to support their arguments regarding the diagnostic, prognostic,
economic and safety features of CTA. They concluded by acknowledging the high value of CTA in
detecting or excluding CAD, but state that strong evidence is still needed to define its safety,
cost-benefit relationship, and ability to predict clinical outcomes and to guide treatment
decisions.
Insights into imaging is the latest periodical from the European Society of Radiology
(ESR). This new electronic publication, edited by Robert Hermans (Leuven) and published by Springer
Verlag, was launched in January 2010. The journal, nicknamed I
3, carries the revealing subtitle “education and strategies in European radiology”. Its
scope is to complement the research-oriented
European Radiology by emphasizing the publication of pictorial reviews, best-practice
reports, educational reviews, practice guidelines and policy statements of the ESR. Abstracts of
the 2010 European Congress of Radiology have been published in a supplement to the first issue of
the journal.
Insights into imaging is available through the Springer platform at no cost to ESR members
who access through the
myESR.org user area. Selected papers are also freely available to all
readers on the journal's website (www.i3-journal.org).
by V. Matarese
ACR data registries: auditing tools to promote quality and drive research
The National Radiology Data Registry (NRDR) is a set of databases collecting information on
radiological practices and patient outcomes for imaging facilities across the United States.
Maintained by the American College of Radiology (ACR), these databases are designed to facilitate
auditing of the performance of imaging facilities and of individual radiologists, by comparison
with similar facilities regionally and nationally.
The NRDR portal currently provides password-protected access to 5 registries. The National
Oncologic PET Registry (NOPR) was activated in 2005. In 2009, the ACR launched three additional
registries: the CT Colonography Registry, the General Radiology Improvement Database (GRID), the
National Mammography Database Registry. A dose index registry is expected to be activated this
year. In addition, the NRDR portal provides access to a database of a joint ACR-Society of
Uroradiology project called IV Contrast Extravasation (ICE).
Participation in the ACR data registries is voluntary, involves the payment of an annual
fee, and is limited to imaging sites within the US and its territories. Participating sites benefit
by receiving twice-yearly reports that document the quality of the services offered and permit
assessment of the efficacy of quality improvement programs. Data collected nationally will be used
to determine the effectiveness of specific radiological procedures and thus will promote
evidenced-based radiology.
by V. Matarese
Noncontrast MDCT for appendicitis: a systematic review
Appendicitis, a common cause of acute abdomen often requiring immediate surgery, remains
difficult to diagnose and many patients undergo appendectomy unnecessarily. Since a clinical
diagnosis is not specific, abdominal CT is the preferred diagnostic method and numerous CT
protocols using oral, rectal or intravenous contrast medium have been developed. Nonetheless, in
hectic emergency departments, the use of noncontrast CT can be advantageous. Therefore, researchers
from New York and Michigan did a systematic review to determine if noncontrast CT was sufficiently
accurate in this emergency setting [
1 ].
The analysis included 7 studies that reported the diagnostic accuracy of noncontrast MDCT,
compared to a reference standard (i.e. surgical findings or long-term clinical follow-up), in
adults presenting with suspected appendicitis. Studies that included children were excluded, as
were numerous others that did not report patients' ages or length of clinical follow-up. According
to the reference diagnostic method, 20.1%-84.5% of enrolled patients had appendicitis. In these
studies, sensitivity of noncontrast CT for diagnosing appendicitis ranged from 87% to 97% and
specificity from 92% to 100%. Pooled estimates of sensitivity and specificity were 92.7% and 96.1%,
and the positive and negative likelihood ratios were 24 and 0.08, respectively.
The diagnostic accuracy estimated by this systematic review was considered by the authors to
be adequate for guiding clinical decisions in emergency room settings. However, given the estimated
7.3% false-negative rate, they stressed that CT findings – like all diagnostic findings – be
evaluated in light of each patient's clinical conditions. They also emphasized the need for
complete reporting of clinical data, so that more studies can be included in systematic reviews.
Finally, observing that inconclusive CT examinations are inconsistently reported, they noted a need
for research on how to manage patients with suspected appendicitis when CT findings are not
diagnostic. This article has been selected for discussion in the
Annals of Emergency Medicine's Journal Club. For this purpose, the journal has posed a
series of questions about the paper [
2 ]. Answers will become available in June of this year.
ECR 2010: a congress designed to create virtuosos in radiology
The theme of the 2010 European Congress of Radiology (ECR), held this year like every year in
Vienna, was virtuosity in radiology. A virtuoso has masterly skill and technique in the arts,
and so the choice of this theme was most suited for the European Society of Radiology (ESR), a
society whose mission, according to ECR President M. Szczerbo-Trojanowska, is “to promote the
highest quality radiology based on science and education”.
The five-day program was certainly rich in science and education, as it offered attendees a
choice of 260 conference sessions, 1500 oral presentations and 3300 electronic posters, worth a
total of 27 hours of continuing medical education. Attendance was impressively high, with over 19
000 persons from almost 100 nations worldwide. Although the most attendees came Austria and
neighboring countries Italy and Germany (1000 participants each), numerous abstracts came from
Japan, China, South Korea, India and USA, documenting the international interest in this annual
event.
The success of this event can be attributed, at least in part, to the efforts of leading
members throughout the history of the ESR. In recognition of this fact, the society gave its
highest award, a Gold Medal, to Prof. A. Adam (London) for his outstanding contributions to the
society and to the field of radiology. Dr. Adam, a professor of interventional radiology, is a
founding member of the association and served as its president in 2006-2007. The ESR also awarded
honorary society membership to four radiologists who have made important contributions to radiology
research and practice: G.J. Becker (Tuscon), W.A. Kalender (Erlangen), J. Qi (Tianjin) and D.L.
Resnick (San Diego). Four additional dignitaries were honored by being name as invited lecturers.
In particular, A.G. Obsorn (Salt Lake City) gave the opening lecture on brain imaging in AIDS, and
additional honorary lectures were given by S.E. Anderson (Sydney) on musculoskeletal imaging, M.N.
Brant-Zawadski (Newport Beach) on radiation exposure and cancer, and A.P. Wieczorek (Lublin) on the
role of radiology in urinary incontinence.
by V. Matarese
Abdominal CT at the 2010 European Congress of Radiology
The twenty-second European Congress of Radiology offered its attendees another high-quality
program, covering radiological topics in a three hundred sixty degree fashion. CT and, especially,
its abdominal applications were central topics of this year's venue, giving participants much food
for thought on the way back to their home countries.
During Friday's New Horizons session, Dr. Stolzmann from Zurich gave an interesting lecture
on multi-energy CT and its relation to functional imaging. In the coming future, this novel imaging
modality may offer new diagnostic possibilities in the abdominal district.
The mini-course entitled “Organs from A–Z: Liver” offered both radiological trainees and
experts new insight into the clinical and radiological aspects of this organ. Different lectures,
focusing on basic and advanced topics, followed one after the other. The program, divided into four
parts, started with an introductory session on anatomy and imaging techniques, including talks on
liver anatomy and the multimodality display approach (Dr. Schima, Vienna), CT and MRI protocols,
(Dr. Marincek, Zurich), and imaging of liver function and structure (Dr. Menu, Paris). This was
then followed by three sessions, each with three lectures, on the assesment of diffuse liver
diseases, the description of primary liver tumors, and treatment strategies. In particular,
vascular diseases of the liver, their detection and role in transplantation, especially in the
context of CT imaging, were addressed in a memorable lecture by Dr. Vilgrain from Clichy.
Scientific sessions also dedicated much attention to abdominal CT, especially regarding new
techniques offered by the latest CT technology, i.e. perfusion and dual-energy approaches. Liver
perfusion, in particular, permits the evaluation of liver fibrosis in cirrhotic patients (as
discussed by Dr. Ronot, Clichy) and the investigation of the response to anti-angiogenic treatment
in patients with multifocal liver lesions (as explained by Dr. Menichini, Rome). Dr. Graser
(Munich) presented an interesting paper on image quality and radiation exposure offered by
second-generation dual-energy CT scanners for abdominal examinations. The quantification of liver
fat, compound analysis of gallstones, and quantitative analysis of virtual noncontrast images as a
possible means of dose reduction in cirrhotic patients were other hot topics in the field of
dual-energy CT imaging of the liver.
Considering the exquisite program that ECR provided its participants this year, it seems
truly that 2010 has started with a “radiological virtuosity”.
by C. Catalano
Dramatic reduction of radiation dose with new cardiac CT scanners: first results presented
at ECR 2010
At the 2010 European Congress in Radiology (ECR), radiation dose associated with cardiac CT was
again highlighted as an important topic, with a special session on Thursday. Recently, new
technological developments such as high-pitch scanning and prospectively triggered acquisition have
raised new expectations for the possibility of reducing radiation dose in cardiac CT. Indeed, these
two different techniques both permit a significant reduction in the exposure time and,
consequently, also in the radiation burden to patients.
The first clinical studies with these new techniques were presented at this year's ECR,
confirming the dramatic reduction in radiation dose that had been expected by these technological
developments. For example, high-pitch spiral data acquisition with prospective ECG triggering was
associated with a radiation dose of only 3 mGy compared to 27 mGy in a comparable low-pitch spiral
CT group. This translates to a 9-fold reduction in radiation dose without substantial loss in image
quality.
In addition, for the first time, the biological effects of X-rays have been assessed by
evaluating DNA double strand breaks (DSB) in lymphocytes. Researchers found a linear relationship
between the number of DSB and the dose length product (expressed in mGy*cm). Another presentation
described how sub-millisievert acquisition can be achieved using large detector technology with
prospectively triggered acquisition and low kilovoltage settings.
On Saturday, a session dedicated to the assessment of atherosclerosis by cardiac CT
underlined the potential of this technique to detect non-calcified as well as calcified plaques.
The researchers pointed out that the evaluation of coronary arteries with MDCT may be predictive of
major adverse cardiac events.
Advanced research in cardiac CT was also the subject of an interesting session on Sunday.
The evaluation of cardiac perfusion now appears as feasible with MDCT, especially after correction
for beam hardening artefacts. Dual-energy acquisition was also suggested to be a helpful tool for
detecting acute and chronic myocardial infarction.
In summary, cardiac CT presentations at ECR were numerous and at a very high scientific
level. The newest generation of CT scanners can overcome the main limitations of cardiac CT (i.e.
radiation dose) and offers new possibilities for deeper analysis of cardiac structure and function.
by J.F. Paul
Report from the ECR: Advances in CT neuroimaging
At this year's European Congress of Radiology, session SS 511b, called “Neuro – Advances in CT”,
took place on Friday, 5 March 2010 in the Austria Center. The session reported new trends in
CT neuroimaging with a special focus on MDCT.
In the first presentation, D. Morhard from Munich gave a presentation entitled “Stroke CT:
CTA or perfusion CT? Which should be done first?” and described a study that had evaluated which
order of CT imaging exams is advantageous in a comprehensive stroke work-up. The study underscored
the point that contrast medium administration prior to perfusion CT did not have a significant
effect on the perfusion parameters. When perfusion CT was performed first, however, there was
contrast agent preloading in the veins. Morhard therefore recommended a reversal of the traditional
order of exams, with CT angiography being performed first, followed by perfusion CT.
The second presentation by E. Smit from Utrecht was called “Arterial input function
characteristics for CT-perfusion in normal patients and patients with carotid stenosis or
occlusion". The background of this study is that the arterial input function (AIF) may result
in incorrect regional perfusion measurements, when dispersion or delay occurs due to pathology or a
higher distance between the region of the AIF and the measured region. This research group found
that TPP and MTT vary between different cerebral arteries especially in patients with unilateral
pathology of the internal carotid artery. Smit therefore concluded that a single AIF may not be
suitable for regional brain perfusion measurements especially in patients with carotid stenoses.
In the next presentation, L. Saba from Cagliari gave a talk entitled “Carotid artery wall
thickness and leukoariosis: Evaluation using multi-detector CT angiography”. This presentation
described a study that retrospectively evaluated carotid artery wall thickness (CAWT) in 98
patients and correlated it to the presence and severity of leukoariosis. The researchers found a
significant correlation between CAWT and the presence of leukoariosis when a threshold value of 0.9
mm for CAWT was chosen.
In the fourth presentation, D. Maintz from Muenster reported on a study entitled “Evaluation
of collateral flow in cerebral vessel occlusion using 4D CT-angiography: impact on the outcome
after multi-modal recanalization therapy” (the first author was V. Hesselmann). In this study,
researchers evaluated volume-rendered 4D-CT angiography-like datasets from perfusion CT to
assess the degree of collateralization and to correlate it to the patients' outcomes. The group
demonstrated that collateral flow could be estimated from the 4D-CT angiography datasets. In
the study population, good collateralization was associated with a significantly better outcome.
Maintz, however, mentioned that a limitation of the study was that the patient population was
comparatively heterogeneous.
The next paper, “Lower radiation dose adaptive statistical iterative reconstruction head CT
examinations match quality of prior conventional dose studies”, was given by L.N. Tanenbaum (first
author, E.G. Stein). In this study, 16 patients were scanned on a Discovery CT750 HD CT
scanner and images were reconstructed with adaptive statistical iterative reconstruction. The data
were compared to prior CT scans with conventional radiation doses and filtered back projection. The
group found the average radiation dose to be significantly reduced by 29% from 1.5 mSv to 1.1 mSv.
At the same time, noise levels were comparable and diagnostic image quality was preserved, as
assessed by blinded reviewers.
Another presentation was given by F.E. Ebner from Graz on the topic “Digital subtraction
volume 4D CT angiography of the brain: reducing radiation dose using a mathematical model for bolus
timing”. This study aimed to find an optimal time window for 4D-CT angiography and to limit
radiation dose accordingly with 320-row volume CT technology. Overall, 46 patients were
included and received a 10 ml test bolus, followed by a 50 ml regular bolus of contrast medium with
an iodine concentration of 370 mg/ml, injected at 6 ml/s. The researchers found the cross-over
point between arterial and venous time-density curves to be the most reliable time point to start
the regular bolus injection. The radiation dose amounted to 460.8 mGy*cm, which is well below the
reference level of 544 mGy*cm for diagnostic head CT.
The subsequent presentation, entitled “Brain perfusion CT using a 256-slice CT: Improvement
of diagnostic information by large volume coverage”, was given by F. Dorn from Munich. Her group
assessed the feasibility and diagnostic value of CT perfusion with an 8-cm detector. A total of 29
patients with signs of cerebral ischemia were included in the study. The data were compared to
those from simulated standard detector CT perfusion at the level of the basal ganglia by two
independent readers. Of the 19 lesions identified in this study, 6 would have been missed by
standard detector CT perfusion and 10 hypoperfused regions would have only partially been covered.
The last three presentations were given by Z. Jiawen from Shanghai. The first paper, “
Experimental studies on functional response in normal rat brain to hypercarbia using perfusion CT”,
described investigations into changes in CT perfusion values in normal rat brain at hypercarbia and
compared these changes to results from immunohistochemical staining. The group found that changes
in CBV and CBF correlated well with the number of vessels staining positively for SMA.
The second presentation by Jiawen was called “Experimental studies on functional response of
tumoral vasculature to hypercarbia in rat brain C6 glioma model using perfusion CT”. This talk
described a study that investigated CT perfusion changes in a rat in vivo glioma model and that
found that CT perfusion can reflect angiogenesis in this model. CBV and CBF values under
hypercarbia, however, did not correlate well with the number of mature vessels nor with the tumoral
vascular maturity index.
Jiawen's third presentation, entitled “Using 64-slice CT perfusion imaging to evaluate the
histopathological grade of intracranial gliomas”, described a study that assessed the role of CT
perfusion with a 64-slice system in the preoperative grading of cerebral gliomas. The study group
included 31 patients with intracranial gliomas who underwent preoperative CT perfusion. CBV
and CBF values correlated well with the grade of the glioma.
In summary, session SS511b provided many insights into the latest advances in neuro-MDCT
with a special focus on CT perfusion and 4D-CT angiography.
State-of-the-science conference on colorectal cancer screening
The US National Institutes of Health (NIH), within its consensus development program, recently
held a “state-of-the-science” conference on colorectal cancer screening. These NIH
conferences are organized on emerging healthcare topics for which the evidence may be limited or
contradictory, with the aims to illustrate the state of knowledge and to set priorities for future
research. During these conferences, the results of a systematic review on the subject are
presented, researchers discuss their work, independent panelists (without financial or career
interests in the matter) present objective views, and a public debate ensues. The result is the
production of a “panel statement” that summarizes current knowledge, without determining a specific
healthcare policy.
The most recent NIH state-of-the-science conference was entitled “Enhancing Use and Quality
of Colorectal Cancer Screening”. The speakers, predominantly from the US, addressed topics
such as trends in the use and quality of colorectal cancer screening, factors influencing the
choice to screen, strategies that increase compliance, medical centers' capacity for screening, and
monitoring of screening progress and quality. Two presentations specifically addressed CT
colonography: one provided data on the ability of US hospitals to offer CT colonography, and
another discussed the training and certification of physicians as well as quality control.
Summaries of these and other presentations are available at
consensus.nih.gov.
In the final panel statement, the panelists concluded that the extent of colorectal cancer
screening in the US is low and that screening does not reach all population subgroups. To improve
this situation, they made several recommendations, including the elimination of "financial
barriers" to screening, research on how to tailor screening programs to the needs of particular
population subgroups, and cost-benefit analysis of different screening methods. The panel statement
is available at
consensus.nih.gov.
by V. Matarese
Toshiba explains its dose- and noise-reducing tools
Maintaining radiation exposure as low as reasonably achievable during CT examinations can be
achieved by reducing tube current, but this also reduces image resolution due to a concomitant
increase in both quantum noise (random pixel fluctuations) and structured noise (artifacts, such as
streaking, due to local areas of high attenuation). Noise can be removed from final images by
applying smoothing filters, but if not done accurately resolution and texture can be lost.
Manufacturers of CT scanners have made major efforts to develop sophisticated algorithms to reduce
noise without losing resolution. For users of Aquilion CT scanners, Toshiba has recently published
a white paper describing its two noise-reducing, dose-saving tools.
Quantum Denoising Software (QDS) eliminates quantum noise by selectively applying smoothing
and sharpening filters to specific parts of an image, resulting in an enhanced image with preserved
contrast. QDS works together with Aquilion's
SUREExposure mA modulation system, so that tube current is optimized to both the
patient's body constitution and the desired image quality. The second tool, called Boost 3D,
eliminates quantum as well as structured noise by searching within the raw data set for areas of
low photon count. Together, these two tools permits radiologists to either improve image
quality with a fixed radiation dose, or reduce radiation dose with a fixed image quality.
Selected literature update
MDCT for gastrointestinal diseases
Researchers from Bari tested the accuracy of 16-slice MDCT with vessel probe (VP) reconstruction
in the preoperative T staging of gastric carcinoma [
1]. VP software permits reconstruction of gastric wall layers
through 3D visualization of arterial vessels during contrast-enhanced imaging. Their study enrolled
53 patients with a diagnosis of gastric adenocarcinoma who underwent MDCT prior to partial or total
gastrectomy. Compared to the histological diagnosis made on resected specimens, MDCT with VP
reconstruction detected 98% of all lesions (missing one early cancer) and accurately determined T
stage in 94% of cases. In contrast, without VP analysis, 90% of lesions were identified but
accurately staged in 68%. The authors suggested that incorporation of VP reconstruction in the MDCT
workup of these patients is a fast and easy way to improve accuracy.
Pediatric Crohn's disease was the focus of a review offered by researchers working in Ann
Arbor (Michigan) [
2]. Radiological evaluation of Crohn's disease is possible by
numerous methods, including CT enterography which reveals both intestinal and extraintestinal
manifestations of the disease. The paper describes the CT enterography examination, especially
regarding contrast medium administration, image acquisition and radiation exposure control. It then
illustrates, with numerous cases, the wide range of CT enterography findings, including bowel and
mesentery involvement, penetrating disease, intra-abdominal fluid, bone and urinary tract disease,
and finally cholelithiasis.
A catchy rule to guide decisions about CT for minor head trauma in children
Minor pediatric head trauma is a common occurrence that rarely requires neurosurgical
intervention. Still, given the fear of intracranial hematoma, emergency physicians often request a
CT examination, despite concerns about costs and radiation exposure. Recognizing the need for
evidence-based guidelines to support decision-making in this difficult situation, a head injury
study group was formed within Pediatric Emergency Research Canada.
The group organized a prospective, 10-center study [
1 ] to collect clinical and outcome data on children (<17 years
of age) who presented with blunt head trauma causing loss of consciousness, amnesia, disorientation
or other symptoms and who had a Glasgow Coma Score ≥13. Children underwent a standardized clinical
and neurological examination, and CT was performed at the physician's discretion. Clinically
important brain injury was defined from CT findings; in cases in which CT was not done
immediately, children were followed up at 14 days and were classified as not having brain injury
unless there were signs or symptoms necessitating recall for CT. Univariate analysis was used to
identify variables associated with the primary outcome (neurological intervention), and then
recursive partitioning was done to find a combination of variables that was both sensitive and
specific in predicting this outcome.
Over more than 4 years, the study enrolled 3866 patients of which 24 (0.6%) had
neurosurgery. CT was performed in 2043 children (52.8%) and brain injury was diagnosed in 159 cases
(4.1%). Recursive partitioning analysis identified seven criteria predictive of brain injury,
including four that defined patients at high risk: Glasgow Coma Score <15 two hours after
injury, evidence of open or depressed skull fracture, worsening headache and irritability. These
four criteria had 100% sensitivity and 70.2% specificity, and implied that about 30% of children
with minor head trauma should have a CT examination. The clinical decision rule based on all seven
criteria, termed Canadian Assessment of Tomography for Childhood Head Injury (CATCH), is expected
to help standardize – and minimize – the use of CT for minor pediatric head trauma.
Hands-on experience in state-of-the-art cardiac CT can be acquired by attending one of the
twice-yearly workshops organized by Marc Dewey and colleagues, from the cardiac imaging group of
the Department of Radiology, Charité Medical University. In two half-day sessions, up
to 20 participants attend lectures and practical demonstrations and are guided in the use of image
processing software. Lectures address patient preparation, scanning, image reconstruction and
analysis, and cardiac anatomy. Clinical CT examinations are demonstrated using Sensation 64
(Siemens) and Aquilion ONE and Aquilion 64 (Toshiba) scanners. Then, participants spend up to 3
hours on Vitrea workstations learning to analyze CT angiographic images.
This year, the workshops will be held in English in April and September 2010 and in German
in June 2010, on the Charité Campus Mitte, in Berlin. A substantially discounted fee is
offered to medical residents. The program has been awarded 20 CME credits by the Berlin
Medical Council. A program and registration information are available at
s196588120.e-shop.info.
by V. Matarese
Selected literature update
MDCT coronary angiography protocols for radiation dose reduction: a review and a
comparative study
To combat the mounting radiation exposure that has accompanied the technological advances in
MDCT, which now permits accurate, noninvasive examination of the coronary arteries, several
dose-reducing scanning protocols have been developed. Two papers selected for inclusion in
MDCT.net's full text literature archive offer analyses of the feasibility, indications and
effectiveness of scanning protocols that limit radiation exposure during MDCT coronary angiography.
Horiguchi and colleagues from Japan compared retrospective ECG-gated spiral CT to the newer
prospective ECG-triggered sequential CT [
1]. This review, published in
Current Cardiovascular Imaging Reports, provides a detailed description of the two
acquisition protocols, examines the radiation exposure of these two methods compared to other
imaging protocols, and summarizes current knowledge on the clinical indications and diagnostic
performance of the prospective ECG-triggered technique which, the authors concluded, permits a
substantial radiation reduction in patients with low, stable cardiac rhythms.
Malagò and coworkers in Verona, Italy, clinically tested two dose-saving protocols compared
to standard 64-slice CT angiography and published their results in
La Radiologia Medica [
2 ]. In the study, the researchers followed an empirical scheme
(based on body mass index and heart rhythm) to select patients for the standard method or for one
of two dose-saving protocols, namely “cardiac dose right” and “step and shoot”. Overall, 14
patients underwent standard CT angiography (constant tube current with retrospective ECG gating),
45 patients had cardiac dose right CT angiography (ECG-modulated current with retrospective ECG
gating), and 6 patients had step and shoot CT angiography (prospective ECG triggering of tube
current). Image quality was apparently comparable in all three groups (although a statistical
analysis was not done, possibly because of the different group sizes). Effective dose was 20.5 mSv
in the standard protocol group, 14.8 mSv in the cardiac dose right group, and 6.6 mSv in the step
and shoot group. The authors concluded that these dose-reducing protocols, when applied to
accurately selected patients, reduce radiation dose by 30% and 70%, respectively.
The first issue of 2010 of the bimonthly Radiological Clinics of North America is dedicated to
MDCT applications in the thorax. Edited by S. Bhalla of the Washington University School of
Medicine (St. Louis, USA), the issue offers 12 chapters on a range of thoracic imaging topics,
authored by radiologists from the USA, Korea and France. Overall, the issue summarizes the advances
of thoracic MDCT in the past decade, achieved both through improving existing clinical protocols
and permitting the development of new ones [
1]. Individual chapters discuss the history of chest CT, contrast
optimization, and clinical imaging applications such pulmonary embolism, acute aortic syndrome,
congenital vascular defects, lung nodules, airways, chest pain. A final chapter discusses thoracic
applications of dual-energy CT.
MDCT is frequently addressed in this journal's thematic issues. The upcoming March 2010
issue will be dedicated to CT angiography
Standardization of CT contrast procedures for improved safety
The safe and effective use of iodinated contrast medium requires an accurate assessment of
patients' clinical risks, a correct choice of protocols, and a rigorous handling of information
regarding contrast reactions. Managing the clinical and imaging data pertinent to contrast medium
use can be challenging, especially in radiology departments that serve large numbers of
outpatients. This is even more difficult within a healthcare system that comprises multiple
hospitals.
Kahlon and colleagues at Partners Healthcare System, a nonprofit organization based in
Boston, realized that across their six member hospitals each CT unit used different approaches to
assess risks for adverse events, different protocols to administer contrast medium, and different
criteria to define contrast medium reactions. Moreover, data on contrast reactions were not
archived in electronic clinical records, hindering physicians' access to important information
prior to prescribing or performing successive CT examinations. Therefore, a “CT contrast team” was
established to assess current procedures, to identify critical areas in the workflow process, and
to develop standardized procedures for all hospitals in the group. The team adopted the American
College of Radiology's classification of contrast reactions, developed a standard patient
questionnaire, established a single contrast medium administration policy, and produced an adverse
event form. The electronic medical record (EMR) software was also updated to permit the recording
of contrast medium information directly into patients' clinical records.
Now that the new materials and protocols have been implemented, radiologists, technologists
and nurses have ready access to each patient's contrast history and can record new adverse events
directly in the EMR system. These standardized procedures and information management strategies now
also permit this healthcare system to monitor its CT safety performance. According to the authors,
this single positive experience can be widely adopted by other large radiology departments
