CM Administration

Contrast-Injection Variables that Affect Contrast Enhancement

Contrast Volume

• If iodine concentration and flow rate are kept constant, a larger contrast volume leads to:
  • Greater enhancement
  • Prolonged enhancement
• Higher contrast volumes are beneficial for extended coverage

Simulated contrast enhancement curves with three different contrast media volumes.

Simulated enhancement curves of the (a)aorta and (b)liver based on injection of 75, 125, and 175 mL of 370 mgI/mL contrast medium at 2 mL/sec. The time to enhancement and the magnitude of the peak enhancements (gray bars) increase with the contrast medium volume. Modified with permission (Bae KT, Heiken JP. Computer modeling approach to contrast medium administration and scan timing for multislice CT. In: Marincek B, Ros PR, Reiser M, Baker ME, eds. Multislice CT: A Practical Guide, Proceedings of the 5th International SOMATOM CT Scientific User Conference, Zurich, June 2000. Heidelberg: Springer-Verlag; 2000:28-36).

Injection Flow Rate

• If contrast volume and iodine concentration are kept constant, a faster injection leads to:
  • A greater magnitude of arterial enhancement
  • A reduced time-to-peak arterial enhancement
  • A narrower arterial peak width
  • The need for a shorter scan delay to scan during peak arterial enhancement, particularly if the scan duration is long.
    Note :These parameters are good for fast scans and useful for CTA and biphasic applications.

• If contrast volume and iodine concentration are kept constant, a slower injection leads to:
  • A lower magnitude of enhancement
  • An increased time-to-peak enhancement
  • A broader peak width ("plateau")
  • More prolonged enhancement
  • The need for a longer scan delay to scan during peak arterial enhancement, particularly if the scan duration is short.
    Note :This is good for more extended coverage.

Simulated contrast enhancement curves with three different contrast medium injection rates.

Simulated enhancement curves of the (a) aorta and (b)liver based on a dose of 150 mL of 370 mgI/mL contrast medium injected at 1, 3, and 5 mL/sec. The curves show that for a constant volume of contrast medium, as the rate of injection increases, the magnitude of contrast enhancement increases while the duration of high-magnitude contrast enhancement decreases. Modified with permission (Bae KT. Technical aspects of contrast delivery in advanced CT. Appl Radiol.Dec. 2003;32(suppl):12-19).

Effect of contrast medium injection rate on the magnitude of peak contrast enhancement (from simulated contrast enhancement curves)..

Peak aortic and hepatic contrast enhancement at different injection rates are simulated based on an injection of 120 mL of 370 mgI/mL contrast medium. Modified with permission (Bae KT, Heiken JP, Brink JA. Aortic and hepatic peak enhancement at CT: effect of contrast medium injection rate — pharmacokinetic analysis and experimental porcine model. Radiology 1998;206:455-464).

Iodine Concentration

• If the iodine dose and flow rate are kept constant, a higher iodine concentration leads to:
  • Greater enhancement
  • A reduced time-to-peak enhancement
  • A narrower peak width
  • The need for a shorter scan delay to scan during the peak arterial enhancement, particularly if the scan duration is long.
    Note :This is good for fast scans and useful for CTA and biphasic applications.

• If the iodine dose and flow rate are kept constant, a lower iodine concentration leads to:
  • A lower magnitude of enhancement
  • An increased time-to-peak enhancement
  • A broader peak width ("plateau")
  • More prolonged enhancement
    Note :However, if coverage is extended, the magnitude of enhancement may become suboptimal.

• If contrast volume and flow rate are kept constant, a higher iodine concentration leads to:
  • Greater enhancement
  • Unchanged time-to-peak enhancement
  • A broader peak width
  • Less critical scan delay timing
    Note :This is good for faster and longer scans.

• If contrast volume and flow rate are kept constant, a lower iodine concentration leads to:
  • A lower magnitude of enhancement (may become suboptimal)
  • Unchanged time-to-peak enhancement
  • A narrower peak width

Simulated contrast enhancement curves with a fixed amount of iodine mass but three different contrast medium concentrations injected at a constant rate.

Simulated enhancement curves of the (a)aorta and (b)liver based on a 5 mL/sec injection of the same amount of iodine mass but at 3 different concentrations and volumes. The aortic and hepatic time-enhancement curves demonstrate that the use of high-concentration contrast material is associated with earlier and greater peak aortic enhancement. The effect of contrast concentration in the liver is not as pronounced as in the aorta. Modified with permission (Bae KT. Technical aspects of contrast delivery in advanced CT. Appl Radiol.Dec. 2003;32(suppl):12-19).

Optimizing the image with contrast… it’s really just pharmacokinetics.

Saline Flush

Saline flush may be delivered by hand bolus, but is more controlled and efficient when delivered by using a dual-head power injector. Dual-head power injectors can be used to inject saline before and after contrast media, and allow better control of volume and flow rates. As scanning times become shorter with the new MDCT scanners, power injectors are essential for optimizing contrast use and image enhancement.

Advantages

• Reduces contrast waste by pushing contrast material through the tubes and peripheral veins
• May permit the required contrast dose to be reduced
• Improves contrast bolus shape in the heart and lungs
• Reduces artifacts caused by dense contrast in central veins

Trade-offs

• More time consuming even with dual-head power injectors
• More expensive due to additional cost of tube set
• Although expense may be offset by contrast media savings

Viscosity

• More viscous contrast solutions require a higher pressure to inject
• Warming contrast media reduces viscosity
• Arterial or parenchymal enhancement is not affected by viscosity of contrast solutions