Scan Timing

Scan Delay

Scan Delay

• If volume, flow rate, and iodine concentration are kept constant, delaying the scan becomes more critical as the:
  • Number of slices per rotation increases (4 to 8 to 16)
  • Scan becomes faster
  • Scan duration shortens
• It is essential to increase scan delay to image during peak arterial enhancement

Scan delay: how to optimize image quality during arterial enhancement

• When using shorter scan durations (16-row scanners), consider
  • Decreasing the contrast volume
  • Using contrast solutions with high iodine concentration (the higher, the better)
  • Using a high flow rate (≥4 mL/s) for contrast administration
  • Increasing the scan delay compared with 4-row scanners
  • Using bolus tracking
• When using longer scan durations (4-row scanners or extended coverage), consider
  • Increasing the contrast volume
  • Using a lower flow rate to increase the injection duration
  • Using contrast solutions with a high iodine concentration to increase the enhancement level for a given injection rate
  • Using bolus tracking or automated settings provided by the scanner manufacture

Scan delay: how to optimize image quality during hepatic parenchymal enhancement

• Iodine dose is critical
  • Use higher volumes of lower iodine concentration
  • Use lower volumes of higher iodine concentration
  • Iodine dose should not be reduced even if faster scanners are used
• Flow rate is not as critical as in arterial enhancement
• Scan delay should be increased if faster scanners are used

Representative scan timing and scan duration curves for single-slice, and 4- and 16-slice MDCT scanners are shown for (a) aortic and (b) hepatic enhancement.

As scanners become faster, scan durations become shorter, and therefore it is critical to delay scanning to capture images during peak enhancement, as illustrated in Panel b. Images courtesy of Kyongtae Ty Bae, MD, PhD, Mallinckrodt Institute of Radiology, St. Louis, MO.