CM Administration

Patient Variables that Affect Contrast Enhancement

Body Weight and Contrast Enhancement

• In many CT applications, for optimal enhancement, tailor the iodine dose to body weight.
• Body weight affects both vascular and parenchymal enhancement.
  • The greater the weight, the lower the enhancement.
  • Time-to-peak enhancement is unchanged.
• The greater the weight, the greater the iodine dose needed to achieve the same degree of enhancement.
• Contrast media with higher iodine concentrations will be useful to administer the iodine dose needed.

Simulated contrast enhancement curves with four different body weights.

Simulated enhancement curves of the (a) aorta and (b)liver based on injection of 125 mL of contrast medium at 5 mL/sec. The magnitude of contrast enhancement is inversely proportional to the body weight. 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).

Body Weight Used to Calculate Iodine Dose

If a standard iodine dose is calculated for a patient weighing 70 kg/150 lbs (=100%), the following dose adjustments would be needed:

Cardiac Output and Contrast Enhancement

• A reduced cardiac output leads to:
  • Delayed enhancement
  • Greater enhancement
  • Prolonged enhancement
  • Therefore
    • Use bolus tracking for scan timing
    • Use a lower iodine dose
    • Use a slower injection rate

Simulated contrast enhancement curves at baseline and reduced cardiac outputs (C.O.) .

Simulated enhancement curves of the aorta, based on injection of 120 mL of 370 mgI/mL contrast medium at 4 mL/sec. A set of (a)aortic and (b) hepatic contrast enhancement curves were generated by reducing the baseline cardiac output, i.e. 6500 mL/min, by 20%, 40%, and 60%. Modified with permission (Bae KT. Technical aspects of contrast delivery in advanced CT. Appl Radiol.Dec. 2003; 32 (suppl):12-19) .

Vascular Access

• High contrast flow rates (≥3 mL/s) can be used in larger caliber veins (e.g., antecubital vein)
• However, lower contrast flow rates should be used when vascular access is limited or a central line is employed