Contrast Enhancement

Optimal Enhancement

Vascular and cardiac blood pool contrast enhancement is determined by the interaction of iodine administration and blood flow. The goals of contrast administration are:

• □

  Adequate opacification of cavities and vessel lumen

• □

  Avoidance of both under- and over-opacification. It is important to recognize that excessive contrast concentration generates high attenuation artifact.

  • Starburst high-attenuation artifacts from the superior vena cava (SVC) are among the most common of all annoying and frustrating artifacts.

  • CT angiography (CTA) requires high left heart/aortic contrast and low right heart contrast (high right heart opacification confounds assessment of the right coronary artery and the right ventricular contours).

• □

  Optimal enhancement depends on the purposes of the study.

  • The optimum contrast effect for vascular enhancement is 300 to 500 HU.

  • The optimal contrast effect for coronary plaque characterization is less: 250 to 350 HU.

• □

  Optimal opacification requires a near-steady level of contrast throughout the entire duration of the study.

• □

  Synchronization of opacification to image acquisition phase is crucial. For CTA, the principal challenge is to synchronize these three variables:

  • The arrival of the contrast medium in the left heart

  • Washout from the right heart with the saline push

  • Acquisition phase

Acquisition Time and Contrast Need

As scanners are developed that can use larger numbers of slices and provide greater breadth of scanning, acquisition time is falling, as is the needed duration of contrast effect, and, therefore, the volume of contrast needed. In comparison to 10-slice scanners, 64-slice scanners need only half the volume of contrast. In comparison to 16-slice scanners, 64-slice scanners need one third less contrast.