Transient interruption of contrast on CT pulmonary angiography: proof of mechanism

To test the hypothesis that a transient interruption of contrast is the result of an increase in flow of unopacified blood from the inferior vena cava (IVC) by comparing the relative IVC contribution to the right side of the heart in cases and age-matched and sex-matched controls.

This retrospective study was approved by our internal review board. Of 234 consecutive patients who had both CT pulmonary angiography and a close follow-up diagnostic pulmonary angiogram, or in one case CT pulmonary angiography, 7 cases were identified which contained a transient interruption of contrast. The study group included 2 men and 5 women. The age range was 37 to 77 years (mean 61.3 y +/-13.3). The artifact consists of a segment of the pulmonary arteries which demonstrates poor blood enhancement between areas of increased attenuation both proximally and distally. Hounsfield units (HU) measurements were made in the areas of decreased attenuation, the areas of higher attenuation both proximally and distally, the superior vena cava, IVC, right atrium (RA), and right ventricle (RV). The relative IVC contribution was calculated by equating density in the RA and RV to a weighted average of the densities of the superior vena cava and IVC. Age-matched and sex-matched controls and a 2-tailed paired t test were used.

In the patients with the artifact, the average relative IVC contributions to the RA and RV are 80.1% and 79.5%, respectively. In the control patients, the values for the RA and RV are 52.8% (P=0.02) and 55.5% (P=0.02), respectively.

Transient interruption of contrast of the pulmonary arteries represents a flow-related phenomenon associated with an increased IVC contribution to the right side of the heart.