Optimal scan delay in spiral CT for the diagnosis of acute pulmonary embolism

The purpose of this work was to assess whether easily obtained clinical parameters can predict optimal scan delay for contrast-enhanced spiral CT of pulmonary arteries and to compare image quality between individualized contrast timing versus a fixed scan delay.

We used an individualized delay in 85 patients by measuring the contrast transit time through the pulmonary circulation (Group A) and assessed the correlation between transit time and clinical parameters. In 56 patients (Group B), we used a 20 s fixed scan delay. The CT examinations of both groups were compared with regard to image quality.

Contrast transit times (mean 10.5 s, range 4-26 s) did not correlate significantly with heart rate, blood pressure, body length, weight, body surface area, or cardiac function. Although contrast transit times were significantly related to gender and age, only 14.8% of the variation could be explained by these clinical parameters. Data of 57 patients in Group A and 50 patients in Group B were available for analysis. Image quality was not significantly different between Groups A and B, which was good, moderate, and poor in 61, 32, and 7% in Group A and 60, 34, and 6% in Group B, respectively (p = 1.0).

One cannot predict individual scan delay from easily obtainable clinical parameters. Fortunately, a 20 s fixed scan delay provides equal image quality as individualized contrast timing.