CONSPICUOUSNESS OF HEPATIC METASTASES ON HELICAL CT - EFFECT OF DIFFERENT TIME DELAYS BETWEEN CONTRAST ADMINISTRATION AND SCANNING

OBJECTIVE. The purpose of this study was to compare two time delays be tween injection of contrast material and helical CT scanning to determ ine relative conspicuity of hepatic metastases. SUBJECTS AND METHODS. Twenty-five patients with hepatic metastases were examined with helica l CT. The first imaging phase was initiated at 50 sec and the second 7 5 sec after the start of contrast material injection (3 ml/sec, 150 ml ). Differences in lesion and liver attenuation were measured quantitat ively. Four radiologists used a 5-point scale to assess lesion conspic uity subjectively.RESULTS. Mean differences in enhancement between liv er and lesion were 41 H during the first phase and 59 H for the second phase (p =.0001). Radiologists' conspicuity score averaged 2.4 for le sions in the first phase versus 3.3 for lesions in the second phase (p =.0001). In 56 (88%) of 64 lesions, objective measurements showed gre ater enhancement of lesions during the later phase. Radiologists found 60 (94%) of 64 lesions to be more conspicuous on these later images. CONCLUSION. Our results show that conspicuity of hepatic metastases an helical CT scans is better with a 75-sec scan delay between contrast administration and scanning than with a 50-sec scan delay. The longer delay time should be used when scanning is used to detect metastases.