Size of colorectal liver metastases at abdominal CT: Comparison of precontrast and postcontrast studies

PURPOSE: To investigate whether measurements of hepatic metastases from col orectal carcinoma before contrast material administration are significantly different statistically from measurements after contrast material administ ration. MATERIALS AND METHODS: Twenty-four patients with hepatic metastases from co lorectal carcinoma underwent spiral computed tomography (CT) with 7-mm coll imation. The liver was imaged before and in the portal-dominant phase after intravenous contrast material administration. For each scan, one to three discrete liver lesions were selected for measurement (n = 49). Three experi enced radiologists performed independent measurements of the selected lesio ns on both pre- and postcontrast images at a computer workstation. A three- way analysis of variance (ANOVA) was performed: subjects by raters (the thr ee independent radiologists) by pre- or postcontrast status. The dependent variable was the product of bidimensional measurements. RESULTS: Sixty-seven percent (33 of 49) of the lesions were measured as lar ger on precontrast images; 33% (16 of 49), as smaller. There was high inter rater reliability, with an intraclass correlation coefficient greater than 0.9. ANOVA showed significant subject, rater, and contrast material effects (P < .001) for the largest lesions in each liver. Contrast material status was a significant factor for all lesion sizes (P < .003). CONCLUSION: On average, hepatic metastases from colorectal carcinoma are si gnificantly smaller after contrast material administration.