DUAL-PHASE HELICAL CT OF THE LIVER - VALUE OF ARTERIAL PHASE SCANS INTHE DETECTION OF SMALL (LESS-THAN-OR-EQUAL-TO-1.5-CM) MALIGNANT HEPATIC NEOPLASMS

OBJECTIVE. Helical CT scanners now allow sequential arterial phase and portal venous phase scans of the entire liver to be obtained during a single bolus injection of contrast material, The purpose of this stud y was to determine if arterial phase scans improve detection of small (less than or equal to 1.5 cm) malignant hepatic neoplasms when compar ed with portal venous scans alone. MATERIALS AND METHODS. Dual-phase h elical CT of the liver was done in 96 patients referred for known or s uspected malignant hepatic lesions. Malignant hepatic neoplasms were d etected in 38 patients (27 with at least one small neoplasm), one pati ent had undetected metastases, one patient had a benign hepatic neopla sm, and 56 patients had no hepatic neoplasm. Proof of individual neopl asms was based on biopsy results, surgical findings, or findings on ot her imaging studies (primarily follow-up CT). The absence of disease w as established by surgical or autopsy findings, findings on subsequent imaging studies, or a combination of clinical and laboratory data. A total of 150 ml of 60% nonionic contrast material was infused at 5 ml/ sec followed by sequential arterial phase and portal venous phase heli cal scans of the liver. Three radiologists retrospectively reviewed th e scans, Individual lesions were measured and the conspicuity of each lesion on arterial phase and portal venous phase scans was compared, T he percentage of patients in whom some malignant neoplasms were detect ed better on the arterial phase scan was calculated using categories b ased on lesion size and typical tumor vascularity. RESULTS. In 10 (37% ) of 27 patients who had at least one small malignant neoplasm, lesion s 1.5 cm or less in diameter were only visible or were more conspicuou s on the arterial phase scan. No malignant neoplasms more than 1.5 cm in diameter were visible only on the arterial phase scan. In four (11% ) of 38 cases, malignant neoplasms more than 1.5 cm in diameter were m ore conspicuous on the arterial phase scan. The arterial phase scans i mproved lesion conspicuity in nine (39%) of 23 patients who had typica lly hypervascular neoplasms, whereas lesion conspicuity was improved i n three (20%) of 15 patients who had typically hypovascular neoplasms (p = .02). The arterial phase scan resulted in the false-positive dete ction of lesions in two (2%) of 96 cases. CONCLUSION. Arterial phase h elical CT of the liver improves detection of some small, malignant hep atic neoplasms when performed in addition to portal venous scanning. T he value is greatest in those patients who have hypervascular neoplasm s.