Objective: The purpose of the study was to develop quantitative and qualitative criteria for diagnosing fatty liver on contrast-enhanced helical CT.
Subjects and methods: Differential liver-spleen attenuation was evaluated between 80 and 120 sec after injection in 76 patients who underwent contrast-enhanced helical CT. Unenhanced CT images had earlier established fatty liver when the liver minus spleen attenuation difference was less than or equal to -10 H (n = 18). Four observers who had not seen the unenhanced images used contrast-enhanced CT images to assess the presence of fatty liver on a five-point Likert scale, the presence of geographic areas spared from fatty infiltration, and the relative liver-spleen attenuation. The diagnostic accuracies of various imaging criteria were compared using McNemar's chi-square test (for sensitivity and specificity) and analysis of receiver operating characteristic curves.
Results: Sensitivity, specificity, and receiver operating characteristic curve areas for observers' qualitative judgments were 54%, 95%, and .91, respectively; for quantitative differential liver-spleen attenuation (80-100 sec; -20.5 H discriminatory value), the values were 86%, 87%, and .94, respectively; and for quantitative differential liver-spleen attenuation (101-120 sec; -18.5 H discriminatory value), the values were 93%, 93%, and .98, respectively. Differential liver-spleen attenuation was time-dependent; overlap was noted between healthy subjects and patients with fatty liver. Qualitatively, geographic sparing was highly specific (94%) for fatty liver, whereas liver attenuation greater than or equal to spleen attenuation excluded fatty liver in all but one case.
Conclusion: Although quantitative and qualitative criteria for diagnosing fatty liver on helical CT can be determined, they are protocol-specific. Limited unenhanced hepatic CT remains the optimal technique for detection of fatty infiltration of the liver.