Unenhanced computed tomography for non-invasive diagnosis of hepatic steatosis with low tube potential protocol.

Background: Lowering kVp affects the image contrast and computed tomography (CT) attenuation values of low kVp CT is different from those of conventional 120-kVp scans. The purpose of this study is to determine the diagnostic performance and to establish the reference range of low-kVp unenhanced CT for the assessment of hepatic steatosis in liver transplantation donors using magnetic resonance (MR) spectroscopy as a reference standard.

Methods: This retrospective study included 165 potential donors (male:female =114:51, 36.5±12.0 years old) who underwent 100-kVp single-slice unenhanced CT scan and MR spectroscopy. The difference between hepatic and splenic attenuation (CT) and liver-to-spleen attenuation ratio (CT) were calculated. Reference standard was the fat signal fraction measured by MR spectroscopy. Limits of agreement between CT measurements and the reference standard were calculated. Areas under receiver operating characteristic curves (AUROCs) of CT and CT were compared for the diagnosis of moderate to severe steatosis. Cut-off values of CT and CT that provided a balance between sensitivity and specificity and the highest specificity using the lower limit of the reference range were calculated.

Results: Eighty-seven subjects had a non-steatotic liver. Sixty-one subjects had mild steatosis and 17 subjects had moderate to severe steatosis based on MR spectroscopy. CT and CT values were negatively correlated with the fat signal fraction (P<0.001) and limits of agreement were -8.4% to 8.4% for CT and -9.6% to 9.6% for CT. AUROCs of CT and CT for diagnosing moderate to severe steatosis were 0.956 and 0.957, respectively. Cut-off values of CT and CT for diagnosis of moderate to severe steatosis by the Youden index were -0.5 HU for CT and 0.99 for CT. Reference ranges of non-steatotic liver were -6.90 to 31.40 HU for CT and 0.89 to 1.77 for CT. Using -6.9 HU for CT and 0.89 for CT as cut-off values, the sensitivity and specificity for diagnosing moderate to severe steatosis were 70.59% and 90.54% (CT) and 76.47% and 90.54% (CT), respectively.

Conclusions: Measurements from a low-kVp unenhanced CT scan were negatively correlated with the degree of hepatic steatosis. Low-kVp unenhanced CT is a robust technique with reduced radiation exposure for diagnosing moderate to severe hepatic steatosis.