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. 2022 Feb;12(2):1348-1358.
doi: 10.21037/qims-21-474.

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

Yunjung Choi  1 , Dong Kyun Kim #  1 , Seo Yeon Youn  1 , Hokun Kim  1 , Joon-Il Choi #  1   2
Affiliations

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

Yunjung Choi et al. Quant Imaging Med Surg. 2022 Feb.

Abstract

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 (CTL-S) and liver-to-spleen attenuation ratio (CTL/S) 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 CTL-S and CTL/S were compared for the diagnosis of moderate to severe steatosis. Cut-off values of CTL-S and CTL/S 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. CTL-S and CTL/S values were negatively correlated with the fat signal fraction (P<0.001) and limits of agreement were -8.4% to 8.4% for CTL-S and -9.6% to 9.6% for CTL/S. AUROCs of CTL-S and CTL/S for diagnosing moderate to severe steatosis were 0.956 and 0.957, respectively. Cut-off values of CTL-S and CTL/S for diagnosis of moderate to severe steatosis by the Youden index were -0.5 HU for CTL-S and 0.99 for CTL/S. Reference ranges of non-steatotic liver were -6.90 to 31.40 HU for CTL-S and 0.89 to 1.77 for CTL/S. Using -6.9 HU for CTL-S and 0.89 for CTL/S as cut-off values, the sensitivity and specificity for diagnosing moderate to severe steatosis were 70.59% and 90.54% (CTL-S) and 76.47% and 90.54% (CTL/S), 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.

Keywords: Liver; computed tomography (CT); magnetic resonance spectroscopy (MRS); steatosis.

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Conflict of interest statement

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://dx.doi.org/10.21037/qims-21-474). JIC reports that he received grants from Guerbet Koreaand Samsung Medison. The other authors have no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Diagram showing donor candidate enrollment. LDLT, living donor liver transplantation; CT, computed tomography; MRS, magnetic resonance spectroscopy.
Figure 2
Figure 2
Magnetic resonance spectroscopy to measure the fat signal fraction. (A) A 3×3×3 cm3 voxel was located in the hepatic parenchyma of the right hemiliver to avoid hepatic vessels; (B) upper color bar shows the T2-corrected fat signal fraction (4.79% in this case). Lower color bar is for R2 water to evaluate iron deposition.
Figure 3
Figure 3
CT attenuation measurement on a low-kVp, single-slice unenhanced CT scan. Liver parenchyma attenuation was measured in two regions of interest (ROIs) of the right hemiliver. An ROI was placed in two different segments. To measure spleen attenuation, two ROI were placed in the spleen, regardless of the anatomical part of the spleen. Liver and spleen attenuation values in the two ROIs were averaged. CT, computed tomography; SD, standard deviation.
Figure 4
Figure 4
Scatter plots showing the results of linear regression analyses. (A) Scatterplots showing the results of linear regression analyses between the fat signal fraction and CTL-S (the difference between hepatic and splenic attenuation). Linear lines are best-fit lines of the linear regression equations; (B) scatterplots showing the results of linear regression analyses between the fat signal fraction and CTL/S (the liver-to-splenic attenuation ratio). Linear lines are best-fit lines of the linear regression equations. CT, computed tomography.
Figure 5
Figure 5
Receiver operating characteristics (ROC) curves for diagnosing moderate to severe hepatic steatosis (≥15.72% of the fat signal fraction on magnetic resonance spectroscopy). (A) ROC curves for diagnosing moderate to severe hepatic steatosis using CTL-S (the difference between hepatic and splenic attenuation). Dots of each figure were the cut-off values by the Youden index; (B) ROC curves for diagnosing moderate to severe hepatic steatosis using CTL/S (the liver-to-splenic attenuation ratio). Dots of each figure were the cut-off values by the Youden index. The areas under the ROC curves of the two CT indices were not significantly different (P=0.6314). AUC, area under the ROC curves; CT, computed tomography; HU, Hounsfield unit.
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