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Detecting Fatty Liver with MRI and CT

September 28, 2009
Written by: , Filed in: Gastrointestinal Imaging
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A recent study published in The Journal of Magnetic Resonance Imaging set out to determine whether unenhanced CT versus chemical-shift MRI is better in the assessment of the severity of fatty infiltration of the liver, and has determined that unenhanced CT and chemical-shift MRI are comparable in their estimation of the degree of hepatic steatosis.

The Study
This study was comprised of 2 groups of patients. The first group consisted of 38 patients who had histological diagnosis of steatosis obtained by biopsy.

A second group consisted of 20 patients who had undergone liver resection for liver metastases or intrahepatic cholangiocarcinoma with no serologic or pathological evidence of cirrhosis or hepatitis.

Methodology
For the second group, the degree of steatosis was graded on a scale of 0 to 4 as follows:

  • grade 0, no steatosis;
  • grade 1, <10% steatosis;
  • grade 2, ≥10% and <30% steatosis;
  • grade 3, ≥30% and <60% steatosis;
  • grade 4, ≥60% steatosis.

The CT index was calculated by subtracting the attenuation of the spleen from the liver. The MRI index was calculated by subtracting the liver signal intensity on out-of-phase images from in-phase images, and that value divided by the signal intensity on in-phase images.

Results
There was significant correlation between the histological grade of steatosis and both the CT and MRI indices.

However, the grade of steatosis predicted by the MRI index demonstrated a significantly better correlation with the histopathological grade.

The sensitivity and specificity for this CT index criterion were 94% and 75%, respectively.

However, when using an MRI index value of <0.03, the accuracy was 91%, with sensitivity and specificity values of 94% and 88%, respectively.

Therefore, chemical-shift MRI was better than unenhanced CT at detecting mild grades of steatosis.

When differentiating grades 0 to 2 steatosis from grade 3 and above, there was an accuracy of 91% when using a CT index value of >-8, and 88% with an MRI index <0.25.

The sensitivity and specificity for this CT index criterion were 67% and 100%, respectively, and 56% and 100%, respectively, when using this MRI index criterion.

Reviewer’s Comments
The results of this study are useful in showing that CT and MRI are comparable in evaluating all grades of hepatic steatosis.

In mild degrees of steatosis, MRI performed better than CT. However, such mild degrees of steatosis might not be clinically relevant.

A limitation reported in this study was that the CT and MRI indices did not take into account for other depositional substances, such as hemosiderin, which would affect CT attenuation or MRI signal.

Author: John C. Sabatino, MD, MSD

Reference:
Yoshimitsu K, Kuroda Y, et al. Noninvasive Estimation of Hepatic Steatosis Using Plain CT vs. Chemical-Shift MR Imaging: Significance for Living Donors. J Magn Reson Imaging; 2008;28 (September): 678-684

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