Korean J Radiol.  2019 Sep;20(9):1399-1407. 10.3348/kjr.2019.0068.

Quantitative Evaluation of Hepatic Steatosis Using Normalized Local Variance in a Rat Model: Comparison with Histopathology as the Reference Standard

• Bae JS
• Lee JY
• Lee DH
• Kim H
• Lee Y
• Han JK

• KMID: 2455768
• DOI: http://doi.org/10.3348/kjr.2019.0068

Abstract

OBJECTIVE
To evaluate the diagnostic performance of the normalized local variance (NLV) ultrasound technique in the assessment of hepatic steatosis, and to identify the factors that influence the NLV value using histopathological examination as the reference standard.
MATERIALS AND METHODS
Forty male Sprague-Dawley rats were fed a methionine-choline-deficient diet for variable periods (0, 2, 4, 6, 8, 10, or 12 days or 2, 3, or 4 weeks; four rats per group). At the end of each diet duration, magnetic resonance spectroscopy (MRS) and NLV examination were performed. Thereafter, the rats were sacrificed and their livers were histopathologically evaluated. Receiver operating characteristic (ROC) curve analysis was performed to assess the diagnostic capability of the NLV value in the detection of varying degrees of hepatic steatosis. Univariate and multivariate linear regressions were used to determine the factors associated with the NLV value.
RESULTS
The areas under the ROC curve for the detection of mild, moderate, and severe hepatic steatosis were 0.953, 0.896, and 0.735, respectively. The NLV value showed comparable diagnostic performance to that of MRS in the detection of ≥ mild or ≥ moderate hepatic steatosis. Multivariate linear regression analysis revealed that the degree of hepatic steatosis was the only significant factor affecting the NLV value (p < 0.001).
CONCLUSION
The NLV value of ultrasound demonstrated satisfactory diagnostic performance in the assessment of varying degrees of hepatic steatosis. The degree of hepatic steatosis was the only significant factor that affected the NLV value.

Keyword

Hepatic steatosis; Quantification; Ultrasound; Normalized local variance; Histopathology

MeSH Terms

Animals
Diet
Evaluation Studies as Topic*
Humans
Linear Models
Liver
Magnetic Resonance Spectroscopy
Male
Models, Animal*
Rats*
Rats, Sprague-Dawley
ROC Curve
Ultrasonography

Figure

• 

  Fig. 1 Representative images of MRS and NLV examination of rat fed MCD diet for 4 days.A. After obtaining volumetric T1-weighted images of liver, 10 × 10 × 10 mm3 voxel was carefully located in central portion of liver, avoiding large hepatic vessels or extrahepatic structures. B. For NLV examination, three ROIs were placed in central portion of liver, not including artifacts or large hepatic vessels. Median NLV value obtained from this rat liver was 1.09, and histopathologic examination revealed moderate steatosis (> 33–66%) (not shown). MCD = methionine-choline-deficient, MRS = magnetic resonance spectroscopy, NLV = normalized local variance, ROI = region of interest

• 

  Fig. 2 Induction of nonalcoholic fatty liver disease in rats with MCD diet.Line graphs with trend lines (blue solid lines) and their 95% confidence intervals (red dashed lines). Graph shows changes in histopathologic findings (A–D), measured fat fraction at MRS (E), and NLV value on ultrasonography (F) according to duration of MCD diet.

• 

  Fig. 3 Relationships between NLV value and histopathological variables.Box plots demonstrate distribution of NLV value according to (A) degree of hepatic steatosis, (B) lobular inflammation, (C) ballooning of hepatocyte, and (D) stage of fibrosis. Boxes represent 25th to 75th percentiles (interquartile range), and lines within boxes represent median values. Vertical lines extended from boxes represent minimum and maximum values, excluding outliers that are shown as solid circles.

• 

  Fig. 4 Representative examples of NLV examinations in rat livers without (A) and with (B) hepatic steatosis.A. Three ROIs were placed in right lobe of liver in rat from control group. Obtained median NLV value was 1.52, and histopathologic examination revealed no steatosis (not shown). B. Two ROIs were drawn in both lobes of liver in rat fed MCD diet for 2 weeks. Obtained median NLV value was 1.04, and histopathologic examination demonstrated severe steatosis (> 66%) (not shown).

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