Diagnostic performance of a rapid magnetic resonance imaging method of measuring hepatic steatosis

Pierre TG, Levelt E, McCann GP. A comparison of liver fat fraction measurement on MRI at 3T and 1.5T

PURPOSE

Volumetric liver fat fraction (VLFF) measurements were made using the HepaFat-Scan® technique at 1.5T and 3T to determine the agreement between the measurements obtained at the two fields.

METHODS

Sixty patients with type 2 diabetes (67% male, mean age 50.92 ± 6.56yrs) and thirty healthy volunteers (50% male, mean age 48.63 ± 6.32yrs) were scanned on 1.5T Aera and 3T Skyra (Siemens, Erlangen, Germany) MRI scanners on the same day using the HepaFat-Scan® gradient echo protocol with modification of echo times for 3T (TEs 2.38, 4.76, 7.14 ms at 1.5T and 1.2, 2.4, 3.6 ms at 3T). The 3T analyses were performed independently of the 1.5T analyses by a different analyst, blinded from the 1.5T results. Data were analysed for agreement and bias using Bland-Altman methods and intraclass correlation coefficients (ICC). A second cohort of 17 participants underwent interstudy repeatability assessment of VLFF measured by HepaFat-Scan® at 3T.

RESULTS

A small, but statistically significant mean bias of 0.48% was observed between 3T and 1.5T with 95% limits of agreement -2.2% to 3.2% VLFF. The ICC for agreement between field strengths was 0.983 (95% CI 0.972-0.989). In the repeatability cohort studied at 3T the repeatability coefficient was 4.2%. The ICC for agreement was 0.971 (95% CI 0.921-0.989).

CONCLUSION

There is minimal bias and excellent agreement between the measures of VLFF using the HepaFat-Scan® at 1.5 and 3T. The test retest repeatability coefficient at 3T is comparable to the 95% limits of agreement between 1.5T and 3T suggesting that measurements can be made interchangeably between field strengths.

Impact of the Analytical Approach on the Reliability of MRI-Based Assessment of Hepatic Fat Content

MRI is a popular noninvasive method for the assessment of liver fat content. After MRI scan acquisition, there is currently no standardized image analysis procedure for the most accurate estimate of liver fat content. We determined intraindividual reliability of MRI-based liver fat measurement using 10 different MRI slice analysis methods in normal-weight, overweight, and obese individuals who underwent 2 same-day abdominal MRI scans. We also compared the agreement in liver fat content between analytical methods and assessed the variability in fat content across the entire liver. Our results indicate that liver fat content varies across the liver, with some slices averaging 54% lower and others 75% higher fat content than the mean of all slices (gold standard). Our data suggest that the entire liver should be contoured on at least every 10th slice to achieve close agreement with the gold standard.

Hepatic iron concentration correlates with insulin sensitivity in nonalcoholic fatty liver disease

Rodent and cell‐culture models support a role for iron‐related adipokine dysregulation and insulin resistance in the pathogenesis of nonalcoholic fatty liver disease (NAFLD); however, substantial human data are lacking. We examined the relationship between measures of iron status, adipokines, and insulin resistance in patients with NAFLD in the presence and absence of venesection. This study forms part of the Impact of Iron on Insulin Resistance and Liver Histology in Nonalcoholic Steatohepatitis (IIRON2) study, a prospective randomized controlled trial of venesection for adults with NAFLD. Paired serum samples at baseline and 6 months (end of treatment) in controls (n = 28) and patients who had venesection (n = 23) were assayed for adiponectin, leptin, resistin, retinol binding protein‐4, tumor necrosis factor α, and interleukin‐6, using a Quantibody, customized, multiplexed enzyme‐linked immunosorbent assay array. Hepatic iron concentration (HIC) was determined using MR FerriScan. Unexpectedly, analysis revealed a significant positive correlation between baseline serum adiponectin concentration and HIC, which strengthened after correction for age, sex, and body mass index (rho = 0.36; P = 0.007). In addition, there were significant inverse correlations between HIC and measures of insulin resistance (adipose tissue insulin resistance (Adipo‐IR), serum insulin, serum glucose, homeostasis model assessment of insulin resistance, hemoglobin A1c, and hepatic steatosis), whereas a positive correlation was noted with the insulin sensitivity index. Changes in serum adipokines over 6 months did not differ between the control and venesection groups. Conclusion: HIC positively correlates with serum adiponectin and insulin sensitivity in patients with NAFLD. Further study is required to establish causality and mechanistic explanations for these associations and their relevance in the pathogenesis of insulin resistance and NAFLD. (Hepatology Communications 2018;2:644‐653)

The natural history of streptozotocin-stimulated non-alcoholic steatohepatitis mice followed by Gd-EOB-DTPA-enhanced MRI: Comparison with simple steatosis mice

PURPOSE

To clarify the development of HCC, temporal change of steatosis and Gd-EOB-DTPA enhancement of non-alcoholic steatohepatitis (NASH) model mice by magnetic resonance imaging (MRI).

MATERIALS AND METHODS

All animal experiments were approved by the institution's Animal Research Committee. MRI was performed on six NASH and six simple steatosis (SS) model mice every 2weeks from the ages of 8weeks to 16weeks. The sequential changes in the number and size of the focal liver lesions detected on Gd-EOB-DTPA-enhanced MRI were evaluated. Additionally, the hepatic fat fraction (HFF), contrast-to-noise ratio (CNR) and relative enhancement (RE) were calculated at each time point. The temporal changes and correlations in these parameters were evaluated.

RESULTS

All alive NASH model mice demonstrated focal liver lesions from week 10, at the latest. Number of the lesions increased with time, and all the lesion enlarged with time. All the lesions larger than 1mm were confirmed as hepatocellular carcinoma (HCC) pathologically. While the HFF remained constant in NASH model mice, HFF in SS model mice dramatically increased with time. CNR of the NASH model mice remained constant through the study period, while CNR in SS model mice decreased with time. Although no correlation was seen in NASH model mice, the HFF showed a negative correlation against CNR and RE in SS model mice.

CONCLUSION

Development of HCC was observed using Gd-EOB-DTPA-enhanced MRI only in NASH model mice. Degree of steatosis and hepatic enhancement by Gd-EOB-DTPA was both constant in NASH model mice, while steatosis increased and hepatic enhancement decreased with time in SS model mice.

Stereological Analysis of Liver Biopsy Histology Sections as a Reference Standard for Validating Non-Invasive Liver Fat Fraction Measurements by MRI

Background and Aims

Validation of non-invasive methods of liver fat quantification requires a reference standard. However, using standard histopathology assessment of liver biopsies is problematical because of poor repeatability. We aimed to assess a stereological method of measuring volumetric liver fat fraction (VLFF) in liver biopsies and to use the method to validate a magnetic resonance imaging method for measurement of VLFF.

Methods

VLFFs were measured in 59 subjects (1) by three independent analysts using a stereological point counting technique combined with the Delesse principle on liver biopsy histological sections and (2) by three independent analysts using the HepaFat-Scan^® technique on magnetic resonance images of the liver. Bland Altman statistics and intraclass correlation (IC) were used to assess the repeatability of each method and the bias between the methods of liver fat fraction measurement.

Results

Inter-analyst repeatability coefficients for the stereology and HepaFat-Scan^® methods were 8.2 (95% CI 7.7–8.8)% and 2.4 (95% CI 2.2–2.5)% VLFF respectively. IC coefficients were 0.86 (95% CI 0.69–0.93) and 0.990 (95% CI 0.985–0.994) respectively. Small biases (≤3.4%) were observable between two pairs of analysts using stereology while no significant biases were observable between any of the three pairs of analysts using HepaFat-Scan^®. A bias of 1.4±0.5% VLFF was observed between the HepaFat-Scan^® method and the stereological method.

Conclusions

Repeatability of the stereological method is superior to the previously reported performance of assessment of hepatic steatosis by histopathologists and is a suitable reference standard for validating non-invasive methods of measurement of VLFF.

Liver enzyme levels and hepatic iron content in Fatty liver: a noninvasive assessment in general population by T2* mapping

RATIONALE AND OBJECTIVES

Existing evidence suggests potential contribution of iron in pathogenesis of nonalcoholic fatty liver disease (NAFLD). We aimed to investigate whether hepatic iron content correlates with liver enzyme levels in NAFLD using a noninvasive magnetic resonance imaging (MRI) technique.

MATERIALS AND METHODS

Subjects from Golestan Cohort Study were randomly selected. Diagnosis of NAFLD was made by combination of ultrasound and MRI. Subjects with NAFLD were divided into two groups with high (H-NAFLD) and low (L-NAFLD) enzyme level according to 95th percentile of alanine aminotransferase (ALT) value in normal population. Quantitative T2* maps of entire cross-sectional area of liver were calculated on pixel-by-pixel basis using a semiautomated software.

RESULTS

A total of 207 subjects were enrolled. Mean T2* values were significantly lower in NAFLD group than controls (P < .001) indicating higher iron content. Male subjects with H-NAFLD had statistically lower T2* values than those with L-NAFLD in multivariate analysis (odds ratio, 0.74; 95% confidence interval [CI], 0.58-0.95), whereas this was not observed in women. Unlike women, there was significant negative correlation between ALT levels and T2* values in men with H-NAFLD (r = -0.66, P = .01). Every 1-millisecond decrement in T2* value was associated with 6.37 IU/L increase in ALT level (95% CI, 1.8-10.9, P = .01) in men with H-NAFLD.

CONCLUSIONS

Higher hepatic iron in men with H-NAFLD, estimated by T2* mapping, may support the role of iron in possible progression of simple steatosis to nonalcoholic steatohepatitis. Lack of such correlation in women could be attributed to relatively lower iron storage or other mechanisms rather than iron.

Improved method for calculating hepatic steatosis using the hepatorenal index

OBJECTIVES

Marshall et al (AJR Am J Roentgenol 2012; 199:997-1002) initially demonstrated that the hepatorenal index is an effective and noninvasive tool to screen patients for hepatic steatosis. The aim of this study was to determine whether the hepatorenal index can be accurately calculated directly from a picture archiving and communication system (PACS) quickly and efficiently without the need for the multiple steps and specialized software used to calculate hepatorenal index in the study by Marshall et al.

METHODS

We evaluated 99 of the 101 patients included in the study by Marshall et al: patients being followed by hepatologists with plans for liver biopsy. The hepatorenal index was calculated by using Digital Imaging and Communications in Medicine (DICOM) images from a PACS and a markup region-of-interest tool. We compared this value to the value that Marshall et al derived by using specialized software and to standard histologic estimates. We created similar subgroups: patients with steatosis based on histologically estimated intracellular fat exceeding 5% and patients without steatosis.

RESULTS

The mean hepatorenal index ± SD for those with steatosis according to histologic findings was 1.87 ± 0.6, and for those without, it was 1.14 ± 0.2. A hepatorenal index of 1.34 or higher had 92% sensitivity for identifying fat exceeding 5%, 85% specificity, a 94% negative predictive value, and a 79% positive predictive value. Substantial agreement was found between the hepatorenal index calculated from DICOM images and macrovesicular fat categorized at the cut point of 1.34 or higher (κ = 0.76; 95% confidence interval, 0.62-0.88; P < .001).

CONCLUSIONS

The hepatorenal index can be quickly and accurately calculated from DICOM images directly on a PACS without supplementary software.

The impact of phlebotomy in nonalcoholic fatty liver disease: A prospective, randomized, controlled trial

Iron is implicated in the pathogenesis of liver injury and insulin resistance (IR) and thus phlebotomy has been proposed as a treatment for nonalcoholic fatty liver disease (NAFLD). We performed a prospective 6-month randomized, controlled trial examining the impact of phlebotomy on the background of lifestyle advice in patients with NAFLD. Primary endpoints were hepatic steatosis (HS; quantified by magnetic resonance imaging) and liver injury (determined by alanine aminotransaminase [ALT] and cytokeratin-18 [CK-18]). Secondary endpoints included insulin resistance measured by the insulin sensitivity index (ISI) and homeostasis model of assessment (HOMA), and systemic lipid peroxidation determined by plasma F2-isoprostane levels. A total of 74 subjects were randomized (33 phlebotomy and 41 control). The phlebotomy group underwent a median (range) of 7 (1-19) venesection sessions and had a significantly greater reduction in ferritin levels over 6 months, compared to controls (-148 ± 114 vs. -38 ± 89 ng/mL; P < 0.001). At 6 months, there was no difference between phlebotomy and control groups in HS (17.7% vs. 15.5%; P = 0.4), serum ALT (36 vs. 46 IU/L; P = 0.4), or CK-18 levels (175 vs. 196 U/L; P = 0.9). Similarly, there was no difference in end-of-study ISI (2.5 vs. 2.7; P = 0.9), HOMA (3.2 vs. 3.2; P = 0.6), or F2-isoprostane levels (1,332 vs. 1,190 pmmol/L; P = 0.6) between phlebotomy and control groups. No differences in any endpoint were noted in patients with hyperferritinemia at baseline. Among patients undergoing phlebotomy, there was no correlation between number of phlebotomy sessions and change in HS, liver injury, or IR from baseline to end of study.

CONCLUSION

Reduction in ferritin by phlebotomy does not improve liver enzymes, hepatic fat, or IR in subjects with NAFLD.

Simultaneous liver iron and fat measures by magnetic resonance imaging in patients with hyperferritinemia

OBJECTIVE

Hyperferritinemia is frequent in chronic liver diseases of any cause, but the extent to which ferritin truly reflects iron stores is variable. In these patients, both liver iron and fat are found in variable amount and association. Liver biopsy is often required to quantify liver fat and iron, but sampling variability and invasiveness limit its use. We aimed to assess single breath-hold multiecho magnetic resonance imaging (MRI) for the simultaneous lipid and iron quantification in patients with hyperferritinemia.

MATERIAL AND METHODS

We compared MRI results for both iron and fat with their respective gold standards - liver iron concentration and computer-assisted image analysis for steatosis on biopsy. We prospectively studied 67 patients with hyperferritinemia and other 10 consecutive patients were used for validation. We estimated two linear calibration equations for the prediction of iron and fat based on MRI. The agreement between MRI and biopsy was evaluated.

RESULTS

MRI showed good performances in both the training and validation samples. MRI information was almost completely in line with that obtained from liver biopsy.

CONCLUSION

Single breath-hold multiecho MRI is an accurate method to obtain a valuable measure of both liver iron and steatosis in patients with hyperferritinemia.

Texture-based classification of liver fibrosis using MRI

PURPOSE

To investigate the ability of texture analysis of MRI images to stage liver fibrosis. Current noninvasive approaches for detecting liver fibrosis have limitations and cannot yet routinely replace biopsy for diagnosing significant fibrosis.

MATERIALS AND METHODS

Forty-nine patients with a range of liver diseases and biopsy-confirmed fibrosis were enrolled in the study. For texture analysis all patients were scanned with a T2 -weighted, high-resolution, spin echo sequence and Haralick texture features applied. The area under the receiver operating characteristics curve (AUROC) was used to assess the diagnostic performance of the texture analysis.

RESULTS

The best mean AUROC achieved for separating mild from severe fibrosis was 0.81. The inclusion of age, liver fat and liver R2 variables into the generalized linear model improved AUROC values for all comparisons, with the F0 versus F1-4 comparison the highest (0.91).

CONCLUSION

Our results suggest that a combination of MRI measures, that include selected texture features from T2 -weighted images, may be a useful tool for excluding fibrosis in patients with liver disease. However, texture analysis of MRI performs only modestly when applied to the classification of patients in the mild and intermediate fibrosis stages.