Michael S. Middleton

In vivo characterization of the liver fat 1H MR spectrum

A theoretical triglyceride model was developed for in vivo human liver fat 1H MRS characterization, using the number of double bonds (CHCH), number of methylene‐interrupted double bonds (CHCHCH2CHCH) and average fatty acid chain length. Five 3 T, single‐voxel, stimulated echo acquisition mode spectra (STEAM) were acquired consecutively at progressively longer TEs in a fat–water emulsion phantom and in 121 human subjects with known or suspected nonalcoholic fatty liver disease. T2‐corrected peak areas were calculated. Phantom data were used to validate the model. Human data were used in the model to determine the complete liver fat spectrum. In the fat–water emulsion phantom, the spectrum predicted by the model (based on known fatty acid chain distribution) agreed closely with spectroscopic measurement. In human subjects, areas of CH2 peaks at 2.1 and 1.3 ppm were linearly correlated (slope, 0.172; r = 0.991), as were the 0.9 ppm CH3 and 1.3 ppm CH2 peaks (slope, 0.125; r = 0.989). The 2.75 ppm CH2 peak represented 0.6% of the total fat signal in high‐liver‐fat subjects. These values predict that 8.6% of the total fat signal overlies the water peak. The triglyceride model can characterize human liver fat spectra. This allows more accurate determination of liver fat fraction from MRI and MRS. Copyright

Heritability of Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the United States. The etiology is believed to be multifactorial with a substantial genetic component; however, the heritability of NAFLD is undetermined. Therefore, a familial aggregation study was performed to test the hypothesis that NAFLD is highly heritable. METHODS Overweight children with biopsy-proven NAFLD and overweight children without NAFLD served as probands. Family members were studied, including the use of magnetic resonance imaging to quantify liver fat fraction. Fatty liver was defined as a liver fat fraction of 5% or higher. Etiologies for fatty liver other than NAFLD were excluded. Narrow-sense heritability estimates for fatty liver (dichotomous) and fat fraction (continuous) were calculated using variance components analysis adjusted for covariate effects. RESULTS Fatty liver was present in 17% of siblings and 37% of parents of overweight children without NAFLD. Fatty liver was significantly more common in siblings (59%) and parents (78%) of children with NAFLD. Liver fat fraction was correlated with body mass index, although the correlation was significantly stronger for families of children with NAFLD than those without NAFLD. Adjusted for age, sex, race, and body mass index, the heritability of fatty liver was 1.000 and of liver fat fraction was 0.386. CONCLUSIONS Family members of children with NAFLD should be considered at high risk for NAFLD. These data suggest that familial factors are a major determinant of whether an individual has NAFLD. Studies examining the complex relations between genes and environment in the development and progression of NAFLD are warranted.

Nonalcoholic Fatty Liver Disease: Diagnostic and Fat-Grading Accuracy of Low-Flip-Angle Multiecho Gradient-Recalled-Echo MR Imaging at 1.5 T

PURPOSE To assess the accuracy of four fat quantification methods at low-flip-angle multiecho gradient-recalled-echo (GRE) magnetic resonance (MR) imaging in nonalcoholic fatty liver disease (NAFLD) by using MR spectroscopy as the reference standard. MATERIALS AND METHODS In this institutional review board-approved, HIPAA-compliant prospective study, 110 subjects (29 with biopsy-confirmed NAFLD, 50 overweight and at risk for NAFLD, and 31 healthy volunteers) (mean age, 32.6 years +/- 15.6 [standard deviation]; range, 8-66 years) gave informed consent and underwent MR spectroscopy and GRE MR imaging of the liver. Spectroscopy involved a long repetition time (to suppress T1 effects) and multiple echo times (to estimate T2 effects); the reference fat fraction (FF) was calculated from T2-corrected fat and water spectral peak areas. Imaging involved a low flip angle (to suppress T1 effects) and multiple echo times (to estimate T2* effects); imaging FF was calculated by using four analysis methods of progressive complexity: dual echo, triple echo, multiecho, and multiinterference. All methods except dual echo corrected for T2* effects. The multiinterference method corrected for multiple spectral interference effects of fat. For each method, the accuracy for diagnosis of fatty liver, as defined with a spectroscopic threshold, was assessed by estimating sensitivity and specificity; fat-grading accuracy was assessed by comparing imaging and spectroscopic FF values by using linear regression. RESULTS Dual-echo, triple-echo, multiecho, and multiinterference methods had a sensitivity of 0.817, 0.967, 0.950, and 0.983 and a specificity of 1.000, 0.880, 1.000, and 0.880, respectively. On the basis of regression slope and intercept, the multiinterference (slope, 0.98; intercept, 0.91%) method had high fat-grading accuracy without statistically significant error (P > .05). Dual-echo (slope, 0.98; intercept, -2.90%), triple-echo (slope, 0.94; intercept, 1.42%), and multiecho (slope, 0.85; intercept, -0.15%) methods had statistically significant error (P < .05). CONCLUSION Relaxation- and interference-corrected fat quantification at low-flip-angle multiecho GRE MR imaging provides high diagnostic and fat-grading accuracy in NAFLD.

Pediatric nonalcoholic fatty liver disease: a critical appraisal of current data and implications for future research.

Although population prevalence is very difficult to establish, nonalcoholic fatty liver disease (NAFLD) is probably the most common cause of liver disease in the preadolescent and adolescent age groups. There seems to be an increase in the prevalence of NAFLD, likely related to the dramatic rise in the incidence of obesity during the past 3 decades. Despite an increase in public awareness, overweight/obesity and related conditions, such as NAFLD, remain underdiagnosed by health care providers. Accurate diagnosis and staging of nonalcoholic steatohepatitis (NASH) requires liver biopsy. The development of noninvasive surrogate markers and the advancements in imaging technology will aid in the screening of large populations at risk for NAFLD. Two distinct histological patterns of NASH have been identified in the pediatric population, and discrete clinical and demographic features are observed in children with these 2 patterns. The propensity for NASH to develop in obese, insulin-resistant pubertal boys of Hispanic ethnicity or a non-Hispanic white race may provide clues to the pathogenesis of NAFLD in children. The natural history of pediatric NASH has yet to be defined, but most biopsies in this age group demonstrate some degree of fibrosis. In addition, cirrhosis can be observed in children as young as 10 years. While the optimal treatment of pediatric NAFLD has yet to be determined, lifestyle modification through diet and exercise should be attempted in children diagnosed with NAFLD. A large, multicenter trial of vitamin E and metformin is underway as part of the NASH clinical research network.

A phase 2 clinical trial of metformin as a treatment for non‐diabetic paediatric non‐alcoholic steatohepatitis

Background : Children with non‐alcoholic steatohepatitis are insulin‐resistant and metformin has been proposed as a potential therapy. However, paediatric safety and efficacy data are absent.

SAFETY Study: Alanine Aminotransferase Cutoff Values Are Set Too High for Reliable Detection of Pediatric Chronic Liver Disease

BACKGROUND & AIMS The appropriate alanine aminotransferase (ALT) threshold value to use for diagnosis of chronic liver disease in children is unknown. We sought to develop gender-specific, biology-based, pediatric ALT thresholds. METHODS The Screening ALT for Elevation in Todays Youth (SAFETY) study collected observational data from acute care childrens hospitals, the National Health and Nutrition Examination Survey (NHANES, 1999-2006), overweight children with and without non-alcoholic fatty liver disease (NAFLD), and children with chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infections. The study compared the sensitivity and specificity of ALT thresholds currently used by childrens hospitals vs study-derived, gender-specific, biology-based, ALT thresholds for detecting children with NAFLD, HCV, or HBV. RESULTS The median upper limit of ALT at childrens hospitals was 53 U/L (range, 30-90 U/L). The 95th percentile levels for ALT in healthy weight, metabolically normal, liver disease-free, NHANES pediatric participants were 25.8 U/L (boys) and 22.1 U/L (girls). The concordance statistics of these NHANES-derived thresholds for liver disease detection were 0.85 (95% confidence interval [CI]: 0.74-0.96) in boys and 0.91 (95% CI: 0.83-0.99) in girls for NAFLD, 0.80 (95% CI: 0.70-0.91) in boys and 0.79 (95% CI: 0.69-0.89) in girls for HBV, and 0.86 (95% CI: 0.77-0.95) in boys and 0.84 (95% CI: 0.75-0.93) in girls for HCV. Using current childrens hospitals ALT thresholds, the median sensitivity for detection of NAFLD, HBV, and HCV ranged from 32% to 48%; median specificity was 92% (boys) and 96% (girls). Using NHANES-derived thresholds, the sensitivities were 72% (boys) and 82% (girls); specificities were 79% (boys) and 85% (girls). CONCLUSIONS The upper limit of ALT used in childrens hospitals varies widely and is set too high to reliably detect chronic liver disease. Biology-based thresholds provide higher sensitivity and only slightly less specificity. Clinical guidelines for use of screening ALT and exclusion criteria for clinical trials should be modified.

Fatty Liver Disease: MR Imaging Techniques for the Detection and Quantification of Liver Steatosis

Fatty liver disease is the most common cause of chronic liver disease in the United States. Noninvasive detection and quantification of fat is becoming more and more important clinically, due in large part to the growing prevalence of nonalcoholic fatty liver disease. Steatosis, the accumulation of fat-containing vacuoles within hepatocytes, is a key histologic feature of fatty liver disease. Liver biopsy, the current standard of reference for the assessment of steatosis, is invasive, has sampling errors, and is not appropriate in some settings. Several magnetic resonance (MR) imaging-based techniques--including chemical shift imaging, frequency-selective imaging, and MR spectroscopy--are currently in clinical use for the detection and quantification of fat-water admixtures, with each technique having important advantages, disadvantages, and limitations. These techniques permit the breakdown of the net MR signal into fat and water signal components, allowing the quantification of fat in liver tissue, and are increasingly being used in the diagnosis, treatment, and follow-up of fatty liver disease.

Utility of magnetic resonance imaging versus histology for quantifying changes in liver fat in nonalcoholic fatty liver disease trials

The magnetic resonance imaging–estimated proton density fat fraction (MRI‐PDFF) is a novel imaging‐based biomarker that allows fat mapping of the entire liver, whereas the magnetic resonance spectroscopy–measured proton density fat fraction (MRS‐PDFF) provides a biochemical measure of liver fat in small regions of interest. Cross‐sectional studies have shown that MRI‐PDFF correlates with MRS‐PDFF. The aim of this study was to show the utility of MRI‐PDFF in assessing quantitative changes in liver fat through a three‐way comparison of MRI‐PDFF and MRS‐PDFF with the liver histology–determined steatosis grade at two time points in patients with nonalcoholic fatty liver disease (NAFLD). Fifty patients with biopsy‐proven NAFLD who participated in a randomized trial underwent a paired evaluation with liver biopsy, MRI‐PDFF, and MRS‐PDFF at the baseline and 24 weeks. The mean age and body mass index were 47.8 ± 11.7 years and 30.7 ± 6.5 kg/m2, respectively. MRI‐PDFF showed a robust correlation with MRS‐PDFF both at week 0 and at week 24 (r = 0.98, P < 0.0001 for both). Cross‐sectionally, MRI‐PDFF and MRS‐PDFF increased with increases in the histology‐determined steatosis grade both at week 0 and at week 24 (P < 0.05 for all). Longitudinally, patients who had a decrease (≥1%) or increase (≥1%) in MRI‐PDFF (confirmed by MRS‐PDFF) showed a parallel decrease or increase in their body weight and serum alanine aminotransferase and aspartate aminotransferase levels at week 24 (P < 0.05). This small increase or decrease in liver fat could not be quantified with histology. Conclusion: In this longitudinal study, MRI‐PDFF correlated well with MRS‐PDFF and was more sensitive than the histology‐determined steatosis grade in quantifying increases or decreases in the liver fat content. Therefore, it could be used to quantify changes in liver fat in future clinical trials. (Hepatology 2013; 58:1930–1940)

Nonalcoholic Fatty Liver Disease: MR Imaging of Liver Proton Density Fat Fraction to Assess Hepatic Steatosis

PURPOSE To evaluate the diagnostic performance of magnetic resonance (MR) imaging-estimated proton density fat fraction (PDFF) for assessing hepatic steatosis in nonalcoholic fatty liver disease (NAFLD) by using centrally scored histopathologic validation as the reference standard. MATERIALS AND METHODS This prospectively designed, cross-sectional, internal review board-approved, HIPAA-compliant study was conducted in 77 patients who had NAFLD and liver biopsy. MR imaging-PDFF was estimated from magnitude-based low flip angle multiecho gradient-recalled echo images after T2* correction and multifrequency fat modeling. Histopathologic scoring was obtained by consensus of the Nonalcoholic Steatohepatitis (NASH) Clinical Research Network Pathology Committee. Spearman correlation, additivity and variance stabilization for regression for exploring the effect of a number of potential confounders, and receiver operating characteristic analyses were performed. RESULTS Liver MR imaging-PDFF was systematically higher, with higher histologic steatosis grade (P < .001), and was significantly correlated with histologic steatosis grade (ρ = 0.69, P < .001). The correlation was not confounded by age, sex, lobular inflammation, hepatocellular ballooning, NASH diagnosis, fibrosis, or magnetic field strength (P = .65). Area under the receiver operating characteristic curves was 0.989 (95% confidence interval: 0.968, 1.000) for distinguishing patients with steatosis grade 0 (n = 5) from those with grade 1 or higher (n = 72), 0.825 (95% confidence interval: 0.734, 0.915) to distinguish those with grade 1 or lower (n = 31) from those with grade 2 or higher (n = 46), and 0.893 (95% confidence interval: 0.809, 0.977) to distinguish those with grade 2 or lower (n = 58) from those with grade 3 (n = 19). CONCLUSION MR imaging-PDFF showed promise for assessment of hepatic steatosis grade in patients with NAFLD. For validation, further studies with larger sample sizes are needed.

Estimation of Hepatic Proton-Density Fat Fraction by Using MR Imaging at 3.0 T

PURPOSE To compare the accuracy of several magnetic resonance (MR) imaging-based methods for hepatic proton-density fat fraction (FF) estimation at 3.0 T, with spectroscopy as the reference technique. MATERIALS AND METHODS This prospective study was institutional review board approved and HIPAA compliant. Informed consent was obtained. One hundred sixty-three subjects (39 with known hepatic steatosis, 110 with steatosis risk factors, 14 without risk factors) underwent proton MR spectroscopy and non-T1-weighted gradient-echo MR imaging of the liver. At spectroscopy, the reference FF was determined from frequency-selective measurements of fat and water proton densities. At imaging, FF was calculated by using two-, three-, or six-echo methods, with single-frequency and multifrequency fat signal modeling. The three- and six-echo methods corrected for T2*; the two-echo methods did not. For each imaging method, the fat estimation accuracy was assessed by using linear regression between the imaging FF and spectroscopic FF. Binary classification accuracy of imaging was assessed at four reference spectroscopic thresholds (0.04, 0.06, 0.08, and 0.10 FF). RESULTS Regression intercept of two-, three-, and six-echo methods were -0.0211, 0.0087, and -0.0062 (P <.001 for all three) without multifrequency modeling and -0.0237 (P <.001), 0.0022, and -0.0007 with multifrequency modeling, respectively. Regression slope of two-, three-, and six-echo methods were 0.8522, 0.8528, and 0.7544 (P <.001 for all three) without multifrequency modeling and 0.9994, 0.9775, and 0.9821 with multifrequency modeling, respectively. Significant deviation of intercept and slope from 0 and 1, respectively, indicated systematic error. Classification accuracy was 82.2%-90.1%, 93.9%-96.3%, and 83.4%-89.6% for two-, three-, and six-echo methods without multifrequency modeling and 88.3%-92.0%, 95.1%-96.3%, and 94.5%-96.3% with multifrequency modeling, respectively, depending on the FF threshold. T2*-corrected (three- and six-echo) multifrequency imaging methods had the overall highest FF estimation and classification accuracy. Among methods without multifrequency modeling, the T2-corrected three-echo method had the highest accuracy. CONCLUSION Non-T1-weighted MR imaging with T2 correction and multifrequency modeling helps accurately estimate hepatic proton-density FF at 3.0 T.