Estimation of hepatic proton-density fat fraction by using MR imaging at 3.0 T

Multisite, multivendor validation of the accuracy and reproducibility of proton-density fat-fraction quantification at 1.5T and 3T using a fat-water phantom

PURPOSE

To evaluate the accuracy and reproducibility of quantitative chemical shift-encoded (CSE) MRI to quantify proton-density fat-fraction (PDFF) in a fat-water phantom across sites, vendors, field strengths, and protocols.

METHODS

Six sites (Philips, Siemens, and GE Healthcare) participated in this study. A phantom containing multiple vials with various oil/water suspensions (PDFF:0%-100%) was built, shipped to each site, and scanned at 1.5T and 3T using two CSE protocols per field strength. Confounder-corrected PDFF maps were reconstructed using a common algorithm. To assess accuracy, PDFF bias and linear regression with the known PDFF were calculated. To assess reproducibility, measurements were compared across sites, vendors, field strengths, and protocols using analysis of covariance (ANCOVA), Bland-Altman analysis, and the intraclass correlation coefficient (ICC).

RESULTS

PDFF measurements revealed an overall absolute bias (across sites, field strengths, and protocols) of 0.22% (95% confidence interval, 0.07%-0.38%) and R²  > 0.995 relative to the known PDFF at each site, field strength, and protocol, with a slope between 0.96 and 1.02 and an intercept between -0.56% and 1.13%. ANCOVA did not reveal effects of field strength (P = 0.36) or protocol (P = 0.19). There was a significant effect of vendor (F = 25.13, P = 1.07 × 10^-10 ) with a bias of -0.37% (Philips) and -1.22% (Siemens) relative to GE Healthcare. The overall ICC was 0.999.

CONCLUSION

CSE-based fat quantification is accurate and reproducible across sites, vendors, field strengths, and protocols. Magn Reson Med 77:1516-1524, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Quantification of renal steatosis in type II diabetes mellitus using dixon-based MRI

PURPOSE

To evaluate renal lipid content in subjects with and without type II diabetes mellitus (DM2) using Dixon-based magnetic resonance imaging (MRI).

MATERIALS AND METHODS

This retrospective study was approved by the Institutional Review Board and compliant with the Health Insurance Portability and Accountability Act. Sixty-nine adults with or without DM2 (n = 29, n = 40) underwent 3T MRI of the abdomen using 3D multiecho Dixon gradient-echo acquisition and proton-density fat fraction (FF) reconstruction. FF values were recorded within segmented regions of interest in the kidneys and liver. The FF measurement error was estimated from the within-subject difference between the right and left kidneys using Bland-Altman analysis. Correlation between renal FF, hepatic FF, and body mass index (BMI) was evaluated. The association between renal FF and DM2 was evaluated by Wilcoxon rank sum test as well as by multivariate regression to correct for potential confounding effects of age, sex, BMI, creatinine, and hepatic FF. P < 0.05 was considered statistically significant.

RESULTS

Per-subject 95% limits of agreement of the renal FF measurement were [-3.26%, +3.22%]. BMI was significantly correlated with renal FF (r = 0.266, P = 0.027) and with liver FF (r = 0.344, P = 0.006). Correlation between renal and hepatic FF did not reach statistical significance (r = 0.215, P = 0.090). Median renal FF (±interquartile range) was 2.18% (±2.52%) in the DM2 cohort, significantly higher than 0.80% (±2.63%) in the non-DM2 cohort (P < 0.001). After correcting for potential confounders, the relationship between DM2 and renal FF remained statistically significant (P = 0.005).

CONCLUSION

Renal lipid content can be measured noninvasively using Dixon-based MRI and may be increased in subjects with DM2 compared to those without DM2. J. Magn. Reson. Imaging 2016;44:1312-1319.

Reproducibility of Intra- and Inter-scanner Measurements of Liver Fat Using Complex Confounder-corrected Chemical Shift Encoded MRI at 3.0 Tesla

The purpose of this study was to prospectively evaluate the reproducibility of the proton density fat-fraction (PDFF) of the liver using the IDEAL algorithm, a quantitative confounder-corrected chemical-shift-encoded MRI method. Data were obtained from 15 volunteers on four different days. The first and the third examinations were conducted on scanner one with one-week intervals, while the second and the fourth tests were performed on scanner two with same time interval. For each test, two MR scans were performed, one before and one after a meal. Regions-of-interest measurements were manually calculated to estimate the PDFF in the right and left lobes on the PDFF images. Reproducibility was measured using the intra-class correlation coefficient (ICC). The ICCs of the PDFF in the right and left lobes were 0.935 and 0.878, respectively. The intra-scanner ICCs of the right lobe before and after a meal or at a one-week interval were 0.924 and 0.953, respectively. The inter-scanner ICCs of PDFF the next day and at a one-week interval were 0.920 and 0.864, respectively. The PDFF of liver derived from IDEAL demonstrated high intra- and inter-scanner measurement reproducibility. The PDFF of the right lobe before a meal was more reproducible than after-meal measurements.

[Techniques for quantification of liver fat in risk stratification of diabetics]

CLINICAL/METHODICAL ISSUE

Fatty liver disease plays an important role in the development of type 2 diabetes. Accurate techniques for detection and quantification of liver fat are essential for clinical diagnostics.

STANDARD RADIOLOGICAL METHODS

Chemical shift-encoded magnetic resonance imaging (MRI) is a simple approach to quantify liver fat content.

METHODICAL INNOVATIONS

Liver fat quantification using chemical shift-encoded MRI is influenced by several bias factors, such as T2* decay, T1 recovery and the multispectral complexity of fat.

PERFORMANCE

The confounder corrected proton density fat fraction is a simple approach to quantify liver fat with comparable results independent of the software and hardware used.

ACHIEVEMENTS

The proton density fat fraction is an accurate biomarker for assessment of liver fat.

PRACTICAL RECOMMENDATIONS

An accurate and reproducible quantification of liver fat using chemical shift-encoded MRI requires a calculation of the proton density fat fraction.

Non-invasive screening of diabetics in primary care for NAFLD and advanced fibrosis by MRI and MRE

BACKGROUND

Current guidelines do not recommend screening for non-alcoholic fatty liver disease (NAFLD) or advanced fibrosis. Patients with type 2 diabetes mellitus (T2DM) are known to be at increased risk for NAFLD and advanced fibrosis.

AIM

To assess the feasibility in diabetics in a primary care setting of screening for NAFLD and advanced fibrosis, by using non-invasive magnetic resonance imaging (MRI) to estimate the hepatic proton density fat fraction (MRI-PDFF) and magnetic resonance elastography (MRE) to estimate hepatic stiffness.

METHODS

We performed a cross-sectional analysis of a prospective study that included 100 (53% men) consecutively enrolled diabetics who did not have any other aetiology of liver disease. All patients underwent a standardised research visit, laboratory tests, MRI-PDFF, and MRE.

RESULTS

Mean (±s.d.) age and body mass index (BMI) was 59.7 (±11.2) years and 30.8 (±6.5) kg/m(2) , respectively. The prevalence of NAFLD (defined as MRI-PDFF ≥5%) and advanced fibrosis (defined as MRE ≥3.6 kPa) was 65% and 7.1%, respectively. One patient with advanced fibrosis had definite hepatocellular carcinoma. When compared to those without NAFLD, patients with NAFLD were younger (P = 0.028) and had higher mean BMI (P = 0.0008), waist circumference (P < 0.0001) and prevalence of metabolic syndrome (84.6% vs. 40.0%, P < 0.0001). Only 26% of those with NAFLD had elevated alanine aminotransferase.

CONCLUSIONS

This proof-of-concept study demonstrates that T2DM has significant rates of both NAFLD and advanced fibrosis. Concomitant screening for NAFLD and advanced fibrosis by using MRI-proton density fat fraction and magnetic resonance elastography in T2DM is feasible and may be considered after validation in a larger cohort.

Total liver fat quantification using three-dimensional respiratory self-navigated MRI sequence

PURPOSE

MRI can produce quantitative liver fat fraction (FF) maps noninvasively, which can help to improve diagnoses of fatty liver diseases. However, most sequences acquire several two-dimensional (2D) slices during one or more breath-holds, which may be difficult for patients with limited breath-holding capacity. A whole-liver 3D FF map could also be obtained in a single acquisition by applying a reliable breathing-motion correction method. Several correction techniques are available for 3D imaging, but they use external devices, interrupt acquisition, or jeopardize the spatial resolution. To overcome these issues, a proof-of-concept study introducing a self-navigated 3D three-point Dixon sequence is presented here.

METHODS

A respiratory self-gating strategy acquiring a center k-space profile was integrated into a three-point Dixon sequence. We obtained 3D FF maps from a water-fat emulsions phantom and fifteen volunteers. This sequence was compared with multi-2D breath-hold and 3D free-breathing approaches.

RESULTS

Our 3D three-point Dixon self-navigated sequence could correct for respiratory-motion artifacts and provided more precise FF measurements than breath-hold multi-2D and 3D free-breathing techniques.

CONCLUSION

Our 3D respiratory self-gating fat quantification sequence could correct for respiratory motion artifacts and yield more-precise FF measurements. Magn Reson Med 76:1400-1409, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

MRI-determined liver proton density fat fraction, with MRS validation: Comparison of regions of interest sampling methods in patients with type 2 diabetes

PURPOSE

To assess the agreement between published magnetic resonance imaging (MRI)-based regions of interest (ROI) sampling methods using liver mean proton density fat fraction (PDFF) as the reference standard.

MATERIALS AND METHODS

This retrospective, internal review board-approved study was conducted in 35 patients with type 2 diabetes. Liver PDFF was measured by magnetic resonance spectroscopy (MRS) using a stimulated-echo acquisition mode sequence and MRI using a multiecho spoiled gradient-recalled echo sequence at 3.0T. ROI sampling methods reported in the literature were reproduced and liver mean PDFF obtained by whole-liver segmentation was used as the reference standard. Intraclass correlation coefficients (ICCs), Bland-Altman analysis, repeated-measures analysis of variance (ANOVA), and paired t-tests were performed.

RESULTS

ICC between MRS and MRI-PDFF was 0.916. Bland-Altman analysis showed excellent intermethod agreement with a bias of -1.5 ± 2.8%. The repeated-measures ANOVA found no systematic variation of PDFF among the nine liver segments. The correlation between liver mean PDFF and ROI sampling methods was very good to excellent (0.873 to 0.975). Paired t-tests revealed significant differences (P < 0.05) with ROI sampling methods that exclusively or predominantly sampled the right lobe. Significant correlations with mean PDFF were found with sampling methods that included higher number of segments, total area equal or larger than 5 cm(2) , or sampled both lobes (P = 0.001, 0.023, and 0.002, respectively).

CONCLUSION

MRI-PDFF quantification methods should sample each liver segment in both lobes and include a total surface area equal or larger than 5 cm(2) to provide a close estimate of the liver mean PDFF.

Modeling of T2* decay in vertebral bone marrow fat quantification

Bone marrow fat fraction mapping using chemical shift encoding-based water-fat separation is becoming a useful tool in investigating the association between bone marrow adiposity and bone health and in assessing cancer treatment-induced bone marrow damage. Vertebral bone marrow is characterized by short T2* relaxation times, which are in general different for the water and fat components and can confound fat quantification. The purpose of the present study is to compare different approaches to T2* correction in chemical shift encoding-based water-fat imaging of vertebral bone marrow using single-voxel MRS as reference. Eight-echo gradient-echo imaging and single-voxel MRS measurements were made on the spine (L3-L5) of 25 healthy volunteers. Different approaches were evaluated for correction of T2* effects: (a) single-T2* correction, (b) dual-T2* correction, (c) T2' correction using the a priori-known T2 from the MRS at each vertebral body and (d) T2' correction using the a priori-known T2 equal to previously measured average values. Dual-T2* correction resulted in noisier imaging fat fraction maps than single-T2* correction or T2' correction using a priori-known T2. Linear regression analysis between imaging and MRS fat fraction showed a slope significantly different from 1 when using single-T2* correction (R(2) = 0.96) or dual-T2* correction (R(2) = 0.87). T2' correction using the a priori-known T2 resulted in a slope not significantly different from 1, an intercept significantly different from 0 (between 2.4% and 3%) and R(2) = 0.96. Therefore, a T2' correction using a priori-known T2 can remove the fat fraction bias induced by the difference in T2* between water and fat components without degrading noise performance in fat fraction mapping of vertebral bone marrow.

Quantitative magnetic resonance imaging of hepatic steatosis: Validation in ex vivo human livers

Emerging magnetic resonance imaging (MRI) biomarkers of hepatic steatosis have demonstrated tremendous promise for accurate quantification of hepatic triglyceride concentration. These methods quantify the proton density fat-fraction (PDFF), which reflects the concentration of triglycerides in tissue. Previous in vivo studies have compared MRI-PDFF with histologic steatosis grading for assessment of hepatic steatosis. However, the correlation of MRI-PDFF with the underlying hepatic triglyceride content remained unknown. The aim of this ex vivo study was to validate the accuracy of MRI-PDFF as an imaging biomarker of hepatic steatosis. Using ex vivo human livers, we compared MRI-PDFF with magnetic resonance spectroscopy-PDFF (MRS-PDFF), biochemical triglyceride extraction, and histology as three independent reference standards. A secondary aim was to compare the precision of MRI-PDFF relative to biopsy for the quantification of hepatic steatosis. MRI-PDFF was prospectively performed at 1.5 Tesla in 13 explanted human livers. We performed colocalized paired evaluation of liver fat content in all nine Couinaud segments using single-voxel MRS-PDFF (n=117) and tissue wedges for biochemical triglyceride extraction (n=117), and five core biopsies performed in each segment for histologic grading (n=585). Accuracy of MRI-PDFF was assessed through linear regression with MRS-PDFF, triglyceride extraction, and histology. Intraobserver agreement, interobserver agreement, and repeatability of MRI-PDFF and histologic grading were assessed through Bland-Altman analyses. MRI-PDFF showed an excellent correlation with MRS-PDFF (r=0.984, confidence interval 0.978-0.989) and strong correlation with histology (r=0.850, confidence interval 0.791-0.894) and triglyceride extraction (r=0.871, confidence interval 0.818-0.909). Intraobserver agreement, interobserver agreement, and repeatability showed a significantly smaller variance for MRI-PDFF than for histologic steatosis grading (all P<0.001).

CONCLUSION

MRI-PDFF is an accurate, precise, and reader-independent noninvasive imaging biomarker of liver triglyceride content, capable of steatosis quantification over the entire liver.

Nonalcoholic Fatty Liver Disease: Correlation of the Liver Parenchyma Fatty Acid with Intravoxel Incoherent Motion MR Imaging-An Experimental Study in a Rat Model

Purpose

To prospectively evaluate the changes in fatty acid concentration after administrating a 60% high-fat diet to a non-alcoholic fatty liver disease rat model and to perform a correlation analysis between fatty acid with molecular diffusion (D_true), perfusion-related diffusion (D_fast), and perfusion fraction (P_fraction).

Material and Methods

This prospective study was approved by the appropriate ethics committee. Ten male Sprague-Dawley rats were fed a 60% high-fat diet until the study was finished. Point-resolved spectroscopy sequence ¹H-MRS with TR = 1,500 msec, TE = 35 msec, NEX = 64, and 8×8×8 mm³ voxel was used to acquire magnetic resonance spectroscopy (MRS) data. Diffusion-weighted imaging was performed on a two-dimensional multi-b value spin echo planar image with the following parameters: repetition time msec/echo time msec, 4500 /63; field of view, 120×120 msec²; matrix, 128×128; section thickness, 3 mm; number of repetition, 8; and multiple b value, 0, 25, 50, 75, 100, 200, 500, 1000 sec/mm². Baseline magnetic resonance imaging and magnetic resonance spectroscopy data (control) were acquired. ¹H proton MRS and diffusion-weighted imaging were obtained every 2 weeks for 8 weeks. The individual contributions of the true molecular diffusion and the incoherent motions of water molecules in the capillary network to the apparent diffusion changes were estimated using a least-square nonlinear fitting in MatLab. A Wilcoxon signed-rank test with the Kruskal-Wallis test was used to compare each week’s fatty acid mean quantification. Spearman’s correlation coefficient was used to evaluate the correlation between each fatty acid (e.g., total lipid (TL), total saturated fatty acid (TSFA), total unsaturated fatty acid (TUSFA), total unsaturated bond (TUSB), and polyunsaturated bond (PUSB)) and intravoxel incoherent motion (IVIM) mapping images (e.g., D_true, D_fast, and P_fraction).

Results

The highest mean TL value was at week 8 (0.278 ± 0.10) after the administration of the 60% high-fat diet, followed by weeks 6, 4, 2, and 0. The concentration level (16.99±2.29) of TSFA at week 4 was the highest. No significant differences in the concentrations of TUSFA, TUSB, or PUSB were observed in different weeks.

Conclusion

After the administration of the 60% high-fat diet in nonalcoholic fatty liver disease model, TL and TSFA depositions had significant changes. The mean concentrations of TUSFA, TUSB, PUSB did not significantly change. Total unsaturated fatty acid and polyunsaturated bond showed positive correlations with D_true and P_fraction.

Bone marrow fat quantification in the presence of trabecular bone: initial comparison between water-fat imaging and single-voxel MRS

PURPOSE

The purpose of the present study was to test the relative performance of chemical shift-based water-fat imaging in measuring bone marrow fat fraction in the presence of trabecular bone, having as reference standard the single-voxel magnetic resonance spectroscopy (MRS).

METHODS

Six-echo gradient echo imaging and single-voxel MRS measurements were performed on the proximal femur of seven healthy volunteers. The bone marrow fat spectrum was characterized based on the magnitude of measurable fat peaks and an a priori knowledge of the chemical structure of triglycerides, in order to accurately extract the water peak from the overlapping broad fat peaks in MRS. The imaging-based fat fraction results were then compared to the MRS-based results both without and with taking into consideration the presence of short T2* water components in MRS.

RESULTS

There was a significant underestimation of the fat fraction using the MRS model not accounting for short T2* species with respect to the imaging-based fat fraction. A good equivalency was observed between the fat fraction using the MRS model accounting for short T2* species and the imaging-based fat fraction (R(2) = 0.87).

CONCLUSION

The consideration of the short T2* water species effect on bone marrow fat quantification is essential when comparing MRS-based and imaging-based fat fraction results.

Proton density fat-fraction is an accurate biomarker of hepatic steatosis in adolescent girls and young women

OBJECTIVES

To compare complex quantitative magnetic resonance imaging (MRI) with MR spectroscopy (MRS) for quantification of hepatic steatosis (HS) and determine clinically significant MRI-based thresholds of HS in female youths.

METHODS

This prospective, cross-sectional study was conducted in 132 healthy females (11-22 years, mean 13.3 ± 2). Proton density fat-fraction (PDFF) was measured using complex quantitative MRI and MRS. Body mass index (BMI), fasting labs [glucose, insulin, alanine aminotransferase (ALT), and other metabolic markers] were obtained. Outcomes were measured using regression analysis, Spearman-rank correlation, and receiver operator characteristics (ROC) analysis. HS was defined as MRI-PDFF >5.6%.

RESULTS

HS was detected by MRI-PDFF in 15% of all subjects. Linear regression demonstrated excellent correlation and agreement [r(2) = 0.96, slope = 0.97 (95 %CI: 0.94-1.00), intercept = 0.78% (95 %CI: 0.58-0.98%)] between MRI-PDFF and MRS-PDFF. MRI-PDFF had a sensitivity of 100% (95 %CI: 0.79-1.00), specificity of 96.6% (95 %CI: 0.91-0.99), and a kappa index of 87% (95 %CI: 0.75-0.99) for identifying HS. In overweight subjects with HS, MRI-PDFF correlated with ALT (r = 0.84, p < 0.0001) and insulin (r = 0.833, p < 0.001), but not with BMI or WC. ROC analysis ascertained an optimal MRI-PDFF threshold of 3.5% for predicting metabolic syndrome (sensitivity = 76 %, specificity = 83 %).

CONCLUSION

Complex quantitative MRI demonstrates strong correlation and agreement with MRS to quantify hepatic triglyceride content in adolescent girls and young women. A low PDFF threshold is predictive of metabolic syndrome in this population.

KEY POINTS

• Confounder-corrected quantitative MRI (ccqMRI) effectively measures hepatic triglyceride content in adolescent girls. • MRS and ccqMRI strongly correlate in liver proton density fat-fraction (PDFF) detection. • A PDFF threshold of 3.5% may be predictive of paediatric metabolic syndrome.

Cross-sectional and longitudinal evaluation of liver volume and total liver fat burden in adults with nonalcoholic steatohepatitis

PURPOSE

To explore the cross-sectional and longitudinal relationships between fractional liver fat content, liver volume, and total liver fat burden.

METHODS

In 43 adults with non-alcoholic steatohepatitis participating in a clinical trial, liver volume was estimated by segmentation of magnitude-based low-flip-angle multiecho GRE images. The liver mean proton density fat fraction (PDFF) was calculated. The total liver fat index (TLFI) was estimated as the product of liver mean PDFF and liver volume. Linear regression analyses were performed.

RESULTS

Cross-sectional analyses revealed statistically significant relationships between TLFI and liver mean PDFF (R 2 = 0.740 baseline/0.791 follow-up, P < 0.001 baseline/P < 0.001 follow-up), and between TLFI and liver volume (R 2 = 0.352/0.452, P < 0.001/< 0.001). Longitudinal analyses revealed statistically significant relationships between liver volume change and liver mean PDFF change (R 2 = 0.556, P < 0.001), between TLFI change and liver mean PDFF change (R 2 = 0.920, P < 0.001), and between TLFI change and liver volume change (R 2 = 0.735, P < 0.001).

CONCLUSION

Liver segmentation in combination with MRI-based PDFF estimation may be used to monitor liver volume, liver mean PDFF, and TLFI in a clinical trial.

Comparison of Multi-Echo Dixon Methods with Volume Interpolated Breath-Hold Gradient Echo Magnetic Resonance Imaging in Fat-Signal Fraction Quantification of Paravertebral Muscle

Objective

To assess whether multi-echo Dixon magnetic resonance (MR) imaging with simultaneous T2* estimation and correction yields more accurate fat-signal fraction (FF) measurement of the lumbar paravertebral muscles, in comparison with non-T2*-corrected two-echo Dixon or T2*-corrected three-echo Dixon, using the FF measurements from single-voxel MR spectroscopy as the reference standard.

Materials and Methods

Sixty patients with low back pain underwent MR imaging with a 1.5T scanner. FF mapping images automatically obtained using T2*-corrected Dixon technique with two (non-T2*-corrected), three, and six echoes, were compared with images from single-voxel MR spectroscopy at the paravertebral muscles on levels L4 through L5. FFs were measured directly by two radiologists, who independently drew the region of interest on the mapping images from the three sequences.

Results

A total of 117 spectroscopic measurements were performed either bilaterally (57 of 60 subjects) or unilaterally (3 of 60 subjects). The mean spectroscopic FF was 14.3 ± 11.7% (range, 1.9-63.7%). Interobserver agreement was excellent between the two radiologists. Lin's concordance correlation between the spectroscopic findings and all the imaging-based FFs were statistically significant (p < 0.001). FFs obtained from the T2*-corrected six-echo Dixon sequences showed a significantly better concordance with the spectroscopic data, with its concordance correlation coefficient being 0.99 and 0.98 (p < 0.001), as compared with two- or three-echo methods.

Conclusion

T2*-corrected six-echo Dixon sequence would be a better option than two- or three-echo methods for noninvasive quantification of lumbar muscle fat quantification.

Association Between Quantity of Liver Fat and Cardiovascular Risk in Patients With Nonalcoholic Fatty Liver Disease Independent of Nonalcoholic Steatohepatitis

BACKGROUND & AIMS

The association between quantity of liver fat and the presence of metabolic syndrome needs to be assessed systematically. We aimed to determine the association between the quantity of liver fat and the presence of the metabolic syndrome in patients with biopsy-proven nonalcoholic fatty liver disease (NAFLD), independent of nonalcoholic steatohepatitis (NASH).

METHODS

We recruited 146 patients with well-characterized biopsy-proven NAFLD and 50 individuals without NAFLD (controls) to participate in a case-control study at the NAFLD Translational Research Unit at the University of California San Diego. Liver fat was quantified in patients with NAFLD and controls using an advanced magnetic resonance imaging-based biomarker, the proton-density-fat-fraction (MRI-PDFF). Patients with NAFLD were divided into groups based on whether they were above or below the median MRI-PDFF value (15.4% in patients with NAFLD); the MRI-PDFF value for controls was less than 5%. The primary outcome was the presence of the metabolic syndrome using Adult Treatment Panel III criteria without and with adjustment for the presence of NASH.

RESULTS

Compared with NAFLD patients with MRI-PDFF values below the median, and compared with controls, NAFLD patients with MRI-PDFF values above the median were more likely to have abdominal obesity (P < .0001), lower levels of high-density cholesterol (P < .0001), higher levels of triglycerides (P < .0001), and higher fasting glucose levels (P < .001). Compared with NAFLD patients with MRI-PDFF values below the median, NAFLD patients with MRI-PDFF above the median were more likely to have the metabolic syndrome (60.3% vs. 44.4%; P < .04), independent of biopsy-detected NASH.

CONCLUSIONS

Increased liver fat content in patients with NAFLD is associated with increased rates of the metabolic syndrome, independent of NASH. There appears to be an association between the quantity of liver fat and the risk for cardiovascular disease in patients with NAFLD.

Accelerating MR Imaging Liver Steatosis Measurement Using Combined Compressed Sensing and Parallel Imaging: A Quantitative Evaluation

PURPOSE

To determine the limits of agreement of hepatic fat fraction and R2* relaxation rate quantified with accelerated magnetic resonance (MR) imaging reconstructed with combined compressed sensing and parallel imaging compared with conventional fully sampled acquisitions.

MATERIALS AND METHODS

Eleven subjects with type 2 diabetes and a healthy control subject were recruited with the approval of the Newcastle and North Tyneside 2 ethics committee and written consent. Undersampled data at ratios of 2.6×, 2.9×, 3.8×, and 4.8× were prospectively acquired in addition to fully sampled data by using five gradient echoes per repetition time at 3.0 T. Fat fraction maps were calculated by using combined compressed sensing and parallel imaging (CS-PI) reconstruction and Bland-Altman analysis performed to assess bias and 95% limits of agreement. Inter- and intrarater analysis was performed for quantitative fat fraction and R2* relaxation rate, and image quality was assessed with a four-point scale by two independent observers.

RESULTS

The fat fractions from the accelerated acquisitions had 95% limits of agreement of 1.2%, 1.2%, 1.1%, and 1.5%, respectively, with no bias. When compared with the intra- and interrater 95% limits of agreement (0.7% and 0.8%), acceleration of up to 3.8× did not greatly degrade the fat fraction measurements. No or minimal artifact was detected at 2.6× and 2.9× accelerations, moderate artifact was detected at 3.8× acceleration, and substantial artifact was detected at 4.8× acceleration.

CONCLUSION

Prospective undersampling and CS-PI reconstruction of liver fat fractions can be used to accelerate liver fat fraction measurements. The fat fractions and image quality produced were acceptable up to a factor of 3.8×, thereby shortening the required breath-hold duration from 17.7 seconds to 4.7 seconds.

Accuracy and the effect of possible subject-based confounders of magnitude-based MRI for estimating hepatic proton density fat fraction in adults, using MR spectroscopy as reference

PURPOSE

To determine the accuracy and the effect of possible subject-based confounders of magnitude-based magnetic resonance imaging (MRI) for estimating hepatic proton density fat fraction (PDFF) for different numbers of echoes in adults with known or suspected nonalcoholic fatty liver disease, using MR spectroscopy (MRS) as a reference.

MATERIALS AND METHODS

In this retrospective analysis of 506 adults, hepatic PDFF was estimated by unenhanced 3.0T MRI, using right-lobe MRS as reference. Regions of interest placed on source images and on six-echo parametric PDFF maps were colocalized to MRS voxel location. Accuracy using different numbers of echoes was assessed by regression and Bland-Altman analysis; slope, intercept, average bias, and R2 were calculated. The effect of age, sex, and body mass index (BMI) on hepatic PDFF accuracy was investigated using multivariate linear regression analyses.

RESULTS

MRI closely agreed with MRS for all tested methods. For three- to six-echo methods, slope, regression intercept, average bias, and R2 were 1.01-0.99, 0.11-0.62%, 0.24-0.56%, and 0.981-0.982, respectively. Slope was closest to unity for the five-echo method. The two-echo method was least accurate, underestimating PDFF by an average of 2.93%, compared to an average of 0.23-0.69% for the other methods. Statistically significant but clinically nonmeaningful effects on PDFF error were found for subject BMI (P range: 0.0016 to 0.0783), male sex (P range: 0.015 to 0.037), and no statistically significant effect was found for subject age (P range: 0.18-0.24).

CONCLUSION

Hepatic magnitude-based MRI PDFF estimates using three, four, five, and six echoes, and six-echo parametric maps are accurate compared to reference MRS values, and that accuracy is not meaningfully confounded by age, sex, or BMI.

Effects of Insulin Glargine and Liraglutide Therapy on Liver Fat as Measured by Magnetic Resonance in Patients With Type 2 Diabetes: A Randomized Trial

OBJECTIVE

This study determined the effects of insulin versus liraglutide therapy on liver fat in patients with type 2 diabetes inadequately controlled with oral agents therapy, including metformin.

RESEARCH DESIGN AND METHODS

Thirty-five patients with type 2 diabetes inadequately controlled on metformin monotherapy or in combination with other oral antidiabetic medications were randomized to receive insulin glargine or liraglutide therapy for 12 weeks. The liver proton density fat fraction (PDFF) was measured by MRS. The mean liver PDFF, the total liver volume, and the total liver fat index were measured by MRI. The Student t test, the Fisher exact test, and repeated-measures ANOVA were used for statistical analysis.

RESULTS

Insulin treatment was associated with a significant improvement in glycated hemoglobin (7.9% to 7.2% [62.5 to 55.2 mmol/mol], P = 0.005), a trend toward a decrease in MRS-PDFF (12.6% to 9.9%, P = 0.06), and a significant decrease in liver mean MRI-PDFF (13.8% to 10.6%, P = 0.005), liver volume (2,010.6 to 1,858.7 mL, P = 0.01), and the total liver fat index (304.4 vs. 209.3 % ⋅ mL, P = 0.01). Liraglutide treatment was also associated with a significant improvement in glycated hemoglobin (7.6% to 6.7% [59.8 to 50.2 mmol/mol], P < 0.001) but did not change MRS-PDFF (P = 0.80), liver mean MRI-PDFF (P = 0.15), liver volume (P = 0.30), or the total liver fat index (P = 0.39).

CONCLUSIONS

The administration of insulin glargine therapy reduced the liver fat burden in patients with type 2 diabetes. However, the improvements in the liver fat fraction and glycemia control were not significantly different from those in the liraglutide group.

In vivo breath-hold (1) H MRS simultaneous estimation of liver proton density fat fraction, and T1 and T2 of water and fat, with a multi-TR, multi-TE sequence

PURPOSE

To examine the intra-examination repeatability of proton density fat fraction (PDFF) and T1 and T2 of liver water and fat as estimated by a novel multi-repetition time (TR)-echo time (TE) (1) H magnetic resonance spectroscopy (MRS)-stimulated echo acquisition mode (STEAM) sequence that acquires 32 spectra for a range of TRs and TEs in single breath-hold.

MATERIALS AND METHODS

Sixty-seven subjects undergoing liver MRI examinations at 3T had three multi-TR-TE sequences acquired consecutively in a single session. This sequence was designed to allow accurate estimation of T1 and T2 of both water and fat, as well as PDFF, in a single breath-hold. A standard long-TR, multi-TE sequence was also acquired to allow comparison of estimated PDFF. Regression and interclass correlation (ICC) analyses were performed.

RESULTS

There was strong agreement between PDFF estimated by the multi-TR-TE and long-TR, multi-TE sequences (slope 0.997; intercept -0.03; R = 0.997). The multi-TR-TE sequence had high repeatability for estimating PDFF (ICC = 0.999), water T2 (ICC = 0.920), water T1 (ICC = 0.845), and fat T2 (ICC = 0.760), and moderate repeatability for estimating fat T1 (ICC = 0.556).

CONCLUSION

A novel multi-TR-TE sequence can estimate PDFF and water and fat T1 and T2 in a single breath-hold. Refinement may be needed to improve repeatability for fat T1 estimation.

Quantification of hepatic steatosis with a multistep adaptive fitting MRI approach: prospective validation against MR spectroscopy

OBJECTIVE. The purpose of this study is to prospectively compare hybrid and complex chemical shift-based MRI fat quantification methods against MR spectroscopy (MRS) for the measurement of hepatic steatosis. SUBJECTS AND METHODS. Forty-two subjects (18 men and 24 women; mean ± SD age, 52.8 ± 14 years) were prospectively enrolled and imaged at 3 T with a chemical shift-based MRI sequence and a single-voxel MRS sequence, each in one breath-hold. Proton density fat fraction and rate constant (R2*) using both single- and dual-R2* hybrid fitting methods, as well as proton density fat fraction and R2* maps using a complex fitting method, were generated. A single radiologist colocalized volumes of interest on the proton density fat fraction and R2* maps according to the spectroscopy measurement voxel. Agreement among the three MRI methods and the MRS proton density fat fraction values was assessed using linear regression, intraclass correlation coefficient (ICC), and Bland-Altman analysis. RESULTS. Correlation between the MRI and MRS measures of proton density fat fraction was excellent. Linear regression coefficients ranged from 0.98 to 1.01, and intercepts ranged from -1.12% to 0.49%. Agreement measured by ICC was also excellent (0.99 for all three methods). Bland-Altman analysis showed excellent agreement, with mean differences of -1.0% to 0.6% (SD, 1.3-1.6%). CONCLUSION. The described MRI-based liver proton density fat fraction measures are clinically feasible and accurate. The validation of proton density fat fraction quantification methods is an important step toward wide availability and acceptance of the MRI-based measurement of proton density fat fraction as an accurate and generalizable biomarker.

Interexamination repeatability and spatial heterogeneity of liver iron and fat quantification using MRI-based multistep adaptive fitting algorithm

PURPOSE

To assess the interexamination repeatability and spatial heterogeneity of liver iron and fat measurements using a magnetic resonance imaging (MRI)-based multistep adaptive fitting algorithm.

MATERIALS AND METHODS

This prospective observational study was Institutional Review Board-approved and Health Insurance Portability and Accountability Act-compliant. Written informed consent was waived. In all, 150 subjects were imaged on 3T MRI systems. A whole-liver volume acquisition was performed twice using a six-echo 3D spoiled gradient echo sequence during two immediately adjacent examinations. Colocalized regions of interest (ROIs) in three different hepatic segments were placed for R2 * and proton density fat fraction (PDFF) measurements by two readers independently. Mean R2 * and PDFF values between readers and acquisitions were compared using the Wilcoxon signed-rank test, intraclass correlation coefficients (ICCs), linear regression, Bland-Altman analysis, and analysis of variance (ANOVA).

RESULTS

The mean R2 * and PDFF values across all ROIs and measurements were 51.2 ± 25.2 s(-1) and 6.9 ± 6.4%, respectively. Mean R2 * and PDFF values showed no significant differences between the two acquisitions (P = 0.05-0.87). Between the two acquisitions, R2 * and PDFF values demonstrated almost perfect agreement (ICCs = 0.979-0.994) and excellent correlation (R(2)  = 0.958-0.989). Bland-Altman analysis also demonstrated excellent agreement. In the ANOVA, the individual patient and ROI location were significant effects for both R2 * and PDFF values (P < 0.05).

CONCLUSION

MRI-based R2 * and PDFF measurements are repeatable between examinations. Between-measurement changes in R2 * of more than 10.1 s(-1) and in PDFF of more than 1.7% are likely due to actual tissue changes. Liver iron and fat content are variable between hepatic segments.

Sensitivity of chemical shift-encoded fat quantification to calibration of fat MR spectrum

PURPOSE

To evaluate the impact of different fat spectral models on proton density fat fraction quantification using chemical shift-encoded MRI (CSE-MRI).

METHODS

In a simulation study, spectral models of fat were compared pairwise. Comparison of magnitude fitting and mixed fitting was performed over a range of echo times and fat fractions. In vivo acquisitions from 41 patients were reconstructed using seven published spectral models of fat. T2-corrected stimulated echo acquisition mode MR spectroscopy was used as a reference.

RESULTS

The simulations demonstrated that imperfectly calibrated spectral models of fat result in biases that depend on echo times and fat fraction. Mixed fitting was more robust against this bias than magnitude fitting. Multipeak spectral models showed much smaller differences among themselves than from the single-peak spectral model. In vivo studies showed that all multipeak models agreed better (for mixed fitting, the slope ranged from 0.967 to 1.045 using linear regression) with the reference standard than the single-peak model (for mixed fitting, slope = 0.76).

CONCLUSION

It is essential to use a multipeak fat model for accurate quantification of fat with CSE-MRI. Furthermore, fat quantification techniques using multipeak fat models are comparable, and no specific choice of spectral model has been shown to be superior to the rest.

Accuracy of multiecho magnitude-based MRI (M-MRI) for estimation of hepatic proton density fat fraction (PDFF) in children

PURPOSE

To assess accuracy of magnitude-based magnetic resonance imaging (M-MRI) in children to estimate hepatic proton density fat fraction (PDFF) using two to six echoes, with magnetic resonance spectroscopy (MRS) -measured PDFF as a reference standard.

METHODS

This was an IRB-approved, HIPAA-compliant, single-center, cross-sectional, retrospective analysis of data collected prospectively between 2008 and 2013 in children with known or suspected nonalcoholic fatty liver disease (NAFLD). Two hundred eighty-six children (8-20 [mean 14.2 ± 2.5] years; 182 boys) underwent same-day MRS and M-MRI. Unenhanced two-dimensional axial spoiled gradient-recalled-echo images at six echo times were obtained at 3T after a single low-flip-angle (10°) excitation with ≥ 120-ms recovery time. Hepatic PDFF was estimated using the first two, three, four, five, and all six echoes. For each number of echoes, accuracy of M-MRI to estimate PDFF was assessed by linear regression with MRS-PDFF as reference standard. Accuracy metrics were regression intercept, slope, average bias, and R(2) .

RESULTS

MRS-PDFF ranged from 0.2-40.4% (mean 13.1 ± 9.8%). Using three to six echoes, regression intercept, slope, and average bias were 0.46-0.96%, 0.99-1.01, and 0.57-0.89%, respectively. Using two echoes, these values were 2.98%, 0.97, and 2.72%, respectively. R(2) ranged 0.98-0.99 for all methods.

CONCLUSION

Using three to six echoes, M-MRI has high accuracy for hepatic PDFF estimation in children.

Quantification of liver fat with respiratory-gated quantitative chemical shift encoded MRI

PURPOSE

To evaluate free-breathing chemical shift-encoded (CSE) magnetic resonance imaging (MRI) for quantification of hepatic proton density fat-fraction (PDFF). A secondary purpose was to evaluate hepatic R2* values measured using free-breathing quantitative CSE-MRI.

MATERIALS AND METHODS

Fifty patients (mean age, 56 years) were prospectively recruited and underwent the following four acquisitions to measure PDFF and R2*; 1) conventional breath-hold CSE-MRI (BH-CSE); 2) respiratory-gated CSE-MRI using respiratory bellows (BL-CSE); 3) respiratory-gated CSE-MRI using navigator echoes (NV-CSE); and 4) single voxel MR spectroscopy (MRS) as the reference standard for PDFF. Image quality was evaluated by two radiologists. MRI-PDFF measured from the three CSE-MRI methods were compared with MRS-PDFF using linear regression. The PDFF and R2* values were compared using two one-sided t-test to evaluate statistical equivalence.

RESULTS

There was no significant difference in the image quality scores among the three CSE-MRI methods for either PDFF (P = 1.000) or R2* maps (P = 0.359-1.000). Correlation coefficients (95% confidence interval [CI]) for the PDFF comparisons were 0.98 (0.96-0.99) for BH-, 0.99 (0.97-0.99) for BL-, and 0.99 (0.98-0.99) for NV-CSE. The statistical equivalence test revealed that the mean difference in PDFF and R2* between any two of the three CSE-MRI methods was less than ±1 percentage point (pp) and ±5 s(-1) , respectively (P < 0.046).

CONCLUSION

Respiratory-gated CSE-MRI with respiratory bellows or navigator echo are feasible methods to quantify liver PDFF and R2* and are as valid as the standard breath-hold technique.

Pancreatic Steatosis Demonstrated at MR Imaging in the General Population: Clinical Relevance

PURPOSE

To determine the relationship between pancreatic fat content and type 2 diabetes and prediabetes.

MATERIALS AND METHODS

From the prospective population-based Study of Health in Pomerania (SHIP), 1367 volunteers (563 men, 678 women; median age, 50 years) underwent whole-body magnetic resonance (MR) imaging at 1.5 T, which included multiecho chemical shift-encoded acquisition of the abdomen. SHIP was approved by the institutional review board, and written informed consent was obtained from all participants. The proton density fat fraction (PDFF) was calculated after correction for T1 bias, T2* bias, multipeak spectral complexity of fat, and noise bias. On the basis of oral glucose tolerance test results, participants were grouped into those with normal glucose tolerance (n = 740), those with prediabetes (n = 431), and those with confirmed type 2 diabetes but without medication (n = 70). PDFF was assessed in the pancreatic head, body, and tail. Multivariable regression analysis was conducted to investigate possible relationships of PDFF with demographic factors, behavioral factors, and laboratory data associated with the metabolic syndrome.

RESULTS

In all subjects, the mean unadjusted pancreatic fat content was 4.4% (head, 4.6%; body, 4.9%; tail, 3.9%; being unequally distributed, P < .001). There was no significant difference in pancreatic PDFF among subjects with normal glucose tolerance, prediabetes, and type 2 diabetes (P = .980). Pancreatic PDFF showed a positive association with age and body mass index and a negative association with serum lipase activity (P < .001).

CONCLUSION

The presence of pancreatic fat is not related to prediabetes or diabetes, which suggests that it has little clinical relevance for an individual's glycemic status.

Reproducibility of MR-based liver fat quantification across field strength: Same-day comparison between 1.5T and 3T in obese subjects

PURPOSE

To examine the reproducibility of quantitative magnetic resonance (MR) methods to estimate hepatic proton density fat-fraction (PDFF) at different magnetic field strengths.

MATERIALS AND METHODS

This Health Insurance Portability and Accountability Act (HIPAA)-compliant study was approved by the Institutional Review Board. Following informed consent, 25 severely obese subjects (mean body mass index [BMI]: 45 ± 4, range: 38-53 kg/m(2) ) were scanned at 1.5T and 3T on the same day. Two confounder-corrected multiecho chemical shift-encoded gradient-echo-based imaging methods were acquired to estimate PDFF over the entire liver: 3D complex-based (MRI-C) and 2D magnitude-based (MRI-M) MRI. Single-voxel MR spectroscopy (MRS) was performed in the right liver lobe. Using linear regression, pairwise comparisons of estimated PDFF were made between methods (MRI-C, MRI-M, MRS) at each field strength and for each method across field strengths.

RESULTS

1.5T vs. 3T regression analyses for MRI-C, MRI-M, and MRS PDFF measurements yielded R(2) values of 0.99, 0.97, and 0.90, respectively. The best-fit line was near unity (slope(m) = 1, intercept(b) = 0), indicating excellent agreement for each case: MRI-C (m = 0.92 [0.87, 0.99], b = 1.4 [0.7, 1.8]); MRI-M (m = 1.0 [0.90, 1.08], b = -1.4 [-2.4, -0.5]); MRS (m = 0.98 [0.82, 1.15], b = 1.2 [-0.2, 3.0]). Comparing MRI-C and MRI-M yielded an R(2)  = 0.98 (m = 1.1 [1.02, 1.16], b = -1.8 [-2.8, -1.1]) at 1.5T, and R(2)  = 0.99 (m = 0.98 [0.93, 1.03], b = 1.2 [0.7, 1.7]) at 3T.

CONCLUSION

This study demonstrates that PDFF estimation is reproducible across field strengths and across two confounder-corrected MR-based methods.

Automated two-point dixon screening for the evaluation of hepatic steatosis and siderosis: comparison with R2-relaxometry and chemical shift-based sequences

OBJECTIVES

To evaluate the automated two-point Dixon screening sequence for the detection and estimated quantification of hepatic iron and fat compared with standard sequences as a reference.

METHODS

One hundred and two patients with suspected diffuse liver disease were included in this prospective study. The following MRI protocol was used: 3D-T1-weighted opposed- and in-phase gradient echo with two-point Dixon reconstruction and dual-ratio signal discrimination algorithm ("screening" sequence); fat-saturated, multi-gradient-echo sequence with 12 echoes; gradient-echo T1 FLASH opposed- and in-phase. Bland-Altman plots were generated and correlation coefficients were calculated to compare the sequences.

RESULTS

The screening sequence diagnosed fat in 33, iron in 35 and a combination of both in 4 patients. Correlation between R2* values of the screening sequence and the standard relaxometry was excellent (r = 0.988). A slightly lower correlation (r = 0.978) was found between the fat fraction of the screening sequence and the standard sequence. Bland-Altman revealed systematically lower R2* values obtained from the screening sequence and higher fat fraction values obtained with the standard sequence with a rather high variability in agreement.

CONCLUSIONS

The screening sequence is a promising method with fast diagnosis of the predominant liver disease. It is capable of estimating the amount of hepatic fat and iron comparable to standard methods.

KEY POINTS

• MRI plays a major role in the clarification of diffuse liver disease. • The screening sequence was introduced for the assessment of diffuse liver disease. • It is a fast and automated algorithm for the evaluation of hepatic iron and fat. • It is capable of estimating the amount of hepatic fat and iron.

Magnetic resonance elastography predicts advanced fibrosis in patients with nonalcoholic fatty liver disease: a prospective study

Retrospective studies have shown that two-dimensional magnetic resonance elastography (2D-MRE), a novel MR method for assessment of liver stiffness, correlates with advanced fibrosis in patients with nonalcoholic fatty liver disease (NAFLD). Prospective data on diagnostic accuracy of 2D-MRE in the detection of advanced fibrosis in NAFLD are needed. The aim of this study is to prospectively assess the diagnostic accuracy of 2D-MRE, a noninvasive imaging biomarker, in predicting advanced fibrosis (stage 3 or 4) in well-characterized patients with biopsy-proven NAFLD. This is a cross-sectional analysis of a prospective study including 117 consecutive patients (56% women) with biopsy-proven NAFLD who underwent a standardized research visit: history, exam, liver biopsy assessment (using the nonalcoholic steatohepatitis Clinical Research Network histological scoring system), and 2D-MRE from 2011 to 2013. The radiologist and pathologist were blinded to clinical and pathology/imaging data, respectively. Receiver operating characteristics (ROCs) were examined to assess the diagnostic test performance of 2D-MRE in predicting advanced fibrosis. The mean (± standard deviation) of age and body mass index was 50.1 (± 13.4) years and 32.4 (± 5.0) kg/m(2), respectively. The median time interval between biopsy and 2D-MRE was 45 days (interquartile range: 50 days). The number of patients with fibrosis stages 0, 1, 2, 3, and 4 was 43, 39, 13, 12, and 10, respectively. The area under the ROC curve for 2D-MRE discriminating advanced fibrosis (stage 3-4) from stage 0-2 fibrosis was 0.924 (P < 0.0001). A threshold of >3.63 kPa had a sensitivity of 0.86 (95% confidence interval [CI]: 0.65-0.97), specificity of 0.91 (95% CI: 0.83-0.96), positive predictive value of 0.68 (95% CI: 0.48-0.84), and negative predictive value of 0.97 (95% CI: 0.91-0.99).

CONCLUSIONS

MRE is accurate in predicting advanced fibrosis and may be utilized for noninvasive diagnosis of advanced fibrosis in patients with NAFLD.

Validation of bone marrow fat quantification in the presence of trabecular bone using MRI

BACKGROUND

To validate six-echo, chemical-shift based MRI with T2 * correction for the quantification of bone marrow fat content in the presence of trabecular bone.

METHODS

Ten bone phantoms were made using trabecular bone cores extracted from the distal femur and proximal tibia of 20 human cadaveric knees. Bone marrow was removed from the cores and the marrow spaces were filled with water-fat gelatin to mimic bone marrow of known fat fractions. A chemical-shift based water-fat separation method with T2 * correction was used to generate fat fraction maps. The proton density fat fractions (PDFF) between marrow regions with and without bone were compared with the reference standard of known fat fraction using the squared Pearson correlation coefficient and unpaired t-test.

RESULTS

Strong correlations were found between the known fat fraction and measured PDFF in marrow without trabecular bone (R(2) = 0.99; slope = 0.99, intercept = 0.94) as well as in marrow with trabecular bone (R(2) = 0.97; slope = 1.0, intercept = -3.58). Measured PDFF between regions with and without bone were not significantly different (P = 0.5). However, PDFF was systematically underestimated by -3.2% fat fraction in regions containing trabecular bone.

CONCLUSION

Our implementation of a six-echo chemical-shift based MRI pulse sequence with T2 * correction provided an accurate means of determining fat content in bone marrow in the presence of trabecular bone.

Sebelipase alfa over 52 weeks reduces serum transaminases, liver volume and improves serum lipids in patients with lysosomal acid lipase deficiency

BACKGROUND & AIMS

Lysosomal acid lipase deficiency is an autosomal recessive enzyme deficiency resulting in lysosomal accumulation of cholesteryl esters and triglycerides. LAL-CL04, an ongoing extension study, investigates the long-term effects of sebelipase alfa, a recombinant human lysosomal acid lipase.

METHODS

Sebelipase alfa (1mg/kg or 3mg/kg) was infused every-other-week to eligible subjects. Safety and tolerability assessments, including liver function, lipid profiles and liver volume assessment, were carried out at regular intervals.

RESULTS

216 infusions were administered to eight adult subjects through week 52 during LAL-CL04. At week 52, mean alanine aminotransferase and aspartate aminotransferase levels were normal with mean change from baseline of -58% and -40%. Mean changes for low-density lipoprotein, total cholesterol, triglyceride and high-density lipoprotein were -60%, -39%, -36%, and +29%, respectively. Mean liver volume by magnetic resonance imaging and hepatic proton density fat fraction decreased (12% and 55%, respectively). Adverse events were mainly mild and unrelated to sebelipase alfa. Infusion-related reactions were uncommon: three events of moderate severity were reported in two subjects; one patient's event was suggestive of a hypersensitivity-like reaction, but additional testing did not confirm this, and the subject has successfully re-started sebelipase alfa. Of samples tested to date, no anti-drug antibodies have been detected.

CONCLUSIONS

Long-term dosing with sebelipase alfa in lysosomal acid lipase-deficient patients is well tolerated and produces sustained reductions in transaminases, improvements in serum lipid profile and reduction in the hepatic fat fraction. A randomized, placebo-controlled phase 3 trial in children and adults is underway (ARISE: NCT01757184).

Quantitative determination of liver triglyceride levels with 3T ¹H-MR spectroscopy in mice with moderately elevated liver fat content

RATIONALE AND OBJECTIVES

To diagnose hepatic steatosis with noninvasive magnetic resonance (MR)-based measurements, threshold values of liver fat percentages are used. However, these differ between studies. Consequently, the choice of threshold values influences diagnostic accuracy, especially in subjects with borderline hepatic steatosis. In this study, we compared (1)H-MR spectroscopy (MRS) and biochemically determined liver fat content in mice with moderately elevated fat content and studied the diagnostic accuracy of (1)H-MRS using two literature-based threshold values.

MATERIALS AND METHODS

Fifty mice were divided into three groups: 21 C57Bl/6OlaHSD (B6) mice on a high-fat diet, 20 B6 mice on a control diet, and 9 LDLr-/- mice on a high-fat high-cholesterol diet. (1)H-MRS was performed using multi-echo STEAM at 3T to derive a fat mass fraction ((1)H-MRS fat content). Biochemical fat content was determined from liver homogenates. Correlation and agreement were assessed with the Pearson correlation coefficient and the Bland-Altman analysis and diagnostic accuracy by calculating sensitivity, specificity, and positive and negative predictive values.

RESULTS

All mice were pooled to form a single cohort. Mean (±standard deviation) biochemical fat content was 32.2 (±13.9) mg/g. Mean (1)H-MRS fat content did not differ at 30.2 (±12.0) mg/g (P = .13). Correlation r was 0.74 (P < .0001). Bland-Altman analysis indicated that (1)H-MRS fat content underestimated biochemical fat content by 2.1 mg/g. The diagnostic accuracy of (1)H-MRS depended to a great extent on the chosen reference threshold value.

CONCLUSIONS

(1)H-MRS measurement of moderately elevated liver fat content in mice correlated substantially with biochemical fat content measurement. Contrary to earlier studies, diagnostic accuracy of (1)H-MRS fat content in borderline liver fat content appears limited.

Quantitative MRI for hepatic fat fraction and T2* measurement in pediatric patients with non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in children. The gold standard for diagnosis is liver biopsy. MRI is a non-invasive imaging method to provide quantitative measurement of hepatic fat content. The methodology is particularly appealing for the pediatric population because of its rapidity and radiation-free imaging techniques.

OBJECTIVE

To develop a multi-point Dixon MRI method with multi-interference models (multi-fat-peak modeling and bi-exponential T2* correction) for accurate hepatic fat fraction (FF) and T2* measurements in pediatric patients with NAFLD.

MATERIALS AND METHODS

A phantom study was first performed to validate the accuracy of the MRI fat fraction measurement by comparing it with the chemical fat composition of the ex-vivo pork liver-fat homogenate. The most accurate model determined from the phantom study was used for fat fraction and T2* measurements in 52 children and young adults referred from the pediatric hepatology clinic with suspected or identified NAFLD. Separate T2* values of water (T2*W) and fat (T2*F) components derived from the bi-exponential fitting were evaluated and plotted as a function of fat fraction. In ten patients undergoing liver biopsy, we compared histological analysis of liver fat fraction with MRI fat fraction.

RESULTS

In the phantom study the 6-point Dixon with 5-fat-peak, bi-exponential T2* modeling demonstrated the best precision and accuracy in fat fraction measurements compared with other methods. This model was further calibrated with chemical fat fraction and applied in patients, where similar patterns were observed as in the phantom study that conventional 2-point and 3-point Dixon methods underestimated fat fraction compared to the calibrated 6-point 5-fat-peak bi-exponential model (P < 0.0001). With increasing fat fraction, T2*W (27.9 ± 3.5 ms) decreased, whereas T2*F (20.3 ± 5.5 ms) increased; and T2*W and T2*F became increasingly more similar when fat fraction was higher than 15-20%. Histological fat fraction measurements in ten patients were highly correlated with calibrated MRI fat fraction measurements (Pearson correlation coefficient r = 0.90 with P = 0.0004).

CONCLUSION

Liver MRI using multi-point Dixon with multi-fat-peak and bi-exponential T2* modeling provided accurate fat quantification in children and young adults with non-alcoholic fatty liver disease and may be used to screen at-risk or affected individuals and to monitor disease progress noninvasively.

MR quantification of total liver fat in patients with impaired glucose tolerance and healthy subjects

Objective

To explore the correlations between liver fat content and clinical index in patients with impaired glucose tolerance (IGT) and healthy subjects.

Materials and Methods

56 subjects were enrolled and each of them underwent upper-abdominal MRI examination that involved a T1 VIBE Dixon sequence. 14 was clinically diagnosed with IGT (collectively as IGT group ) while 42 showed normal glucose tolerance,(collectively as NGT group). NGT group was further divided into NGTFat (BMI≥25, 18 subjects) and NGTLean (BMI<25, 24 subjects). The total liver fat contents was measured and compared with clinical findings and laboratory results in order to determine statistical correlations between these parameters. Differences among IGT, NGTFat and NGTLean groups were evaluated.

Results

For all the subjects, fat volume fractions (FVFs) ranged from 4.2% to 24.2%, positive correlations was observed with BMI, waist hip ratio(WHR), low density lipoprotein(LDL), fasting plasma insulin(FPI), homeostasis model assessment insulin resistance (HOMA-IR) and homeostasis model assessment β(HOMAβ). FVFs of IGT group (p = 0.004) and NGTFat group (p = 0.006) were significantly higher than those of NGTLean group.

Conclusions

People with higher BMI, WHR and LDL levels tend to have higher liver fat content. Patients with BMI≥25 are more likely to develop IGT. Patients with higher FVF showed higher resistance to insulin, thus obtained a higher risk of developing type 2 diabetes mellitus.

Effect of hepatocyte-specific gadolinium-based contrast agents on hepatic fat-fraction and R2(⁎)

The purpose of this work was to investigate the effect of a hepatocyte-specific gadolinium based contrast agent (GBCA) on quantitative hepatic fat-fraction (FF) and R2* measurements. Fifty patients were imaged at 1.5T, using chemical-shift encoded water-fat MRI with low (5°) and high (15°) flip angles (FA), both before and after administration of a hepatocyte-specific GBCA (gadoxetic acid). Low and high FA, pre- and post-contrast FF and R2* values were measured for each subject. Available serum laboratory studies related to liver disease were also recorded. Linear regression and Bland-Altman analysis were performed to compare measurements. Hepatic FF was unaffected by GBCA at low FA (slope=1.02±0.02, p=0.32). FF was overestimated at high FA pre-contrast (slope=1.33±0.03, p<10(-10)), but underestimated post-contrast (slope=0.81±0.02, p<10(-10)). Hepatic R2* was unaffected by FA (mean difference±95% CI pre-contrast:2.2±4.9s(-1), post-contrast:2.8±3.6s(-1)), but increased post-contrast in patients with total bilirubin <2.5mg/dL (ΔR2*=13.4±12.7s(-1)). Regression analysis of serum values demonstrated a correlation of post-contrast change in R2* with total bilirubin (p<0.01) and model for end-stage liver disease (MELD) score (p≈0.01). In conclusion, GBCA has no effect on hepatic FF at low FA due to a lack of T1-weighting, potentially allowing flexibility for FF imaging with hepatobiliary imaging protocols. Hepatic R2* increased significantly after GBCA administration, particularly in the biliary tree. Therefore, R2* maps should be obtained prior to contrast administration.

Accuracy of MR imaging-estimated proton density fat fraction for classification of dichotomized histologic steatosis grades in nonalcoholic fatty liver disease

PURPOSE

To evaluate the diagnostic performance of previously proposed high-specificity magnetic resonance (MR) imaging-estimated proton density fat fraction (PDFF) thresholds for diagnosis of steatosis grade 1 or higher (PDFF threshold of 6.4%), grade 2 or higher (PDFF threshold of 17.4%), and grade 3 (PDFF threshold of 22.1%) by using histologic findings as a reference in an independent cohort of adults known to have or suspected of having nonalcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

This prospective, cross-sectional, institutional review board-approved, HIPAA-compliant single-center study was conducted in an independent cohort of 89 adults known to have or suspected of having NAFLD who underwent contemporaneous liver biopsy. MR imaging PDFF was estimated at 3 T by using magnitude-based low-flip-angle multiecho gradient-recalled-echo imaging with T2* correction and multipeak modeling. Steatosis was graded histologically (grades 0, 1, 2, and 3, according to the Nonalcoholic Steatohepatitis Clinical Research Network scoring system). Sensitivity, specificity, and binomial confidence intervals were calculated for the proposed MR imaging PDFF thresholds.

RESULTS

The proposed MR imaging PDFF threshold of 6.4% to diagnose grade 1 or higher steatosis had 86% sensitivity (71 of 83 patients; 95% confidence interval [CI]: 76, 92) and 83% specificity (five of six patients; 95% CI: 36, 100). The threshold of 17.4% to diagnose grade 2 or higher steatosis had 64% sensitivity (28 of 44 patients; 95% CI: 48, 78) and 96% specificity (43 of 45 patients; 95% CI: 85, 100). The threshold of 22.1% to diagnose grade 3 steatosis had 71% sensitivity (10 of 14 patients; 95% CI: 42, 92) and 92% specificity (69 of 75 patients; 95% CI: 83, 97).

CONCLUSION

In an independent cohort of adults known to have or suspected of having NAFLD, the previously proposed MR imaging PDFF thresholds provided moderate to high sensitivity and high specificity for diagnosis of grade 1 or higher, grade 2 or higher, and grade 3 steatosis. Prospective multicenter studies are now needed to further validate these high-specificity thresholds.

Radiologic evaluation of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a frequent cause of chronic liver diseases, ranging from simple steatosis to nonalcoholic steatohepatitis (NASH)-related liver cirrhosis. Although liver biopsy is still the gold standard for the diagnosis of NAFLD, especially for the diagnosis of NASH, imaging methods have been increasingly accepted as noninvasive alternatives to liver biopsy. Ultrasonography is a well-established and cost-effective imaging technique for the diagnosis of hepatic steatosis, especially for screening a large population at risk of NAFLD. Ultrasonography has a reasonable accuracy in detecting moderate-to-severe hepatic steatosis although it is less accurate for detecting mild hepatic steatosis, operator-dependent, and rather qualitative. Computed tomography is not appropriate for general population assessment of hepatic steatosis given its inaccuracy in detecting mild hepatic steatosis and potential radiation hazard. However, computed tomography may be effective in specific clinical situations, such as evaluation of donor candidates for hepatic transplantation. Magnetic resonance spectroscopy and magnetic resonance imaging are now regarded as the most accurate practical methods of measuring liver fat in clinical practice, especially for longitudinal follow-up of patients with NAFLD. Ultrasound elastography and magnetic resonance elastography are increasingly used to evaluate the degree of liver fibrosis in patients with NAFLD and to differentiate NASH from simple steatosis. This article will review current imaging methods used to evaluate hepatic steatosis, including the diagnostic accuracy, limitations, and practical applicability of each method. It will also briefly describe the potential role of elastography techniques in the evaluation of patients with NAFLD.

Evidence and recommendations for imaging liver fat in children, based on systematic review

BACKGROUND & AIMS

Fatty liver is a common problem in children and increases their risk for cirrhosis, diabetes, and cardiovascular disease. Liver biopsy is the clinical standard for diagnosing and grading fatty liver. However, noninvasive imaging modalities are needed to assess liver fat in children. We performed a systematic review of studies that evaluated imaging liver fat in children.

METHODS

We searched PubMed for original research articles in peer-reviewed journals from January 1, 1982, through December 31, 2012, using the key words "imaging liver fat." Studies included those in English, and those performed in children from birth to 18 years of age. To be eligible for inclusion, studies were required to measure hepatic steatosis via an imaging modality and a quantitative comparator as the reference standard.

RESULTS

We analyzed 9 studies comprising 610 children; 4 studies assessed ultrasonography and 5 studies assessed magnetic resonance imaging (MRI). Ultrasonography was used in the diagnosis of fatty liver with positive predictive values of 47% to 62%. There was not a consistent relationship between ultrasound steatosis score and the reference measurement of hepatic steatosis. Liver fat as measurements by MRI or by spectroscopy varied with the methodologies used. Liver fat measurements by MRI correlated with results from histologic analyses, but sample size did not allow for an assessment of diagnostic accuracy.

CONCLUSIONS

Available evidence does not support the use of ultrasonography for the diagnosis or grading of fatty liver in children. Although MRI is a promising approach, the data are insufficient to make evidence-based recommendations regarding its use in children for the assessment of hepatic steatosis.

Fat and iron quantification in the liver: past, present, and future

Liver fat, iron, and combined overload are common manifestations of diffuse liver disease and may cause lipotoxicity and iron toxicity via oxidative hepatocellular injury, leading to progressive fibrosis, cirrhosis, and eventually, liver failure. Intracellular fat and iron cause characteristic changes in the tissue magnetic properties in predictable dose-dependent manners. Using dedicated magnetic resonance pulse sequences and postprocessing algorithms, fat and iron can be objectively quantified on a continuous scale. In this article, we will describe the basic physical principles of magnetic resonance fat and iron quantification and review the imaging techniques of the "past, present, and future." Standardized radiological metrics of fat and iron are introduced for numerical reporting of overload severity, which can be used toward objective diagnosis, grading, and longitudinal disease monitoring. These noninvasive imaging techniques serve an alternative or complimentary role to invasive liver biopsy. Commercial solutions are increasingly available, and liver fat and iron quantitative imaging is now within reach for routine clinical use and may soon become standard of care.

Hepatic steatosis in living liver donor candidates: preoperative assessment by using breath-hold triple-echo MR imaging and 1H MR spectroscopy

PURPOSE

To evaluate the diagnostic performance of both breath-hold T2*-corrected triple-echo spoiled gradient-echo water-fat separation magnetic resonance (MR) imaging (triple-echo imaging) and high-speed T2-corrected multiecho hydrogen 1 ((1)H) MR spectroscopy in the assessment of macrovesicular hepatic steatosis in living liver donor candidates by using histologic assessment as a reference standard.

MATERIALS AND METHODS

The institutional review board approved this retrospective study with waiver of the need to obtain informed consent. One hundred eighty-two liver donor candidates who had undergone preoperative triple-echo imaging and single-voxel (3 × 3 × 3 cm) MR spectroscopy performed with a 3.0-T imaging unit and who had also undergone histologic evaluation of macrovesicular steatosis were included in this study. In part 1 of the study (n = 84), the Pearson correlation coefficient was calculated. Receiver operating characteristic (ROC) curve analysis was performed to detect substantial (≥10%) macrovesicular steatosis. In part 2 of the study, with a different patient group (n = 98), diagnostic performance was evaluated by using the diagnostic cutoff values determined in part 1 of the study.

RESULTS

The correlation coefficients of triple-echo MR imaging and MR spectroscopy with macrovesicular steatosis were 0.886 and 0.887, respectively. The areas under the ROC curve for detection of substantial macrovesicular steatosis were 0.959 and 0.988, with cutoff values of 4.93% and 5.79%, respectively, and without a significant difference (P = .328). In the part 2 study group, sensitivity and specificity were 90.9% (10 of 11) and 86.2% (75 of 87) for triple-echo MR imaging and 90.9% (10 of 11) and 86.2% (75 of 87) for MR spectroscopy, respectively.

CONCLUSION

Either breath-hold triple-echo MR imaging or MR spectroscopy can be used to detect substantial macrovesicular steatosis in living liver donor candidates. In the future, this may allow selective biopsy in candidates who are expected to have substantial macrovesicular steatosis on the basis of MR-based hepatic fat fraction.

Comparison of vertebral bone marrow fat assessed by 1H MRS and inphase and out-of-phase MRI among family members

Inphase and out-of-phase magnetic resonance imaging is a robust and fast method which can provide similar vertebral bone marrow fat estimation as (1)H proton magnetic resonance spectroscopy, indicating that this technique is a potentially useful tool in both research and clinical practice.

INTRODUCTION

The importance of evaluating bone marrow fat lies in the fact that osteoporosis and obesity, two disorders of body composition, are growing in prevalence. Bone fat mass can be reliably assessed using proton magnetic resonance spectroscopy ((1)H MRS), but this method is technically demanding and needs advanced post-processing unlike inphase and out-of-phase magnetic resonance imaging (MRI), which is a robust and fast method.

METHODS

We compared vertebral bone marrow fat (BMF) content assessed by inphase and out-of-phase MRI and (1)H MRS using a 1.5-T MRI scanner in mothers (n = 34, aged 49.4 years), fathers (n = 31, aged 53.1 years) and their daughters (n = 40, aged 20.3 years) who participated in the CALEX family study. Signal intensity on the inphase and out-of-phase MRI was analyzed from the same location and size of the single-voxel (1)H MRS measurement.

RESULTS

Positive correlations were found between (1)H MRS and inphase and out-of-phase MRI in the axial plane (r = 0.746, p < 0.001) and sagittal plane (r = 0.804, p < 0.001). The mean differences between (1)H MRS and inphase and out-of-phase MRI in the axial and sagittal planes were relatively small, at 4.13 and 2.67 %, and the agreement between techniques was 89.4 and 93.2 %, respectively. Girls had a significantly lower vertebral BMF than mothers and fathers with both methods (for all, p < 0.001).

CONCLUSIONS

We conclude that inphase and out-of-phase MRI can provide similar vertebral BMF estimation as (1)H MRS, indicating that this technique is a potentially useful tool in both research and clinical practice.

Automated patient-tailored screening of the liver for diffuse steatosis and iron overload using MRI

OBJECTIVE

The purpose of this article is to validate an automated screening method for evaluation of hepatic steatosis or siderosis.

MATERIALS AND METHODS

This was a two-part study, with retrospective and prospective portions. First, 130 consecutive abdominal MRI examinations, including both the automated algorithm and reference standard fat and iron quantification, were retrospectively identified. The algorithm's performance was validated against the reference standard and was compared with the performance of three expert readers. Subsequently, 39 subjects undergoing liver MRI were prospectively identified and enrolled. These subjects were scanned with a protocol where quantification sequences were either performed or not performed on the basis of the recommendation of the algorithm. Total examination time in these subjects was compared with examination times in the 90 subjects from the retrospective cohort who had undergone a similar liver MRI protocol with complete quantification.

RESULTS

The automated algorithm was accurate in determining the presence of deposition disease (93.1%), with no significant difference between its conclusions and those of any of the readers (p=0.48-1.0). Use of the algorithm resulted in a small but statistically significant time savings compared with performing quantification in all subjects (28 minutes 56 seconds vs 31 minutes 20 seconds; p<0.05).

CONCLUSION

Automated screening for hepatic steatosis and siderosis can be performed in real time during abdominal MRI examinations, can save total scan time compared with always performing quantification, and could serve as a gatekeeper for dedicated quantification sequences.

Liver fat quantification using a multi-step adaptive fitting approach with multi-echo GRE imaging

PURPOSE

The purpose of this study was to develop a multi-step adaptive fitting approach for liver proton density fat fraction (PDFF) and R(2)* quantification, and to perform an initial validation on a broadly available hardware platform.

THEORY AND METHODS

The proposed method uses a multi-echo three-dimensional gradient echo acquisition, with initial guesses for the fat and water signal fractions based on a Dixon decomposition of two selected echoes. Based on magnitude signal equations with a multi-peak fat spectral model, a multi-step nonlinear fitting procedure is then performed to adaptively update the fat and water signal fractions and R(2)* values. The proposed method was validated using numeric phantoms as ground truth, followed by preliminary clinical validation of PDFF calculations against spectroscopy in 30 patients.

RESULTS

The results of the proposed method agreed well with the ground truth of numerical phantoms, and were relatively insensitive to changes in field strength, field homogeneity, monopolar/bipolar readout, signal to noise ratio, and echo time selections. The in vivo patient study showed excellent consistency between the PDFF values measured with the proposed approach compared with spectroscopy.

CONCLUSION

This multi-step adaptive fitting approach performed well in both simulated and initial clinical evaluation, and shows potential in the quantification of hepatic steatosis.

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/m(2), 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.