Hepatic fat fraction: MR imaging for quantitative measurement and display--early experience

Accelerated free-breathing liver fat and R 2 * quantification using multi-echo stack-of-radial MRI with motion-resolved multidimensional regularized reconstruction: Initial retrospective evaluation

PURPOSE

To improve image quality, mitigate quantification biases and variations for free-breathing liver proton density fat fraction (PDFF) andR 2 * $$ {\mathrm{R}}_2^{\ast } $$ quantification accelerated by radial k-space undersampling.

METHODS

A free-breathing multi-echo stack-of-radial MRI method was developed with compressed sensing with multidimensional regularization. It was validated in motion phantoms with reference acquisitions without motion and in 11 subjects (6 patients with nonalcoholic fatty liver disease) with reference breath-hold Cartesian acquisitions. Images, PDFF, andR 2 * $$ {\mathrm{R}}_2^{\ast } $$ maps were reconstructed using different radial view k-space sampling factors and reconstruction settings. Results were compared with reference-standard results using Bland-Altman analysis. Using linear mixed-effects model fitting (p < 0.05 considered significant), mean and SD were evaluated for biases and variations of PDFF andR 2 * $$ {\mathrm{R}}_2^{\ast } $$ , respectively, and coefficient of variation on the first echo image was evaluated as a surrogate for image quality.

RESULTS

Using the empirically determined optimal sampling factor of 0.25 in the accelerated in vivo protocols, mean differences and limits of agreement for the proposed method were [-0.5; -33.6, 32.7] s-1 forR 2 * $$ {\mathrm{R}}_2^{\ast } $$ and [-1.0%; -5.8%, 3.8%] for PDFF, close to those of a previous self-gating method using fully sampled radial views: [-0.1; -27.1, 27.0] s-1 forR 2 * $$ {\mathrm{R}}_2^{\ast } $$ and [-0.4%; -4.5%, 3.7%] for PDFF. The proposed method had significantly lower coefficient of variation than other methods (p < 0.001). Effective acquisition time of 64 s or 59 s was achieved, compared with 171 s or 153 s for two baseline protocols with different radial views corresponding to sampling factor of 1.0.

CONCLUSION

This proposed method may allow accelerated free-breathing liver PDFF andR 2 * $$ {\mathrm{R}}_2^{\ast } $$ mapping with reduced biases and variations.

Imaging and prognostic characterization of fat-containing hepatocellular carcinoma subtypes

PURPOSE

Steatohepatitic hepatocellular carcinoma (SH-HCC) is characterized by intratumoral fat with > 50% inflammatory changes. However, intratumoral fat (with or without inflammation) can also be found in not-otherwise specified HCC (NOS-HCC). We compared the imaging features and outcome of resected HCC containing fat on pathology including SH-HCC (> 50% steatohepatitic component), NOS-HCC with < 50% steatohepatitic component (SH-NOS-HCC), and fatty NOS-HCC (no steatohepatitic component).

MATERIAL AND METHODS

From September 2012 to June 2021, 94 patients underwent hepatic resection for fat-containing HCC on pathology. Imaging features and categories were assessed using LIRADS v2018. Fat quantification was performed on chemical-shift MRI. Recurrence-free and overall survival were estimated.

RESULTS

Twenty-one patients (26%) had nonalcoholic steatohepatitis (NASH). The median intra-tumoral fat fraction was 8%, with differences between SH-HCC and SH-NOS-HCC (9.5% vs. 5% p = 0.03). There was no difference in major LI-RADS features between all groups; most tumors were classified as LR-4/5. A mosaic architecture on MRI was rare (7%) in SH-HCC, a fat in mass on CT was more frequently depicted (48%) in SH-HCC. A combination of NASH with no mosaic architecture on MRI or NASH with fat in mass on CT yielded excellent specificity for diagnosing SH-HCC (97.6% and 97.7%, respectively). The median recurrence-free and overall survival were 58 and 87 months, with no difference between groups (p = 0.18 and p = 0.69).

CONCLUSION

In patients with NASH, an SH-HCC may be suspected in L4/LR-5 observations with no mosaic architecture at MRI or with fat in mass on CT. Oncological outcomes appear similar between fat-containing HCC subtypes.

Comparison of spin-echo echo planar imaging and gradient-recalled echo sequences in magnetic resonance elastography of liver at 1.5T same MRI scanner

PURPOSE

Magnetic resonance elastography (MRE) is used to measure liver stiffness with gradient-recalled echo (GRE)-based and spin-echo echo planar imaging (SE-EPI)-based sequences. We compared the liver stiffness (LS) values of the two sequences on a 1.5-T MR imaging scanner.

METHODS

This is a retrospective study. An MRE imaging section was obtained from a horizontal section of the liver. Region of interest was drawn on the elastogram, and the mean LS and pixel values were measured and compared. The correlations between proton density fat fraction, R2* values, and biochemical data from electronic medical records were confirmed, and multivariate analysis was performed.

RESULTS

The mean LS values were 3.01 ± 1.78 kPa for GRE and 3.13 ± 1.57 kPa for SE-EPI, showing excellent agreement and a strong correlation between the two sequences (correlation coefficient r = 0.96). The mean pixel values were 369.5 ± 142.7 pixels for GRE and 490.1 ± 197.9 pixels for SE-EPI, showing a significant difference by the Wilcoxon rank sum test (p < 0.01). There were no LS unmeasurable cases in SE-EPI, but seven (2.5%) were unmeasurable in GRE, and multivariate analysis showed a significant difference with p < 0.001 in R2* values (mean, 92.7 Hz) for the GRE method.

CONCLUSION

The GRE and SE-EPI methods were comparable for LS measurements in 1.5-T liver MRE, indicating that SE-EPI MRE is more useful because GRE MRE may not measure cases with high R2* values and the region of interest tends to be smaller.

Quantification of Hepatic Steatosis on Dual-Energy CT in Comparison With MRI mDIXON-Quant Sequence in Breast Cancer

OBJECTIVE

The study aimed to evaluate the correlation and diagnostic value of liver fat quantification in unenhanced dual-energy CT (DECT) using quantitative magnetic resonance imaging (MRI) mDIXON-Quant sequence as reference standard in patients with breast cancer.

METHODS

Patients with breast cancer were prospectively recruited between June 2018 and April 2020. Each patient underwent liver DECT and MRI mDIXON-Quant examination. The DECT-fat volume fraction (FVF) and liver-spleen attenuation differences were compared with the MRI-proton density fat fraction using scatterplots, Bland-Altman plots, and concordance correlation coefficient. Receiver operating characteristic curves were established to determine the diagnostic accuracy of hepatic steatosis by DECT.

RESULTS

A total of 216 patients with breast cancer (mean age, 50.08 ± 9.33 years) were evaluated. The DECT-FVF correlated well with MRI-proton density fat fraction ( r2 = 0.902; P < 0.001), which was higher than the difference in liver-spleen attenuation ( r2 = 0.728; P < 0.001). Bland-Altman analysis revealed slight positive bias; the mean difference was 3.986. The DECT-FVF yielded an average concordance correlation coefficient of 0.677, which was higher than the difference of liver-spleen attenuation (-0.544). The DECT-FVF and the difference in liver-spleen attenuation both lead to mild overestimation of hepatic steatosis. The areas under the curve of DECT-FVF (0.956) were higher than the difference in liver-spleen attenuation (0.807) in identifying hepatic steatosis ( P < 0.001).

CONCLUSIONS

Dual-energy CT-FVF may serve as a reliable screening and quantitative tool for hepatic steatosis in patients with breast cancer.

Evaluation of proton density fat fraction (PDFF) obtained from a vendor-neutral MRI sequence and MRQuantif software

OBJECTIVE

To validate the proton density fat fraction (PDFF) obtained by the MRQuantif software from 2D chemical shift encoded MR (CSE-MR) data in comparison with the histological steatosis data.

METHODS

This study, pooling data from 3 prospective studies spread over time between January 2007 and July 2020, analyzed 445 patients who underwent 2D CSE-MR and liver biopsy. MR derived liver iron concentration (MR-LIC) and PDFF was calculated using the MRQuantif software. The histological standard steatosis score (SS) served as reference. In order to get a value more comparable to PDFF, histomorphometry fat fraction (HFF) were centrally determined for 281 patients. Spearman correlation and the Bland and Altman method were used for comparison.

RESULTS

Strong correlations were found between PDFF and SS (rs = 0.84, p < 0.001) or HFF (rs = 0.87, p < 0.001). Spearman's coefficients increased to 0.88 (n = 324) and 0.94 (n = 202) when selecting only the patients without liver iron overload. The Bland and Altman analysis between PDFF and HFF found a mean bias of 5.4% ± 5.7 [95% CI 4.7, 6.1]. The mean bias was 4.7% ± 3.7 [95% CI 4.2, 5.3] and 7.1% ± 8.8 [95% CI 5.2, 9.0] for the patients without and with liver iron overload, respectively.

CONCLUSION

The PDFF obtained by MRQuantif from a 2D CSE-MR sequence is highly correlated with the steatosis score and very close to the fat fraction estimated by histomorphometry. Liver iron overload reduced the performance of steatosis quantification and joint quantification is recommended. This device-independent method can be particularly useful for multicenter studies.

CLINICAL RELEVANCE STATEMENT

The quantification of liver steatosis using a vendor-neutral 2D chemical-shift MR sequence, processed by MRQuantif, is well correlated to steatosis score and histomorphometric fat fraction obtained from biopsy, whatever the magnetic field and the MR device used.

KEY POINTS

• The PDFF measured by MRQuantif from 2D CSE-MR sequence data is highly correlated to hepatic steatosis. • Steatosis quantification performance is reduced in case of significant hepatic iron overload. • This vendor-neutral method may allow consistent estimation of PDFF in multicenter studies.

Silencing of STE20-type kinase TAOK1 confers protection against hepatocellular lipotoxicity through metabolic rewiring

BACKGROUND

NAFLD has become the leading cause of chronic liver disease worldwide afflicting about one quarter of the adult population. NASH is a severe subtype of NAFLD, which in addition to hepatic steatosis connotes liver inflammation and hepatocyte ballooning. In light of the exponentially increasing prevalence of NAFLD, it is imperative to gain a better understanding of its molecular pathogenesis. The aim of this study was to examine the potential role of STE20-type kinase TAOK1 -a hepatocellular lipid droplet-associated protein-in the regulation of liver lipotoxicity and NAFLD etiology.

METHODS

The correlation between TAOK1 mRNA expression in liver biopsies and the severity of NAFLD was evaluated in a cohort of 62 participants. Immunofluorescence microscopy was applied to describe the subcellular localization of TAOK1 in human and mouse hepatocytes. Metabolic reprogramming and oxidative/endoplasmic reticulum stress were investigated in immortalized human hepatocytes, where TAOK1 was overexpressed or silenced by small interfering RNA, using functional assays, immunofluorescence microscopy, and colorimetric analysis. Migration, invasion, and epithelial-mesenchymal transition were examined in TAOK1-deficient human hepatoma-derived cells. Alterations in hepatocellular metabolic and pro-oncogenic signaling pathways were assessed by immunoblotting.

RESULTS

We observed a positive correlation between the TAOK1 mRNA abundance in human liver biopsies and key hallmarks of NAFLD (i.e., hepatic steatosis, inflammation, and ballooning). Furthermore, we found that TAOK1 protein fully colocalized with intracellular lipid droplets in human and mouse hepatocytes. The silencing of TAOK1 alleviated lipotoxicity in cultured human hepatocytes by accelerating lipid catabolism (mitochondrial β-oxidation and triacylglycerol secretion), suppressing lipid anabolism (fatty acid influx and lipogenesis), and mitigating oxidative/endoplasmic reticulum stress, and the opposite changes were detected in TAOK1-overexpressing cells. We also found decreased proliferative, migratory, and invasive capacity, as well as lower epithelial-mesenchymal transition in TAOK1-deficient human hepatoma-derived cells. Mechanistic studies revealed that TAOK1 knockdown inhibited ERK and JNK activation and repressed acetyl-CoA carboxylase (ACC) protein abundance in human hepatocytes.

CONCLUSIONS

Together, we provide the first experimental evidence supporting the role of hepatic lipid droplet-decorating kinase TAOK1 in NAFLD development through mediating fatty acid partitioning between anabolic and catabolic pathways, regulating oxidative/endoplasmic reticulum stress, and modulating metabolic and pro-oncogenic signaling.

Diagnostic comparison of vibration-controlled transient elastography and MRI techniques in overweight and obese patients with NAFLD

Non-invasive imaging techniques have greatly advanced the assessment of liver fibrosis and steatosis but are not fully evaluated in overweight patients. We evaluated the diagnostic performance of vibration-controlled transient elastography (VCTE) and magnetic resonance elastography (MRE) to assess fibrosis and controlled attenuation parameter (CAP) and MR imaging (MRI)-proton density fat fraction (MRI-PDFF) to assess steatosis in overweight and obese patients with non-alcoholic fatty liver disease (NAFLD). We included 163 biopsy-proven patients with NAFLD who underwent VCTE, MRE/MRI-PDFF, and liver biopsy (years 2014-2020) who were classified according to their body mass index (BMI) as normal (BMI < 25 kg/m², n = 38), overweight (25 ≤ BMI < 30 kg/m², n = 68), and obese (BMI ≥ 30 kg/m², n = 57). VCTE and MRE detected fibrosis of stages ≥ 2, ≥ 3, and 4 with an area under the receiver operating curve (AUROC) of 0.83-0.94 (VCTE) and 0.85-0.95 (MRE) in all groups, without considerable differences. MRI-PDFF detected steatosis of grades ≥ 2 and 3 with high AUROC in all groups (0.81-1.00). CAP's diagnostic ability (0.63-0.95) was lower than that of MRI-PDFF and decreased with increasing BMI compared to MRI-PDFF. VCTE and MRE similarly accurately assess fibrosis, although MRI-PDFF is more accurate than CAP in detecting steatosis in overweight and obese patients with NAFLD.

Improvement of liver fibrosis, but not steatosis, after HCV eradication as assessment by MR-based imaging: Role of metabolic derangement and host genetic variants

Significant liver fibrosis regression occurs after hepatitis C virus (HCV) therapy. However, the impact of direct-acting antivirals (DAAs) on steatosis is less clear. This study was aimed at evaluating serial fibrosis and steatosis alterations in patients with HCV genotype 1, who achieved sustained virological response (SVR). We enrolled 55 HCV mono-infected and 28 HCV/HIV co-infected patients receiving elbasvir/grazoprevir from a clinical trial. Fibrosis and steatosis were assessed at baseline, follow-up week-24 (FUw24) and week-72 (FUw72) by magnetic resonance elastography (MRE) and proton density fat fraction (PDFF), respectively. Patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409, transmembrane six superfamily member 2 (TM6SF2) rs58542926 and membrane bound O-acyltransferase domain-containing 7 (MBOAT7) rs641738 polymorphisms were determined by allelic discrimination. Overall, mean MRE decreased significantly from baseline to FUw24 and FUw72. At FUw72, patients with baseline F2-F4 had higher rate of ≥30% MRE decline compared with individuals with baseline F0-F1 (30.2%vs.3.3%, P = 0.004). In multivariate analysis, significant fibrosis was associated with MRE reduction. The prevalence of steatosis (PDFF≥5.2%) at baseline was 21.7%. Compared to baseline, there were 17 (20.5%) patients with decreased PDFF values at FUw72 (<30%), while 23 (27.7%) patients had increased PDFF values (≥30%). Regarding the overall cohort, mean PDFF significantly increased from baseline to FUw72, and displayed positive correlation with body mass index (BMI) alteration. In multivariate analysis, the presence of diabetes, PNPLA3 CG+GG genotypes and increased BMI at FUw72 were significantly associated with progressive steatosis after SVR. Other genetic variants were not related to fibrosis and steatosis alteration. This study concluded that HCV eradication was associated with fibrosis improvement. However, progressive steatosis was observed in a proportion of patients, particularly among individuals with metabolic derangement and PNPLA3 variants. The combined clinical parameters and host genetic factors might allow a better individualized strategy in this sub-group of patients to alleviate progressive steatosis after HCV cure.

Point-of-care magnetic resonance technology to measure liver fat: Phantom and first-in-human pilot study

PURPOSE

To assess feasibility and accuracy of point-of-care (POC) NMR-proton density fat fraction (PDFF) in phantoms and in a human pilot study in a POC setting.

METHODS

POC NMR (LiverScope, Livivos, San Diego CA) PDFF measurements were obtained of certified phantoms with known PDFF values (0%-40%). In an institutional review board-approved, Health Insurance Portability and Accountability Act-compliant prospective human study, a convenience sample of participants from an obesity clinic was enrolled (November 2020 to June 2021). The inclusion criteria required body mass index (BMI) = 27-40 kg/m² and willingness to undergo POC NMR and MRI-PDFF measurements. Liver PDFF was measured by POC NMR and, within 35 days after, by a confounder corrected CSE MRI PDFF acquisition and reconstruction method. The adverse events were documented and linear regression analyses were performed.

RESULTS

POC NMR-PDFF measurements agreed with known phantom PDFF values (R²  = 0.99). Fourteen participants were enrolled in the pilot human study. MRI-PDFF could not be obtained in 4 participants (claustrophobia reaction, n = 3, exceeded size of MR scanner bore, n = 1). POC NMR was unevaluable in 2 participants (insufficient signal penetration depth, n = 1, failure to comply with instructions, n = 1). Technical success was 11 of 13 (85%) for POC NMR PDFF. In 7 participants (4 female; 31-74 years old; median BMI 35 kg/m² ), MRI-PDFF (range, 2.8%-18.1%), and POC NMR-PDFF (range, 3%-25.2%), agreed with R²  = 0.94. POC NMR had no adverse events.

CONCLUSION

POC NMR measures PDFF accurately in phantoms and, in a first-in-human pilot study, is feasible and accurate in adults with obesity. Further testing to determine precision and accuracy across larger and more diverse cohorts is needed.

Gender- and Age-Associated Differences in Bone Marrow Adipose Tissue and Bone Marrow Fat Unsaturation Throughout the Skeleton, Quantified Using Chemical Shift Encoding-Based Water-Fat MRI

Bone marrow adipose tissue (BMAT) is a dynamic tissue which is associated with osteoporosis, bone metastasis, and primary bone tumors. The aim of this study is to determine region-specific variations and age- and gender-specific differences in BMAT and BMAT composition in healthy subjects. In this cross-sectional study, we included 40 healthy subjects (26 male: mean age 49 years, range 22-75 years; 14 female: mean age 50 years, range 29-71) and determined the bone marrow signal fat fraction and bone marrow unsaturation in the spine (C3-L5), pelvis, femora, and tibiae using chemical shift encoding-based water-fat imaging (WFI) with multiple gradient echoes (mGRE). Regions of interest covered the individual vertebral bodies, pelvis and proximal epimetaphysis, diaphysis, and distal epimetaphysis of the femur and tibia. The spinal fat fraction increased from cervical to lumbar vertebral bodies (mean fat fraction ( ± SD or (IQR): cervical spine 0.37 ± 0.1; thoracic spine 0.41 ± 0.08. lumbar spine 0.46 ± 0.01; p < 0.001). The femoral fat fraction increased from proximal to distal (proximal 0.78 ± 0.09; diaphysis 0.86 (0.15); distal 0.93 ± 0.02; p < 0.001), while within the tibia the fat fraction decreased from proximal to distal (proximal 0.92 ± 0.01; diaphysis 0.91 (0.02); distal 0.90 ± 0.01; p < 0.001). In female subjects, age was associated with fat fraction in the spine, pelvis, and proximal femur (ρ = 0.88 p < 0.001; ρ = 0.87 p < 0.001; ρ = 0.63 p = 0.02; ρ = 0.74 p = 0.002, respectively), while in male subjects age was only associated with spinal fat fraction (ρ = 0.40 p = 0.04). Fat fraction and unsaturation were negatively associated within the spine (r = -0.40 p = 0.01), while in the extremities fat fraction and unsaturation were positively associated (distal femur: r = 0.42 p = 0.01; proximal tibia: r = 0.47, p = 0.002; distal tibia: r = 0.35 p = 0.03), both independent of age and gender. In conclusion, we confirm the distinct, age- and gender-dependent, distribution of BMAT throughout the human skeleton and we show that, contradicting previous animal studies, bone marrow unsaturation in human subjects is highest within the axial skeleton compared to the appendicular skeleton. Furthermore, we show that BMAT unsaturation was negatively correlated with BMAT within the spine, while in the appendicular skeleton, BMAT and BMAT unsaturation were positively associated.

A proposed model on MR elastography for predicting postoperative major complications in patients with hepatocellular carcinoma

Objective

To develop a model for predicting post-operative major complications in patients with hepatocellular carcinoma (HCC).

Methods

In all, 186 consecutive patients with pre-operative MR elastography were included. Complications were categorised using Clavien‒Dindo classification, with major complications defined as ≥Grade 3. Liver-stiffness measurement (LSM) values were measured on elastogram. The indocyanine green clearance rate of liver remnant (ICG-Krem) was based on the results of CT volumetry, intraoperative data, and ICG-K value. For an easy application to the prediction model, the continuous variables were converted to categories. Moreover, logistic regression analysis and fivefold cross-validation were performed. The prediction model's discriminative performance was evaluated using the area under the receiver operating characteristic curve (AUC), and the calibration of the model was assessed by the Hosmer‒Lemeshow test.

Results

43 of 186 patients (23.1%) had major complications. The multivariate analysis demonstrated that LSM, albumin-bilirubin (ALBI) score, intraoperative blood loss, and ICG-Krem were significantly associated with major complications. The median AUC of the five validation subsets was 0.878. The Hosmer-Lemeshow test confirmed no evidence of inadequate fit (p = 0.13, 0.19, 0.59, 0.59, and 0.73) on the fivefold cross-validation. The prediction model for major complications was as follows: -2.876 + 2.912 [LSM (>5.3 kPa)]+1.538 [ALBI score (>-2.28)]+0.531 [Intraoperative blood loss (>860 ml)]+0.257 [ICG-Krem (<0.10)].

Conclusion

The proposed prediction model can be used to predict post-operative major complications in patients with HCC.

Advances in knowledge

The proposed prediction model can be used in routine clinical practice to identify post-operative major complications in patients with HCC and to strategise appropriate treatments of HCC.

Accelerated k-space shift calibration for free-breathing stack-of-radial MRI quantification of liver fat and R 2 ∗

PURPOSE

To develop an accelerated k-space shift calibration method for free-breathing 3D stack-of-radial MRI quantification of liver proton-density fat fraction (PDFF) and R 2 ∗ .

METHODS

Accelerated k-space shift calibration was developed to partially skip acquisition of k-space shift data in the through-plane direction then interpolate in processing, as well as to reduce the in-plane averages. A multi-echo stack-of-radial sequence with the baseline calibration was evaluated on a phantom versus vendor-provided reference-standard PDFF and R 2 ∗ values at 1.5T, and in 13 healthy subjects and 5 clinical subjects at 3T with respect to reference-standard breath-hold Cartesian acquisitions. PDFF and R 2 ∗ maps were calculated with different calibration acceleration factors offline and compared to reference-standard values using Bland-Altman analysis. Bias and uncertainty were evaluated using normal distribution and Bayesian probability of difference (P < .05 considered significant).

RESULTS

Bland-Altman plots of phantom and in vivo data showed that substantial acceleration was highly feasible in both through-plane and in-plane directions. Compared to the baseline calibration without acceleration, Bayesian analysis revealed no significant differences on biases and uncertainties of PDFF and R 2 ∗ measurements with all acceleration methods in this study, except the method with through-plane acceleration equaling slices and averages equaling 20 for PDFF and R 2 ∗ (both P < .001) for the phantom. A six-fold reduction in equivalent calibration acquisition time (time saving ≥25 s and ≥80.7%) was achieved using recommended acceleration factors for the in vivo protocols in this study.

CONCLUSION

This proposed method may allow accelerated calibration for free-breathing stack-of-radial MRI PDFF and R 2 ∗ mapping.

Feasibility of Hepatic Fat Quantification Using Proton Density Fat Fraction by Multi-Echo Chemical-Shift-Encoded MRI at 7T

Fat fraction quantification and assessment of its distribution in the hepatic tissue become more important with the growing epidemic of obesity, and the increasing prevalence of diabetes mellitus type 2 and non-alcoholic fatty liver disease. At 3Tesla, the multi-echo, chemical-shift-encoded magnetic resonance imaging (CSE-MRI)-based acquisition allows the measurement of proton density fat-fraction (PDFF) even in clinical protocols. Further improvements in SNR can be achieved by the use of phased array coils and increased static magnetic field. The purpose of the study is to evaluate the feasibility of PDFF imaging using a multi-echo CSE-MRI technique at ultra-high magnetic field (7Tesla). Thirteen volunteers (M/F) with a broad range of age, body mass index, and hepatic PDFF were measured at 3 and 7T by multi-gradient-echo MRI and single-voxel spectroscopy MRS. All measurements were performed in breath-hold (exhalation); the MRI protocols were optimized for a short measurement time, thus minimizing motion-related problems. 7T data were processed off-line using Matlab® (MRI:multi-gradient-echo) and jMRUI (MRS), respectively. For quantitative validation of the PDFF results, a similar protocol was performed at 3T, including on-line data processing provided by the system manufacturer, and correlation analyses between 7 and 3T data were performed off-line. The multi-echo CSE-MRI measurements at 7T with a phased-array coil configuration and an optimal post-processing yielded liver volume coverage ranging from 30 to 90% for high- and low-BMI subjects, respectively. PDFFs ranged between 1 and 20%. We found significant correlations between 7T MRI and -MRS measurements (R² ≅ 0.97; p < 0.005), and between MRI-PDFF at 7T and 3T fields (R² ≅ 0.94; p < 0.005) in the evaluated volumes. Based on the measurements and analyses performed, the multi-echo CSE-MRI method using a 32-channel coil at 7T showed its aptitude for MRI-based quantitation of PDFF in the investigated volumes. The results are the first step toward qMRI of the whole liver at 7T with further improvements in hardware.

Prediction of Hepatocellular Carcinoma by Liver Stiffness Measurements Using Magnetic Resonance Elastography After Eradicating Hepatitis C Virus

INTRODUCTION

Liver fibrosis stage is one of the most important factors in stratifying the risk of developing hepatocellular carcinoma (HCC). We evaluated the usefulness of liver stiffness measured by magnetic resonance elastography (MRE) to stratify the risk of developing HCC in patients who underwent MRE before receiving direct-acting antivirals (DAAs) and subsequently achieved sustained virological response (SVR).

METHODS

A total of 537 consecutive patients with persistent hepatitis C virus who underwent initial MRE before DAA therapy and achieved SVR were enrolled. Factors associated with HCC development were analyzed by univariate and multivariate Cox proportional hazards models.

RESULTS

Albumin-bilirubin score ≥ -2.60 (adjusted hazard ratio [aHR] 6.303), fibrosis-4 (FIB-4) score >3.25 (aHR 7.676), and MRE value ≥4.5 kPa (aHR 13.190) were associated with HCC development according to a univariate Cox proportional hazards model. A multivariate Cox proportional hazards model showed that an MRE value ≥4.5 kPa (aHR 7.301) was the only factor independently associated with HCC development. Even in patients with an FIB-4 score >3.25, the cumulative incidence rate of HCC development in those with an MRE value <4.5 kPa was significantly lower than that in patients with an MRE value ≥4.5 kPa.

DISCUSSION

Liver stiffness measured by MRE before DAA therapy was an excellent marker for predicting subsequent HCC development in patients with hepatitis C virus infection who achieved SVR. The same results were observed in patients with high FIB-4 scores.

FIB-4 index-based surveillance for advanced liver fibrosis in diabetes patients

Liver fibrosis is associated with lifestyle-related diseases, including diabetes. The identification of diabetic patients with severe liver fibrosis is important, but a simple and reliable diagnostic procedure remains to be determined. We conducted an observational study to evaluate the performance of a FIB-4 index-based screening strategy for the diagnosis of advanced liver fibrosis in patients with diabetes or prediabetes. Two hundred and forty-two patients underwent abdominal imaging in our Study. According to the abdominal imaging findings, fatty liver, liver cirrhosis, and hepatocellular carcinoma were defined, and their association with FIB-4 index evaluated. The prevalences of liver cirrhosis and hepatocellular carcinoma in patients with a high (≥ 2.67; liver cirrhosis: 42.9%, hepatocellular carcinoma: 14.3%) FIB-4 index were significantly higher than in those with an intermediate (1.3 ≤ FIB-4 < 2.67; liver cirrhosis: 1.6%, hepatocellular carcinoma: 0.8%) or low FIB-4 index (< 1.3; liver cirrhosis: 1.2%, hepatocellular carcinoma: 0%). The diagnostic accuracy, specificity, and sensitivity of the FIB-4 index for the diagnosis of liver cirrhosis or hepatocellular carcinoma were 84.3%, 85.5%, and 89.3%, respectively, with an optimized cut-off value of 2.96 (sensitivity = 0.86, specificity = 0.98). Using an optimized cut-off value, FIB-4 index might be useful to identify liver cirrhosis or hepatocellular carcinoma in diabetes patients with high diagnostic accuracy.

Regulation of the cytochrome P450 epoxyeicosanoid pathway is associated with distinct histologic features in pediatric non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a significant health burden in obese children for which there is currently no specific therapy. Preclinical studies indicate that epoxyeicosanoids, a class of bioactive lipid mediators that are generated by cytochrome P450 (CYP) epoxygenases and inactivated by the soluble epoxide hydrolase (sEH), play a protective role in NAFLD. We performed a comprehensive lipidomics analysis using liver tissue and blood samples of 40 children with NAFLD. Proteomics was performed to determine CYP epoxygenase and sEH expressions. Hepatic epoxyeicosanoids significantly increased with higher grades of steatosis, while their precursor PUFAs were unaltered. Concomitantly, total CYP epoxygenase activity increased while protein level and activity of sEH decreased. In contrast, hepatic epoxyeicosanoids showed a strong decreasing trend with higher stages of fibrosis, accompanied by a decrease of CYP epoxygenase activity and protein expression. These findings suggest that the CYP epoxygenase/sEH pathway represents a potential pharmacologic target for the treatment of NAFLD.

Attenuation imaging based on ultrasound technology for assessment of hepatic steatosis: A comparison with magnetic resonance imaging-determined proton density fat fraction

AIM

A new method has recently been developed for diagnosing hepatic steatosis based on attenuation measurement using ultrasound. We investigated the ability of attenuation imaging (ATI) to detect steatosis that was identified by proton density fat fraction (PDFF) on magnetic resonance imaging (MRI) in patients with chronic liver disease.

METHODS

A total of 119 patients with chronic liver disease (non-B, non-C) were analyzed. The relationship between ATI values and steatosis grades determined by PDFF was evaluated. Additionally, the diagnostic ability of ATI was evaluated using receiver operating characteristic curve analysis, and the correlation between ATI values and PDFF values was determined.

RESULTS

The ATI values of steatosis grades 0, 1, 2, and 3 were 0.55, 0.61, 0.74, and 0.84 dB/cm/MHz, respectively (P < 0.001). There was a statistically significant trend of higher ATI values with higher steatosis grades (P < 0.001). The correlation coefficient (r) between PDFF values and ATI values was 0.70 (95% confidence interval [CI] 0.59-0.78; P < 0.001), corresponding to a strong relationship. The diagnostic ability of ATI for steatosis grades ≥1, ≥2, and 3, as determined by PDFF, were 0.81 (95% CI 0.73-0.89), 0.87 (95% CI 0.79-0.96), and 0.94 (95% CI 0.89-0.98), respectively. The r between PDFF values and ATI values was 0.49 (95% CI 0.31-0.63; P < 0.001) for patients with mild or no steatosis (grade ≤1), and 0.75 (95% CI 0.57-0.86; P < 0.001) for obese patients (body mass index ≥25 kg/m² ).

CONCLUSION

ATI values had an excellent diagnostic ability to detect hepatic steatosis.

Fat fractions from high-resolution 3D radial Dixon MRI for predicting metastatic axillary lymph nodes in breast cancer patients

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High-Resolution 3D radial Dixon MRI allows for the creation of quantitative fat fraction images.

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Lymph node fat fractions improves diagnostic performance of MRI to detect axillary lymph node metastases.

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Lymph node fat fractions are a promising quantitative indicator of metastases in axillary lymph nodes.

Purpose

To assess diagnostic performance of fat fractions (FF) from high-resolution 3D radial Dixon MRI for differentiating metastatic and non-metastatic axillary lymph nodes in breast cancer patients.

Method

High-resolution 3D radial Dixon MRI was prospectively performed on 1.5 T in 70 biopsy-verified breast cancer patients. 35 patients were available for analysis with histopathologic and imaging data. FF images were calculated as fat / in-phase. Two radiologists measured lymph node FF and assessed morphological features in one ipsilateral and one contralateral lymph node in consensus. Diagnostic performance of lymph node FF and morphological criteria were compared using histopathology as reference.

Results

22 patients had metastatic axillary lymph nodes. Mean lymph node FF were 0.20 ± 0.073, 0.31 ± 0.079, and 0.34 ± 0.15 (metastatic, non-metastatic ipsi- and non-metastatic contralateral lymph nodes, respectively). Metastatic lymph node FF were significantly lower than non-metastatic ipsi- (p <  0.001) and contralateral lymph nodes (p <  0.001). Area under the receiver operating characteristics curve for lymph node FF was 0.80 compared to 0.76 for morphological criteria (p =  0.29). Lymph node FF yielded sensitivity 0.91, specificity 0.69, positive predictive value (PPV) 0.83, and negative predictive value (NPV) 0.82, while morphological criteria yielded sensitivity 0.91, specificity 0.62, PPV 0.80, and NPV 0.80 (p =  0.71). Combining lymph node FF and morphological criteria increased diagnostic performance with sensitivity 1.00, specificity 0.67, PPV 0.86, NPV 1.00, and AUC 0.83.

Conclusions

Lymph node FF from high-resolution 3D Dixon images are a promising quantitative indicator of metastases in axillary lymph nodes.

Genetic Risk for Hepatic Fat among an Ethnically Diverse Cohort of Youth: The Exploring Perinatal Outcomes among Children Study

OBJECTIVE

To assess the importance of genetic and nongenetic risk factors contributing to hepatic fat accumulation in a multiethnic population of youth.

STUDY DESIGN

We investigated the relationship between genetic factors and hepatic fat fraction (HFF) in 347 children aged 12.5-19.5 years. We examined 5 single nucleotide polymorphisms previously associated with HFF and a weighted genetic risk score (GRS) and examined how these associations varied with ethnicity (Hispanic vs non-Hispanic white) and body mass index (BMI) category. We also compared how much variation in HFF was explained by genetic factors vs cardiometabolic factors (BMI z-score and the Homeostasis Model of Insulin Resistance) or diet.

RESULTS

PNPLA3 rs738409 and the GRS were each associated with HFF among Hispanic (β = 0.39; 95% CI, 0.16-0.62; P = .001; and β = 0.20; 95% CI, 0.05-0.34; P = .007, respectively) but not non-Hispanic white (β = 0.04; 95% CI, -0.18 to 0.26; P = .696; and β = 0.03; 95% CI, -0.09 to 0.14; P = .651, respectively) youth. Cardiometabolic risk factors explained more of the variation in HFF than genetic risk factors among non-lean Hispanic individuals (27.2% for cardiometabolic markers vs 6.4% for rs738409 and 4.3% for the GRS), and genetic risk factors were more important among lean individuals (2.7% for cardiometabolic markers vs 12.6% for rs738409 and 4.4% for the GRS).

CONCLUSIONS

Poor cardiometabolic health may be more important than genetic factors when predicting HFF in overweight and obese young populations. Genetic risk is an important contributor to pediatric HFF among lean Hispanics, but further studies are necessary to elucidate the strength of the association between genetic risk and HFF in non-Hispanic white youth.

Utility of MR proton density fat fraction and its correlation with ultrasonography and biochemical markers in nonalcoholic fatty liver disease in overweight adolescents

Background Clinical or biochemical markers that have good correlation with magnetic resonance proton density fat fraction (MR PDFF) can be used as simple tools for the screening for nonalcoholic fatty liver disease (NAFLD) and in determining the degree of fatty infiltration of the liver. The objective of this study was to determine the degree of relationship between MR PDFF and ultrasonography (USG) grades of fatty liver, and clinical and biochemical parameters of adolescents and to determine the sensitivity and specificity of USG for diagnosis of NAFLD. Methods This prospective study included 34 overweight adolescents (mean age, 12.1 ± 1.5 years; range, 10-15.1 years; 10 girls and 24 boys) who underwent both USG and magnetic resonance imaging (MRI). Correlation analysis was performed between MR fat fraction and USG grades of fatty liver, and clinical and biochemical parameters of fatty liver disease. Results MR fat fraction had a moderate positive correlation with serum alanine transaminase (ALT) and aspartate transaminase (AST) (ρ = 0.634, p < 0.001, ρ = 0.516, p = 0.002, respectively) and had a negligible or weak correlation with body mass index (BMI), BMI standard deviation score (SDS), waist circumference (WC), fasting insulin, homeostatic model assessment of insulin resistance (HOMA-IR), serum triglyceride, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and total cholesterol levels. The sensitivity and specificity of USG in the diagnosis of NAFLD were 81% (95% confidence interval 54%-95%) and 50% (27%-73%), respectively. The MR fat fraction had a moderate positive correlation with ultrasound grades of fatty liver (ρ = 0.487, p = 0.003). Conclusions Serum ALT and AST are potential biochemical markers to assess the degree of hepatic steatosis in NAFLD, which needs validation in further studies. USG can be used as a screening tool for NAFLD, but the diagnosis should be confirmed by estimating the MR fat fraction.

Fat-water separation by fast metabolite cycling magnetic resonance spectroscopic imaging at 3 T: A method to generate separate quantitative distribution maps of musculoskeletal lipid components

PURPOSE

To provide a rapid, noninvasive fat-water separation technique that allows producing quantitative maps of particular lipid components.

METHODS

The calf muscles in 5 healthy adolescents (age 12-16 years; body mass index = 20 ± 3 kg/m² ) were scanned by two different fat fraction measurement methods. A density-weighted concentric-ring trajectory metabolite-cycling MRSI technique was implemented to collect data with a nominal resolution of 0.25 mL within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data.

RESULTS

The proposed MRSI technique provided individual fat fraction maps for eight musculoskeletal lipid components identified by LCModel analysis (IMC/L [CH₃ ], EMCL [CH₃ ], IMC/L [CH₂ ]_n , EMC/L [CH₂ ]_n , IMC/L [CH₂ -CH], EMC/L [CH₂ -CH], IMC/L [-CH=CH-], and EMC/L [-CH=CH-]) with mean structural similarity indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively, compared with the maps generated by the used Dixon method. Further analysis of voxels with zero structural similarity demonstrated an increased sensitivity of fat fraction lipid maps from the data acquired using this MRSI technique over the standard Dixon technique. The lipid spatial distribution over calf muscles was consistent with previously published findings in adults.

CONCLUSION

This MRSI technique can be a useful tool when individual lipid fat fraction maps are desired within a clinically acceptable time and with a nominal spatial resolution of 0.25 mL.

Liver stiffness does not affect ultrasound-guided attenuation coefficient measurement in the evaluation of hepatic steatosis

AIM

Recently, a new method has been developed to diagnose hepatic steatosis with attenuation coefficients based on the ultrasound-guided attenuation parameter (UGAP). We investigated whether fibrosis identified by hepatic stiffness measurements based on magnetic resonance elastography (MRE) affects attenuation coefficient measurement using UGAP for the evaluation of hepatic steatosis.

METHODS

A total of 608 patients with chronic liver disease were analyzed. Correlations between magnetic resonance imaging-determined proton density fat fraction (PDFF) or MRE value and attenuation coefficients were evaluated. In addition, the interaction between hepatic fibrosis and the attenuation coefficient was analyzed.

RESULTS

The correlation coefficient (r) between PDFF values and attenuation coefficient values was 0.724, indicating a strong relationship. Conversely, the r between MRE values and attenuation coefficient values was -0.187, indicating almost no relationship. In the multiple regression assessment of the effect of PDFF and MRE on the attenuation coefficient based on UGAP, the P-values for PDFF, MRE, and PDFF × MRE were < 0.001, 0.277, and 0.903, respectively. In patients with non-alcoholic fatty liver disease (n = 169), the r between PDFF values and attenuation coefficient values was 0.695, indicating a moderate relationship. Conversely, the r between MRE values and attenuation coefficient values was -0.068, indicating almost no relationship. In the multiple regression assessment of the effect of PDFF and MRE on the attenuation coefficient based on UGAP, the P-values for PDFF, MRE, and PDFF × MRE were <0.001, 0.948, and 0.706, respectively.

CONCLUSION

UGAP-determined attenuation coefficient was weakly affected by liver stiffness, an indicator of hepatic fibrosis.

Whole hepatic lipid volume quantification and color mapping by multi-slice and multi-point magnetic resonance imaging

AIM

Current approaches for hepatic steatosis assess only a small point within the liver and might cause inaccuracy for longitudinal observation. We aimed to establish a reliable non-invasive method for whole hepatic lipid content evaluation.

METHODS

A total of 52 patients with hepatic steatosis underwent liver biopsy. Hepatic lipid content was assessed by Dixon in-phase/out-of-phase magnetic resonance imaging and proton magnetic resonance spectroscopy. Using multi-slice and multi-point magnetic resonance imaging, we calculated the lipid intensity of every voxel throughout the liver and showed the color-mapped lipid distributions. This new analysis could also quantify the whole hepatic lipid and whole liver volumes absolutely. The diagnostic performance of hepatic lipid content between the new analysis and proton magnetic resonance spectroscopy methods was compared by receiver operating characteristic curve analysis referring to the steatosis scores of the liver biopsy.

RESULTS

Areas under the receiver operating characteristic for the diagnosis of steatosis scores ≥1, ≥2, and ≥3 using magnetic resonance imaging and proton magnetic resonance spectroscopy were 0.86 (95% confidence interval [CI] 0.70-1.00) and 0.98 (95% CI 0.93-1.00), 0.94 (95% CI 0.87-1.00) and 0.93 (95% CI 0.86-1.00), and 0.95 (95% CI 0.89-1.00) and 0.97 (95% CI 0.93-1.00), respectively, showing comparable diagnostic accuracies. However, color mapping showed some inconsistencies between the methods.

CONCLUSIONS

We described a non-invasive and repeatable evaluation method of whole hepatic lipid accumulation with absolute quantification and color mapping. Hepatic steatosis was accurately evaluated regardless of heterogeneous lipid accumulation. The whole hepatic lean volume, reflecting the hepatic parenchymal condition, can also be determined by this method.

Constraints in estimating the proton density fat fraction

The study evaluates four physically motivated constraints in the estimation of the proton density fat fraction (PDFF). Least squares approaches were developed for constraining the parameters in PDFF quantification based on the physics of magnetic resonance imaging. These were smooth fieldmap, smooth initial phase, nonnegative proton density and moderate R₂^∗ values. The constraints were evaluated in terms of their influence on the bias and standard deviation of the estimated parameters using numerical simulations and in vivo data acquired at 0.35 T. Results show that unconstrained least squares estimation is noisy and biased and that constraints can be effective at reducing both the standard deviation and bias.

Effect of respiratory motion on free-breathing 3D stack-of-radial liver R 2 ∗ relaxometry and improved quantification accuracy using self-gating

PURPOSE

To develop an accurate free-breathing 3D liver R 2 ∗ mapping approach and to evaluate it in vivo.

METHODS

A free-breathing multi-echo stack-of-radial sequence was applied in 5 normal subjects and 6 patients at 3 Tesla. Respiratory motion compensation was implemented using the inherent self-gating signal. A breath-hold Cartesian acquisition was the reference standard. Proton density fat fraction and R 2 ∗ were measured and compared between radial and Cartesian methods using Bland-Altman plots. The normal subject results were fitted to a linear mixed model (P < .05 considered significant).

RESULTS

Free-breathing stack-of-radial without self-gating exhibited signal attenuation in echo images and artifactually elevated apparent R 2 ∗ values. In the Bland-Altman plots of normal subjects, compared to breath-hold Cartesian, free-breathing stack-of-radial acquisitions of 22, 30, 36, and 44 slices, had mean R 2 ∗ differences of 27.4, 19.4, 10.9, and 14.7 s^-1 with 800 radial views, and they had 18.4, 11.9, 9.7, and 27.7 s^-1 with 404 views, which were reduced to 0.4, 0.9, -0.2, and -0.7 s^-1 and to -1.7, -1.9, -2.1, and 0.5 s^-1 with self-gating, respectively. No substantial proton density fat fraction differences were found. The linear mixed model showed free-breathing radial R 2 ∗ results without self-gating were significantly biased by 17.2 s^-1 averagely (P = .002), which was eliminated with self-gating (P = .930). Proton density fat fraction results were not different (P > .234). For patients, Bland-Altman plots exhibited mean R 2 ∗ differences of 14.4 and 0.1 s^-1 for free-breathing stack-of-radial without self-gating and with self-gating, respectively, but no substantial proton density fat fraction differences.

CONCLUSION

The proposed self-gating method corrects the respiratory motion bias and enables accurate free-breathing stack-of-radial quantification of liver R 2 ∗ .

Chinese tree shrews as a primate experimental animal eligible for the study of alcoholic liver disease: characterization and confirmation by MRI

There has been a lack of suitable fatty liver models and characterization techniques for histopathological evaluation of alcoholic fatty liver (AFL). This work aimed to exploit an magnetic resonance imaging (MRI) technique for characterizing an alcohol-induced fatty liver model established in tree shrews (Tupaia belangeri chinese). The animals were treated with 15% alcohol for two weeks instead of drinking water to induce AFL. Blood alanine aminotransferase (ALT), aspartate aminotransferase (AST), alcohol, and liver malondialdehyde (MDA) concentrations were determined, and the histopathology of the liver was checked by hematoxylin & eosin (HE) and Oil red O staining on day 0 and on the 4th, 7th and 14th days after alcohol feeding. MRI was used to trace the histopathological changes in the liver of tree shrews in real time. Compared with the control group, the levels of ALT, AST, and MDA significantly increased in the alcohol-induced group and were positively correlated with the induction time. HE and Oil red O staining revealed that a moderate fatty lesion occurred in the liver on the 4th day and that a serious AFL was successfully induced on the 14th day. MRI further confirmed the formation of AFL. MRI, as noninvasive examination technique, provides an alternative tool for accurate characterization of AFL in live subjects. It is comparable to HE or Oil red O staining for histopathological examination, but is more suitable by virtue of its high flexibility and compliance. The AFL model of tree shrews combined with MRI characterization can work as a platform for studying fatty liver diseases and medications for their treatment.

The Value of CT and MRI for Determining Thymoma in Patients With Myasthenia Gravis

The aim of the study was to evaluate the usefulness of computed tomography (CT) and magnetic resonance imaging (MRI) for differentiating thymoma from nonthymoma abnormalities in patients with myasthenia gravis (MG). A cross-sectional study of 53 patients with MG, who had undergone surgical thymectomy, was conducted at 103 Hospital (Hanoi, Vietnam) and Cho Ray Hospital (Ho Chi Minh City, Vietnam) during August 2014 and January 2017. The CT and MRI images of patients with MG were qualitatively and quantitatively (radiodensity and chemical shift ratio [CSR]) analyzed to determine and compare their ability to distinguish thymoma from nonthymoma abnormalities. Logistic regression was used to identify the association between imaging parameters (eg, CSR) and the thymoma status. The receiver operating curve (ROC) analysis was used to determine the differentiating ability of CSR and radiodensity. As results, of the 53 patients with MG, 33 were with thymoma and 20 were with nonthymoma abnormalities. At qualitative assessment, MRI had significantly higher accuracy than did CT in differentiating thymoma from nonthymoma abnormalities (94.3% vs 83%). At quantitative assessment, both the radiodensity and CSR were significantly higher for thymoma compared with nonthymoma groups (P < .001). The ROC analysis showed that CSR had significantly higher sensitivity (Se) and specificity (Sp) than radiodensity in discriminating between the 2 groups (CSR: Se 100%, Sp 95% vs radiodensity: Se 90.9%, Sp 70%). When combining both qualitative and quantitative parameters, MRI had even higher accuracy than did CT in thymoma diagnosis (P = .031). In conclusion, chemical shift MRI was more accurate than CT for differentiating thymoma from nonthymoma in patients with MG.

Protein kinase MST3 modulates lipid homeostasis in hepatocytes and correlates with nonalcoholic steatohepatitis in humans

Ectopic lipid storage in the liver is considered the main risk factor for nonalcoholic steatohepatitis (NASH). Understanding the molecular networks controlling hepatocellular lipid deposition is therefore essential for developing new strategies to effectively prevent and treat this complex disease. Here, we describe a new regulator of lipid partitioning in human hepatocytes: mammalian sterile 20-like (MST) 3. We found that MST3 protein coats lipid droplets in mouse and human liver cells. Knockdown of MST3 attenuated lipid accumulation in human hepatocytes by stimulating β-oxidation and triacylglycerol secretion while inhibiting fatty acid influx and lipid synthesis. We also observed that lipogenic gene expression and acetyl-coenzyme A carboxylase protein abundance were reduced in MST3-deficient hepatocytes, providing insight into the molecular mechanisms underlying the decreased lipid storage. Furthermore, MST3 expression was positively correlated with key features of NASH (i.e., hepatic lipid content, lobular inflammation, and hepatocellular ballooning) in human liver biopsies. In summary, our results reveal a role of MST3 in controlling the dynamic metabolic balance of liver lipid catabolism vs. lipid anabolism. Our findings highlight MST3 as a potential drug target for the prevention and treatment of NASH and related complex metabolic diseases.-Cansby, E., Kulkarni, N. M., Magnusson, E., Kurhe, Y., Amrutkar, M., Nerstedt, A., Ståhlman, M., Sihlbom, C., Marschall, H.-U., Borén, J., Blüher, M., Mahlapuu, M. Protein kinase MST3 modulates lipid homeostasis in hepatocytes and correlates with nonalcoholic steatohepatitis in humans.

Evaluation of hepatic iron concentration heterogeneities using the MRI R2* mapping method

OBJECTIVE

To measure hepatic iron concentration (HIC) heterogeneities using a magnetic resonance R2* mapping method.

PATIENTS AND METHODS

Ninety-four patients with suspected hepatic iron overload and 10 volunteers were included prospectively. A multi-echo R2* sequence with fat saturation and with three post-processing fitting methods (a single exponential decay model with or without truncation, SED and SEDt, and a constant offset model, COS) was compared to a signal intensity ratio method (SIR), considered as the reference. HIC heterogeneity was evaluated from R2* mapping after placing a ROI on each liver segment.

RESULTS

A strong linear correlation between SIR and R2* methods using the SEDt and COS models was observed (r = 0.973 and 0.955, respectively). Volunteers and patient liver variabilities, quantified by mean intra-liver standard deviation (SD) were 1.58 μmol/g (mean range 5.06 μmol/g) and 4.73 μmol/g (mean range 19.08 μmol/g), respectively. For the patient group, the highest HIC was observed in the IV^th segment. Heterogeneity increased for patients with an HIC > 60 μmol/g (mean intra-liver SD = 13.90 μmol/g; mean range = 50.60 μmol/g).

CONCLUSION

This study is the first to demonstrate in vivo HIC heterogeneities using whole-liver mapping analysis. These preliminary results require confirmation through further studies, but might be useful in cases of single ROI analysis.

Magnitude-intrinsic water-fat ambiguity can be resolved with multipeak fat modeling and a multipoint search method

Purpose

To develop a postprocessing algorithm for multiecho chemical‐shift encoded water–fat separation that estimates proton density fat fraction (PDFF) maps over the full dynamic range (0‐100%) using multipeak fat modeling and multipoint search optimization. To assess its accuracy, reproducibility, and agreement with state‐of‐the‐art complex‐based methods, and to evaluate its robustness to artefacts in abdominal PDFF maps.

Methods

We introduce MAGO (MAGnitude‐Only), a magnitude‐based reconstruction that embodies multipeak liver fat spectral modeling and multipoint optimization, and which is compatible with asymmetric echo acquisitions. MAGO is assessed first for accuracy and reproducibility on publicly available phantom data. Then, MAGO is applied to N = 178 UK Biobank cases, in which its liver PDFF measures are compared using Bland‐Altman analysis with those from a version of the hybrid iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) algorithm, LiverMultiScan IDEAL (LMS IDEAL, Perspectum Diagnostics Ltd, Oxford, UK). Finally, MAGO is tested on a succession of high field challenging cases for which LMS IDEAL generated artefacts in the PDFF maps.

Results

Phantom data showed accurate, reproducible MAGO PDFF values across manufacturers, field strengths, and acquisition protocols. Moreover, we report excellent agreement between MAGO and LMS IDEAL for 6‐echo, 1.5 tesla human acquisitions (bias = −0.02% PDFF, 95% confidence interval = ±0.13% PDFF). When tested on 12‐echo, 3 tesla cases from different manufacturers, MAGO was shown to be more robust to artefacts compared to LMS IDEAL.

Conclusion

MAGO resolves the water–fat ambiguity over the entire fat fraction dynamic range without compromising accuracy, therefore enabling robust PDFF estimation where phase data is inaccessible or unreliable and complex‐based and hybrid methods fail.

The association of hepatic fat percentage with selected anthropometric and biochemical parameters at 3-Tesla magnetic resonance imaging

BACKGROUND AND AIM

This relatively comprehensive and multi-parametric study was conducted to investigate an association between hepatic fat percentage (HFP) values measured using high-field magnetic resonance imaging (MRI), anthropometric and biochemical measurements in healthy adults.

METHODS

Abdominal MRI, anthropometric and biochemical measurements were determined in 156 healthy subjects. HFP values were derived from the MRI, whilst routine lipids, leptin, resistin, IL6 and adiponectin were measured by routine methods.

RESULTS

Eighty per cent of the calculated HFP values were in the normal range of hepatic fat accumulation. Significant sex-adjusted correlations were found between HFP and waist circumference (WC) (measured by tape), BMI, leptin, resistin, WC (measured by MRI) and hip circumference (all p<0.001) and triglycerides (p=0.01). A significant inverse correlation was detected between HFP and adiponectin (p<0.001).

CONCLUSIONS

A multi-parametric approach of MRI, biochemical and anthropometric measurements could be adopted to identify subjects at risk of developing non-alcoholic fatty liver disease.

Domain-specific data augmentation for segmenting MR images of fatty infiltrated human thighs with neural networks

BACKGROUND

Fat-fraction has been established as a relevant marker for the assessment and diagnosis of neuromuscular diseases. For computing this metric, segmentation of muscle tissue in MR images is a first crucial step.

PURPOSE

To tackle the high degree of variability in combination with the high annotation effort for training supervised segmentation models (such as fully convolutional neural networks).

STUDY TYPE

Prospective.

SUBJECTS

In all, 41 patients consisting of 20 patients showing fatty infiltration and 21 healthy subjects. Field Strength/Sequence: The T₁ -weighted MR-pulse sequences were acquired on a 1.5T scanner.

ASSESSMENT

To increase performance with limited training data, we propose a domain-specific technique for simulating fatty infiltrations (i.e., texture augmentation) in nonaffected subjects' MR images in combination with shape augmentation. For simulating the fatty infiltrations, we make use of an architecture comprising several competing networks (generative adversarial networks) that facilitate a realistic artificial conversion between healthy and infiltrated MR images. Finally, we assess the segmentation accuracy (Dice similarity coefficient).

STATISTICAL TESTS

A Wilcoxon signed rank test was performed to assess whether differences in segmentation accuracy are significant.

RESULTS

The mean Dice similarity coefficients significantly increase from 0.84-0.88 (P < 0.01) using data augmentation if training is performed with mixed data and from 0.59-0.87 (P < 0.001) if training is conducted with healthy subjects only.

DATA CONCLUSION

Domain-specific data adaptation is highly suitable for facilitating neural network-based segmentation of thighs with feasible manual effort for creating training data. The results even suggest an approach completely bypassing manual annotations.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 3.

T2-relaxation mapping and fat fraction assessment to objectively quantify clinical activity in thyroid eye disease: an initial feasibility study

Imaging in thyroid eye disease (TED) is used to exclude other diagnoses, assess for apical crowding and plan surgery. But to quantify TED activity objectively, subjective clinical scoring assessments remain the norm. Magnetic resonance imaging (MRI) T2-relaxation times correlate with extra-ocular muscle (EOM) inflammation, but are confounded by signal from fat. We investigated whether T2-relaxation mapping in combination with fat fraction (FF) measurements could quantify disease activity in EOMs objectively. Sixty-two TED patients and six controls were enroled for coronal short tau inversion recovery (STIR), T2 multi-echo fast-spin echo and multi-echo fast-gradient echo MRI of the orbits. STIR signal intensity ratios (SIRs), T2-relaxation times and percentage FF were derived for inferior, lateral, superior and medial recti bilaterally. Twelve patients were re-scanned following immunosuppressive treatment. The results found a positive correlation for all subjects between T2 and SIR (p < 0.001), but only mean T2 differed significantly between patients and controls (p < 0.001). We measured FF in EOMs for the first time and found it greater in TED (p < 0.001). There was also a significant reduction in mean T2 after treatment, with a corresponding reduction in the clinical activity score (CAS) in almost all patients. We show that T2-relaxation times differentiate between normal and inflamed EOMs and are responsive to treatment. Combined, uniquely, with FF measurement in EOMs, an objective, quantitative marker of inflammation in TED-affected muscles could be derived. T2-relaxation times mirrored improvements in CAS after treatment, occasionally preceding them. Rarely, they diverged, suggesting limitations in the CAS as a disease burden marker.

Magnetic resonance elastography increases usefulness and safety of non-invasive screening for esophageal varices

BACKGROUND AND AIMS

The Baveno VI criteria enable non-invasive screening for esophageal varices. However, these criteria were established based on studies examining a large proportion of patients with viral hepatitis and relatively few patients with non-alcoholic fatty liver disease (NAFLD). Furthermore, because vibration-controlled transient elastography (VCTE) has a high incidence of measurement error, improved criteria are needed. We aimed to develop criteria based on magnetic resonance elastography (MRE) even among patients with NAFLD.

METHODS

We performed a cross-sectional analysis of patients who had undergone MRE and/or VCTE as well as an esophagogastroduodenoscopy. The patients were classified as having either a low risk or a high risk of varices. The optimal cut-offs for ruling out esophageal varices were calculated for the MRE and VCTE liver stiffness measurement (LSM), the platelet count in an estimation cohort, and the cut-offs were then evaluated using validation cohorts composed of patients who had undergone only MRE or VCTE.

RESULTS

The study included 627 patients (39% with NAFLD). The optimal cut-off values for the MRE-LSM and the platelet count were 4.2 kPa and 18.0 × 10⁴ /μL, respectively. An MRE-LSM of 4.2 kPa plus a platelet count of 18.0 × 10⁴ /μL had a negative predictive value of 1.00 for both low-risk plus high-risk varices as well as for high-risk varices in a validation cohort, enabling the presence of varices to be ruled out.

CONCLUSIONS

Magnetic resonance elastography might enable a safer avoidance of screening endoscopy, with a smaller measurement error, among patient populations with a high prevalence of NAFLD.

Utility of Attenuation Coefficient Measurement Using an Ultrasound-Guided Attenuation Parameter for Evaluation of Hepatic Steatosis: Comparison With MRI-Determined Proton Density Fat Fraction

OBJECTIVE

Recently, a new method was developed to diagnose hepatic steatosis by measuring attenuation coefficients that are based on the ultrasound-guided attenuation parameter (UGAP). We investigated the diagnostic ability of these coefficients to detect steatosis that was identified using the proton density fat fraction (PDFF) on MRI in patients with chronic liver disease.

MATERIALS AND METHODS

A total of 126 patients with chronic liver disease (non-hepatitis B, non-hepatitis C) were analyzed. The diagnostic ability of UGAP-determined attenuation coefficients was evaluated using ROC curve analysis, and the correlation between MRI-determined PDFF values and attenuation coefficient values was determined.

RESULTS

The correlation coefficient (r) between PDFF values and attenuation coefficient values was 0.746 (95% CI, 0.657-0.815) (p < 0.001), corresponding to a strong relationship. The diagnostic ability of attenuation coefficients for steatosis grades ≥ 1, ≥ 2, and 3 as determined by PDFF were 0.922 (95% CI, 0.870-0.973), 0.874 (95% CI, 0.814-0.934), and 0.892 (95% CI, 0.835-0.949), respectively. The r between PDFF values and attenuation coefficient values was 0.559 (95% CI, 0.391-0.705) (p < 0.001) in patients with mild or no steatosis (grade ≤ 1). In addition, the r between PDFF values and attenuation coefficient values was 0.773 (95% CI, 0.657-0.853) (p < 0.001) in obese patients (body mass index [weight in kilograms divided by the square of height in meters] ≥ 25). The diagnostic ability of attenuation coefficients for patients with steatosis grades ≥ 1, ≥ 2, and 3 as determined by PDFF were 0.884 (95% CI, 0.792-0.976), 0.863 (95% CI, 0.778-0.947), and 0.889 (95% CI, 0.813-0.965), respectively.

CONCLUSION

UGAP-determined attenuation coefficient values had a good diagnostic ability to detect hepatic steatosis.

MRI liver fat quantification in an oncologic population: the added value of complex chemical shift-encoded MRI

INTRODUCTION

Chemotherapy prolongs the survival of patients with advanced and metastatic tumors. Since the liver plays an active role in the metabolism of chemotherapy agents, hepatic injury is a common adverse effect. The purpose of this study is to compare a novel quantitative chemical shift encoded magnetic resonance imaging (CSE-MRI) method with conventional T1-weighted In and Out of phase (T1 IOP) MR for evaluating the reproducibility of the methods in an oncologic population exposed to chemotherapy.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board with a waiver for informed consent. The study included patients who underwent chemotherapy, no suspected liver iron overload, and underwent upper abdomen MRI. Two radiologists independently draw circular ROIsin the liver parenchyma. The fat fraction was calculated from IOP imaging and measured from IDEAL-IQ fat fraction maps. Two different equations were used to estimate fat with IOP sequences. Intra-class correlation coefficient and repeatability coefficient were estimated to evaluate agreement between two readers on iron level and fat fraction measurement.

RESULTS

CSE-MRI showed a higher reliability in fat quantification compared with both IOP methods, with a substantially higher inter-reader agreement (0.961 vs 0.372). This has important clinical implications.

CONCLUSION

The novel CSE-MRI method described here provides increased reproducibility and confidence in diagnosing hepatic steatosis in a oncologic clinical setting. IDEAL-IQ has been proved to be more reproducible than conventional IOP imaging.

Gut microbiota in adolescents and the association with fatty liver: the EPOCH study

BACKGROUND

Recent evidence supports that the gut microbiota may be involved in the pathophysiology of non-alcoholic fatty liver disease (NAFLD), and may also offer avenues for treatment or prevention.

METHODS

We investigated the associations among gut microbiota, diet, and hepatic fat fraction (HFF) in 107 adolescents. Magnetic resonance imaging (MRI) was used to assess HFF, and 16S rRNA gene sequencing was performed on collected fecal samples. Dietary intake was assessed using Food Frequency Questionnaires. We examined the association between gut microbiota alpha diversity and HFF, and assessed the predictive accuracy for HFF of (1) taxonomic composition, (2) dietary intake, (3) demographic and comorbid conditions, and (4) the combination of these.

RESULTS

Lower alpha diversity was associated with higher HFF (β=-0.19, 95% confidence interval (CI) -0.36, -0.02). The selected taxa explained 17.7% (95% CI: 16.0-19.4%) of the variation in HFF. The combination of two of these taxa, Bilophila and Paraprevotella, with dietary intake of monounsaturated fatty acids and BMI z-scores explained 32.0% (95% CI: 30.3-33.6%) of the variation in HFF.

CONCLUSION

The gut microbiota is associated with HFF in adolescents and may be useful to help identify youth who would be amenable to gut microbiota-based interventions.

Non-invasive quantification of hepatic fat content in healthy dogs by using proton magnetic resonance spectroscopy and dual gradient echo magnetic resonance imaging

The objective of the present study was to describe two non-invasive methods for fat quantification in normal canine liver by using magnetic resonance imaging (MRI) and spectroscopy. Eleven adult beagle dogs were anesthetized and underwent magnetic resonance examination of the cranial abdomen by performing morphologic, modified Dixon (mDixon) dual gradient echo sequence, and proton magnetic resonance spectroscopy (¹H MRS) imaging. In addition, ultrasonographic liver examination was performed, fine-needle liver aspirates and liver biopsies were obtained, and hepatic triglyceride content was assayed. Ultrasonographic, cytologic, and histologic examination results were unremarkable in all cases. The median hepatic fat fraction calculated was 2.1% (range, 1.3%-5.5%) using mDixon, 0.3% (range, 0.1%-1.0%) using ¹H MRS, and 1.6% (range 1.0%-2.5%) based on triglyceride content. The hepatic fat fractions calculated using mDixon and ¹H MRS imaging were highly correlated to that based on triglyceride content. A weak correlation between mDixon and ¹H MRS imaging was detected. The results show that hepatic fat content can be estimated using non-invasive techniques (mDixon or ¹H MRS) in healthy dogs. Further studies are warranted to evaluate the use of these techniques in dogs with varying hepatic fat content and different hepatic disorders.

Z-spectrum appearance and interpretation in the presence of fat: Influence of acquisition parameters

PURPOSE

Chemical exchange saturation transfer (CEST) MRI is increasingly evolving from brain to body applications. One of the known problems in the body imaging is the presence of strong lipid signals. Although their influence on the CEST effect is acknowledged, there was no study that focuses on the interplay among echo time, fat fraction, and Z-spectrum. This study strives to address these points, with the emphasis on the application in the breast.

METHODS

Z-spectra were simulated in phase and out of phase of the main fat peak at -3.4 ppm, with the fat fraction varying from 0 to 100%. The magnetization transfer ratio asymmetry in two ranges, centering at the exchanging pool and at 3.5 ppm approximately opposite the nonexchanging fat pool, were calculated and were plotted against fat fraction. The results were verified in phantoms and in vivo.

RESULTS

The results demonstrate the combined influence of fat fraction and echo time on the Z-spectrum for gradient echo based CEST acquisitions. The influence is straightforward in the in-phase images, but it is more complicated in the out-of-phase images, potentially leading to erroneous CEST contrast.

CONCLUSIONS

This study provides a basis for understanding the origin and appearance of lipid artifacts in CEST imaging, and lays the foundation for their efficient removal. Magn Reson Med 79:2731-2737, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Viral eradication reduces both liver stiffness and steatosis in patients with chronic hepatitis C virus infection who received direct-acting anti-viral therapy

BACKGROUND

Whether direct-acting anti-viral therapy can reduce liver fibrosis and steatosis in patients with chronic hepatitis C virus (HCV) infection is unclear.

AIMS

To evaluate changes in liver stiffness and steatosis in patients with HCV who received direct-acting anti-viral therapy and achieved sustained virological response (SVR).

METHODS

A total of 198 patients infected with HCV genotype 1 or 2 who achieved SVR after direct-acting anti-viral therapy were analysed. Liver stiffness as evaluated by magnetic resonance elastography, steatosis as evaluated by magnetic resonance imaging-determined proton density fat fraction (PDFF), insulin resistance, and laboratory data were assessed before treatment (baseline) and at 24 weeks after the end of treatment (SVR24).

RESULTS

Alanine aminotransferase and homeostatic model assessment-insulin resistance levels decreased significantly from baseline to SVR24. Conversely, platelet count, which is inversely associated with liver fibrosis, increased significantly from baseline to SVR24. In patients with high triglyceride levels (≥150 mg/dL), triglyceride levels significantly decreased from baseline to SVR24 (P = 0.004). The median (interquartile range) liver stiffness values at baseline and SVR24 were 3.10 (2.70-4.18) kPa and 2.80 (2.40-3.77) kPa respectively (P < 0.001). The PDFF values at baseline and SVR 24 were 2.4 (1.7-3.4)% and 1.9 (1.3-2.8)% respectively (P < 0.001). In addition, 68% (19/28) of patients with fatty liver at baseline (PDFF ≥5.2%; n = 28) no longer had fatty liver (PDFF <5.2%) at SVR24.

CONCLUSION

Viral eradication reduces both liver stiffness and steatosis in patients with chronic HCV who received direct-acting anti-viral therapy (UMIN000017020).

Noninvasive Quantification of Liver Fat Content by Different Gradient Echo Magnetic Resonance Imaging Sequences in Patients with Nonalcoholic Fatty Liver Disease

Background

Noninvasive quantification of liver fat by gradient echo (GRE) technique is an interesting issue in quantitative magnetic resonance imaging. In this study, the fat content in patients with nonalcoholic fatty liver disease (NAFLD) was quantified with GRE sequences with different T ₁ and T ₂* weighting.

Methods

This prospective, cross-sectional study was performed on thirty NAFLD patients. Sixteen GRE sequences with different T ₁ weighting were performed with four echo times. In each sequence, repetition time (TR) or flip angle was changed and other parameters were fixed. Forty-eight fat indexes (FIs) from 16 sequences were calculated based on three methods. To determine the relationship between FIs and histological findings, Pearson's correlation coefficient was used at the level of 1% significance.

Results

Mean FIs which obtained from Eq. 3 have the maximum values in comparison to other FIs. The maximum FI was 23.58%, which related to heavily T ₁ weighted sequence obtained with method 3. The minimum FI was -2.49%, which related to the minimal T ₁ weighted obtained with method 2. FIs increase with a flip angle, especially at low flip angles. Increase the TR parameter decrease the FIs gradually. Calculated FIs with methods 1 and 3 stronger correlated with histological findings relative to calculated FIs with method 2.

Conclusion

For fat quantification, T ₁ relaxation effects probably more critical than T ₂*. Flip angle parameter could be a major factor causing the overestimation of liver fat content. Sequences with low flip angle are more suitable for fat quantification with methods 1 and 3. In fat quantification with GRE techniques, it is possible that the third and fourth echoes are unnecessary.

Differential diagnosis of hemangiomas from spinal osteolytic metastases using 3.0 T MRI: comparison of T1-weighted imaging, chemical-shift imaging, diffusion-weighted and contrast-enhanced imaging

The retrospective study investigated accuracy of quantitative evaluation of T1-weighted imaging (T1WI) with and without fat suppression (FS), chemical-shift, diffusion-weighted imaging (DWI) and enhanced imaging at 3.0 T MRI for distinguishing spinal hemangiomas from metastases. 27 patients with 33 spinal hemangiomas (15 atypical hemangiomas) and 26 patients with 71 metastases were recruited. T1WI, FS T1WI, in- and out-phase, DWI and enhanced T1WI were acquired. Signal intensities (SIs) of lesions were obtained. Signal intensity ratios (SIRs) and enhancement ratios of lesions in enhanced imaging were assessed. Ratio of SI loss of hemangiomas or atypical hemangiomas between T1WI and FS T1WI was higher than those of metastases (p < 0.001). The accuracies of ratio of SI loss between T1WI and FS T1WI for differentiating hemangiomas and atypical hemangiomas from metastases were 96.15% and 91.86%. Ratio of SI loss between in- and out- phase could differentiate hemangiomas and atypical hemangiomas from metastases with accuracies of 74.04% and 84.88%. Cutoff values for hemangiomas in SIRs of ≤ 1.52 (early phase) and ≤ 1.38 (middle phase) yielded accuracies of 92.31% and 82.69%. Enhancement ratios of atypical hemangiomas in middle and delayed phases were higher than that of metastases. Accuracies of apparent diffusion coefficient for differentiating hemangiomas and atypical hemangiomas from metastases were 70.19% and 89.53%. T1WI with and without fat suppression could distinguish spinal hemangiomas from metastases. Quantitative assessment of chemical-shift, DWI and enhanced imaging were helpful to identification of spinal hemangiomas and metastases.

Quantification of Liver Fat with mDIXON Magnetic Resonance Imaging, Comparison with the Computed Tomography and the Biopsy

INTRODUCTION

Accurate, non-invasive method of fat estimation is a valuable test for evaluation of diseases with abnormal hepatic fat.

AIM

To determine the accuracy of mDixon MR technique in assessment of liver fat over CT and to correlate the CT and MRI findings with biopsy.

MATERIALS AND METHODS

A prospective observational study was conducted at Imaging Services of Narayana Multispeciality Hospital between March 2011- December 2012. Thirty patients who attended the clinic for non-hepatic complaints were included in the study. Patients with known liver disease, cirrhosis, alcoholic liver disease, bleeding diathesis and claustrophobic patients were excluded from the study. Subjects underwent sonography, CT liver and MR examination of liver for fat estimation using mDixon protocol. Biopsy of the liver was performed either by image guidance or by direct biopsy. Liver Attenuation Index (LAI), fat estimation by MR methods were reviewed independently by two observers and compared with biopsy results. The statistical analysis was performed by SPSS. Pearson correlation was used to find the correlation between the left and right lobe of liver segments by CT and histological correlation.

RESULTS

There was good correlation between the MR estimation of liver fat and histological grading. Majority (90%) of patients had fat content of less than 10%. Maximal fat content of 28% was observed in one patient. LAI values poorly correlated with the MRI and histological observations.

CONCLUSION

MR estimation of the liver using mDixon technique yielded specific information about liver fat, correlated well with the histological grading. Technique is more accurate than CT, does not involve ionising radiation, hence recommended as method of choice.

Automatized spleen segmentation in non-contrast-enhanced MR volume data using subject-specific shape priors

To develop the first fully automated 3D spleen segmentation framework derived from T1-weighted magnetic resonance (MR) imaging data and to verify its performance for spleen delineation and volumetry. This approach considers the issue of low contrast between spleen and adjacent tissue in non-contrast-enhanced MR images. Native T1-weighted MR volume data was performed on a 1.5 T MR system in an epidemiological study. We analyzed random subsamples of MR examinations without pathologies to develop and verify the spleen segmentation framework. The framework is modularized to include different kinds of prior knowledge into the segmentation pipeline. Classification by support vector machines differentiates between five different shape types in computed foreground probability maps and recognizes characteristic spleen regions in axial slices of MR volume data. A spleen-shape space generated by training produces subject-specific prior shape knowledge that is then incorporated into a final 3D level set segmentation method. Individually adapted shape-driven forces as well as image-driven forces resulting from refined foreground probability maps steer the level set successfully to the segment the spleen. The framework achieves promising segmentation results with mean Dice coefficients of nearly 0.91 and low volumetric mean errors of 6.3%. The presented spleen segmentation approach can delineate spleen tissue in native MR volume data. Several kinds of prior shape knowledge including subject-specific 3D prior shape knowledge can be used to guide segmentation processes achieving promising results.

Free-breathing liver fat quantification using a multiecho 3D stack-of-radial technique

PURPOSE

The diagnostic gold standard for nonalcoholic fatty liver disease is an invasive biopsy. Noninvasive Cartesian MRI fat quantification remains limited to a breath-hold (BH). In this work, a novel free-breathing 3D stack-of-radial (FB radial) liver fat quantification technique is developed and evaluated in a preliminary study.

METHODS

Phantoms and healthy subjects (n = 11) were imaged at 3 Tesla. The proton-density fat fraction (PDFF) determined using FB radial (with and without scan acceleration) was compared to BH single-voxel MR spectroscopy (SVS) and BH 3D Cartesian MRI using linear regression (correlation coefficient ρ and concordance coefficient ρ_c ) and Bland-Altman analysis.

RESULTS

In phantoms, PDFF showed significant correlation (ρ > 0.998, ρ_c  > 0.995) and absolute mean differences < 2.2% between FB radial and BH SVS, as well as significant correlation (ρ > 0.999, ρ_c  > 0.998) and absolute mean differences < 0.6% between FB radial and BH Cartesian. In the liver and abdomen, PDFF showed significant correlation (ρ > 0.986, ρ_c  > 0.985) and absolute mean differences < 1% between FB radial and BH SVS, as well as significant correlation (ρ > 0.996, ρ_c  > 0.995) and absolute mean differences < 0.9% between FB radial and BH Cartesian.

CONCLUSION

Accurate 3D liver fat quantification can be performed in 1 to 2 min using a novel FB radial technique. Magn Reson Med 79:370-382, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Effect of intravenous gadoxetate disodium and flip angle on hepatic proton density fat fraction estimation with six-echo, gradient-recalled-echo, magnitude-based MR imaging at 3T

PURPOSE

The aim of the study was to determine in patients undergoing gadoxetate disodium (Gx)-enhanced MR exams whether proton density fat fraction (PDFF) estimation accuracy of magnitude-based multi-gradient-echo MRI (MRI-M) could be improved by using high flip angle (FA) on post-contrast images.

MATERIALS AND METHODS

Thirty-one adults with known or suspected hepatic steatosis undergoing 3T clinical Gx-enhanced liver MRI were enrolled prospectively. MR spectroscopy (MRS), the reference standard, was performed before Gx to measure MRS-PDFF. Low (10°)- and high (50°)-flip angle (FA) MRI-M sequences were acquired before and during the hepatobiliary phase after Gx administration; MRI-PDFF was estimated in the MRS-PDFF voxel location. Linear regression parameters (slope, intercept, average bias, R ²) were calculated for MRS-PDFF as a function of MRI-PDFF for each MRI-M sequence (pre-Gx low-FA, pre-Gx high-FA, post-Gx low-FA, post-Gx high-FA) for all patients and for patients with MRS-PDFF <10%. Regression parameters were compared (Bonferroni-adjusted bootstrap-based tests).

RESULTS

Three of the four MRI-M sequences (pre-Gx low-FA, post-Gx low-FA, post-Gx high-FA) provided relatively unbiased PDFF estimates overall and in the low-PDFF range, with regression slopes close to 1 and intercepts and biases close to zero. Pre-Gx high-FA MRI overestimated PDFF in proportion to MRS-PDFF, with slopes of 0.72 (overall) and 0.63 (low-PDFF range). Based on regression bias closest to 0, the post-Gx high-FA sequence was the most accurate overall and in the low-PDFF range. This sequence provided statistically significant improvements in at least two regression parameters compared to every other sequence.

CONCLUSION

In patients undergoing Gx-enhanced MR exams, PDFF estimation accuracy of MRI-M can be improved by using high-FA on post-contrast images.

Combined quantification of fatty infiltration, T 1-relaxation times and T 2*-relaxation times in normal-appearing skeletal muscle of controls and dystrophic patients

OBJECTIVES

To evaluate the combination of a fat-water separation method with an automated segmentation algorithm to quantify the intermuscular fatty-infiltrated fraction, the relaxation times, and the microscopic fatty infiltration in the normal-appearing muscle.

MATERIALS AND METHODS

MR acquisitions were performed at 1.5T in seven patients with facio-scapulo-humeral dystrophy and eight controls. Disease severity was assessed using commonly used scales for the upper and lower limbs. The fat-water separation method provided proton density fat fraction (PDFF) and relaxation times maps (T ₂* and T ₁). The segmentation algorithm distinguished adipose tissue and normal-appearing muscle from the T ₂* map and combined active contours, a clustering analysis, and a morphological closing process to calculate the index of fatty infiltration (IFI) in the muscle compartment defined as the relative amount of pixels with the ratio between the number of pixels within IMAT and the total number of pixels (IMAT + normal appearing muscle).

RESULTS

In patients, relaxation times were longer and a larger fatty infiltration has been quantified in the normal-appearing muscle. T ₂* and PDFF distributions were broader. The relaxation times were correlated to the Vignos scale whereas the microscopic fatty infiltration was linked to the Medwin-Gardner-Walton scale. The IFI was linked to a composite clinical severity scale gathering the whole set of scales.

CONCLUSION

The MRI indices quantified within the normal-appearing muscle could be considered as potential biomarkers of dystrophies and quantitatively illustrate tissue alterations such as inflammation and fatty infiltration.

Exploring the metabolic syndrome: Nonalcoholic fatty pancreas disease

After the first description of fatty pancreas in 1933, the effects of pancreatic steatosis have been poorly investigated, compared with that of the liver. However, the interest of research is increasing. Fat accumulation, associated with obesity and the metabolic syndrome (MetS), has been defined as “fatty infiltration” or “nonalcoholic fatty pancreas disease” (NAFPD). The term “fatty replacement” describes a distinct phenomenon characterized by death of acinar cells and replacement by adipose tissue. Risk factors for developing NAFPD include obesity, increasing age, male sex, hypertension, dyslipidemia, alcohol and hyperferritinemia. Increasing evidence support the role of pancreatic fat in the development of type 2 diabetes mellitus, MetS, atherosclerosis, severe acute pancreatitis and even pancreatic cancer. Evidence exists that fatty pancreas could be used as the initial indicator of “ectopic fat deposition”, which is a key element of nonalcoholic fatty liver disease and/or MetS. Moreover, in patients with fatty pancreas, pancreaticoduodenectomy is associated with an increased risk of intraoperative blood loss and post-operative pancreatic fistula.

Definitions of Normal Liver Fat and the Association of Insulin Sensitivity with Acquired and Genetic NAFLD-A Systematic Review

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of disease ranging from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) and fibrosis. “Obese/Metabolic NAFLD” is closely associated with obesity and insulin resistance and therefore predisposes to type 2 diabetes and cardiovascular disease. NAFLD can also be caused by common genetic variants, the patatin-like phospholipase domain-containing 3 (PNPLA3) or the transmembrane 6 superfamily member 2 (TM6SF2). Since NAFL, irrespective of its cause, can progress to NASH and liver fibrosis, its definition is of interest. We reviewed the literature to identify data on definition of normal liver fat using liver histology and different imaging tools, and analyzed whether NAFLD caused by the gene variants is associated with insulin resistance. Histologically, normal liver fat content in liver biopsies is most commonly defined as macroscopic steatosis in less than 5% of hepatocytes. In the population-based Dallas Heart Study, the upper 95th percentile of liver fat measured by proton magnetic spectroscopy (¹H-MRS) in healthy subjects was 5.6%, which corresponds to approximately 15% histological liver fat. When measured by magnetic resonance imaging (MRI)-based techniques such as the proton density fat fraction (PDFF), 5% macroscopic steatosis corresponds to a PDFF of 6% to 6.4%. In contrast to “Obese/metabolic NAFLD”, NAFLD caused by genetic variants is not associated with insulin resistance. This implies that NAFLD is heterogeneous and that “Obese/Metabolic NAFLD” but not NAFLD due to the PNPLA3 or TM6SF2 genetic variants predisposes to type 2 diabetes and cardiovascular disease.

Magnetic Resonance Imaging More Accurately Classifies Steatosis and Fibrosis in Patients With Nonalcoholic Fatty Liver Disease Than Transient Elastography

BACKGROUND & AIMS

Noninvasive methods have been evaluated for the assessment of liver fibrosis and steatosis in patients with nonalcoholic fatty liver disease (NAFLD). We compared the ability of transient elastography (TE) with the M-probe, and magnetic resonance elastography (MRE) to assess liver fibrosis. Findings from magnetic resonance imaging (MRI)-based proton density fat fraction (PDFF) measurements were compared with those from TE-based controlled attenuation parameter (CAP) measurements to assess steatosis.

METHODS

We performed a cross-sectional study of 142 patients with NAFLD (identified by liver biopsy; mean body mass index, 28.1 kg/m(2)) in Japan from July 2013 through April 2015. Our study also included 10 comparable subjects without NAFLD (controls). All study subjects were evaluated by TE (including CAP measurements), MRI using the MRE and PDFF techniques.

RESULTS

TE identified patients with fibrosis stage ≥2 with an area under the receiver operating characteristic (AUROC) curve value of 0.82 (95% confidence interval [CI]: 0.74-0.89), whereas MRE identified these patients with an AUROC curve value of 0.91 (95% CI: 0.86-0.96; P = .001). TE-based CAP measurements identified patients with hepatic steatosis grade ≥2 with an AUROC curve value of 0.73 (95% CI: 0.64-0.81) and PDFF methods identified them with an AUROC curve value of 0.90 (95% CI: 0.82-0.97; P < .001). Measurement of serum keratin 18 fragments or alanine aminotransferase did not add value to TE or MRI for identifying nonalcoholic steatohepatitis.

CONCLUSIONS

MRE and PDFF methods have higher diagnostic performance in noninvasive detection of liver fibrosis and steatosis in patients with NAFLD than TE and CAP methods. MRI-based noninvasive assessment of liver fibrosis and steatosis is a potential alternative to liver biopsy in clinical practice. UMIN Clinical Trials Registry No. UMIN000012757.