Quantification of hepatic steatosis: a comparison of the accuracy among multiple magnetic resonance techniques

Automated liver volumetry and hepatic steatosis quantification with magnetic resonance imaging proton density fat fraction

BACKGROUND

Preoperative imaging evaluation of liver volume and hepatic steatosis for the donor affects transplantation outcomes. However, computed tomography (CT) for liver volumetry and magnetic resonance spectroscopy (MRS) for hepatic steatosis are time consuming. Therefore, we investigated the correlation of automated 3D-multi-echo-Dixon sequence magnetic resonance imaging (ME-Dixon MRI) and its derived proton density fat fraction (MRI-PDFF) with CT liver volumetry and MRS hepatic steatosis measurements in living liver donors.

METHODS

This retrospective cross-sectional study was conducted from December 2017 to November 2022. We enrolled donors who received a dynamic CT scan and an MRI exam within 2 days. First, the CT volumetry was processed semiautomatically using commercial software, and ME-Dixon MRI volumetry was automatically measured using an embedded sequence. Next, the signal intensity of MRI-PDFF volumetric data was correlated with MRS as the gold standard.

RESULTS

We included the 165 living donors. The total liver volume of ME-Dixon MRI was significantly correlated with CT (r = 0.913, p < 0.001). The fat percentage measured using MRI-PDFF revealed a strong correlation between automatic segmental volume and MRS (r = 0.705, p < 0.001). Furthermore, the hepatic steatosis group (MRS ≥5%) had a strong correlation than the non-hepatic steatosis group (MRS <5%) in both volumetric (r = 0.906 vs. r = 0.887) and fat fraction analysis (r = 0.779 vs. r = 0.338).

CONCLUSION

Automated ME-Dixon MRI liver volumetry and MRI-PDFF were strongly correlated with CT liver volumetry and MRS hepatic steatosis measurements, especially in donors with hepatic steatosis.

Validity of an automated screening Dixon technique for quantifying hepatic steatosis in living liver donors

PURPOSE

This retrospective study aimed to evaluate the validity of an automated screening Dixon (e-DIXON) technique for quantifying hepatic steatosis in living liver-donor patients by comparison with magnetic resonance spectroscopy (MRS) as a reference standard.

METHODS

A total of 285 living liver-donor candidates were examined with the e-DIXON technique and single-voxel MRS to assess hepatic steatosis and iron deposition between January 2014 and February 2019. The sensitivity, specificity, and positive and negative predictive values (PPV and NPV) of the e-DIXON technique for hepatic steatosis were calculated. The mean fat signal fractions obtained in MRS were compared between the donors diagnosed with hepatic steatosis and the normal group. The mean R2 values of donors with or without hepatic siderosis also were compared.

RESULTS

The e-DIXON technique diagnosed normal in 133 (47%), fat in 124 (44%), iron in one (0.4%), and a combination of both fat and iron in 27 (10%) donors. The sensitivity, specificity, PPV, and NPV ​​for diagnosing hepatic steatosis were 94%, 70%, 64%, and 96%, respectively. There was a significant difference in the mean fat signal fraction obtained in MRS between the steatosis and normal groups (p < 0.001), but R2 values were not significantly different between siderosis and normal groups (p = 0.11). The e-DIXON technique showed a strong correlation with MRS in fat measurement (r2 = 0.92, p < 0.001).

CONCLUSION

The e-DIXON technique reliably screens for hepatic steatosis but may not accurate for detecting hepatic iron deposition.

Application of multi-echo Dixon and MRS in quantifying hepatic fat content and staging liver fibrosis

This study associated the liver proton density fat fraction (PDFF), measured by multi-echo Dixon (ME-Dixon) and breath-hold single-voxel high-speed T2-corrected multi-echo 1H magnetic resonance spectroscopy (HISTO) at 1.5 T, with serum biomarkers and liver fibrosis stages. This prospective study enrolled 75 patients suspected of liver fibrosis and scheduled for liver biopsy and 23 healthy participants with normal liver function. The participant underwent ME-Dixon and HISTO scanning. The agreement of PDFF measured by ME-Dixon (PDFF-D) and HISTO (PDFF-H) were compared. Correlations between PDFF and serum fat biomarkers (total cholesterol, triglyceride, and high- and low-density lipoproteins) and the liver fibrosis stages were assessed. PDFF were compared among the liver fibrosis stages (F0-F4) based on clinical liver biopsies. The Bland-Altman plot showed agreement between PDFF-D and PDFF-H(LoA, - 4.44 to 6.75), which have high consistency (ICC 0.752, P < 0.001). The correlations with the blood serum markers were mild to moderate (PDFF-H: r = 0.261-0.410, P < 0.01; PDFF-D: r = 0.265-0.367, P < 0.01). PDFF-D, PDFF-H, and steatosis were distributed similarly among the liver fibrosis stages. PDFF-H showed a slight negative correlation with the liver fibrosis stages (r = - 0.220, P = 0.04). Both ME-Dixon and HISTO sequences measured liver fat content noninvasively. Liver fat content was not directly associated with liver fibrosis stages.

Local fat content determines global and local stiffness in livers with simple steatosis

Fat accumulation during liver steatosis precedes inflammation and fibrosis in fatty liver diseases, and is associated with disease progression. Despite a large body of evidence that liver mechanics play a major role in liver disease progression, the effect of fat accumulation by itself on liver mechanics remains unclear. Thus, we conducted ex vivo studies of liver mechanics in rodent models of simple steatosis to isolate and examine the mechanical effects of intrahepatic fat accumulation, and found that fat accumulation softens the liver. Using a novel adaptation of microindentation to permit association of local mechanics with microarchitectural features, we found evidence that the softening of fatty liver results from local softening of fatty regions rather than uniform softening of the liver. These results suggest that fat accumulation itself exerts a softening effect on liver tissue. This, along with the localized heterogeneity of softening within the liver, has implications in what mechanical mechanisms are involved in the progression of liver steatosis to more severe pathologies and disease. Finally, the ability to examine and associate local mechanics with microarchitectural features is potentially applicable to the study of the role of heterogeneous mechanical microenvironments in both other liver pathologies and other organ systems.

Radiofrequency coil design for improving human liver fat quantification in a portable single-side magnetic resonance system

Earlier diagnosis of nonalcoholic fatty liver disease (NAFLD) is important to prevent progression of the disease. Recently, a low-cost portable magnetic resonance (MR) system was developed as a point-of-care screening tool for in vivo liver fat quantification. However, subcutaneous fat may confound the liver fat quantification, particularly in the NAFLD population. In this work, we propose a novel radiofrequency (RF) coil design composed of a set of "saturation" coils sandwiching a main coil to improve human liver fat quantification. By comparison with conventional MR imaging, we demonstrate the capability and effectiveness of the novel RF coil design in phantom experiments as well as in vivo liver scans. In the phantom experiment, the saturation coil reduced the error in the measured proton density fat fraction (PDFF) results from 28.9% to 4.0%, and in the in vivo experiment, it reduced the discrepancy in the PDFF results from 13.2% to 4.0%. The novel coil design, together with the adapted Carr-Purcell-Meiboom-Gill-based sequence, improves the practicability and robustness of the portable single-side MR system.

Imaging of the chemotherapy-induced hepatic damage: Yellow liver, blue liver, and pseudocirrhosis

The liver is the major drug-metabolizing and drug-detoxifying organ. Many drugs can cause liver damage through various mechanisms; however, the liver response to injury includes a relatively narrow spectrum of alterations that, regardless of the cause, are represented by phlogosis, oxidative stress and necrosis. The combination of these alterations mainly results in three radiological findings: vascular alterations, structural changes and metabolic function reduction. Chemotherapy has changed in recent decades in terms of the drugs, protocols and duration, allowing patients a longer life expectancy. As a consequence, we are currently observing an increase in chemotherapy-associated liver injury patterns once considered unusual. Recognizing this form of damage in an early stage is crucial for reconsidering the therapy regimen and thus avoiding severe complications. In this frontier article, we analyze the role of imaging in detecting some of these pathological patterns, such as pseudocirrhosis, “yellow liver” due to chemotherapy-associated steatosis-steatohepatitis, and “blue liver”, including sinusoidal obstruction syndrome, veno-occlusive disease and peliosis.

A single-sided magnet for deep-depth fat quantification

Early detection of fatty-liver disease is important before further aggravations of the disease, such as cirrhosis, can develop. In this study, we developed a low-cost, movable single-sided magnet for in vivo liver fat quantification. A gradient field of 73.5 G/cm and a field strength of 0.0725 T were obtained by structurally optimizing the concave U-shaped magnet, on which the region of interest (ROI) was a curved shape about 0.4 mm thick, 8 cm above the surface of the radiofrequency (RF) coil. We constructed a prototype nuclear magnetic-resonance (NMR) relaxometry system based on this optimized magnet. Subsequent phantom experiments demonstrated the effectiveness of the single-sided magnet in evaluating different proton density fat fraction (PDFF) phantoms. As expected, the results of the six phantoms showed good positive correlation between PDFF and the fitted fat amplitude, which suggested that single-sided NMR relaxometry could be used to quantify liver fat in vivo.

Evaluation of liver iron overload with R2* relaxometry with versus without fat suppression: both are clinically accurate but there are differences

OBJECTIVES

To assess clinically relevant difference in hepatic iron quantification using R2* relaxometry with (FS) and without (non-FS) fat saturation for the evaluation of patients with suspected hepatic iron overload.

METHODS

We prospectively enrolled 134 patients who underwent 1.5-T MRI R2* relaxometry with FS and non-FS gradient echo sequences (12 echoes, initial TE = 0.99 ms). Proton density fat fraction for the quantification of steatosis was assessed. Linear regression analyses and Bland-Altman plots including Lin's concordance correlation coefficient were performed for correlation of FS R2* with non-FS R2*. Patients were grouped into 4 severity classes of iron overload (EASL based), and agreement was evaluated by contingency tables and the proportion of overall agreement.

RESULTS

A total of 41.8% of patients showed hepatic iron overload; 67.9% had concomitant steatosis; and 58.2% revealed no iron overload of whom 60.3% had steatosis. The mean R2* value for all FS data was 102.86 1/s, for non-FS 108.16 1/s. Linear regression resulted in an R-squared value of 0.99 (p < 0.001); Bland-Altman plot showed a mean R2* difference of 5.26 1/s (SD 17.82). The concordance correlation coefficient was only slightly lower for patients with steatosis compared with non-steatosis (0.988 vs. 0.993). The overall agreement between FS and non-FS R2* measurements was 94.8% using either method to classify patients according to severity of iron storage. No correlation between R2* and proton density fat fraction was found for both methods.

CONCLUSION

R2* relaxometry showed an excellent overall agreement between FS and non-FS acquisition. Both variants can therefore be used in daily routine. However, clinically relevant differences might result when switching between the two methods or during patient follow-up, when fat content changes over time. We therefore recommend choosing a method and keeping it straight in the context of follow-up examinations.

KEY POINTS

• Both variants of R2* relaxometry (FS and non-FS) may be used in daily routine. • Clinically relevant differences might result when switching between the two methods or during patient follow-up, when fat content changes over time. • It seems advisable choosing one method and keeping it straight in the context of follow-up examinations.

Role of Magnetic Resonance Imaging in the Monitoring of Patients with Nonalcoholic Fatty Liver Disease: Comparison with Ultrasonography, Lipid Profile, and Body Mass Index

AIM

The aim of this study was to study the role of magnetic resonance imaging (MRI) in monitoring hepatic fat content in cases of nonalcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

41 adults (mean age: 39 years, 22 males; 19 females) with NAFLD were included after obtaining approval from the institutional ethics committee. The baseline clinical (weight, body mass index [BMI]) and biochemical parameters, fatty liver grade on ultrasonography (USG), and hepatic fat signal fraction (FSF) using dual-echo chemical shift imaging and proton density fat fraction on magnetic resonance spectroscopy (MRS-PDFF) were assessed, before and after intervention (dietary and lifestyle changes and oral vitamin E for six months). They were categorized into Group A (good compliance to intervention) and Group B (poor compliance), and the clinical and imaging parameters were compared between them.

RESULTS

After intervention, Group A (n = 30) showed significant reduction in BMI (28.35 ± 3.25 to 27.14 ± 3.24 kg/m²; P < 0.001), hepatic FSF (19.30 ± 9.09% to 11.18 ± 7.61%; P < 0.05), and MRS-PDFF (18.79 ± 8.53% to 10.64 ± 6.66%). In Group B (n = 11), there was significant increase in BMI (28.85 ± 2.41 to 29.31 ± 2.57 kg/m²; P < 0.001), hepatic FSF (18.96 ± 9.79% to 21.48 ± 11.80%; P < 0.05), and reduction in high-density lipoproteins (P < 0.05). Although there was good correlation between USG and MRS in quantifying liver fat (r = 0.84-0.87; P < 0.001), USG was unable to detect <5.3% change in hepatic fat. There was poor correlation between lipid profile and MRS-PDFF. Change in body weight significantly correlated with change in hepatic fat content (r = 0.76; P < 0.001).

CONCLUSION

MRI is useful in accurately quantifying and in monitoring hepatic fat content and is better than clinical and biochemical parameters and USG.

Considerations of Ultrasound Scanning Approaches in Non-alcoholic Fatty Liver Disease Assessment through Acoustic Structure Quantification

Non-alcoholic fatty liver disease (NAFLD) is a risk factor for hepatic fibrosis and cirrhosis. Acoustic structure quantification (ASQ), based on statistical analysis of ultrasound echoes, is an emerging technique for hepatic steatosis diagnosis. A standardized measurement protocol for ASQ analysis was suggested previously; however, an optimal ultrasound scanning approach has not been concluded thus far. In this study, the suitability of scanning approaches for the ASQ-based evaluation of hepatic steatosis was investigated. Hepatic fat fractions (HFFs; liver segments VIII, III and VI) of 70 living liver donors were assessed with magnetic resonance spectroscopy. A clinical ultrasound machine equipped with a 3-MHz convex transducer was used to scan each participant using the intercostal, epigastric and subcostal planes to acquire raw data for estimating two ASQ parameters (C_m² and focal disturbance [FD] ratio) of segments VIII, III and VI, respectively. The parameters were plotted as functions of the HFF for calculating the values of the correlation coefficient (r) and probability value (p). The diagnostic performance of the parameters in discriminating between the normal and steatotic (≥5 and ≥10%) groups was also compared using receiver operating characteristic (ROC) curves. The C_m² and FD ratio values measured using the epigastric and subcostal planes did not correlate with the severity of hepatic steatosis. However, intercostal imaging exhibited a higher correlation between the ASQ parameters and HFF (r = -0.64, p < 0.001). The diagnostic performance of C_m² and FD ratio in detecting hepatic steatosis using intercostal imaging was also satisfactory (areas under ROC curves >0.8). Intercostal imaging is an appropriate scanning approach for ASQ analysis of the liver.

Diagnostic accuracy of controlled attenuation parameter (CAP) as a non-invasive test for steatosis in suspected non-alcoholic fatty liver disease: a systematic review and meta-analysis

Background

Controlled attenuation parameter (CAP) is a non-invasive method for diagnosing hepatic steatosis. Despite good diagnostic performance, clinical application of CAP is limited due to the influences of covariates. Here, a systematic review on the performance of CAP in the diagnosis and staging of hepatic steatosis in NAFLD patients was performed.

Methods

The sensitivity, specificity, diagnostic odds ratio (DOR) and area under receiver operating characteristics (AUROC) curves of the pooled data for CAP in diagnosing and staging the mild (Stage 1), moderate (Stage 2) and severe (Stage 3) steatosis in NAFLD patients were assessed. The clinical utility of CAP was evaluated by Fagan plot. Heterogeneity was explored using subgroup analysis.

Results

Nine studies involving 1297 patients with liver biopsy-proven NAFLD were analyzed. The pooled sensitivity of CAP in detecting mild hepatic steatosis was 87% with a specificity of 91% and a DOR of 84.35. The pooled sensitivity of CAP in detecting moderate hepatic steatosis was 85% with a specificity of 74% and a DOR of 21.28. For severe steatosis, the pooled sensitivity was 76% with a specificity of 58% and a DOR of 4.70. The mean AUROC value for CAP in the diagnosis of mild, moderate, and severe steatosis was 0.96, 0.82 and 0.70, respectively. A subgroup analysis indicated that variation in the geographic regions, cutoffs, age and body mass index (BMI) could be the potential sources of heterogeneity in the diagnosis of moderate to severe steatosis.

Conclusions

CAP should be cautiously considered as a non-invasive substitute for liver biopsy in clinical practice.

Electronic supplementary material

The online version of this article (10.1186/s12876-019-0961-9) contains supplementary material, which is available to authorized users.

Controlled attenuation parameter for steatosis grading in chronic hepatitis C compared with digital morphometric analysis of liver biopsy: impact of individual elastography measurement quality

BACKGROUND AND OBJECTIVE

Controlled attenuation parameter (CAP) diagnostic performance for steatosis grading has been controversial and considerable observer-related variability in liver biopsy has been reported. This is a subanalysis of a larger chronic hepatitis C study on noninvasive fibrosis staging.

MATERIALS AND METHODS

Patients were prospectively enrolled for paired liver biopsy and transient elastography. Biopsy fragments were subjected to digital morphometric steatosis quantification. Associated patient and technical factors, including a newly described elastogram quality score, were evaluated.

RESULTS

A total of 312 patients were included in the final analysis. The mean liver stiffness was 8.7±2.1 kPa. Morphometry showed S0 in 19.2% of patients, S1 in 28.5%, S2 in 31.1%, and S3 in 21.2%. CAP showed S0 in 11.2% of patients, S1 in 26.6%, S2 in 56.7%, and S3 in 5.4%. Spearman coefficient showed a positive and independent correlation between CAP and morphometric analysis (r=0.48, P<0.05), except for distinguishing S1 and S2 (P=0.11). Area under the receiver operating characteristic curves for the presence or absence of steatosis was 0.944; differentiation between levels I, II, and III were 0.776, 0.812, and 0.879. Elastogram quality independently predicted accuracy [odds ratio (OR): 6.95, 95% confidence interval (95%CI): 4.45-9.06 as well as CAP interquartile range OR: 2.81, 95%CI: 1.67-3.99] and liver stiffness (OR: 0.78, 95%CI: 0.51-0.80).

CONCLUSION

We present an external validation for CAP against the objective steatosis quantification provided by digital morphometry. Fairly good performance indicators were found, except for S1 versus S2 differentiation. Variability and higher liver stiffness were associated with lower performance. Achieving higher quality measurements, however, overcame such limitations with excellent accuracy.

Imaging of nonalcoholic fatty liver disease and its clinical utility

The prevalence of nonalcoholic fatty liver disease has been continuously rising over the last three decades and is projected to become the most common indication for liver transplantation in the near future. Its pathophysiology and complex interplay with diabetes and the metabolic syndrome are not as yet fully understood despite growing scientific interest and research. Modern imaging techniques offer significant assistance in this field by enabling the study of the liver noninvasively and evaluation of the degree of both steatosis and fibrosis, and even in attempting to diagnose the presence of inflammation (steatohepatitis). The derived measurements are highly precise, accurate and reproducible, performing better than biopsy in terms of quantification. In this article, these imaging techniques are overviewed and their performance regarding diagnosis, stratification and monitoring are evaluated. Their expanding role both in the research arena and in clinical practice along with their limitations is also discussed.

Revisiting donor risk over two decades of single-center experience: More attention on the impact of overweight

OBJECTIVE

Morbidity rates after living donor hepatectomy vary greatly among centers. Donor morbidity in a tertiary center over the past two decades was revisited.

METHODS

Clinical data and grading of complications were reviewed by a nontransplant surgeon based on Clavien 5 tier grading. Risk factors were analyzed.

RESULTS

In total, 473 consecutive living liver donors from 1997 to 2016 were included for analysis; 305 were right liver donors and 168 left liver donors, and the corresponding morbidity rates were 27.2% and 9.5%. The majority (81/99, 81.2%) of complications were grade I and II. Donors with morbidity compared with those without were significantly younger, nonoverweight body figure (BMI < 25), more as the right liver donors, and longer length of hospital stay. Right liver donation had significantly higher morbidity rates than did left liver donation in earlier periods (before 2011), but not thereafter. Multivariate modeling revealed that right lobe donation and overweight (BMI ≥ 25 kg/m²) were significant factors associated with donor morbidity, with adjusted hazard ratios HR (95% confidence interval) of 3.401 (1.909-6.060) and 0.550 (0.304-0.996), respectively. Further, overweight was a paradoxical risk factor in right donor hepatectomy with HR 0.422 (0.209-0.851), but the effect was nonsignificant in left liver donors. Most complications in overweight donors were grade I and not specific to liver surgery.

CONCLUSIONS

The overall complication rate was 20.9%. Overweight might be protective against morbidity in right hepatectomy and warrants further deliberation.

Association between MRI-derived hepatic fat fraction and blood pressure in participants without history of cardiovascular disease

OBJECTIVES

We assessed whether liver fat content, as determined by MRI, correlates with blood pressure (BP), a major vascular risk factor, in individuals from the general population without history of stroke and coronary or peripheral artery disease.

METHODS

Cross-sectional data from 384 participants (161 women; aged 39-73 years) of a MRI substudy of the KORA FF4 survey were used. Hepatic fat fraction (HFF) was measured in the left and right lobe of the liver using single voxel multiecho H-spectroscopy and at the level of the portal vein using a multiecho Dixon-sequence. Associations of HFF with SBP and DBP as well as hypertension were assessed by right censored normal regression (accounting for antihypertensive treatment) and by logistic regression, respectively.

RESULTS

High levels of HFF measured on the level of the portal vein (90th percentile, 21.8%), compared with low HFF levels (10th percentile, 1.7%), were associated with higher SBP (131 vs. 122 mmHg; overall P = 0.001), higher DBP (82 vs. 76 mmHg, P < 0.001) and with higher odds of hypertension [odds ratio (OR) = 2.16, P = 0.025]. A level of 5.13% (54th percentile) was identified as optimal HFF cut-off for the prediction of hypertension (OR = 2.00, P = 0.015). Alcohol consumption emerged as an effect modifier for the association between HFF and hypertension (nonalcohol drinker: OR = 3.76, P = 0.025; alcohol drinker: OR = 1.59, P = 0.165).

CONCLUSION

MRI-derived subclinical HFF is associated with SBP and DBP as well as with hypertension in participants from the general population without history of cardiovascular disease.

A comparison of hepatic steatosis index, controlled attenuation parameter and ultrasound as noninvasive diagnostic tools for steatosis in chronic hepatitis B

AIMS

To evaluate the value of noninvasive tools for diagnosis of hepatic steatosis in patients with chronic hepatitis B (CHB).

METHODS

Consecutive treatment-naïve patients with CHB with body mass index less than 30kg/m² who underwent liver biopsy, ultrasound and FibroScan^® were enrolled. The diagnostic performance of controlled attenuation parameter (CAP), hepatic steatosis index (HSI) and ultrasound for hepatic steatosis compared with liver biopsy was assessed. The areas under receiver operating characteristics curves (AUROCs) were calculated to determine the diagnostic efficacy, with comparisons using the DeLong test.

RESULTS

CAP and HSI accuracies were significantly higher than that of ultrasound to detect patients with biopsy-proven mild steatosis (S1, 65.3%, 56.5%, respectively, vs. 17.7%, χ²=46.305, 31.736, both P<0.05)and moderate-severe (S2-3) steatosis (92.3%, 100%, respectively, vs. 53.8%, χ²=4.887, 7.800, P=0.037, 0.007, respectively). Both CAP and HSI had lower underestimation rates of steatosis grade than ultrasound (12%, 14.8%, respectively, vs. 29.5%, χ²=9.765, 6.452; P<0.05 for both), but they exhibited higher overestimation rates (30.5%, 38.2%, respectively, vs. 12.4%, χ²=39.222, 70.986; both P<0.05). The AUROCs of CAP and HSI were 0.780 (95% confidence intervals [CIs] 0.735-0.822) and 0.655 (95%CI 0.604-0.704) for S ≥1, 0.932 (95%CI 0.902-0.956) and 0.755 (95%CI 0.707-0.799) for S ≥2, 0.990 (95%CI 0.974-0.998) and 0.786 (95% CI 0.740-0.827) for S3, respectively.

CONCLUSION

CAP might be more accurate for detecting hepatic steatosis than HSI and ultrasound in patients with CHB, but further studies are needed to reduce the overestimation rates.

Individual patient data meta-analysis of controlled attenuation parameter (CAP) technology for assessing steatosis

BACKGROUND & AIMS

The prevalence of fatty liver underscores the need for non-invasive characterization of steatosis, such as the ultrasound based controlled attenuation parameter (CAP). Despite good diagnostic accuracy, clinical use of CAP is limited due to uncertainty regarding optimal cut-offs and the influence of covariates. We therefore conducted an individual patient data meta-analysis.

METHODS

A review of the literature identified studies containing histology verified CAP data (M probe, vibration controlled transient elastography with FibroScan®) for grading of steatosis (S0-S3). Receiver operating characteristic analysis after correcting for center effects was used as well as mixed models to test the impact of covariates on CAP. The primary outcome was establishing CAP cut-offs for distinguishing steatosis grades.

RESULTS

Data from 19/21 eligible papers were provided, comprising 3830/3968 (97%) of patients. Considering data overlap and exclusion criteria, 2735 patients were included in the final analysis (37% hepatitis B, 36% hepatitis C, 20% NAFLD/NASH, 7% other). Steatosis distribution was 51%/27%/16%/6% for S0/S1/S2/S3. CAP values in dB/m (95% CI) were influenced by several covariates with an estimated shift of 10 (4.5-17) for NAFLD/NASH patients, 10 (3.5-16) for diabetics and 4.4 (3.8-5.0) per BMI unit. Areas under the curves were 0.823 (0.809-0.837) and 0.865 (0.850-0.880) respectively. Optimal cut-offs were 248 (237-261) and 268 (257-284) for those above S0 and S1 respectively.

CONCLUSIONS

CAP provides a standardized non-invasive measure of hepatic steatosis. Prevalence, etiology, diabetes, and BMI deserve consideration when interpreting CAP. Longitudinal data are needed to demonstrate how CAP relates to clinical outcomes.

LAY SUMMARY

There is an increase in fatty liver for patients with chronic liver disease, linked to the epidemic of the obesity. Invasive liver biopsies are considered the best means of diagnosing fatty liver. The ultrasound based controlled attenuation parameter (CAP) can be used instead, but factors such as the underlying disease, BMI and diabetes must be taken into account. Registration: Prospero CRD42015027238.

Quantification of liver fat: A comprehensive review

Fat accumulation in the liver causes metabolic diseases such as obesity, hypertension, diabetes or dyslipidemia by affecting insulin resistance, and increasing the risk of cardiac complications and cardiovascular disease mortality. Fatty liver diseases are often reversible in their early stage; therefore, there is a recognized need to detect their presence and to assess its severity to recognize fat-related functional abnormalities in the liver. This is crucial in evaluating living liver donors prior to transplantation because fat content in the liver can change liver regeneration in the recipient and donor. There are several methods to diagnose fatty liver, measure the amount of fat, and to classify and stage liver diseases (e.g. hepatic steatosis, steatohepatitis, fibrosis and cirrhosis): biopsy (the gold-standard procedure), clinical (medical physics based) and image analysis (semi or fully automated approaches). Liver biopsy has many drawbacks: it is invasive, inappropriate for monitoring (i.e., repeated evaluation), and assessment of steatosis is somewhat subjective. Qualitative biomarkers are mostly insufficient for accurate detection since fat has to be quantified by a varying threshold to measure disease severity. Therefore, a quantitative biomarker is required for detection of steatosis, accurate measurement of severity of diseases, clinical decision-making, prognosis and longitudinal monitoring of therapy. This study presents a comprehensive review of both clinical and automated image analysis based approaches to quantify liver fat and evaluate fatty liver diseases from different medical imaging modalities.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Hepatic fat quantification magnetic resonance for monitoring treatment response in pediatric nonalcoholic steatohepatitis

AIM: To evaluate the possibility of treatment effect monitoring using hepatic fat quantification magnetic resonance (MR) in pediatric nonalcoholic steatohepatitis (NASH).

METHODS: We retrospectively reviewed the medical records of patients who received educational recommendations and vitamin E for NASH and underwent hepatic fat quantification MR from 2011 to 2013. Hepatic fat fraction (%) was measured using dual- and triple-echo gradient-recalled-echo sequences at 3T. The compliant and non-compliant groups were compared clinically, biochemically, and radiologically.

RESULTS: Twenty seven patients (M:F = 24:3; mean age: 12 ± 2.3 years) were included (compliant group = 22, non-compliant = 5). None of the baseline findings differed between the 2 groups, except for triglyceride level (compliant vs non-compliant, 167.7 mg/dL vs 74.2 mg/dL, P = 0.001). In the compliant group, high-density lipoprotein increased and all other parameters decreased after 1-year follow-up. However, there were various changes in the non-compliant group. Dual-echo fat fraction (-19.2% vs 4.6, P < 0.001), triple-echo fat fraction (-13.4% vs 3.5, P < 0.001), alanine aminotransferase (-110.7 IU/L vs -10.6 IU/L, P = 0.047), total cholesterol (-18.1 mg/dL vs 3.8 mg/dL, P = 0.016), and triglyceride levels (-61.3 mg/dL vs 11.2 mg/dL, P = 0.013) were significantly decreased only in the compliant group. The change in body mass index and dual-echo fat fraction showed a positive correlation (ρ = 0.418, P = 0.030).

CONCLUSION: Hepatic fat quantification MR can be a non-invasive, quantitative and useful tool for monitoring treatment effects in pediatric NASH.

Magnetic resonance imaging and liver histology as biomarkers of hepatic steatosis in children with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in children. In order to advance the field of NAFLD, noninvasive imaging methods for measuring liver fat are needed. Advanced magnetic resonance imaging (MRI) has shown great promise for the quantitative assessment of hepatic steatosis but has not been validated in children. Therefore, this study was designed to evaluate the correlation and diagnostic accuracy of MRI-estimated liver proton density fat fraction (PDFF), a biomarker for hepatic steatosis, compared to histologic steatosis grade in children. The study included 174 children with a mean age of 14.0 years. Liver PDFF estimated by MRI was significantly (P < 0.01) correlated (0.725) with steatosis grade. The correlation of MRI-estimated liver PDFF and steatosis grade was influenced by both sex and fibrosis stage. The correlation was significantly (P < 0.01) stronger in girls (0.86) than in boys (0.70). The correlation was significantly (P < 0.01) weaker in children with stage 2-4 fibrosis (0.61) than children with no fibrosis (0.76) or stage 1 fibrosis (0.78). The diagnostic accuracy of commonly used threshold values to distinguish between no steatosis and mild steatosis ranged from 0.69 to 0.82. The overall accuracy of predicting the histologic steatosis grade from MRI-estimated liver PDFF was 56%. No single threshold had sufficient sensitivity and specificity to be considered diagnostic for an individual child.

CONCLUSIONS

Advanced magnitude-based MRI can be used to estimate liver PDFF in children, and those PDFF values correlate well with steatosis grade by liver histology. Thus, magnitude-based MRI has the potential for clinical utility in the evaluation of NAFLD, but at this time no single threshold value has sufficient accuracy to be considered diagnostic for an individual child.

Diagnostic value of MRI proton density fat fraction for assessing liver steatosis in chronic viral C hepatitis

OBJECTIVE

To assess the diagnostic performance of a T1-independent, T2*-corrected multiecho magnetic resonance imaging (MRI) technique for the quantification of hepatic steatosis in a cohort of patients affected by chronic viral C hepatitis, using liver biopsy as gold standard.

METHODS

Eighty-one untreated patients with chronic viral C hepatitis were prospectively enrolled. All included patients underwent MRI, transient elastography, and liver biopsy within a time interval <10 days.

RESULTS

Our cohort of 77 patients included 43/77 (55.8%) males and 34/77 (44.2%) females with a mean age of 51.31 ± 11.27 (18-81) years. The median MRI PDFF showed a strong correlation with the histological fat fraction (FF) (r = 0.754, 95% CI 0.637 to 0.836, P < 0.0001), and the correlation was influenced by neither the liver stiffness nor the T2* decay. The median MRI PDFF result was significantly lower in the F4 subgroup (P < 0.05). The diagnostic accuracy of MRI PDFF evaluated by AUC-ROC analysis was 0.926 (95% CI 0.843 to 0.973) for S ≥ 1 and 0.929 (95% CI 0.847 to 0.975) for S = 2.

CONCLUSIONS

Our MRI technique of PDFF estimation allowed discriminating with a good diagnostic accuracy between different grades of hepatic steatosis.

Correlation of the controlled attenuation parameter with indices of liver steatosis in overweight or obese individuals: a pilot study

OBJECTIVE

The aim of this study was to assess the clinical relevance of the controlled attenuation parameter (CAP) by analyzing the correlations between CAP and indirect indices of liver steatosis in obese or overweight individuals.

METHODS

Consecutive participants were prospectively enrolled. BMI, waist circumference, hepatic steatosis index, fatty liver index, percent fat mass and regional fat masses as assessed by dual-energy X-ray absorptiometry (DXA), fat signal fraction as assessed by MRI, and CAP were obtained. Pearson's r coefficient was used to test the correlation between two study variables.

RESULTS

A total of 88 individuals were studied. They included 31 men [age, 50.4 years (12.9 years); BMI, 30.7 kg/m (4.8 kg/m)] and 57 women [age, 49.0 years (12.6 years); BMI, 31.4 kg/m (5.6 kg/m)]. DXA, anthropometric parameters, and fatty liver index were moderately correlated with CAP in men. In women, there was a moderate correlation of CAP with the hepatic steatosis index and anthropometric parameters and only a slight or fair correlation of CAP with DXA parameters. CAP and fat signal fraction showed a good correlation (r=0.65 in men, P=0.002; r=0.68 in women, P=0.0009).

CONCLUSION

Measurement of CAP is a reliable method for noninvasive assessment of liver steatosis, showing a correlation with other indirect markers of central obesity and a good correlation with MRI results.

Normal range of hepatic fat fraction on dual- and triple-echo fat quantification MR in children

Objectives

To evaluate hepatic fat fraction on dual- and triple-echo gradient-recalled echo MRI sequences in healthy children.

Materials and Methods

We retrospectively reviewed the records of children in a medical check-up clinic from May 2012 to November 2013. We excluded children with abnormal laboratory findings or those who were overweight. Hepatic fat fraction was measured on dual- and triple-echo sequences using 3T MRI. We compared fat fractions using the Wilcoxon signed rank test and the Bland-Altman 95% limits of agreement. The correlation between fat fractions and clinical and laboratory findings was evaluated using Spearman’s correlation test, and the cut-off values of fat fractions for diagnosing fatty liver were obtained from reference intervals.

Results

In 54 children (M:F = 26:28; 5–15 years; mean 9 years), the dual fat fraction (0.1–8.0%; median 1.6%) was not different from the triple fat fraction (0.4–6.5%; median 2.7%) (p = 0.010). The dual- and triple-echo fat fractions showed good agreement using a Bland-Altman plot (-0.6 ± 2.8%). Eight children (14.8%) on dual-echo sequences and six (11.1%) on triple-echo sequences had greater than 5% fat fraction. From these children, six out of eight children on dual-echo sequences and four out of six children on triple-echo sequences had a 5–6% hepatic fat fraction. When using a cut-off value of a 6% fat fraction derived from a reference interval, only 3.7% of children were diagnosed with fatty liver. There was no significant correlation between clinical and laboratory findings with dual and triple-echo fat fractions.

Conclusions

Dual fat fraction was not different from triple fat fraction. We suggest a cut-off value of a 6% fat fraction is more appropriate for diagnosing fatty liver on both dual- and triple-echo sequences in children.