Does Meal or Water Intake Affect Ultrasound Attenuation Coefficient Estimate?

OBJECTIVES

To assess whether meal or water intake may affect the measurement of the ultrasound (US) attenuation coefficient (AC) imaging, a parameter that is directly related to liver fat content.

METHODS

The study was performed in two centers (Italy and USA). AC was obtained using the ATI algorithm implemented in the Aplio i-series US systems (Canon Medical Systems, Japan) by one operator at each center. Measurements were performed at baseline and 5, 15, 30, 45 minutes after drinking 500 mL of water (group 1), or 30, 45, 60, 90, 120 minutes after eating a meal of about 600 kcal (group 2). Multilevel generalized estimating equations for repeated measures were used for the statistical analysis to consider the clustered nature of the data.

RESULTS

Twenty-six individuals were enrolled: 11 (10 females; age, 43.7 ± 12.5 years) in Italy and 15 (10 females; age, 60.7 ± 6.3 years) in USA. At B-mode US, 10 (38.5%) had liver steatosis. The baseline AC values, in decibel/centimeter/megahertz, were 0.64 (0.12) in group 1 and 0.66 (0.13) in group 2. There was not any significant difference in AC values at every time-point after water or meal intake either in group 1 or group 2. This result did not change including sex, age, and skin-to-liver capsule into the models.

CONCLUSIONS

The measurement of the AC, which is a biomarker of liver steatosis, does not require a fasting state and drinking water does not affect the result.

Deep Learning for Inference of Hepatic Proton Density Fat Fraction From T1-Weighted In-Phase and Opposed-Phase MRI: Retrospective Analysis of Population-Based Trial Data

BACKGROUND. The confounder-corrected chemical shift-encoded MRI (CSE-MRI) sequence used to determine proton density fat fraction (PDFF) for hepatic fat quantification is not widely available. As an alternative, hepatic fat can be assessed by a two-point Dixon method to calculate signal fat fraction (FF) from conventional T1-weighted in- and opposed-phase (IOP) images, although signal FF is prone to biases, leading to inaccurate quantification. OBJECTIVE. The purpose of this study was to compare hepatic fat quantification by use of PDFF inferred from conventional T1-weighted IOP images and deep-learning convolutional neural networks (CNNs) with quantification by use of two-point Dixon signal FF with CSE-MRI PDFF as the reference standard. METHODS. This study entailed retrospective analysis of data from 292 participants (203 women, 89 men; mean age, 53.7 ± 12.0 [SD] years) enrolled at two sites from September 1, 2017, to December 18, 2019, in the Strong Heart Family Study (a prospective population-based study of American Indian communities). Participants underwent liver MRI (site A, 3 T; site B, 1.5 T) including T1-weighted IOP MRI and CSE-MRI (used to reconstruct CSE PDFF and CSE R2* maps). With CSE PDFF as reference, a CNN was trained in a random sample of 218 (75%) participants to infer voxel-by-voxel PDFF maps from T1-weighted IOP images; testing was performed in the other 74 (25%) participants. Parametric values from the entire liver were automatically extracted. Per-participant median CNN-inferred PDFF and median two-point Dixon signal FF were compared with reference median CSE-MRI PDFF by means of linear regression analysis, intraclass correlation coefficient (ICC), and Bland-Altman analysis. The code is publicly available at github.com/kang927/CNN-inference-of-PDFF-from-T1w-IOP-MR. RESULTS. In the 74 test-set participants, reference CSE PDFF ranged from 1% to 32% (mean, 11.3% ± 8.3% [SD]); reference CSE R2* ranged from 31 to 457 seconds-1 (mean, 62.4 ± 67.3 seconds-1 [SD]). Agreement metrics with reference to CSE PDFF for CNN-inferred PDFF were ICC = 0.99, bias = -0.19%, 95% limits of agreement (LoA) = (-2.80%, 2.71%) and for two-point Dixon signal FF were ICC = 0.93, bias = -1.11%, LoA = (-7.54%, 5.33%). CONCLUSION. Agreement with reference CSE PDFF was better for CNN-inferred PDFF from conventional T1-weighted IOP images than for two-point Dixon signal FF. Further investigation is needed in individuals with moderate-to-severe iron overload. CLINICAL IMPACT. Measurement of CNN-inferred PDFF from widely available T1-weighted IOP images may facilitate adoption of hepatic PDFF as a quantitative bio-marker for liver fat assessment, expanding opportunities to screen for hepatic steatosis and nonalcoholic fatty liver disease.

Non-Invasive Imaging Methods to Evaluate Non-Alcoholic Fatty Liver Disease with Fat Quantification: A Review

Hepatic steatosis without specific causes (e.g., viral infection, alcohol abuse, etc.) is called non-alcoholic fatty liver disease (NAFLD), which ranges from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH), fibrosis, and NASH-related cirrhosis. Despite the usefulness of the standard grading system, liver biopsy has several limitations. In addition, patient acceptability and intra- and inter-observer reproducibility are also concerns. Due to the prevalence of NAFLD and limitations of liver biopsies, non-invasive imaging methods such as ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) that can reliably diagnose hepatic steatosis have developed rapidly. US is widely available and radiation-free but cannot examine the entire liver. CT is readily available and helpful for detection and risk classification, significantly when analyzed using artificial intelligence; however, it exposes users to radiation. Although expensive and time-consuming, MRI can measure liver fat percentage with magnetic resonance imaging proton density fat fraction (MRI-PDFF). Specifically, chemical shift-encoded (CSE)-MRI is the best imaging indicator for early liver fat detection. The purpose of this review is to provide an overview of each imaging modality with an emphasis on the recent progress and current status of liver fat quantification.

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.

A Pre-Release Algorithm With a Confidence Map for Estimating the Attenuation Coefficient for Liver Fat Quantification

OBJECTIVES

To compare the estimates of attenuation coefficient (AC) for liver fat quantification between 2 Ultrasound systems and to evaluate the quality measure of a pre-released software.

METHODS

AC were obtained in 30 participants in this single-center IRB-approved, HIPAA compliant study. Images were obtained on the Philips Epiq Elite system using experimental software and the Canon Medical Systems Aplio i800 with released software. Five AC measurements were taken and the median and IQR/M were calculated. Region of interest placement was based on a confidence map. ROI was at the same depth and size for each system. The concordance was estimated using the Lin's concordance correlation coefficient (CCC), the r Pearson's correlation coefficient, the bias-correction factor (Cb), and the Bland-Altman method.

RESULTS

The ACs varied from 0.45 to 1.0 dB/cm/MHz for the Philips system and 0.30 to 0.96 dB/cm/MHz for the Canon system. The CCC (95% CI) was 0.792 (0.666-0.918), Pearson's r was 0.839 with Cb of 0.944, and the mean difference was 0.03 (-0.101; 0.162) suggesting the 2 methods are considered to be in agreement. Based on a Philips confidence map to determine the best location for performing the measurements, a depth of 3.5 to 4.0 cm from the liver capsule was determined, which might be significantly different than that of the Canon system.

CONCLUSIONS

Estimation of the AC of the 2 systems showed a high agreement, that is, a similar trend. Assessment of the placement of the measurement box based on the quality of the measurement might be different between the 2 systems.

Quantitative Ultrasound Assessment of Hepatic Steatosis

BACKGROUND/AIMS

Non-alcoholic fatty liver disease (NAFLD) is widespread chronic disease of the live in humans with the prevalence of 30% of the United States population.^1,2 The goal of the study is to validate the performance of quantitative ultrasound algorithms in the assessment of hepatic steatosis in patients with suspected NAFLD.

METHODS

This prospective study enrolled a total of 31 patients with clinical suspicion of NAFLD to receive liver fat measurements by quantitative ultrasound and reference MRI measurements (proton density fat-fraction, PDFF). The following ultrasound (US) parameters based on both raw ultrasound RF (Radio Frequency) data and 2D B-mode images of the liver were analyzed with subsequent correlation with MRI-PDFF: hepatorenal index, acoustic attenuation coefficient, Nakagami coefficient parameter, shear wave viscosity, shear wave dispersion and shear wave elasticity. Ultrasound parameters were also correlated with the presence of hypertension and diabetes.

RESULTS

The mean (± SD) age and body mass index of the patients were 49.03 (± 12.49) and 30.12 (± 6.15), respectively. Of the aforementioned ultrasound parameters, the hepatorenal index and acoustic attenuation coefficient showed a strong correlation with MRI-PDFF derivations of hepatic steatosis, with r-values of 0.829 and 0.765, respectively. None of the remaining US parameters showed strong correlations with PDFF. Significant differences in Nakagami parameters and acoustic attenuation coefficients were found in those patients with and without hypertension.

CONCLUSIONS

Hepatorenal index and acoustic attenuation coefficient correlate well with MRI-PDFF-derived measurements of hepatic steatosis. Quantitative ultrasound is a promising tool for the diagnosis and assessment of patients with NAFLD.

Ultrasound Stratification of Hepatic Steatosis Using Hepatorenal Index

Hepatorenal index (HRI) has been shown to be an effective, noninvasive ultrasound tool to screen patients for those with or without >5% hepatic steatosis. Objective: The aim of this study was to further refine this HRI tool in order to stratify patients according to their degree of liver steatosis and give direction as to which patients should undergo random liver biopsy. Methods: We conducted a retrospective review of 267 consecutive patients from 2015 to 2017 who had abdominal ultrasounds and a subsequent random liver biopsy within one month. The HRI was calculated and compared with the percent steatosis as assessed by histology. Results: An HRI of ≤1.17 corresponds with >95% positive predictive value of ≤5% steatosis. Between HRI values 1.18 and 1.39, performance of steatosis prediction is mixed. However, for values <1.37 there is an increased likelihood of steatosis ≤5% and likewise the opposite for values >1.37. An HRI of ≥1.4 corresponds with >95% positive predictive value of ≥10% steatosis. Conclusion: HRI is an accurate noninvasive tool to quantify degree of steatosis and guide who should undergo random liver biopsy, potentially significantly reducing the total number of necessary liver biopsies.

Quantification of Liver Fat by MRI-PDFF Imaging in Patients with Suspected Non-alcoholic Fatty Liver Disease and Its Correlation with Metabolic Syndrome, Liver Function Test and Ultrasonography

BACKGROUND

Magnetic resonance imaging (MRI)-estimated proton density fat fraction (PDFF) has emerged to be a promising tool in quantification of liver fat. Aim of this study was to quantify liver fat using MRI-PDFF in patients with suspected non-alcoholic fatty liver disease (NAFLD) and to correlate it with the presence of metabolic syndrome (MetS), ultrasonography (USG) and liver function test (LFT).

METHODS

We included 111 consecutive patients who were suspected to have NAFLD on the basis of clinical, laboratory or USG findings. A 3 Tesla Phillips MRI machine was used with a software named "mDixon Quant" for quantification of the liver fat.

RESULTS

MRI-PDFF revealed hepatic steatosis grading as Grade 0 in 31 patients (28%), Grade I in 40 (36%), Grade II in 19 (17.1%) and Grade III in 21 patients (18.9%). MetS patients had higher proportion of advanced steatosis (Grades II and III) as compared to those without MetS (P < 0.001). ALT (alanine transaminase) was found to be significantly elevated (>1.5 times) in the patients with advanced steatosis as compared to patients with Grades I and 0 fatty liver on MRI-PDFF (P < 0.001). The Kappa measure of agreement between USG and MRI-PDFF was found to be 0.2, which suggests a low level of agreement between the two tests.

CONCLUSION

MetS patients have higher proportion of advanced steatosis (Grades II and III) at MRI-PDFF as compared to those without MetS. Patients with advanced steatosis at MRI-PDFF had higher proportion of abnormal LFTs as compared to those with Grades 0 and I hepatic steatosis. There was a dis-correlation between MRI-PDFF and USG in the evaluation of NAFLD.

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.

Comparative accuracy of CT, dual-echo MRI and MR spectroscopy for preoperative liver fat quantification in living related liver donors

Background:

It is of significant importance to assess the extent of hepatic steatosis in living donor liver transplant (LDLT) surgery to ensure optimum graft regeneration as well as donor safety.

Aim:

To establish the accuracy of non-invasive imaging methods including computed tomography (CT), dual-echo in- and opposed-phase magnetic resonance imaging (MRI), and MR spectroscopy (MRS) for quantification of liver fat content (FC) in prospective LDLT donors with histopathology as reference standard.

Settings and Design:

This retrospective study was conducted at our institution on LDLT donors being assessed for biliary and vascular anatomy depiction by Magnetic Resonance Cholangiopancreatography (MRCP) and CT scan, respectively, between July 2013 and October 2014.

Materials and Methods:

Liver FC was measured in 73 donors by dual-echoT1 MRI and MRS. Of these, CT liver attenuation index (LAI) values were available in 62 patients.

Statistical Analysis:

CT and MRI FC were correlated with histopathological reference standard using Spearman correlation coefficient. Sensitivity, specificity, positive predictive value, negative predicative value, and positive and negative likelihood ratios with 95% confidence intervals were obtained.

Results:

CT LAI, dual-echo MRI, and MRS correlated well with the histopathology results (r = 0.713, 0.871, and 0.882, respectively). An accuracy of 95% and 96% was obtained for dual-echo MRI and MRS in FC estimation with their sensitivity being 97% and 94%, respectively. False-positive rate, positive predictive value (PPV), and negative predicative value (NPV) were 0.08, 0.92, and 0.97, respectively, for dual-echo MRI and 0.03, 0.97, and 0.95, respectively, for MRS. CT LAI method of fat estimation has a sensitivity, specificity, PPV, and NPV of 73%, 77.7%, 70.4%, and 80%, respectively.

Conclusion:

Dual-echo MRI, MRS, and CT LAI are accurate measures to quantify the degree of hepatic steatosis in LDLT donors, thus reducing the need for invasive liver biopsy and its associated complications. Dual-echo MRI and MRS results correlate better with histological results in the study, as compared to CT LAI method for fat quantification.

Effect of PRESS and STEAM sequences on magnetic resonance spectroscopic liver fat quantification

PURPOSE

To compare PRESS and STEAM MR spectroscopy for assessment of liver fat in human subjects.

MATERIALS AND METHODS

Single-voxel (20 x 20 x 20 mm) PRESS and STEAM spectra were obtained at 1.5T in 49 human subjects with known or suspected fatty liver disease. PRESS and STEAM sequences were obtained with fixed TR (1500 msec) and different TE (five PRESS spectra between TE 30-70 msec, five STEAM spectra between TE 20-60 msec). Spectra were quantified and T2 and T2-corrected peak area were calculated by different techniques. The values were compared for PRESS and STEAM.

RESULTS

Water T2 values from PRESS and STEAM were not significantly different (P = 0.33). Fat peak T2s were 25%-50% shorter on PRESS than on STEAM (P < 0.02 for all comparisons) and there was no correlation between T2s of individual peaks. PRESS systematically overestimated the relative fat peak areas (by 7%-263%) compared to STEAM (P < 0.005 for all comparisons). The peak area given by PRESS was more dependent on the T2-correction technique than STEAM.

CONCLUSION

Measured liver fat depends on the MRS sequence used. Compared to STEAM, PRESS underestimates T2 values of fat, overestimates fat fraction, and provides a less consistent fat fraction estimate, probably due to J coupling effects.