Multisite multivendor validation of a quantitative MRI and CT compatible fat phantom

Exploring the association between dietary fiber intake and hepatic steatosis: insights from NHANES

PURPOSE

The link between dietary fiber intake and Non-alcoholic fatty liver disease (NAFLD) is under exploration, yielding inconsistent findings. Considering the limitations of previous research and the significance of dietary fiber in hepatic steatosis, this study investigates the association between dietary fiber intake and Controlled Attenuation Parameter (CAP) among 5935 participants from the National Health and Nutrition Examination Survey (NHANES).

MATERIALS AND METHODS

Multivariable regression was used to evaluate the association between dietary fiber intake and CAP. Smoothed curve fitting and threshold effect analysis techniques were applied to illustrate non-linear relationships.

RESULTS

After adjusting for other variables, a negative correlation emerged between dietary fiber intake and CAP. Subgroup analysis by gender and race/ethnicity revealed a sustained negative association between dietary fiber intake and CAP among females and Whites. Additionally, an inverted U-shaped relationship was observed between dietary fiber intake and CAP among women and other race, with inflection points at 13.80 g/day and 33.45 g/day, respectively.

CONCLUSION

Our research indicates that in the majority of Americans, there is an inverse relationship between dietary fiber intake and hepatic steatosis. This relationship exhibits an inverted U-shaped curve in women and other race, with a threshold effect. The findings of this study hold potential significance for clinical nutrition interventions, personalized dietary guidance, and advancing research into the diet-disease mechanism relationship.

Photon-counting CT using multi-material decomposition algorithm enables fat quantification in the presence of iron deposits

PURPOSE

A new generation of CT detectors were recently developed with the ability to measure individual photon's energy and thus provide spectral information. The aim of this work was to assess the performance of simultaneous fat and iron quantification using a clinical photon-counting CT (PCCT) and its comparison to dual-energy CT (DECT), MRS and MRI at 3 T.

METHODS

Two 3D printed cylindrical phantoms with 32 samples (n = 12 fat fractions between 0 % and 100 %, n = 20 with mixtures of fat and iron) were scanned with PCCT and DECT scanners for comparison. A three-material decomposition approach was used to estimate the volume fractions of fat (FF), iron and soft tissue. The same phantoms were examined by MRI (6-echo DIXON, a.k.a. Q-DIXON) and MRS (multi-echo STEAM, a.k.a. HISTO) at 3 T for comparison.

RESULTS

PCCT, DECT, MRI and MRS computed FFs showed correlation with reference fat fraction values in samples with no iron (r > 0.98). PCCT decomposition showed slightly weaker correlation with FFref in samples with added iron (r = 0.586) compared to MRI (r = 0.673) and MRS (r = 0.716) methods. On the other hand, it showed no systematic over- or underestimation. Surprisingly, DECT decomposition-derived FF showed strongest correlation (r = 0.758) in these samples, however systematic overestimation was observed. FF values computed by three-material PCCT decomposition, DECT decomposition, MRI and MRS were unaffected by iron concentration.

CONCLUSIONS

This in-vitro study shows for the first time that photon-counting computed tomography may be used for quantification of fat content in the presence of iron deposits.

MRI proton density fat fraction for estimation of tumor grade in steatotic hepatocellular carcinoma

OBJECTIVES

Image-based detection of intralesional fat in focal liver lesions has been established in diagnostic guidelines as a feature indicative of hepatocellular carcinoma (HCC) and associated with a favorable prognosis. Given recent advances in MRI-based fat quantification techniques, we investigated a possible relationship between intralesional fat content and histologic tumor grade in steatotic HCCs.

METHODS

Patients with histopathologically confirmed HCC and prior MRI with proton density fat fraction (PDFF) mapping were retrospectively identified. Intralesional fat of HCCs was assessed using an ROI-based analysis and the median fat fraction of steatotic HCCs was compared between tumor grades G1-3 with non-parametric testing. ROC analysis was performed in case of statistically significant differences (p < 0.05). Subgroup analyses were conducted for patients with/without liver steatosis and with/without liver cirrhosis.

RESULTS

A total of 57 patients with steatotic HCCs (62 lesions) were eligible for analysis. The median fat fraction was significantly higher for G1 lesions (median [interquartile range], 7.9% [6.0─10.7%]) than for G2 (4.4% [3.2─6.6%]; p = .001) and G3 lesions (4.7% [2.8─7.8%]; p = .036). PDFF was a good discriminator between G1 and G2/3 lesions (AUC .81; cut-off 5.8%, sensitivity 83%, specificity 68%) with comparable results in patients with liver cirrhosis. In patients with liver steatosis, intralesional fat content was higher than in the overall sample, with PDFF performing better in distinguishing between G1 and G2/3 lesions (AUC .92; cut-off 8.8%, sensitivity 83%, specificity 91%).

CONCLUSIONS

Quantification of intralesional fat using MRI PDFF mapping allows distinction between well- and less-differentiated steatotic HCCs.

CLINICAL RELEVANCE

PDFF mapping may help optimize precision medicine as a tool for tumor grade assessment in steatotic HCCs. Further investigation of intratumoral fat content as a potential prognostic indicator of treatment response is encouraged.

KEY POINTS

• MRI proton density fat fraction mapping enables distinction between well- (G1) and less- (G2 and G3) differentiated steatotic hepatocellular carcinomas. • In a retrospective single-center study with 62 histologically proven steatotic hepatocellular carcinomas, G1 tumors showed a higher intralesional fat content than G2 and G3 tumors (7.9% vs. 4.4% and 4.7%; p = .004). • In liver steatosis, MRI proton density fat fraction mapping was an even better discriminator between G1 and G2/G3 steatotic hepatocellular carcinomas.

Repeatability of MRI Biomarkers in Nonalcoholic Fatty Liver Disease: The NIMBLE Consortium

Background There is a need for reliable noninvasive methods for diagnosing and monitoring nonalcoholic fatty liver disease (NAFLD). Thus, the multidisciplinary Non-invasive Biomarkers of Metabolic Liver disease (NIMBLE) consortium was formed to identify and advance the regulatory qualification of NAFLD imaging biomarkers. Purpose To determine the different-day same-scanner repeatability coefficient of liver MRI biomarkers in patients with NAFLD at risk for steatohepatitis. Materials and Methods NIMBLE 1.2 is a prospective, observational, single-center short-term cross-sectional study (October 2021 to June 2022) in adults with NAFLD across a spectrum of low, intermediate, and high likelihood of advanced fibrosis as determined according to the fibrosis based on four factors (FIB-4) index. Participants underwent up to seven MRI examinations across two visits less than or equal to 7 days apart. Standardized imaging protocols were implemented with six MRI scanners from three vendors at both 1.5 T and 3 T, with central analysis of the data performed by an independent reading center (University of California, San Diego). Trained analysts, who were blinded to clinical data, measured the MRI proton density fat fraction (PDFF), liver stiffness at MR elastography (MRE), and visceral adipose tissue (VAT) for each participant. Point estimates and CIs were calculated using χ2 distribution and statistical modeling for pooled repeatability measures. Results A total of 17 participants (mean age, 58 years ± 8.5 [SD]; 10 female) were included, of which seven (41.2%), six (35.3%), and four (23.5%) participants had a low, intermediate, or high likelihood of advanced fibrosis, respectively. The different-day same-scanner mean measurements were 13%-14% for PDFF, 6.6 L for VAT, and 3.15 kPa for two-dimensional MRE stiffness. The different-day same-scanner repeatability coefficients were 0.22 L (95% CI: 0.17, 0.29) for VAT, 0.75 kPa (95% CI: 0.6, 0.99) for MRE stiffness, 1.19% (95% CI: 0.96, 1.61) for MRI PDFF using magnitude reconstruction, 1.56% (95% CI: 1.26, 2.07) for MRI PDFF using complex reconstruction, and 19.7% (95% CI: 15.8, 26.2) for three-dimensional MRE shear modulus. Conclusion This preliminary study suggests that thresholds of 1.2%-1.6%, 0.22 L, and 0.75 kPa for MRI PDFF, VAT, and MRE, respectively, should be used to discern measurement error from real change in patients with NAFLD. ClinicalTrials.gov registration no. NCT05081427 © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Kozaka and Matsui in this issue.

Quantitative MRI of diffuse liver diseases: techniques and tissue-mimicking phantoms

Quantitative magnetic resonance imaging (MRI) techniques are emerging as non-invasive alternatives to biopsy for assessment of diffuse liver diseases of iron overload, steatosis and fibrosis. For testing and validating the accuracy of these techniques, phantoms are often used as stand-ins to human tissue to mimic diffuse liver pathologies. However, currently, there is no standardization in the preparation of MRI-based liver phantoms for mimicking iron overload, steatosis, fibrosis or a combination of these pathologies as various sizes and types of materials are used to mimic the same liver disease. Liver phantoms that mimic specific MR features of diffuse liver diseases observed in vivo are important for testing and calibrating new MRI techniques and for evaluating signal models to accurately quantify these features. In this study, we review the liver morphology associated with these diffuse diseases, discuss the quantitative MR techniques for assessing these liver pathologies, and comprehensively examine published liver phantom studies and discuss their benefits and limitations.

Liver fat quantification in photon counting CT in head to head comparison with clinical MRI - First experience

PURPOSE

To compare liver fat quantification between MRI and photon-counting CT (PCCT).

METHOD

A cylindrical phantom with inserts containing six concentrations of oil (0, 10, 20, 30, 50 and 100%) and oil-iodine mixtures (0, 10, 20, 30 and 50% fat +3 mg/mL iodine) was imaged with a PCCT (NAEOTOM Alpha) and a 1.5 T MRI system (MR 450w, IDEAL-IQ sequence), using clinical parameters. An IRB-approved prospective clinical evaluation included 12 obese adult patients with known fatty liver disease (seven women, mean age: 61.5 ± 13 years, mean BMI: 30.3 ± 4.7 kg/m²). Patients underwent a same-day clinical MRI and PCCT of the abdomen. Liver fat fractions were calculated for four segments (I, II, IVa and VII) using in- and opposed-phase on MRI ((Mean_in - Mean_opp)/2*Mean_in) and iodine-fat, tissue decomposition analysis in PCCT (Syngo.Via VB60A). CT and MRI Fat fractions were compared using two-sample t-tests with equal variance. Statistical analysis was performed using RStudio (Version1.4.1717).

RESULTS

Phantom results showed no significant differences between the known fat fractions (P = 0.32) or iodine (P = 0.6) in comparison to PCCT-measured concentrations, and no statistically significant difference between known and MRI-measured fat fractions (P = 0.363). In patients, the mean fat signal fraction measured on MRI and PCCT was 13.1 ± 9.9% and 12.0 ± 9.0%, respectively, with an average difference of 1.1 ± 1.9% between the modalities (P = 0.138).

CONCLUSION

First experience shows promising accuracy of liver fat fraction quantification for PCCT in obese patients. This method may improve opportunistic screening for CT in the future.

T 1-T 2 dual-modal magnetic resonance contrast-enhanced imaging for rat liver fibrosis stage

The development of an effective method for staging liver fibrosis has always been a hot topic of research in the field of liver fibrosis. In this paper, PEGylated ultrafine superparamagnetic iron oxide nanocrystals (SPIO@PEG) were developed for T ₁-T ₂ dual-modal contrast-enhanced magnetic resonance imaging (MRI) and combined with Matrix Laboratory (MATLAB)-based image fusion for staging liver fibrosis in the rat model. Firstly, SPIO@PEG was synthesized and characterized with physical and biological properties as a T ₁-T ₂ dual-mode MRI contrast agent. Secondly, in the subsequent MR imaging of liver fibrosis in rats in vivo, conventional T ₁ and T ₂-weighted imaging, and T ₁ and T ₂ mapping of the liver pre- and post-intravenous administration of SPIO@PEG were systematically collected and analyzed. Thirdly, by creative design, we fused the T ₁ and T ₂ mapping images by MATLAB and quantitively measured each rat's hepatic fibrosis positive pixel ratio (PPR). SPIO@PEG was proved to have an ultrafine core size (4.01 ± 0.16 nm), satisfactory biosafety and T ₁-T ₂ dual-mode contrast effects under a 3.0 T MR scanner (r ₂/r ₁ = 3.51). According to the image fusion results, the SPIO@PEG contrast-enhanced PPR shows significant differences among different stages of liver fibrosis (P < 0.05). The combination of T ₁-T ₂ dual-modal SPIO@PEG and MATLAB-based image fusion technology could be a promising method for diagnosing and staging liver fibrosis in the rat model. PPR could also be used as a non-invasive biomarker to diagnose and discriminate the stages of liver fibrosis.

MRI-based quantification of renal fat in obese individuals using different image analysis approaches

PURPOSE

The purpose of this study was to evaluate different renal proton density fat fraction (PDFF) analysis approaches. Additionally, we assessed renal fat in obese individuals and lean individuals.

METHODS

This was a retrospective observational case-control study. Twenty-eight obese individuals and 14 lean controls underwent MRI with multi-point Dixon technique for PDFF maps. The following renal PDFF image analysis approaches were performed and compared: (1) five circular regions of interest (ROIs) in six slices, (2) three circular ROIs in one slice, (3) freehand segmentation of renal parenchyma in one slice, and (4) freehand segmentation of renal parenchyma avoiding the renal border in one slice. Furthermore, renal PDFF was compared between obese and lean individuals.

RESULTS

Methods 1, 2, and 4 were positively correlated (r ≥ 0.498, p ≤ 0.001). Renal PDFF values varied more with regards to ROI placement within slices than mean PDFF between slices. Using all methods, the obese individuals had significantly higher renal PDFF values compared with the lean controls.

CONCLUSION

Renal PDFF should be measured covering large areas of the kidney while excluding artifacts. This can be achieved using multiple circular ROIs. Increased lipid accumulation in the kidneys was related to obesity.

Hepatic Steatosis: CT-based Prevalence in Adults in China and the United States and Associations with Age, Sex, and Body Mass Index

Background: Calibrated CT fat fraction (FFCT) measurements derived from non-enhanced abdominal CT reliably reflect liver fat content, allowing largescale population-level investigations of steatosis prevalence and associations. Objective: To compare prevalence of hepatic steatosis, assessed by calibrated CT measurements, between population-based Chinese and U.S. cohorts, and to investigate in these populations the relationship of steatosis with age, sex, and body mass index (BMI). Methods: This retrospective study included 3176 adults (1985 women, 1191 men) from seven Chinese provinces and 8748 adults (4834 women, 3914 men) from a single U.S. medical center, drawn from earlier studies. All participants were at least 40 years old and underwent unenhanced abdominal CT for the earlier studies. Liver fat content measurements on CT were cross-calibrated to MRI proton density fat fraction measurements using phantoms and expressed as adjusted FFCT. Mild, moderate, and severe steatosis were defined as adjusted FFCT of 5.0%-14.9%, 15.0%-24.9%, and ≥25.0%, respectively. The two cohorts were compared. Results: Median adjusted FFCT was for women 4.7% and 4.8%, and for men 5.8% and 6.2%, in the Chinese and U.S. cohorts, respectively. Steatosis prevalence was for women 46.3% and 48.7%, and for men 58.9% and 61.9%, in the Chinese and U.S. cohorts, respectively. Severe steatosis prevalence was for women 0.9% and 1.8%, and for men, 0.2% and 2.6%, in the Chinese and U.S. cohorts, respectively. Adjusted FFCT did not vary across age decades in women or men in the Chinese cohort, though increased across age decades in women and men in the U.S. cohort. Adjusted FFCT and BMI exhibited weak correlation (r=0.312-0.431). Among participants with normal BMI, 36.8% and 38.5% of those in the Chinese and U.S. cohorts had mild steatosis, and 3.0% and 1.5% had moderate or severe steatosis, respectively. Among U.S. participants with BMI ≥40.0, 17.7% had normal liver content. Conclusion: Steatosis and severe steatosis had higher prevalence in the U.S. than Chinese cohort in both women and men. BMI did not reliably predict steatosis. Clinical Impact: The findings provide new information on the dependence of hepatic steatosis on age, sex, and BMI.