Liver R2* is affected by both iron and fat: A dual biopsy-validated study of chronic liver disease

Liver fibrosis is associated with left ventricular remodeling: insight into the liver-heart axis

OBJECTIVE

In nonalcoholic fatty liver disease (NAFLD), liver fibrosis is the strongest predictor of adverse outcomes. We sought to investigate the relationship between liver fibrosis and cardiac remodeling in participants from the general population using magnetic resonance imaging (MRI), as well as explore potential mechanistic pathways by analyzing circulating cardiovascular biomarkers.

METHODS

In this cross-sectional study, we prospectively included participants with type 2 diabetes and individually matched controls from the SCAPIS (Swedish CArdioPulmonary bioImage Study) cohort in Linköping, Sweden. Between November 2017 and July 2018, participants underwent MRI at 1.5 Tesla for quantification of liver proton density fat fraction (spectroscopy), liver fibrosis (stiffness from elastography), left ventricular (LV) structure and function, as well as myocardial native T1 mapping. We analyzed 278 circulating cardiovascular biomarkers using a Bayesian statistical approach.

RESULTS

In total, 92 participants were enrolled (mean age 59.5 ± 4.6 years, 32 women). The mean liver stiffness was 2.1 ± 0.4 kPa. 53 participants displayed hepatic steatosis. LV concentricity increased across quartiles of liver stiffness. Neither liver fat nor liver stiffness displayed any relationships to myocardial tissue characteristics (native T1). In a regression analysis, liver stiffness was related to increased LV concentricity. This association was independent of diabetes and liver fat (Beta = 0.26, p = 0.0053), but was attenuated (Beta = 0.17, p = 0.077) when also adjusting for circulating levels of interleukin-1 receptor type 2.

CONCLUSION

MRI reveals that liver fibrosis is associated to structural LV remodeling, in terms of increased concentricity, in participants from the general population. This relationship could involve the interleukin-1 signaling.

CLINICAL RELEVANCE STATEMENT

Liver fibrosis may be considered a cardiovascular risk factor in patients without cirrhosis. Further research on the mechanisms that link liver fibrosis to left ventricular concentricity may reveal potential therapeutic targets in patients with non-alcoholic fatty liver disease (NAFLD).

KEY POINTS

Previously, studies on liver fibrosis and cardiac remodeling have focused on advanced stages of liver fibrosis. Liver fibrosis is associated with left ventricular (LV) concentricity and may relate to interleukin-1 receptor type 2. Interleukin-1 signaling is a potential mechanistic interlink between early liver fibrosis and LV remodeling.

Effect of particle size on liver MRI R 2 * relaxometry: Monte Carlo simulation and phantom studies

PURPOSE

To investigate the effect of particle size on liverR 2 * $$ {\mathrm{R}}_2^{\ast } $$ by Monte Carlo simulation and phantom studies at both 1.5 T and 3.0 T.

METHODS

Two kinds of particles (i.e., iron sphere and fat droplet) with varying sizes were considered separately in simulation and phantom studies. MRI signals were synthesized and analyzed for predictingR 2 * $$ {\mathrm{R}}_2^{\ast } $$ , based on simulations by incorporating virtual liver model, particle distribution, magnetic field generation, and proton movement into phase accrual. In the phantom study, iron-water and fat-water phantoms were constructed, and each phantom contained 15 separate vials with combinations of five particle concentrations and three particle sizes.R 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements in the phantom were made at both 1.5 T and 3.0 T. Finally, differences inR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions or measurements were evaluated across varying particle sizes.

RESULTS

In the simulation study, strong linear and positively correlated relationships were observed betweenR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions and particle concentrations across varying particle sizes and magnetic field strengths (r ≥ 0.988 $$ r\ge 0.988 $$ ). The relationships were affected by iron sphere size (p < 0.001 $$ p<0.001 $$ ), where smaller iron sphere size yielded higher predictedR 2 * $$ {\mathrm{R}}_2^{\ast } $$ , whereas fat droplet size had no effect onR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions (p ≥ 0.617 $$ p\ge 0.617 $$ ) for constant total fat concentration. Similarly, the phantom study showed thatR 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements were relatively sensitive to iron sphere size (p ≤ 0.004 $$ p\le 0.004 $$ ) unlike fat droplet size (p ≥ 0.223 $$ p\ge 0.223 $$ ).

CONCLUSION

LiverR 2 * $$ {\mathrm{R}}_2^{\ast } $$ is affected by iron sphere size, but is relatively unaffected by fat droplet size. These findings may lead to an improved understanding of the underlying mechanisms ofR 2 * $$ {\mathrm{R}}_2^{\ast } $$ relaxometry in vivo, and enable improved quantitative MRI phantom design.

Sex-specific associations in multiparametric 3 T MRI measurements in adult livers

BACKGROUND

MRI relaxometry mapping and proton density fat fraction (PDFF) have been proposed for the evaluation of hepatic fibrosis. However, sex-specific relationships of age and body fat with these MRI parameters have not been studied in detail among adults without clinically manifest hepatic disease. We aimed to determine the sex-specific correlation of multiparametric MRI parameters with age and body fat and to evaluate their interplay associations.

METHODS

147 study participants (84 women, mean age 48±14 years, range 19-85 years) were prospectively enrolled. 3 T MRI including T1, T2 and T1ρ mapping and PDFF and R2* map were acquired. Visceral and subcutaneous fat were measured on the fat images from Dixon water-fat separation sequence.

RESULTS

All MRI parameters demonstrated sex difference except for T1ρ. PDFF was more related to visceral than subcutaneous fat. Per 100 ml gain of visceral or subcutaneous fat is associated with 1 or 0.4% accretion of liver fat, respectively. PDFF and R2* were higher in men (both P = 0.01) while T1 and T2 were higher in women (both P < 0.01). R2* was positively but T1 and T2 were negatively associated with age in women (all P < 0.01), while T1ρ was positively related to age in men (P < 0.05). In all studies, R2* was positively and T1ρ was negatively associated with PDFF (both P <0.0001).

CONCLUSION

Visceral fat plays an essential role in the elevated liver fat. When using MRI parametric measures for liver disease evaluation, the interplay between these parameters should be considered.

Monte Carlo modeling of hepatic steatosis based on stereology and spatial distribution of fat droplets

BACKGROUND AND OBJECTIVE

To model hepatic steatosis in adult humans with non-alcoholic fatty liver disease based on stereology and spatial distribution of fat droplets from liver biopsy specimens.

METHODS

Histological analysis was performed on 30 adult human liver biopsy specimens with varying degrees of steatosis. Morphological features of fat droplets were characterized by gamma distribution function (GDF) in both two-dimensional (2D) and three-dimensional (3D) spaces from three aspects: 1) size distribution indicating non-uniformity of fat droplets in radius; 2) nearest neighbor distance distribution indicating heterogeneous accumulation (i.e., clustering) of fat droplets; 3) regional anisotropy indicating inter-regional variability in fat fraction (FF). To generalize the morphological description of hepatic steatosis to different FFs, correlation analysis was performed among the estimated GDF parameters and FFs for all specimens. Finally, Monte Carlo modeling of hepatic steatosis was developed to simulate fat droplet distribution in tissue.

RESULTS

Morphological features, including size and nearest neighbor distance in 2D and 3D spaces as well as regional anisotropy, statistically captured the distribution of fat droplets by the GDF fit (R2 > 0.54). The estimated GDF parameters (i.e., scale and shape parameters) and FFs were well correlated, with R2 > 0.55. In addition, simulated 3D liver morphological models demonstrated similar sections to real histological samples both visually and quantitatively.

CONCLUSIONS

The morphology of hepatic steatosis is well characterized by stereology and spatial distribution of fat droplets. Simulated models demonstrate similar appearances to real histological samples. Furthermore, the model may help understand MRI signal behavior in the presence of liver steatosis.

APTw combined with mDixon-Quant imaging to distinguish the differentiation degree of cervical squamous carcinoma

Background

To investigate the value of amide proton transfer weighted (APTw) imaging combined with modified Dixon fat quantification (mDixon-Quant) imaging in determining the degree of differentiation of cervical squamous carcinoma (CSC) against histopathologic.

Methods

Magnetic resonance imaging (MRI) data were collected from 52 CSC patients. According to histopathologic results, patients were divided into the poorly differentiated group (37 cases) and the well/moderately differentiated group (15 cases). The APTw value by APTw imaging and the fat fraction (FF) and transverse relaxation rate R 2 * values by mDixon-Quant were independently measured by two radiologists. Intra-class correlation coefficients (ICCs) were used to test the consistency of APTw, FF, and R 2 * values measured by the two observers. The Mann-Whitney U test was used to analyze the difference in each parameter between the two groups. Logistic regression analysis was used to assess the association between the degree of differentiation on histopathology and imaging parameters by APTw and mDixon Quant. The ROC curve was used to evaluate the diagnostic efficacy of various parameters and their combination in distinguishing the degree of CSC differentiation on histopathology. The DeLong test was used to access the differences among the area under the ROC curves (AUCs). The Pearson correlation coefficient was used to evaluate the correlation between APTw and mDixon-Quant imaging parameters.

Results

The APTw means were 2.95 ± 0.78% and 2.05 (1.85, 2.65)% in the poorly and well/moderately differentiated groups, respectively. The R 2 * values were 26.62 (21.99, 33.31)/s and 22.93 ± 6.09/s in the poorly and well/moderately differentiated groups, respectively (P < 0.05). The AUCs of APTw, R 2 * , and their combination were 0.762, 0.686, and 0.843, respectively. The Delong test suggested statistical significance between R 2 * and the combination of APTw and R 2 * . R 2 * values showed a significant correlation with APTw values in the poorly differentiated group.

Conclusions

APTw combined with mDixon-Quant can be used to efficiently distinguish the differention degrees of CSC diagnosed on histopathology.

Magnetic resonance imaging R2* sequences can better detect microstructural cartilage changes than T2 mapping in cynomolgus monkeys with limited knee kinematics: preliminary imaging findings

BACKGROUND

The difference between MRI (Magnetic resonance imaging)-R2* and T2 mapping sequences regarding their superiority in the detection of microstructural cartilage changes in knees with limited ROM (range of motion) was unknown.

METHODS

Twenty male cynomolgus monkeys (mean age: 10.65 ± 0.97 years) underwent knee ROM evaluations and were divided into three groups: Group A (n = 10), with similar left and right knee ROM; Group B (n = 5), with left knee ROM superior to right; and Group C (n = 5), with left knee ROM inferior to right. Twenty-eight ROIs (regions of interest) in the cartilage of the lateral (L) and medial (M) femoral trochlea (FT), anterior (A)/central (C)/posterior (P) femoral condyle (FC) and tibial plateau (TP) of both knees were identified in each monkey. The corresponding ROI values in R2* and T2 mapping sequences were recorded for analysis. One-way ANOVA, Chi-square tests and Pearson's correlation analysis were used for statistical analyses.

RESULTS

Among the total 1120 ROIs, significant differences in R2* values among the three groups existed in two ROIs: cartilage of the right MPTP (F = 5.216, P = 0.017) and left MAFC (F = 4.919, P = 0.021). However, the T2 mapping values of all ROIs were similar among the three groups. Microstructural cartilage changes occurred more frequently in the medial (40 ROIs) than in the lateral (0 ROIs) knee compartment (χ² = 43.077, P < 0.001). The Group B cartilage R2* value of the right MPTP increased with the difference in bilateral knee ROM (r = 0.913, P = 0.030).

CONCLUSIONS

In knees with limited ROM, MRI-R2* sequence is superior to T2 mapping in the detection of microstructural cartilage changes, which the medial knee compartment was more susceptible to. Cartilage R2* values tend to increase with the amount of knee ROM loss.

Ectopic fat is associated with cardiac remodeling—A comprehensive assessment of regional fat depots in type 2 diabetes using multi-parametric MRI

Background

Different regional depots of fat have distinct metabolic properties and may relate differently to adverse cardiac remodeling. We sought to quantify regional depots of body fat and to investigate their relationship to cardiac structure and function in Type 2 Diabetes (T2D) and controls.

Methods

From the SCAPIS cohort in Linköping, Sweden, we recruited 92 subjects (35% female, mean age 59.5 ± 4.6 years): 46 with T2D and 46 matched controls. In addition to the core SCAPIS data collection, participants underwent a comprehensive magnetic resonance imaging examination at 1.5 T for assessment of left ventricular (LV) structure and function (end-diastolic volume, mass, concentricity, ejection fraction), as well as regional body composition (liver proton density fat fraction, visceral adipose tissue, abdominal subcutaneous adipose tissue, thigh muscle fat infiltration, fat tissue-free thigh muscle volume and epicardial adipose tissue).

Results

Compared to the control group, the T2D group had increased: visceral adipose tissue volume index (P &lt; 0.001), liver fat percentage (P &lt; 0.001), thigh muscle fat infiltration percentage (P = 0.02), LV concentricity (P &lt; 0.001) and LV E/e'-ratio (P &lt; 0.001). In a multiple linear regression analysis, a negative association between liver fat percentage and LV mass (St Beta −0.23, P &lt; 0.05) as well as LV end-diastolic volume (St Beta −0.27, P &lt; 0.05) was found. Epicardial adipose tissue volume and abdominal subcutaneous adipose tissue volume index were the only parameters of fat associated with LV diastolic dysfunction (E/e'-ratio) (St Beta 0.24, P &lt; 0.05; St Beta 0.34, P &lt; 0.01, respectively). In a multivariate logistic regression analysis, only visceral adipose tissue volume index was significantly associated with T2D, with an odds ratio for T2D of 3.01 (95% CI 1.28–7.05, P &lt; 0.05) per L/m2 increase in visceral adipose tissue volume.

Conclusions

Ectopic fat is predominantly associated with cardiac remodeling, independently of type 2 diabetes. Intriguingly, liver fat appears to be related to LV structure independently of VAT, while epicardial fat is linked to impaired LV diastolic function. Visceral fat is associated with T2D independently of liver fat and abdominal subcutaneous adipose tissue.

Hepatic Iron Quantification Using a Free-Breathing 3D Radial Gradient Echo Technique and Validation With a 2D Biopsy-Calibrated R2* Relaxometry Method

BACKGROUND

Hepatic iron content (HIC) is an important parameter for the management of iron overload. Non-invasive HIC assessment is often performed using biopsy-calibrated two-dimensional breath-hold Cartesian gradient echo (2D BH GRE) R2* -MRI. However, breath-holding is not possible in most pediatric patients or those with respiratory problems, and three-dimensional free-breathing radial GRE (3D FB rGRE) has emerged as a viable alternative.

PURPOSE

To evaluate the performance of a 3D FB rGRE and validate its R2* and fat fraction (FF) quantification with 3D breath-hold Cartesian GRE (3D BH cGRE) and biopsy-calibrated 2D BH GRE across a wide range of HICs.

STUDY TYPE

Retrospective.

SUBJECTS

Twenty-nine patients with hepatic iron overload (22 females, median age: 15 [5-25] years).

FIELD STRENGTH/SEQUENCE

Three-dimensional radial and 2D and 3D Cartesian multi-echo GRE at 1.5 T.

ASSESSMENT

R2* and FF maps were computed for 3D GREs using a multi-spectral fat model and 2D GRE R2* maps were calculated using a mono-exponential model. Mean R2* and FF values were calculated via whole-liver contouring and T2* -thresholding by three operators.

STATISTICAL TESTS

Inter- and intra-observer reproducibility was assessed using Bland-Altman and intraclass correlation coefficient (ICC). Linear regression and Bland-Altman analysis were performed to compare R2* and FF values among the three acquisitions. One-way repeated-measures ANOVA and Wilcoxon signed-rank tests, respectively, were used to test for significant differences between R2* and FF values obtained with different acquisitions. Statistical significance was assumed at P < 0.05.

RESULTS

The mean biases and ICC for inter- and intra-observer reproducibility were close to 0% and >0.99, respectively for both R2* and FF. The 3D FB rGRE R2* and FF values were not significantly different (P > 0.44) and highly correlated (R2  ≥ 0.98) with breath-hold Cartesian GREs, with mean biases ≤ ±2.5% and slopes 0.90-1.12. In non-breath-holding patients, Cartesian GREs showed motion artifacts, whereas 3D FB rGRE exhibited only minimal streaking artifacts.

DATA CONCLUSION

Free-breathing 3D radial GRE is a viable alternative in non-breath-hold patients for accurate HIC estimation.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Distribution and Associated Factors of Hepatic Iron-A Population-Based Imaging Study

Hepatic iron overload can cause severe organ damage; therefore, an early diagnosis and the identification of potential risk factors is crucial. We aimed to investigate the sex-specific distribution of hepatic iron content (HIC) in a population-based cohort and identify relevant associated factors from a panel of markers. We analyzed N = 353 participants from a cross-sectional sample (KORA FF4) who underwent whole-body magnetic resonance imaging. HIC was assessed by single-voxel spectroscopy with a high-speed T2-corrected multi-echo technique. A large panel of markers, including anthropometric, genetic, and laboratory values, as well as behavioral risk factors were assessed. Relevant factors associated with HIC were identified by variable selection based on LASSO regression with bootstrap resampling. HIC in the study sample (mean age at examination: 56.0 years, 58.4% men) was significantly lower in women (mean ± SD: 39.2 ± 4.1 s^-1) than in men (41.8 ± 4.7 s^-1, p < 0.001). Relevant factors associated with HIC were HbA1c as well as prediabetes for men and visceral adipose tissue as well as age for women. Hepatic fat, alcohol consumption, and genetic risk score for iron levels were associated with HIC in both sexes. In conclusion, there are sex-specific associations of HIC with markers of body composition, glucose metabolism, and alcohol consumption.

Spectroscopy-based multi-parametric quantification in subjects with liver iron overload at 1.5T and 3T

PURPOSE

To evaluate the precision profile (repeatability and reproducibility) of quantitative STEAM-MRS and to determine the relationships between multiple MR biomarkers of chronic liver disease in subjects with iron overload at both 1.5 Tesla (T) and 3T.

METHODS

MRS data were acquired in patients with known or suspected liver iron overload. Two STEAM-MRS sequences (multi-TE and multi-TE-TR) were acquired at both 1.5T and 3T (same day), including test-retest acquisition. Each acquisition enabled estimation of R1, R2, and FWHM (each separately for water and fat); and proton density fat fraction. The test-retest repeatability and reproducibility across acquisition modes (multi-TE vs. multi-TE-TR) of the estimates were evaluated using intraclass correlation coefficients, linear regression, and Bland-Altman analyses. Multi-parametric relationships between parameters at each field strength, across field strengths, and with liver iron concentration were also evaluated using linear and nonlinear regression.

RESULTS

Fifty-six (n = 56) subjects (10 to 73 years, 37 males/19 females) were successfully recruited. Both STEAM-MRS sequences demonstrated good-to-excellent precision (intraclass correlation coefficient ≥ 0.81) for the quantification of R1_water , R2_water , FWHM_water , and proton density fat fraction at both 1.5T and 3T. Additionally, several moderate (R² = 0.50 to 0.69) to high (R² ≥ 0.70) correlations were observed between biomarkers, across field strengths, and with liver iron concentration.

CONCLUSIONS

Over a broad range of liver iron concentration, STEAM-MRS enables rapid and precise measurement of multiple biomarkers of chronic liver disease. By evaluating the multi-parametric relationships between biomarkers, this work may advance the comprehensive MRS-based assessment of chronic liver disease and may help establish biomarkers of chronic liver disease.

Quantitative Susceptibility Mapping versus R2*-based Histogram Analysis for Evaluating Liver Fibrosis: Preliminary Results

PURPOSE

The staging of liver fibrosis is clinically important, and a less invasive method is preferred. Quantitative susceptibility mapping (QSM) has shown a great potential in estimating liver fibrosis in addition to R2* relaxometry. However, few studies have compared QSM analysis and liver fibrosis. We aimed to evaluate the feasibility of estimating liver fibrosis by using QSM and R2*-based histogram analyses by comparing it with ultrasound-based transient elastography and the stage of histologic fibrosis.

METHODS

Fourteen patients with liver disease were enrolled. Data sets of multi-echo gradient echo sequence with breath-holding were acquired on a 3-Tesla scanner. QSM and R2* were reconstructed by water-fat separation method, and ROIs were analyzed for these images. Quantitative parameters with histogram features (mean, variance, skewness, kurtosis, and 1st, 10th, 50th, 90th, and 99th percentiles) were extracted. These data were compared with the elasticity measured by ultrasound transient elastography and histological stage of liver fibrosis (F0 to F4, based on the new Inuyama classification) determined by biopsy or hepatectomy. The correlation of histogram parameters with intrahepatic elasticity and histologically confirmed fibrosis stage was examined. Texture parameters were compared between subgroups divided according to fibrosis stage. Receiver operating characteristic (ROC) analysis was also performed. P < 0.05 indicated statistical significance.

RESULTS

The six histogram parameters of both QSM and R2*were significantly correlated with intrahepatic elasticity. In particular, three parameters (variance, percentiles [90th and 99th]) of QSM showed high correlation (r = 0.818-0.844), whereas R2* parameters showed a moderate correlation with elasticity. Four parameters of QSM were significantly correlated with fibrosis stage (ρ = 0.637-0.723) and differentiated F2-4 from F0-1 fibrosis and F3-4 from F0-2 fibrosis with areas under the ROC curve of > 0.8, but those of R2* did not.

CONCLUSION

QSM may serve as a promising surrogate indicator in detecting liver fibrosis.

Low hepatic manganese concentrations in patients with hepatic steatosis - A cohort study of copper, iron and manganese in liver biopsies

BACKGROUND AND AIMS

Hepatic steatosis is the most common histopathological finding on liver biopsy, with the most prevalent etiology being NAFLD. The pathogenesis of hepatic steatosis and NAFLD is multifactorial, however, studies on the importance of manganese in NAFLD are limited. We aimed to study hepatic manganese content, and other trace elements, in relation to hepatic steatosis in patients with chronic liver diseases of different etiology, mainly NAFLD.

METHODS

Patients with chronically elevated liver function tests underwent a diagnostic work-up, including routine blood tests and two liver biopsies. One of the biopsies was sent for histopathological evaluation, and the other for ultra-trace elemental determinations. Steatosis was graded using conventional histopathological methodology, and fat content was also quantitated in biopsy samples by measuring the steatotic area of the section using stereological point counting (SPC). Ultra-trace elemental analysis was utilized for determining manganese, iron, and copper using inductively coupled plasma sector field mass spectrometry (ICP-SFMS).

RESULTS

76 patients were included in the study. Hepatic manganese concentrations in patients with steatosis were lower than in patients without hepatic steatosis (3.8 ± 1.1 vs. 6.4 ± 1.8, P < 0.001). Similar results were seen for blood manganese levels and hepatic steatosis. We found a strong inverse correlation between steatosis grade and hepatic manganese content (ρ=-0.743, P < 0.001). Also, low levels of manganese independently predicted the presence of steatosis (aOR 0.07 [95%CI: 0.01-0.63]).

CONCLUSION

Patients with NAFLD, or other CLD and concomitant hepatic steatosis, showed lower levels of hepatic manganese content with increasing grade of steatosis.

Comparison of Inline R2* MRI versus FerriScan for liver iron quantification in patients on chelation therapy for iron overload: preliminary results

OBJECTIVES

MRI quantification of liver iron concentration (LIC) using R₂ or R₂* relaxometry requires offline post-processing causing reporting delays, administrative overhead, and added costs. A prototype 3D multi-gradient-echo pulse sequence, with inline post-processing, allows immediate calculation of LIC from an R₂* map (inline R₂*-LIC) without offline processing. We compared inline R₂*-LIC to FerriScan and offline R₂* calibration methods.

METHODS

Forty patients (25 women, 15 men; age 18-82 years), prospectively underwent FerriScan and the prototype sequence, which produces two R₂* maps, with and without fat modeling, as well as an inline R₂*-LIC map derived from the R₂* map with fat modeling, with informed consent. For each map, the following contours were drawn: ROIs, whole-axial-liver contour, and an exact copy of contour utilized by FerriScan. LIC values from the FerriScan report and those calculated using an alternative R₂ calibration were the reference standards. Results were compared using Pearson and interclass correlation coefficients (PCC, ICC), linear regression, Bland-Altman analysis, and estimation of area under the receiver operator curve (ROC-AUC).

RESULTS

Inline R₂*-LIC demonstrated good agreement with the reference standards. Compared to FerriScan, inline R₂*-LIC with whole-axial-liver contour, ROIs, and FerriScan contour demonstrated PCC of 94.8%, 94.8%, and 92%; ICC 93%, 92.7%, and 90.2%; regression slopes 1.004, 0.974, and 1.031; mean bias 5.54%, 10.91%, and 0.36%; and ROC-AUC estimates 0.903, 0.906, and 0.890 respectively. Agreement was maintained when adjusted for sex, age, diagnosis, liver fat content, and fat-water swap.

CONCLUSION

Inline R₂*-LIC provides robust and comparable quantification of LIC compared to FerriScan, without the need for offline post-processing.

KEY POINTS

• In patients being treated for iron overload with chelation therapy, liver iron concentration (LIC) is regularly assessed in order to monitor and adjust therapy. • Magnetic resonance imaging (MRI) is commonly used to quantify LIC. Several R₂ and R₂* methods are available, all of which require offline post-processing. • A novel R₂* MRI method allows for immediate calculation of LIC and provides comparable quantification of LIC to the FerriScan and recently published alternative R₂* methods.

Quantitative magnetic resonance imaging for chronic liver disease

Chronic liver disease (CLD) has rapidly increased in prevalence over the past two decades, resulting in significant morbidity and mortality worldwide. Historically, the clinical gold standard for diagnosis, assessment of severity, and longitudinal monitoring of CLD has been liver biopsy with histological analysis, but this approach has limitations that may make it suboptimal for clinical and research settings. Magnetic resonance (MR)-based biomarkers can overcome the limitations by allowing accurate, precise, and quantitative assessment of key components of CLD without the risk of invasive procedures. This review briefly describes the limitations associated with liver biopsy and the need for non-invasive biomarkers. It then discusses the current state-of-the-art for MRI-based biomarkers of liver iron, fat, and fibrosis, and inflammation.

Multiparametric MR mapping in clinical decision-making for diffuse liver disease

Accurate diagnosis, monitoring and treatment decisions in patients with chronic liver disease currently rely on biopsy as the diagnostic gold standard, and this has constrained early detection and management of diseases that are both varied and can be concurrent. Recent developments in multiparametric magnetic resonance imaging (mpMRI) suggest real potential to bridge the diagnostic gap between non-specific blood-based biomarkers and invasive and variable histological diagnosis. This has implications for the clinical care and treatment pathway in a number of chronic liver diseases, such as haemochromatosis, steatohepatitis and autoimmune or viral hepatitis. Here we review the relevant MRI techniques in clinical use and their limitations and describe recent potential applications in various liver diseases. We exemplify case studies that highlight how these techniques can improve clinical practice. These techniques could allow clinicians to increase their arsenals available to utilise on patients and direct appropriate treatments.

Liver fat accumulation measured by high-speed T2-corrected multi-echo magnetic resonance spectroscopy can predict risk of cholelithiasis

BACKGROUND

Liver fat accumulation is associated with increased cholesterol synthesis and hypersecretion of biliary cholesterol, which may be related to the development of cholelithiasis.

AIM

To investigate whether liver fat accumulation measured by high-speed T2-corrected multi-echo magnetic resonance spectroscopy (MRS) is a risk factor for cholelithiasis.

METHODS

Forty patients with cholelithiasis and thirty-one healthy controls were retrospectively enrolled. The participants underwent high-speed T2-corrected multi-echo single-voxel MRS of the liver at a 3T MR scanner. The proton density fat fraction (PDFF) and R2 value were calculated. Serum parameters and waist circumference (WC) were recorded. Spearman’s correlation analysis was used to analyze the relationship between PDFF, R2, and WC values. Multivariate logistic regression analysis was carried out to determine the significant predictors of the risk of cholelithiasis. Receiver operating characteristic curve (ROC) analysis was used to evaluate the discriminative performance of significant predictors.

RESULTS

Patients with cholelithiasis had higher PDFF, R2, and WC values compared with healthy controls (5.8% ± 4.2% vs 3.3% ± 2.4%, P = 0.001; 50.4 ± 24.8/s vs 38.3 ± 8.8/s, P = 0.034; 85.3 ± 9.0 cm vs 81.0 ± 6.9 cm, P = 0.030; respectively). Liver iron concentration extrapolated from R2 values was significantly higher in the cholelithiasis group (2.21 ± 2.17 mg/g dry tissue vs 1.22 ± 0.49 mg/g dry tissue, P = 0.034) than in the healthy group. PDFF was positively correlated with WC (r = 0.502, P < 0.001) and R2 (r = 0.425, P < 0.001). Multivariate logistic regression analysis showed that only PDFF was an independent risk factor for cholelithiasis (odds ratio = 1.79, 95%CI: 1.22-2.62, P = 0.003). ROC analysis showed that the area under the curve of PDFF was 0.723 for discriminating cholelithiasis from healthy controls, with a sensitivity of 55.0% and specificity of 83.9% when the cut-off value of PDFF was 4.4%.

CONCLUSION

PDFF derived from high speed T2-corrected multi-echo MRS can predict the risk of cholelithiasis.

Design and evaluation of quantitative MRI phantoms to mimic the simultaneous presence of fat, iron, and fibrosis in the liver

PURPOSE

To design, construct, and evaluate quantitative MR phantoms that mimic MRI signals from the liver with simultaneous control of three parameters: proton-density fat fraction (PDFF), R 2 ∗ , and T₁ . These parameters are established biomarkers of hepatic steatosis, iron overload, and fibrosis/inflammation, respectively, which can occur simultaneously in the liver.

METHODS

Phantoms including multiple vials were constructed. Peanut oil was used to modulate PDFF, MnCl₂ and iron microspheres were used to modulate R 2 ∗ , and NiCl₂ was used to modulate the T₁ of water (T_1,water ). Phantoms were evaluated at both 1.5 T and 3 T using stimulated-echo acquisition-mode MRS and chemical shift-encoded MRI. Stimulated-echo acquisition-mode MRS data were processed to estimate T_1,water , T_1,fat , R 2 , water ∗ , and R 2 , fat ∗ for each vial. Chemical shift-encoded MRI data were processed to generate PDFF and R 2 ∗ maps, and measurements were obtained in each vial. Measurements were evaluated using linear regression and Bland-Altman analysis.

RESULTS

High-quality PDFF and R 2 ∗ maps were obtained with homogeneous values throughout each vial. High correlation was observed between imaging PDFF with target PDFF (slope = 0.94-0.97, R² = 0.994-0.997) and imaging R 2 ∗ with target R 2 ∗ (slope = 0.84-0.88, R² = 0.935-0.943) at both 1.5 T and 3 T. The values of R 2 , fat ∗ and R 2 , water ∗ were highly correlated with slope close to 1.0 at both 1.5 T (slope = 0.90, R² = 0.988) and 3 T (slope = 0.99, R² = 0.959), similar to the behavior observed in vivo. The value of T_1,water (500-1200 ms) was controlled with varying NiCl₂ concentration, while T_1,fat (300 ms) was independent of NiCl₂ concentration.

CONCLUSION

Novel quantitative MRI phantoms that mimic the simultaneous presence of fat, iron, and fibrosis in the liver were successfully developed and validated.

Consensus-based technical recommendations for clinical translation of renal BOLD MRI

Harmonization of acquisition and analysis protocols is an important step in the validation of BOLD MRI as a renal biomarker. This harmonization initiative provides technical recommendations based on a consensus report with the aim to move towards standardized protocols that facilitate clinical translation and comparison of data across sites. We used a recently published systematic review paper, which included a detailed summary of renal BOLD MRI technical parameters and areas of investigation in its supplementary material, as the starting point in developing the survey questionnaires for seeking consensus. Survey data were collected via the Delphi consensus process from 24 researchers on renal BOLD MRI exam preparation, data acquisition, data analysis, and interpretation. Consensus was defined as ≥ 75% unanimity in response. Among 31 survey questions, 14 achieved consensus resolution, 12 showed clear respondent preference (65-74% agreement), and 5 showed equal (50/50%) split in opinion among respondents. Recommendations for subject preparation, data acquisition, processing and reporting are given based on the survey results and review of the literature. These technical recommendations are aimed towards increased inter-site harmonization, a first step towards standardization of renal BOLD MRI protocols across sites. We expect this to be an iterative process updated dynamically based on progress in the field.

Consensus-based technical recommendations for clinical translation of renal BOLD MRI

Harmonization of acquisition and analysis protocols is an important step in the validation of BOLD MRI as a renal biomarker. This harmonization initiative provides technical recommendations based on a consensus report with the aim to move towards standardized protocols that facilitate clinical translation and comparison of data across sites. We used a recently published systematic review paper, which included a detailed summary of renal BOLD MRI technical parameters and areas of investigation in its supplementary material, as the starting point in developing the survey questionnaires for seeking consensus. Survey data were collected via the Delphi consensus process from 24 researchers on renal BOLD MRI exam preparation, data acquisition, data analysis, and interpretation. Consensus was defined as ≥ 75% unanimity in response. Among 31 survey questions, 14 achieved consensus resolution, 12 showed clear respondent preference (65-74% agreement), and 5 showed equal (50/50%) split in opinion among respondents. Recommendations for subject preparation, data acquisition, processing and reporting are given based on the survey results and review of the literature. These technical recommendations are aimed towards increased inter-site harmonization, a first step towards standardization of renal BOLD MRI protocols across sites. We expect this to be an iterative process updated dynamically based on progress in the field.

Measurement of spleen fat on MRI-proton density fat fraction arises from reconstruction of noise

PURPOSE

This study compares splenic proton density fat fraction (PDFF) measured using confounder-corrected chemical shift-encoded (CSE)-MRI to magnetic resonance spectroscopy (MRS) in human patients at 3T.

METHODS

This was a prospectively designed ancillary study to various previously described single-center studies performed in adults and children with known or suspected nonalcoholic fatty liver disease. Patients underwent magnitude-based MRI (MRI-M), complex-based MRI (MRI-C), high signal-to-noise variants (Hi-SNR MRI-M and Hi-SNR MRI-C), and MRS at 3T for spleen PDFF estimation. PDFF from CSE-MRI methods were compared to MRS-PDFF using Wilcoxon signed-rank tests. Demographics were summarized descriptively. Spearman's rank correlations were computed pairwise between CSE-MRI methods. Individual patient measurements were plotted for qualitative assessment. A significance level of 0.05 was used.

RESULTS

Forty-seven patients (20 female, 27 male) including 12 adults (median 55 years old) and 35 children (median 12 years old). Median PDFF estimated by MRS, MRI-M, Hi-SNR MRI-M, MRI-C, and Hi-SNR MRI-C was 1.0, 2.3, 1.9, 2.2, and 2.0%. The four CSE-MRI methods estimated statistically significant higher spleen PDFF values compared to MRS (p < 0.0001 for all). Pairwise associations in spleen PDFF values measured by different CSE-MRI methods were weak, with the highest Spearman's rank correlations being 0.295 between MRI-M and Hi-SNR MRI-M; none were significant after correction for multiple comparisons. No qualitative relationship was observed between PDFF measurements among the various methods.

CONCLUSION

Overestimation of PDFF by CSE-MRI compared to MRS and poor agreement between related CSE-MRI methods suggest that non-zero PDFF values in human spleen are artifactual.

Susceptibility based multiparametric quantification of liver disease: Non-invasive evaluation of steatosis and iron overload

PURPOSE

To evaluate if single-voxel MR spectroscopy (MRS) of iron and fat correlates with biopsy results of hepatic steatosis and iron overload, and to compare MR-measurements with room-temperature susceptometer (RTS), ultrasound, controlled attenuation parameter (CAP) and serum ferritin.

MATERIAL AND METHODS

In this prospective study, a set of 42 patients out of 47 screened patients with several chronic liver diseases underwent MRI-examination at 1.5 T including R2-measurements by single-voxel high-speed T2-corrected multiecho spectroscopy, additional liver biopsy, abdominal ultrasound, CAP, and RTS. Routine blood and serum parameters were determined, including ferritin. Atomic absorption spectroscopy (AAS) and histologically confirmed extent of hepatic steatosis from liver biopsy were used as reference standard. For correlation of R2, RTS, CAP, ferritin, and ultrasound with results of AAS and histologically determined fat fraction of liver biopsy specimen, Spearman's and Pearson's correlation as well as receiver operating characteristics curve (ROC) analysis with cut-off values determined by maximizing Youden index was used.

RESULTS

MRS iron assessment correlated best with AAS, with a Pearson correlation coefficient of 0.715 (p < 0.001), followed by RTS 0.520 (p < 0.001), and serum ferritin 0.213 (p = 0.088, not significant). MRS fat quantification correlated best with the histological confirmed extent of steatosis hepatis with a Spearman correlation coefficient of 0.836 (p < 0.001), followed by CAP 0.604 (p < 0.001) and sonographically diagnosed steatosis 0.358 (p = 0.013).

CONCLUSION

MRS by T2-corrected multiecho single-voxel spectroscopy correlated best with histological results of hepatic fat and iron content compared to RTS, CAP, abdominal ultrasound, and ferritin. Non-invasive methods to assess hepatic fat and iron are of clinical interest for follow-up examinations of patients with chronic liver diseases, where repeated biopsy is not indicated.

Liver MRI susceptibility-weighted imaging (SWI) compared to T2* mapping in the presence of steatosis and fibrosis

PURPOSE

To show that both susceptibility-weighted imaging (SWI) and T2*-mapping are dependent on liver steatosis, which should be taken into account when using these parameters to grade liver fibrosis and cirrhosis.

METHODS

In this prospective study, a total of 174 patients without focal liver disease underwent multiparametric MRI at 3 T including SWI, T1- and T2* mapping, proton density fat fraction (PDFF) quantification and MR elastography. SWI, T2* and T1 were measured in the liver (4 locations), as well as in paraspinal muscles, to calculate the liver-to-muscle ratio (LMR). Liver and LMR values were compared among patients with different steatosis grades (PDFF < 5%, 5-10%, 10-20% and >20%), patients with normal, slightly increased and increased liver stiffness (<2.8 kPa, 2.8-3.5 kPa and >3.5 kPa, respectively). ANOVA with Bonferroni-corrected post hoc tests as well as a multivariate analysis were used to compare values among groups and parameters.

RESULTS

SWI and T2* both differed significantly among groups with different steatosis grades (p < 0.001). However, SWI allowed a better differentiation among liver fibrosis grades (p < 0.001) than did T2* (p = 0.05). SWI LMR (p < 0.001) and T2* LMR (p = 0.036) showed a similar performance in differentiating among liver fibrosis grades.

CONCLUSION

SWI and T2*-mapping are strongly dependent on the liver steatosis grades. Nevertheless, both parameters are useful predictors for liver fibrosis when using a multiparametric approach.