Comparison of T2, T1rho, and diffusion metrics in assessment of liver fibrosis in rats

Detecting Early-Stage Liver Fibrosis Using Macromolecular Proton Fraction Mapping Based on Spin-Lock MRI: Preliminary Observations

BACKGROUND

Liver fibrosis is characterized by macromolecule depositions. Recently, a novel technology termed macromolecular proton fraction quantification based on spin-lock magnetic resonance imaging (MPF-SL) is reported to measure macromolecule levels.

HYPOTHESIS

MPF-SL can detect early-stage liver fibrosis by measuring macromolecule levels in the liver.

STUDY TYPE

Retrospective.

SUBJECTS

Fifty-five participants, including 22 with no fibrosis (F0) and 33 with early-stage fibrosis (F1-2), were recruited.

FIELD STRENGTH/SEQUENCE

3 T; two-dimensional (2D) MPF-SL turbo spin-echo sequence, 2D spin-lock T1rho turbo spin-echo sequence, and multi-slice 2D gradient echo sequence.

ASSESSMENT

Macromolecular proton fraction (MPF), T1rho, liver iron concentration (LIC), and fat fraction (FF) biomarkers were quantified within regions of interest.

STATISTICAL TESTS

Group comparison of the biomarkers using Mann-Whitney U tests; correlation between the biomarkers assessed using Spearman's rank correlation coefficient and linear regression with goodness-of-fit; fibrosis stage differentiation using receiver operating characteristic curve (ROC) analysis. P-value < 0.05 was considered statistically significant.

RESULTS

Average T1rho was 41.76 ± 2.94 msec for F0 and 41.15 ± 3.73 msec for F1-2 (P = 0.60). T1rho showed nonsignificant correlation with either liver fibrosis (ρ = -0.07; P = 0.61) or FF (ρ = -0.14; P = 0.35) but indicated a negative correlation with LIC (ρ = -0.66). MPF was 4.73 ± 0.45% and 5.65 ± 0.81% for F0 and F1-2 participants, respectively. MPF showed a positive correlation with liver fibrosis (ρ = 0.59), and no significant correlations with LIC (ρ = 0.02; P = 0.89) or FF (ρ = 0.05; P = 0.72). The area under the ROC curve was 0.85 (95% confidence interval [CI] 0.75-0.95) and 0.55 (95% CI 0.39-0.71; P = 0.55) for MPF and T1rho to discriminate between F0 and F1-2 fibrosis, respectively.

DATA CONCLUSION

MPF-SL has the potential to diagnose early-stage liver fibrosis and does not appear to be confounded by either LIC or FF.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 3.

Quantitative Magnetization EXchange MRI Measurement of Liver Fibrosis Model in Rodents

BACKGROUND

Quantitative MRI can elucidate the complex microstructural changes in liver disease. The Magnetization EXchange (MEX) method estimates macromolecular fraction, such as collagen, and can potentially aid in this task.

HYPOTHESIS

MEX sequence, and its derived quantitative macromolecular fraction, should correlate with collagen deposition in rodents liver fibrosis model.

STUDY TYPE

Prospective.

ANIMAL MODEL

Sixteen adults Sprague-Dawley rats and 13 adults C57BL/6 strain mice given carbon tetrachloride (CCl₄ ) twice weekly for 6 or 8 weeks.

FIELD STRENGTH/SEQUENCE

A 7 T scanner. MEX sequence (selective suppression and magnetization exchange), spin-echo and gradient-echo scans.

ASSESSMENT

Macromolecular fraction (F) and T₁ were extracted for each voxel and for livers' regions of interest, additional to calculating the percentage of F > 0.1 pixels in F maps (high-F). Histology included staining with hematoxylin and eosin, picrosirius red and Masson trichrome, and inflammation scoring. Quantitative collagen percentage calculated using automatic spectral-segmentation of the staining.

STATISTICAL TESTS

Comparing CCl₄ -treated groups and controls using Welch's t-test and paired t-test between different time points. Pearson's correlation used between ROI MEX parameters or high-F fraction, and quantitative histology. F or T₁ , and inflammation scores were tested with one-sided t-test. P < 0.05 was deemed significant.

RESULTS

Rats: F values were significantly different after 6 weeks of treatment (0.10 ± 0.02) compared to controls (0.080 ± 0.003). After 8 weeks, F significantly increased (0.11 ± 0.02) in treated animals, while controls are not significant (0.0814 ± 0.0008, P = 0.079). F correlated with quantitative histology (R = 0.87), and T₁ was significantly different between inflammation scores (1: 1332 ± 224 msec, 2: 2007 ± 464 msec). Mice: F was significantly higher (0.062 ± 0.006) in treatment group compared to controls (0.042 ± 0.006). F and high-F fraction correlated with quantitative histology (R = 0.88; R = 0.84). T₁ was significantly different between inflammation scores (1:1366 ± 99 msec; 2:1648 ± 45 msec).

DATA CONCLUSION

MEX extracted parameters are sensitive to collagen deposition and inflammation and are correlated with histology results of mouse and rat liver fibrosis model.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

Myocardial Approximate Spin-lock Dispersion Mapping using a Simultaneous T2 and TRAFF2 Mapping at 3T MRI

Ischemic heart disease (IHD) is one of the leading causes of death worldwide. Myocardial infarction (MI) represents a third of all IHD cases, and cardiac magnetic resonance imaging (MRI) is often used to assess its damage to myocardial viability. Late gadolinium enhancement (LGE) is the current gold standard, but the use of gadolinium-based agents limits the clinical applicability in some patients. Spin-lock (SL) dispersion has recently been proposed as a promising non-contrast biomarker for the assessment of MI. However, at 3T, the required range of SL preparations acquired at different amplitudes suffers from specific absorption rate (SAR) limitations and off-resonance artifacts. Relaxation Along a Fictitious Field (RAFF) is an alternative to SL preparations with lower SAR requirements, while still sampling relaxation in the rotating frame. In this study, a single breath-hold simultaneous TRAFF2 and T2 mapping sequence is proposed for SL dispersion mapping at 3T. Excellent reproducibility (coefficient of variations lower than 10%) was achieved in phantom experiments, indicating good intrascan repeatability. The average myocardial TRAFF2, T2, and SL dispersion obtained with the proposed sequence (68.0±10.7 ms, 44.0±4.0 ms, and 0.4±0.2 ×10-4 s2, respectively) were comparable to the reference methods (62.7±11.7 ms, 41.2±2.4 ms, and 0.3±0.2x 10-4s2, respectively). High visual map quality, free of B0 and B1+ related artifacts, for T2, TRAFF2, and SL dispersion maps were obtained in phantoms and in vivo, suggesting promise in clinical use at 3T. Clinical relevance - and imaging promises non-contrast assessment of scar and focal fibrosis in a single breath-hold using approximate spin-lock dispersion mapping.

Metabolites Alterations and Liver Injury in Hepatic Encephalopathy Models Evaluated by Use of 7T-MRI

This study is to observe a thioacetamide (TAA) administered Hepatic encephalopathy (HE) model rats at three and ten days after TAA administration using liver MRI and brain MR Spectroscopy (MRS) by use of 7T-MRI. Forty-two Wistar rats (control group, n = 14) were intraperitoneally administered at 300 mg/kg (low-dose group, n = 14) or 400 mg/kg (high-dose group, n = 14) doses of TAA for induced of HE. At three days after TAA administration, glutamine (Gln) measured by MRS in high-dose and low-dose TAA groups showed significant increases in comparison to those of the control group (p < 0.05). Other metabolites measured by MRS showed no significant changes. Liver T1ρ and T2 relaxation times significantly increased three days after TAA injection compared to pre-injection. There was a correlation between Gln levels in the brain and the relaxation time of the liver. Furthermore, Gln levels and relaxation time changed depending on the TAA dose. The Gln concentration in the brain increased with the deterioration of liver function, as inferred from the prolonged relaxation time of the liver. The prolonged relaxation time of the liver corresponded with the level of Gln in the brain. Gln concentration for the alterations of brain metabolites and T1ρ relaxation time for the assessment of liver damage are useful markers for inter-organ association analysis in the HE model.

Evaluation of liver T1rho and T2 values in acute liver inflammation models using 7T-MRI

PURPOSE

We measured the T 1rho and T 2 values the liver of acute liver inflammation model mice administered carbon tetrachloride (CCl 4) after 3 days and 6 days after dispensed, and we compared and examined whether each relaxation time can be used for detect acute liver inflammation.

METHODS

To create an acute liver inflammation model, a mixture of 0.2 ml / 100 g of CCl 4 with an equal amount of Sesame Oil was administered once intraperitoneally to C57BL / 6JJmsSlc mice (n = 15). On the 3 days and 6 days after administration, we acquired T 1rho mapping images and T 2 mapping images of the liver under respiratory synchronization using for preclinical 7T-MRI, and we measured T 1rho and T 2 values and compared statistically.

RESULTS

The liver T 1rho value of control mice was 33.9 ± 2.5 ms before CCl 4 administration, 43.2 ± 4.9 ms (p < 0.01) on the 3 days post CCl 4 injection, and 41.0 ± 1.2 ms (p < 0.001) on the 6 days post CCl 4 injection. The rate showed a significant increase of 27% on the 3 days after, as well as significant increase of 21% on the 6 days after. On the other hand, the liver T 2 value of control mice was 26.7 ± 1.9 ms before CCl 4 administration, 31.5 ± 3.4 ms (p < 0.05) 3 days post CCl 4 injection, and 29.0 ± 2.0 ms (p = 0.06) 6 days post CCl4 injection. The rate 3 days after CCl 4 administration showed a significant increase of 18%, after 6 days rate increased 9%, but no significant difference was confirmed compared with normal mice.

CONCLUSIONS

The T 1rho value changed significantly compared to the T 2 value, and a continuous change was observed even after 6 days. T 1rho mapping can diagnose acute liver inflammation.

Diagnostic potential of T1ρ and T2 relaxations in assessing the severity of liver fibrosis and necro-inflammation

PURPOSE

To investigate the utility of T1ρ and T2 relaxations for assessing the severity of liver fibrosis (F stage) and necro-inflammation (A stage) in patients with chronic liver disease (CLD).

MATERIALS AND METHODS

We calculated T1ρ and T2 relaxations of the liver parenchyma in 82 patients who underwent liver surgery. F and A stages of enrolled patients were assessed by referring to surgically resected specimens. The relationships between T1ρ or T2 relaxation and F or A stage were assessed using one-way analysis of variance followed by Tukey's multiple comparison test, Spearman's rank correlation test and a receiver operating characteristic analysis.

RESULTS

The T1ρ and T2 values of the liver parenchyma were significantly increased as the F and A stages progressed. The T1ρ and T2 values showed significant differences between F0 and F4, between F1 and F4, and between F2 and F4. In addition, T1ρ values showed a significant difference between F0 and F3 as well. The highest diagnostic ability for fibrosis was obtained when differentiating ≥F3 from ≤F2 using T1ρ: the sensitivity was 82.8%, the specificity 79.2% and the area under the curve (AUC) 0.87. The sensitivity and AUC of T1ρ relaxation (46.9% and 0.67) were significantly higher than those of T2 relaxation (29.7% and 0.60) for differentiating ≥A1 from A0.

CONCLUSION

T1ρ and T2 relaxations have potential as a biochemical marker for assessing the severity of liver fibrosis and necro-inflammation. T1ρ relaxation may be slightly superior to T2 relaxation in terms of diagnostic ability for liver fibrosis and necro-inflammation.

Multiparameter magnetic resonance imaging of liver fibrosis in a bile duct ligation mouse model

BACKGROUND

Bile duct ligation (BDL) in animals is a classical method for mimicking cholestatic fibrosis. Although different surgical techniques have been described in rats and rabbits, mouse models can be more cost-effective and reproducible for investigating cholestatic fibrosis. Magnetic resonance imaging (MRI) has made great advances for noninvasive assessment of liver fibrosis. More comprehensive liver fibrotic features of BDL on MRI are important. However, the utility of multiparameter MRI to detect liver fibrosis in a BDL mouse model has not been assessed.

AIM

To evaluate the correlation between the pathological changes and multiparameter MRI characteristics of liver fibrosis in a BDL mouse model.

METHODS

Twenty-eight healthy adult male balb/c mice were randomly divided into four groups: sham, week 2 BDL, week 4 BDL, and week 6 BDL. Multiparameter MRI sequences, included magnetic resonance cholangiopancreatography, T1-weighted, T2-weighted, T2 mapping, and pre- and post-enhanced T1 mapping, were performed after sham and BDL surgery. Peripheral blood and liver tissue were collected after MRI. For statistical analysis, Student’s t-test and Pearson’s correlation coefficient were used.

RESULTS

Four mice died after BDL surgery; seven, six, five and six mice were included separately from the four groups. Signal intensities of liver parenchyma showed no difference on TI- and T2-weighted images. Bile duct volume, ΔT1 value, T2 value, and the rate of liver fibrosis increased steadily in week 2 BDL, week 4 BDL and week 6 BDL groups compared with those in the sham group (P < 0.01). Alanine aminotransferase and aspartate transaminase levels initially surged after surgery, followed by a gradual decline over time. Strong correlations were found between bile duct volume (r = 0.84), T2 value (r = 0.78), ΔT1 value (r = 0.62), and hepatic fibrosis rate (all P < 0.01) in the BDL groups.

CONCLUSION

The BDL mouse model induces changes that can be observed on MRI. The MRI parameters correlate with the hepatic fibrosis rate and allow for detection of cholestatic fibrosis.

Relaxivity-iron calibration in hepatic iron overload: Reproducibility and extension of a Monte Carlo model

The aim of this study was to reproduce relaxivity-iron calibration in hepatic iron overload using a Monte Carlo model, and further extend the model with multiple spin echo (MSE) imaging. As previously reported, relationships between relaxation rates ( R2* and single spin echo R₂ ) and liver iron concentration (LIC) can be characterized by a Monte Carlo model incorporating realistic liver structure, iron distribution, and proton mobility. In this study, relaxivity-iron calibration curves at 1.5 and 3.0 T were simulated using the Monte Carlo model. Furthermore, the model was extended with MSE imaging, and iron calibrations were evaluated using two different fitting models: mononexponential with a constant offset and nonmonoexponential. Results consistent with previous empirical calibrations and Monte Carlo predictions were accurately reproduced for relaxivity-iron calibration. The predicted R2* and single spin echo R₂ increased by a factor of 2.00 and 1.51, respectively, at 1.5 versus 3.0 T. MSE signals and their corresponding R₂ depended strongly on LIC, interecho time, and field strength. Preliminary results showed that a nonmonoexponential model accurately characterizes the simulated MSE signals, and that strong correlations were found between predicted relaxation parameters and LIC. In conclusion, relaxivity-iron calibration is reproducible using the proposed Monte Carlo model. Furthermore, this model can be readily extended to other important applications, including predicting signal behavior for MSE imaging.

Renal tubular dilation and fibrosis after unilateral ureter obstruction revealed by relaxometry and spin-lock exchange MRI

We evaluated the use of quantitative MRI relaxometry, including the dispersion of spin-lock relaxation with different locking fields, for detecting and assessing tubular dilation and fibrosis in a mouse model of unilateral ureter obstruction (UUO). C57BL/6 J and BALB/c mice that exhibit different levels of tubular dilation and renal fibrosis after UUO were subjected to MR imaging at 7 T. Mice were imaged before UUO surgery, and at 5, 10 and 15 days after surgery. We acquired maps of relaxation rates and fit the dispersion of spin-lock relaxation rates R1ρ at different locking fields (frequencies) to a model of exchanging water pools, and assessed the sensitivity of the derived quantities for detecting tubular dilation and fibrosis in kidney. Histological scores for tubular dilation and fibrosis, based on luminal space and positive fibrotic areas in sections, were obtained for comparison. Histology detected extensive tubular dilation and mild to moderate fibrosis in the UUO kidneys, in which enlargement of luminal space, deposition of collagen, and reductions in capillary density were observed in the cortex and outer stripe of the outer medulla. Relaxation rates R1 , R2 and R1ρ clearly decreased in these regions of UUO kidneys longitudinally. While R1 showed the highest detectability to tubular dilation and overall changes in UUO kidneys, Sρ , a parameter derived from R1ρ dispersion data, showed the highest correlation with renal fibrosis in UUO. While relaxation parameters are sensitive to tubular dilation in UUO kidneys, Sρ depends primarily on the average exchange rate between water and other chemically shifted resonances such as hydroxyls and amides, and provides additional specific information for evaluating fibrosis in kidney disease.

Staging Liver Fibrosis: Comparison of Native T1 Mapping, T2 Mapping, and T1ρ: An Experimental Study in Rats With Bile Duct Ligation and Carbon Tetrachloride at 11.7 T MRI

BACKGROUND

T1, T2, and T1ρ might be potential biomarkers for assessing liver fibrosis. However, few studies reported the value of them in different animal models.

PURPOSE

To investigate and compare the performances of T1, T2, and T1ρ for noninvasively staging liver fibrosis in bile duct ligation (BDL) or carbon tetrachloride (CCl₄ ) model.

STUDY TYPE

Prospective animal model.

SUBJECTS

Liver fibrosis was induced by BDL or injection of CCl₄ in 120 rats.

FIELD STRENGTH/SEQUENCE

11.7 T, T1 mapping with 10 repetition times, T2 mapping with 32 echo times, and T1ρ with 10 spin-lock times.

ASSESSMENT

T1, T2, and T1ρ were measured and correlated with liver fibrosis stages, as well as the degree of inflammation, steatosis, iron deposition, and the expression of cytokeratin 19. The discriminative performance of T1, T2, and T1ρ for staging liver fibrosis was compared.

STATISTICAL TESTS

One-way analysis of variance (ANOVA), Spearman's correlation analysis, factorial design ANOVA, and receiver operating characteristic curves (P < 0.05 was considered statistically significant).

RESULTS

T1, T2, and T1ρ (BDL: rho = 0.73, 0.85, 0.68; CCl₄ : rho = 0.80, 0.29, 0.61) were significantly correlated with liver fibrosis stages, while there was no significant difference in T2 among stage F0-F4 in the CCl₄ model (P = 0.204). The area under the curves (AUCs) range of T1, T2, and T1ρ for predicting ≥F1, ≥F2, ≥F3, and F4 were 0.76-0.95, 0.89-0.98, and 0.80-0.94 in the CCl₄ model. For the CCl₄ model, the AUCs range of T1, T2, and T1ρ for predicting ≥F1, ≥F2, ≥F3, and F4 were 0.83-0.95, 0.61-0.74, and 0.73-0.89, respectively. T2 had significantly higher AUC in the BDL model than CCl₄ model for diagnosing liver fibrosis.

DATA CONCLUSION

The most sensitive and accurate method for staging liver fibrosis appeared to be T1 in our animal models followed by T1ρ. T2 may not be suitable for evaluating liver fibrosis.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 2.

The feasibility of T2 mapping in the assessment of hepatic steatosis, inflammation, and fibrosis in patients with non-alcoholic fatty liver disease: a preliminary study

AIM

To determine the feasibility of magnetic resonance imaging T2 mapping in the quantification of liver steatosis in patients with biopsy-proven non-alcoholic fatty liver disease (NAFLD), and to assess the effect of inflammation and fibrosis on T2 values of the liver.

MATERIAL AND METHODS

Twenty-three consecutive patients with biopsy-proven NAFLD who underwent T2 mapping between December 2013 and September 2014 were included in this study. All patients underwent fast spin echo multi-echo sequence with eight echoes for T2 measurements.

RESULTS

The mean liver T2 value and percentage of histological steatosis was 64.9 ± 7.4 ms and 46.5 ± 27.6%, respectively. There was a good correlation between the liver T2 value and histology-determined steatosis (r = 0.780, p<0.001) and grade of steatosis (r_s = 0.779, p<0.001). The mean T2 value in patients with definitive non-alcoholic steatohepatitis (NASH) was significantly higher in comparison with patients without NASH (69 ± 7.37 versus 61.73 ± 5.99 ms, p=0.016). The correlation between T2 value and NAFLD activity score (NAS) was significant (r_s = 0.443, p=0.034); however, the correlation disappeared after adjustment for hepatic steatosis and fibrosis (r=0.131, p=0.572). There was a close inverse correlation between T2 value and fibrosis stage after adjusting for hepatic steatosis (r=-0.536, p=0.012).

CONCLUSION

T2 mapping can be used for quantification of hepatic steatosis, as there is a close correlation between T2 relaxation values and histology-determined steatosis. Patients with definite NASH have increased T2 values and there is an inverse correlation between the T2 value and fibrosis stage of the liver. T2 mapping in NAFLD may be a useful clinical tool for disease assessment and prognostication.

Correlation of Native Liver Parenchyma T1 and T2 Relaxation Times and Liver Synthetic Function Tests: A Pilot Study

MR relaxometry increasingly contributes to liver imaging. Studies on native relaxation times mainly describe relation to the presence of fibrosis. The hypothesis was that relaxation times are also influenced by other inherent factors, including changes in liver synthesis function. With the approval of the local ethics committee and written informed consent, data from 94 patients referred for liver MR imaging, of which 20 patients had cirrhosis, were included. Additionally to standard sequences, both native T1 and T2 parametric maps and T1 maps in the hepatobiliary phase of gadoxetate disodium were acquired. Associations with laboratory variables were assessed. Altogether, there was a negative correlation between albumin and all acquired relaxation times in cirrhotic patients. In non-cirrhotic patients, only T1 values exhibited a negative correlation with albumin. In all patients, bilirubin correlated significantly with post-contrast T1 relaxation times, whereas native relaxation times correlated only in cirrhotic patients. Evaluating patients with pathological INR values, post-contrast relaxation times were significantly higher, whereas native relaxation times did not correlate. In conclusion, apart from confirming the value of hepatobiliary phase T1 mapping, our results show a correlation of native T1 with serum albumin even in non-cirrhotic liver parenchyma, suggesting a direct influence of liver’s synthesis capacity on T1 relaxation times.

Zi Qi Decoction Alleviates Liver Fibrosis by Inhibiting the Toll-Like Receptor 4 (TLR4)-Related Nuclear Factor kappa b (NF-κB) and Mitogen-Activated Protein Kinase (MAPK) Signaling Pathways

Background

Hepatic stellate cells (HSCs) play a vital role in hepatic fibrogenesis. Our recent clinical study indicated that the Zi Qi decoction, a Traditional Chinese Medicine formula, exhibited good efficacy in alleviating liver fibrosis, but the underlying mechanism remains elusive.

Material/Methods

Rats repeatedly injected with CCl₄ and cells stimulated with lipopolysaccharide were used as in vivo and in vitro models for liver fibrosis, respectively. The viability of LX-2 cells was evaluated with MTT assay. Relative messenger RNA (mRNA) expression of representative extracellular matrix (ECM) components was detected with real-time quantitative polymerase chain reaction (RT-qPCR). Moreover, total and phosphorylation levels of ECM proteins and pathway-related proteins were detected with western blotting. Immunofluorescent staining was used to show the nuclear translocation of nuclear factor kappa b (NF-κB) p65. Hematoxylin & eosin (H&E) and Masson trichrome staining and immunohistochemistry were performed to evaluate the extent of liver fibrosis. The levels of alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyl transpeptidase (GGT), Hyp, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were tested with an enzyme-linked immunosorbent assay. In addition, 7.0T micro-magnetic resonance imaging (micro-MRI) was used to evaluate the severity of hepatic damage.

Results

The Zi Qi decoction inhibited lipopolysaccharide-mediated upregulation of mRNA and protein levels of representative ECM proteins both in vivo and in vitro. The Zi Qi decoction also suppressed activation of the Toll-like receptor 4 (TLR4)-related NF-κB signaling pathway and subsequently inhibited the nuclear translocation of activated NF-κB. Moreover, another TLR4 downstream pathway, mitogen-activated protein kinase (MAPK), was simultaneously restrained. The results of liver pathology and MRI in rat models also suggested the efficacy of the Zi Qi decoction in attenuating liver damage.

Conclusions

The Zi Qi decoction inhibited liver fibrosis by inhibiting the TLR4-related NF-κB and MAPK signaling pathways and preventing activation of HSCs.

MRI Measures of Murine Liver Fibrosis

BACKGROUND

An imaging method that allows quantitative fibrosis estimates is needed to facilitate the diagnosis of chronic liver disease. Amide proton transfer (APT) and tissue sodium concentration (TSC) estimates could meet this need.

HYPOTHESIS

APT and TSC estimates correlate with fibrosis in a mouse model of chronic liver disease.

STUDY TYPE

Prospective.

PHANTOMS/ANIMAL MODEL

Male C57Bl/6 mice given CCl₄ or vehicle (N = 8 each) twice weekly for 16 weeks.

FIELD STRENGTH/SEQUENCE

Liver T₁ (Look-Locker gradient recalled echo [GRE] sequence), T₂ (multiecho spin echo sequence), T_1rho (fast spin echo sequence with 500 Hz spin locking pulse), and APT (GRE sequence with off-resonance pulses) data were acquired at 7 T at 12 and 16 weeks. Liver sodium data (multiple echo GRE sequence) were acquired at 12 weeks at 9.4 T.

ASSESSMENT

Liver proton T₁ , T₂ , T_1rho , APT, sodium T₂ *, and TSC were calculated. Histological measures included Sirius Red, hematoxylin and eosin, liver hydroxyproline content, and serum alanine transaminase (ALT).

STATISTICAL TESTS

Welch's two-sided t-test was used to test for differences between control and CCl₄ -treated groups for serum ALT, hydroxyproline, Sirius Red staining, T₁ , T₂ , T_1rho , APT, TSC, and sodium T₂ *. Pearson's correlations between liver T₁ , APT, TSC, or sodium T₂ * with Sirius Red staining and hydroxyproline levels were calculated.

RESULTS

APT was significantly different (P < 0.05) between groups in the left liver lobe at 16 weeks (CCl₄ : 8.0% ± 1.2%, controls: 6.2% ± 1.0%), as were average liver TSC at 12 weeks (CCl₄ : 38 mM ± 5 mM, controls: 27 mM ± 2 mM), and average sodium liver T₂ * at 12 weeks (CCl₄ : 10 msec ± 1.0 msec, controls: 12 msec ± 1.9 msec). APT, TSC, and sodium T₂ * correlated significantly (P < 0.05) with Sirius Red staining and hydroxyproline levels.

DATA CONCLUSION

Liver TSC and APT significantly correlated with histopathologic markers of fibrosis in this mouse model.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

T2 Values for Diagnosing Acute-on-Chronic Liver Failure in Hepatitis B Patients

OBJECTIVES

The aim of this study was to investigate the value of hepatic T2 imaging for the evaluation of chronic hepatitis-B-related acute-on-chronic liver failure (HBV-ACLF).

METHODS

Three groups of patients underwent liver MRI utilising m-GRASE sequence (multi-echo gradient and spin echo): HBV-ACLF patients (n = 28), chronic hepatitis B patients (n = 11), and healthy control patients (n = 14). A T₂ image was produced using post-processing software, and the mean T₂ (relaxation time) value was calculated. Blood biochemical indices for the HBV-ACLF and Chronic Hepatitis B were obtained within 2 days pre- or post-MR scanning. The patients' T₂ values, and the correlation between their biochemical indices and T₂ values were analysed. A receiver operating characteristic curve was employed to evaluate the efficiency of utilising T₂ values in the diagnosis of HBV-ACLF.

RESULTS

There were significant variations in the T₂ values (χ² = 19.074, P < 0.001) among the 3 groups. The AUC of T₂ values for diagnosing HBV-ACLF was 0.86 (P < 0.001), with a cut-off value of 57.73 ms. A moderately positive correlation was observed between the T2 value and the international normalised ratio, prothrombin time, and hyaluronic acid values (r_s = 0.65, P < 0.001; r_s = 0.67, P < 0.001; r_s = 0.39, P = 0.025). A moderately negative correlation was observed between the T₂ value and the prothrombin activity, albumin, and prealbumin values (r_s = -0.67, P < 0.001; r_s = -0.48, P = 0.004; r_s = -0.37, P = 0.030).

CONCLUSION

T₂ values could accurately reflect liver function state, as they correlated well with certain biochemical indices, illustrating good diagnostic efficiency for diagnosing HBV-ACLF.

Quantitative T2 mapping of rats with chronic hepatitis

The aim of the study was to explore the diagnostic value of T2 mapping in an experimental rat model of chronic liver disease. Chronic hepatitis was induced in Sprague-Dawley male rats (n=88) by intraperitoneal and abdominal subcutaneous injection of carbon tetrachloride in olive oil. The normal control rats (n=12) were similarly injected with the same dose of normal saline. All rats were randomly selected and subjected to T2-weighted/spectral adiabatic inversion recovery and multiple gradient- and spin-echo sequence. After scanning, rats were sacrificed immediately and livers removed for staining with hematoxylin and eosin, as well as Masson's trichrome, to determine the pathological stage of hepatic fibrosis, necroinflammatory activity and steatosis. The T2 values were measured and associated with histopathological findings. The T2 values were significantly associated with hepatic fibrosis (P<0.05), but not with hepatitis (P>0.05) or steatosis (P>0.05). By partial correlation analysis, a significant positive correlation was observed between the T2 values and stages of liver fibrosis (r=0.820; P<0.05). T2 values increased with progressive hepatic fibrosis. The differences between T2 values and stages of liver fibrosis were statistically significant. Statistically significant differences were observed between different stages of liver fibrosis (P<0.05), with an area under the curve value of 0.944 for predicting stage F1 or greater, 0.942 for stage F2 or greater, 0.958 for stage F3 or greater, and 0.948 for F4. Thus, the T2 value is one of the quantitative indices of imaging and accurately reflects the stages of liver fibrosis.

Fast multicomponent 3D-T1ρ relaxometry

NMR relaxometry can provide information about the relaxation of the magnetization in different tissues, increasing our understanding of molecular dynamics and biochemical composition in biological systems. In general, tissues have complex and heterogeneous structures composed of multiple pools. As a result, bulk magnetization returns to its original state with different relaxation times, in a multicomponent relaxation. Recovering the distribution of relaxation times in each voxel is a difficult inverse problem; it is usually unstable and requires long acquisition time, especially on clinical scanners. MRI can also be viewed as an inverse problem, especially when compressed sensing (CS) is used. The solution of these two inverse problems, CS and relaxometry, can be obtained very efficiently in a synergistically combined manner, leading to a more stable multicomponent relaxometry obtained with short scan times. In this paper, we will discuss the details of this technique from the viewpoint of inverse problems.

T1ρ magnetic resonance fingerprinting

T_1ρ relaxation imaging is a quantitative imaging technique that has been used to assess cartilage integrity, liver fibrosis, tumors, cardiac infarction, and Alzheimer's disease. T₁ , T₂ , and T_1ρ relaxation time constants have each demonstrated different degrees of sensitivity to several markers of fibrosis and inflammation, allowing for a potential multi-parametric approach to tissue quantification. Traditional magnetic resonance fingerprinting (MRF) has been shown to provide quick, quantitative mapping of T₁ and T₂ relaxation time constants. In this study, T_1ρ relaxation is added to the MRF framework using spin lock preparations. An MRF sequence involving an RF-spoiled sequence with T_R , flip angle, T_1ρ , and T₂ preparation variation is described. The sequence is then calibrated against conventional T₁ , T₂ , and T_1ρ relaxation mapping techniques in agar phantoms and the abdomens of four healthy volunteers. Strong intraclass correlation coefficients (ICC > 0.9) were found between conventional and MRF sequences in phantoms and also in healthy volunteers (ICC > 0.8). The highest ICC correlation values were seen in T₁ , followed by T_1ρ and then T₂ . In this study, T_1ρ relaxation has been incorporated into the MRF framework by using spin lock preparations, while still fitting for T₁ and T₂ relaxation time constants. The acquisition of these parameters within a single breath hold in the abdomen alleviates the issues of movement between breath holds in conventional techniques.

Non-Gaussian Diffusion Models and T1 rho Quantification in the Assessment of Hepatic Sinusoidal Obstruction Syndrome in Rats

BACKGROUND

Non-Gaussian diffusion models and T₁ rho quantification may reflect the changes in tissue heterogeneity in hepatic sinusoidal obstruction syndrome (SOS).

PURPOSE

To investigate the feasibility of diffusion kurtosis imaging (DKI), stretched exponential model (SEM), and T₁ rho quantification in detecting and staging SOS in a monocrotaline (MCT)-induced rat model.

STUDY TYPE

Animal study.

POPULATION

Thirty male Sprague-Dawley rats gavaged with MCT to induce hepatic SOS and six male rats without any intervention.

FIELD STRENGTH/SEQUENCE

3.0T, DWI with five b-values (0-2000 s/mm² ) and T₁ rho with five spin lock times (1-60 msec).

ASSESSMENT

MRI was performed 1 day before and 1, 3, 5, 7, and 10 days after MCT administration. The corrected apparent diffusion coefficient (D_app ), kurtosis coefficient (K_app ), distributed diffusion coefficient (DDC), and intravoxel water molecular diffusion heterogeneity (α) were calculated from the corresponding non-Gaussian diffusion model. The T₁ rho value was calculated using a monoexponential model. Specimens obtained from the six timepoints were categorized into normal liver (n = 6), early-stage (n = 16), and late-stage (n = 14) SOS in accordance with the pathological score.

STATISTICAL TESTS

Parametric statistical methods and receiver operating characteristic (ROC) curves were employed to determine diagnostic accuracy.

RESULTS

The D_app , K_app , DDC, α, and T₁ rho values were correlated with pathological score with r values of -0.821, 0.726, -0.828, -0.739, and 0.714 (all P < 0.001), respectively. DKI (combined D_app and K_app ) and SEM (combined DDC and α) were better than T₁ rho for staging SOS. The areas under the ROC curve of DKI, SEM, and T₁ rho for differentiating normal liver and early-stage SOS were 0.97, 1.00, and 0.79, whereas those of DKI, SEM, and T₁ rho for differentiating early-stage and late-stage SOS were 1.00, 0.97, and 0.92, respectively.

DATA CONCLUSION

DKI, SEM, and T₁ rho may be helpful in staging SOS.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2 J. Magn. Reson. Imaging 2020;52:1110-1121.

Spin-lock relaxation rate dispersion reveals spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney

PURPOSE

To develop and evaluate a reliable non-invasive means for assessing the severity and progression of fibrosis in kidneys. We used spin-lock MR imaging with different locking fields to detect and characterize progressive renal fibrosis in an hHB-EGF^Tg/Tg mouse model.

METHODS

Male hHB-EGF^Tg/Tg mice, a well-established model of progressive fibrosis, and age-matched normal wild type (WT) mice, were imaged at 7T at ages 5-7, 11-13, and 30-40 weeks. Spin-lock relaxation rates R_{1 ρ} were measured at different locking fields (frequencies) and the resultant dispersion curves were fit to a model of exchanging water pools. The obtained MRI parameters were evaluated as potential indicators of tubulointerstitial fibrosis in kidney. Histological examinations of renal fibrosis were also carried out post-mortem after MRI.

RESULTS

Histology detected extensive fibrosis in the hHB-EGF^Tg/Tg mice, in which collagen deposition and reductions in capillary density were observed in the fibrotic regions of kidneys. R₂ and R_{1 ρ} values at different spin-lock powers clearly dropped in the fibrotic region as fibrosis progressed. There was less variation in the asymptotic locking field relaxation rate R 1 ρ ∞ between the groups. The exchange parameter S_ρ and the inflection frequency ω_infl changed by larger factors.

CONCLUSION

Both S_ρ and ω_infl depend primarily on the average exchange rate between water and other chemically shifted resonances such as hydroxyls and amides. Spin-lock relaxation rate dispersion, rather than single measurements of relaxation rates, provides more comprehensive and specific information on spatiotemporal changes associated with tubulointerstitial fibrosis in murine kidney.

Liver injury monitoring, fibrosis staging and inflammation grading using T1rho magnetic resonance imaging: an experimental study in rats with carbon tetrachloride intoxication

Background

To investigate the merit of T1rho relaxation for the evaluation of liver fibrosis, inflammatory activity, and liver injury monitoring in a carbon tetrachloride (CCl₄)-induced rat model.

Methods

Model rats from CCl₄-induced liver fibrosis (fibrosis group: n = 41; regression group: n = 20) and control (n = 11) groups underwent black blood T1rho magnetic resonance (MR) imaging (MRI). Injection of CCl₄ was done twice weekly for up to 12 weeks in the fibrosis group and for up to 6 weeks in the regression group. MR scanning time points were at baseline and at 2, 4, 6, 8, 10 and 12 weeks after CCl₄ injection in the fibrosis group and at baseline and at 2, 4, 6 (CCl₄ withdrawal), 7, 8, 10 and 12 weeks in the regression group.

Results

In the fibrosis group, liver T1rho values increased gradually within week 8 and then decreased. In the regression group, T1rho values dropped gradually after the withdrawal of CCl₄ and fell below those at baseline. The T1rho values at S0 were lower than those at any other stage (all P < 0.05). The T1rho values at G0 were significantly lower than those at any other grade, and G1 was lower than G2 (all P < 0.01). The T1rho values mildly correlated with fibrosis stages (r = 0.362) and moderately correlated with grades of inflammation (r = 0.568). The T1rho values of rats with the same inflammation grades showed no significant difference among different fibrosis stages, and the T1rho values at S3 showed a significant difference among different grades of inflammation (P = 0.024). Inflammation grade was an independent variable associated with T1rho values (P < 0.001).

Conclusion

T1rho MRI can be used to monitor CCl₄-induced liver injury, and inflammatory activity had a greater impact on liver T1rho values than fibrosis.

Volumetric multicomponent T1ρ relaxation mapping of the human liver under free breathing at 3T

PURPOSE

To develop a 3D sequence for T_1ρ relaxation mapping using radial volumetric encoding (3D-T_1ρ -RAVE) and to evaluate the multi relaxation components in the liver of healthy controls and chronic liver disease (CLD) patients.

METHODS

Fat saturation and T_1ρ preparation modules were followed by a train of gradient-echo acquisitions and T₁ restoration delay. The series of T_1ρ -weighted images were fitted using mono-exponential, bi-exponential, and stretched-exponential models. The repeatability and reproducibility of the proposed technique were evaluated on National Institute of Standards and Technology phantom by calculating the coefficient of variation between test-retest scans on the same scanner and between two different 3T scanners, respectively. Mann-Whitney U-test was performed to assess differences in T_1ρ components among patients (n = 3) and a control group (n = 10).

RESULTS

The phantom study showed an error of 8.9% and 11.5% in mono T₂ relaxation time measurement relative to the reference on 2 different scanners. The coefficient of variation for test-retest scans performed on the same scanner was 5.7% and 2.4% for scans performed on 2 scanners. The comparison between healthy controls and CLD patients showed a significant difference (P < .05) in mono relaxation time (P = .002), stretched-exponential relaxation parameter (P = .04). The Akaike information criteria C criterion showed 2.53 ± 0.9% (2.3 ± 0.3% for CLD) of the voxels are bi-exponential while in 65.3 ± 5.8% (81.2 ± 0.06% for CLD) of the liver voxels, the stretched-exponential model was preferred.

CONCLUSION

The 3D-T_1ρ -RAVE sequence allows volumetric, multicomponent T_1ρ assessment of the liver during free breathing and can distinguish between healthy volunteers and CLD patients.

Image Quality and ADC Assessment in Turbo Spin-Echo and Echo-Planar Diffusion-Weighted MR Imaging of Tumors of the Head and Neck

RATIONALE AND OBJECTIVES

We aimed to compare the distortion ratio (DR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) between turbo spin-echo (TSE)-diffusion-weighted imaging (DWI) and echo-planar imaging (EPI)-DWI of the orofacial region and prove the usefulness of TSE-DWI for the differential diagnosis of orofacial lesions.

MATERIALS AND METHODS

The DR, SNR, and CNR of both sequences were compared in 42 cases. Then, the apparent diffusion coefficient (ADC) of various orofacial lesions obtained by TSE-DWI was investigated in 143 lesions.

RESULTS

In the first study, 38 of 42 cases were analyzed. TSE-DWI showed a significantly lower DR (p < 0.05) and higher SNR and CNR than EPI-DWI (p < 0.05), indicating the superiority of TSE-DWI. In the second study, 114 cases (79.3%) were successfully analyzed. When lesions were divided into cysts, benign tumors, squamous cell carcinoma, malignant lymphoma, and other malignant tumors (OT), significant differences were observed in all pairs of lesions (p < 0.05) except squamous cell carcinoma and OT (p = 0.877). The area under the curve for distinguishing benign from malignant tumors was 0.80 with a cutoff ADC of 1.29 × 10^-3 mm²/s.

CONCLUSION

TSE-DWI produced better quality images than EPI-DWI. TSE-DWI yields the high possibility of obtaining ADC in the orofacial region, and this value was considered useful for the differential diagnosis of orofacial lesions.

Increased extracellular volume in the liver of pediatric Fontan patients

BACKGROUND

Patients with single ventricle physiology are at increased risk for developing liver fibrosis. Its extent and prevalence in children with bidirectional cavopulmonary connection (BCPC) and Fontan circulation are unclear. Extracellular volume fraction (ECV), derived from cardiovascular magnetic resonance (CMR) and T1 relaxometry, reflect fibrotic remodeling and/or congestion in the liver. The aim of this study was to investigate whether pediatric patients with single ventricle physiology experience increased native T1 and ECV as markers of liver fibrosis/congestion.

METHODS

Hepatic native T1 times and ECV, using a cardiac short axis modified Look-Locker inversion recovery sequence displaying the liver, were measured retrospectively in children with BCPC- and Fontan circulations and compared to pediatric controls.

RESULTS

Hepatic native T1 time were increased in Fontan patients (n = 62, 11.4 ± 4.4 years, T1 762 ± 64 ms) versus BCPC patients (n = 20, 2.8 ± 0.9 years, T1 645 ± 43 ms, p = 0.04). Both cohorts had higher T1 than controls (n = 44, 13.7 ± 2.9 years, T1 604 ± 54 ms, p < 0.001 for both). ECV was 41.4 ± 4.8% in Fontan and 36.4 ± 4.8% in BCPC patients, respectively (p = 0.02). In Fontan patients, T1 values correlated with exposure to cardiopulmonary bypass time (R = 0.3, p = 0.02), systolic and end diastolic volumes (R = 0.3, p = 0.04 for both) and inversely with oxygen saturations and body surface area (R = -0.3, p = 0.04 for both). There were no demonstrable associations of T1 or ECV with central venous pressure or age after Fontan.

CONCLUSION

Fontan and BCPC patients have elevated CMR markers suggestive of hepatic fibrosis and/or congestion, even at a young age. The tissue changes do not appear to be related to central venous pressures.

TRIAL REGISTRATION

Retrospectively registered data.

Combined morphological and functional liver MRI using spin-lattice relaxation in the rotating frame (T1ρ) in conjunction with Gadoxetic Acid-enhanced MRI

Noninvasive early detection of liver cirrhosis and fibrosis is essential for management and therapy. The aim was to investigated whether a combination of the functional parameter relative enhancement (RE) on Gadoxetic Acid magnetic resonance imaging (Gd-EOB-DTPA-enhanced MRI) and the fibrosis parameter T1ρ distinguishes cirrhosis and healthy liver. We analyzed patients with Gd-EOB-DTPA-enhanced MRI and T1ρ mapping. Signal intensity was measured before and after contrast; RE was calculated. T1ρ was measured with circular regions of interest (T1ρ-cROI). A quotient of RE and T1ρ-cROI was calculated: the fibrosis function quotient (FFQ). Cirrhosis was evaluated based on morphology and secondary changes. 213 datasets were included. The difference between cirrhotic and noncirrhotic liver was 51.11 ms vs. 47.56 ms for T1ρ-cROI (p < 0.001), 0.59 vs. 0.70 for RE (p < 0.001), and 89.53 vs. 70.83 for FFQ (p < 0.001). T1ρ-cROI correlated with RE, r = −0.14 (p < 0.05). RE had an AUC of 0.73. The largest AUC had the FFQ with 0.79. The best cutoff value was 48.34 ms for T1ρ-cROI, 0.70 for RE and 78.59 ms for FFQ. In conclusion T1ρ and RE can distinguish between cirrhotic and noncirrhotic liver. The FFQ, which is the combination of the two, improves diagnostic performance.

Putting it all together: established and emerging MRI techniques for detecting and measuring liver fibrosis

Chronic injury to the liver leads to inflammation and hepatocyte necrosis, which when untreated can lead to myofibroblast activation and fibrogenesis with deposition of fibrous tissue. Over time, liver fibrosis can accumulate and lead to cirrhosis and end-stage liver disease with associated portal hypertension and liver failure. Detection and accurate measurement of the severity of liver fibrosis are important for assessing disease severity and progression, directing patient management, and establishing prognosis. Liver biopsy, generally considered the clinical standard of reference for detecting and measuring liver fibrosis, is invasive and has limitations, including sampling error, relatively high cost, and possible complications. For these reasons, liver biopsy is suboptimal for fibrosis screening, longitudinal monitoring, and assessing therapeutic efficacy. A variety of established and emerging qualitative and quantitative noninvasive MRI methods for detecting and staging liver fibrosis might ultimately serve these purposes. In this article, we review multiple MRI methods for detecting and measuring liver fibrosis and discuss the diagnostic performance and specific strengths and limitations of the various techniques.

Regularly incremented phase encoding - MR fingerprinting (RIPE-MRF) for enhanced motion artifact suppression in preclinical cartesian MR fingerprinting

PURPOSE

The regularly incremented phase encoding-magnetic resonance fingerprinting (RIPE-MRF) method is introduced to limit the sensitivity of preclinical MRF assessments to pulsatile and respiratory motion artifacts.

METHODS

As compared to previously reported standard Cartesian-MRF methods (SC-MRF), the proposed RIPE-MRF method uses a modified Cartesian trajectory that varies the acquired phase-encoding line within each dynamic MRF dataset. Phantoms and mice were scanned without gating or triggering on a 7T preclinical MRI scanner using the RIPE-MRF and SC-MRF methods. In vitro phantom longitudinal relaxation time (T₁ ) and transverse relaxation time (T₂ ) measurements, as well as in vivo liver assessments of artifact-to-noise ratio (ANR) and MRF-based T₁ and T₂ mean and standard deviation, were compared between the two methods (n = 5).

RESULTS

RIPE-MRF showed significant ANR reductions in regions of pulsatility (P < 0.005) and respiratory motion (P < 0.0005). RIPE-MRF also exhibited improved precision in T₁ and T₂ measurements in comparison to the SC-MRF method (P <  0.05). The RIPE-MRF and SC-MRF methods displayed similar mean T₁ and T₂ estimates (difference in mean values < 10%).

CONCLUSION

These results show that the RIPE-MRF method can provide effective motion artifact suppression with minimal impact on T₁ and T₂ accuracy for in vivo small animal MRI studies. Magn Reson Med 79:2176-2182, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Evaluation of hepatic fibrosis: a review from the society of abdominal radiology disease focus panel

Hepatic fibrosis is potentially reversible; however early diagnosis is necessary for treatment in order to halt progression to cirrhosis and development of complications including portal hypertension and hepatocellular carcinoma. Morphologic signs of cirrhosis on ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) alone are unreliable and are seen with more advanced disease. Newer imaging techniques to diagnose liver fibrosis are reliable and accurate, and include magnetic resonance elastography and US elastography (one-dimensional transient elastography and point shear wave elastography or acoustic radiation force impulse imaging). Research is ongoing with multiple other techniques for the noninvasive diagnosis of hepatic fibrosis, including MRI with diffusion-weighted imaging, hepatobiliary contrast enhancement, and perfusion; CT using perfusion, fractional extracellular space techniques, and dual-energy, contrast-enhanced US, texture analysis in multiple modalities, quantitative mapping, and direct molecular imaging probes. Efforts to advance the noninvasive imaging assessment of hepatic fibrosis will facilitate earlier diagnosis and improve patient monitoring with the goal of preventing the progression to cirrhosis and its complications.