Water-Fat Separated T1 Mapping in the Liver and Correlation to Hepatic Fat Fraction

Accurate and precise in vivo liver 3D T1 mapping at 3T

PURPOSE

To develop an accurate and precise liver 3DT 1 $$ {T}_1 $$ mapping method using only scanner-agnostic sequences.

METHODS

While the spoiled gradient-recalled echo sequence is widely available on clinical scanners, variable flip angleT 1 $$ {T}_1 $$ mapping methods based on this sequence provide biasedT 1 $$ {T}_1 $$ estimates, with the largest systematic error arising fromB 1 + $$ {B}_1^{+} $$ inhomogeneities. To correct for this, the flip angle was mapped using a 2D gradient-echo double-angle method approach. To correct for the confounding effect of fat on liverT 1 $$ {T}_1 $$ andB 1 + $$ {B}_1^{+} $$ , Dixon and fat saturation techniques were used in combination with the variable flip angle and theB 1 + $$ {B}_1^{+} $$ map acquisitions, respectively. TheT 1 $$ {T}_1 $$ andB 1 + $$ {B}_1^{+} $$ mapping methods were validated with aT 1 $$ {T}_1 $$ -phantom against gold standard methods. An intra- and inter-repeatability study was conducted at 3T in 10 healthy individuals' livers.

RESULTS

The developed 3DT 1 $$ {T}_1 $$ mapping method achieved an excellent agreement with the gold standard, with a weighted root mean squared normalized error below 2.8%. In vivo, a medianT 1 $$ {T}_1 $$ standard deviation of 31 ms and an interquartile range of [27, 39] ms was achieved across all measurements, including the intra- and inter-repeatability study data. A within-subject standard deviation forT 1 $$ {T}_1 $$ of 21 ± 5 ms had a corresponding repeatability coefficient of 60 ms. The measuredT 1 $$ {T}_1 $$ values agree well with MOLLI and SASHAT 1 $$ {T}_1 $$ mapping methods, with averageT 1 $$ {T}_1 $$ differences of 5%.

CONCLUSION

Accurate and precise 3DT 1 $$ {T}_1 $$ liver measurements can lead the way to the wider adoption of a clinically feasibleT 1 $$ {T}_1 $$ measurement as a marker of hepatic fibro-inflammation.

Multiparametric MRI Including T1ρ Mapping for Hepatic Fibrosis Assessment in Preclinical Models of Steatotic Liver Disease

OBJECTIVES

The diagnostic value of hepatic native T1, extracellular volume fraction (ECV), and T2 mapping for noninvasive assessment of liver fibrosis is limited in the complex spectrum of steatotic liver disease due to confounding factors, including hepatic fat and inflammation. Therefore, this study aimed to histologically validate T1ρ mapping and compare it with conventional mapping parameters for assessing hepatic fibrosis across different animal models of steatotic liver disease.

MATERIALS AND METHODS

In male Sprague-Dawley rats, different models of steatotic liver disease were induced using a high-fat diet (HFD) and carbon-tetrachloride (CCl4) inhalation: (1) 12-week HFD group resulting in steatosis/steatohepatitis without fibrosis; (2) 6-week HFD + CCl4 group resulting in steatohepatitis with fibrosis; (3) 12-week HFD + CCl4 resulting in steatohepatitis-associated cirrhosis. Hepatic T1, ECV, T2, and T1ρ were assessed by quantitative MRI. Portal pressure was invasively measured. Hepatic fibrosis was assessed using Sirius red, alpha-smooth muscle actin (α-SMA) staining, and measurement of hydroxyproline content. Hepatic fat content was estimated in Oil red staining and triglyceride content.

RESULTS

Fifty-seven animals were analyzed (12-week HFD, n = 15; 6-week HFD + CCl4, n = 14; 12-week HFD + CCl4; n = 16; controls, n = 12). T1ρ values were higher in the fibrosis groups, for example, 12-week HFD + CCl4 versus HFD group (71 msec ±5 vs 60 msec ±3, P < 0.001). T1ρ values correlated with fibrosis markers (Sirius red r = 0.41; α-SMA: r = 0.67; hydroxyproline: r = 0.76; each P < 0.001) and portal pressure (r = 0.55, P < 0.001). T1ρ had the highest diagnostic performance for the detection of histologically defined fibrosis and invasively measured portal hypertension (eg, for fibrosis, T1ρ: AUC 0.96, P < 0.001; T1: AUC 0.74, P = 0.017; ECV: AUC 0.79, P = 0.043; T2: AUC 0.51, P < 0.001). T1ρ was an independent marker for the detection of histologically defined fibrosis (odds ratio: 3.81, P = 0.02).

CONCLUSIONS

In preclinical models of steatotic liver disease, T1ρ mapping could most reliably detect hepatic fibrosis and portal hypertension across different mapping parameters.

Accelerated Abdominal MRI: A Review of Current Methods and Applications

MRI is widely used for the diagnosis and management of various abdominal diseases involving organs such as the liver, pancreas, and kidneys. However, one major limitation of MRI is its relatively slow imaging speed compared to other modalities. In addition, respiratory motion poses a significant challenge in abdominal MRI, often requiring patients to hold their breath multiple times during an exam. This requirement can be particularly challenging for sick, elderly, and pediatric patients, who may have reduced breath-holding capacity. As a result, rapid imaging plays an important role in routine clinical abdominal MRI exams. Accelerated data acquisition not only reduces overall exam time but also shortens breath-hold durations, thereby improving patient comfort and compliance. Over the past decade, significant advancements in rapid MRI have led to the development of various accelerated imaging techniques for routine clinical use. These methods improve abdominal MRI by enhancing imaging speed, motion compensation, and overall image quality. Integrating these techniques into clinical practice also enables new applications that were previously challenging. This paper provides a concise yet comprehensive overview of rapid imaging techniques applicable to abdominal MRI and discusses their advantages, limitations, and potential clinical applications. By the end of this review, readers are expected to learn the latest advances in accelerated abdominal MRI and explore new frontiers in this evolving field. Evidence Level: N/A Technical Efficacy: Stage 5.

Fat-separated T1 mapping for liver function analysis on gadoxetic acid-enhanced MR imaging: 2D two-point Dixon Look-Locker inversion recovery sequence for differentiation of Child-Pugh class B/C from Child-Pugh class A/chronic liver disease

Background

T1 relaxation time is a tissue-specific parameter that correlates with liver fibrosis, and can be a valuable tool for detecting and staging of liver disease. However, T1 can be affected by histological factors such as fat, so it is necessary to study the effects of hepatic steatosis when assessing liver function and fibrosis. The purpose of this study is to investigate the fat separation effect of T1 mapping using Dixon watermap Look-Locker inversion recovery (LLIR) in the assessment of liver function on gadoxetic acid (GA)-enhanced magnetic resonance imaging (MRI).

Methods

A total of 226 patients who underwent 3T MRI, including a 2D Dixon fat-separated LLIR T1 mapping, were included retrospectively. Two independent readers measured pre- and post-contrast T1 relaxation times (preT1 and postT1) on composite and watermap T1, and reproducibility was evaluated. The correlation of T1 parameters with biochemical and imaging biomarkers of liver function were assessed on both composite and Dixon watermap images; T1 parameters included averaged preT1, postT1 values, changes between pre- and post-T1liver (deltaT1) and adjusted T1liver (postT1liver - T1spleen/T1spleen). And the diagnostic performance of T1 parameters for Child-Pugh (CP) class was also evaluated.

Results

Inter- and intra-reader reproducibility showed almost perfect agreement [intraclass correlation coefficient (ICC) 0.929-0.999]. Watermap preT1 (r=-0.125, P=0.068) and watermap deltaT1 (r=0.055, P=0.414) showed loss of correlation with fat fraction (FF) compared with preT1 and deltaT1. Albumin, total bilirubin (TB), hepatobiliary enhancement grade, and R2* (1/T2*), were significantly associated with watermap T1, eliminating the effect of FF. Area under the curve (AUC) of preT1, watermap preT1, deltaT1, postT1, watermap adjusted T1, and adjusted T1 were 0.681 [standard error (SE) 0.114], 0.748 (SE 0.098), 0.921 (SE 0.033), 0.951 (SE 0.018), 0.950 (SE 0.018), and 0.973 (SE 0.013) respectively, for differentiating patient with CP class B/C from CP-A/chronic liver disease (CLD).

Conclusions

T1 values using Dixon watermap LLIR eliminated the confounding effect of fat and showed the correlation with serological and imaging markers of liver function. Adjusted T1, watermap adjusted T1, and postT1 showed the highest diagnostic performance in differentiating CP class B/C from CP-A/CLD.

Practical approach to quantitative liver and pancreas MRI in children

Quantitative abdominal magnetic resonance imaging (MRI) offers non-invasive, objective assessment of diseases in the liver, pancreas, and other organs and is increasingly being used in the pediatric population. Certain quantitative MRI techniques, such as liver proton density fat fraction (PDFF), R2* mapping, and MR elastography, are already in wide clinical use. Other techniques, such as liver T1 mapping and pancreas quantitative imaging methods, are emerging and show promise for enhancing diagnostic sensitivity and treatment monitoring. Quantitative imaging techniques have historically required a breath-hold, making them more difficult to implement in the pediatric population. However, technological advances, including free-breathing techniques and compressed sensing imaging, are making these techniques easier to implement. The purpose of this article is to review current liver and pancreas quantitative techniques and to provide a practical guide for implementing these techniques in pediatric practice. Future directions of liver and pancreas quantitative imaging will be briefly discussed.

Native and Gd-EOB-DTPA-Enhanced T1 mapping for Assessment of Liver Fibrosis in NAFLD: Comparative Analysis of Modified Look-Locker Inversion Recovery and Water-specific T1 mapping

RATIONALE AND OBJECTIVES

To investigate the diagnostic performance of water-specific T1 mapping for staging liver fibrosis in a non-alcoholic fatty liver disease (NAFLD) rabbit model, in comparison to Modified Look-Locker Inversion recovery (MOLLI) T1 mapping.

MATERIALS AND METHODS

60 rabbits were randomly divided into the control group (12 rabbits) and NAFLD model groups (eight rabbits per subgroup) corresponding to different durations of high-fat high cholesterol diet feeding. All rabbits underwent MRI examination including MOLLI T1 mapping and 3D multi-echo variable flip angle (VFAME- GRE) sequences were acquired before and 20 min after the administration of Gd- EOB-DTPA. Histological assessments were performed to evaluate steatosis, inflammation, ballooning, and fibrosis. Statistical analysis included the intraclass correlation coefficient, analysis of variance, spearman correlation, multiple linear regression, and receiver operating characteristic curve.

RESULTS

A moderate correlation was observed between conventional native T1 and MRI-PDFF (r = -0.513, P < 0.001), as well as between conventional native T1 and liver steatosis grades (r = -0.319, P = 0.016). However, no significant correlation was found between the native wT1 and PDFF (r = 0.137, P = 0.314), or between the native wT1 and steatosis grades (r = 0.106, P = 0.435). In the multiple regression analysis, liver fibrosis, and hepatocellular ballooning were identified as independent factors influencing native wT1 in this study (R2 =0.545, P < 0.05), while steatosis was independently associated with conventional native T1 (R2 =0.321, P < 0.05). The AUC values for native T1, native wT1, HBP T1, and HBP wT1 were 0.549(0.410-0.682), 0.811(0.684-0.903), 0.775(0.644-0.876), and 0.752(0.619-0.858) for F1 or higher, 0.581(0.441-0.711), 0.828(0.704-0.916), 0.832(0.708-0.919), and 0.854(0.734-0.934) for F2 or higher, respectively.

CONCLUSION

The native wT1 may provide a more reliable assessment of early liver fibrosis in the context of NAFLD compared to conventional native T1.

MRI Dixon Fat-Corrected Look-Locker T1 Mapping for Quantification of Liver Fibrosis and Inflammation-A Comparison With the Non-Fat-Corrected Shortened Modified Look-Locker Inversion Recovery Technique

OBJECTIVES

This study evaluates the impact of liver steatosis on the discriminative ability for liver fibrosis and inflammation using a novel Dixon water-only fat-corrected Look-Locker T1 mapping sequence, compared with a standard shortened Modified Look-Locker Inversion Recovery (shMOLLI) sequence, with the aim of overcoming the limitation of steatosis-related confounding in liver T1 mapping.

MATERIALS AND METHODS

3 T magnetic resonance imaging of the liver including the 2 T1 mapping sequences and proton density fat fraction (PDFF) was prospectively performed in 24 healthy volunteers and 38 patients with histologically proven liver fibrosis evaluated within 90 days of liver biopsy. Paired Mann-Whitney test compared sequences between participants with and without significant liver steatosis (PDFF cutoff 10%), and unpaired Kruskal-Wallis test compared healthy volunteers to patients with early (F0-2) and advanced (F3-4) liver fibrosis, as well as low (A0-1) and marked (A2-3) inflammatory activity. Univariate and multivariate logistic regression models assessed the impact of liver steatosis on both sequences.

RESULTS

Dixon_W T1 was higher than shMOLLI T1 in participants without steatosis (median 896 ms vs 890 ms, P = 0.04), but lower in participants with liver steatosis (median 891 ms vs 973 ms, P < 0.001). Both methods accurately differentiated between volunteers and patients with early and advanced fibrosis (Dixon_W 849 ms, 910 ms, 947 ms, P = 0.011; shMOLLI 836 ms, 918 ms, 978 ms, P < 0.001), and those with mild and marked inflammation (Dixon_W 849 ms, 896 ms, 941 ms, P < 0.01; shMOLLI 836 ms, 885 ms, 978 ms, P < 0.001). Univariate logistic regression showed slightly lower performance of the Dixon_W sequence in differentiating fibrosis (0.69 vs 0.73, P < 0.01), compensated by adding liver PDFF in the multivariate model (0.77 vs 0.75, P < 0.01).

CONCLUSIONS

Dixon water-only fat-corrected Look-Locker T1 mapping accurately identifies liver fibrosis and inflammation, with less dependency on liver steatosis than the widely adopted shMOLLI T1 mapping technique, which may improve its predictive value for these conditions.

An Empirical Approach to Derive Water T1 from Multiparametric MR Images Using an Automated Pipeline and Comparison With Liver Stiffness

BACKGROUND

Water T1 of the liver has been shown to be promising in discriminating the progressive forms of fatty liver diseases, inflammation, and fibrosis, yet proper correction for iron and lipid is required.

PURPOSE

To examine the feasibility of an empirical approach for iron and lipid correction when measuring imaging-based T1 and to validate this approach by spectroscopy on in vivo data.

STUDY TYPE

Retrospective.

POPULATION

Next to mixed lipid-iron phantoms, individuals with different hepatic lipid content were investigated, including people with type 1 diabetes (N = 15, %female = 15.6, age = 43.5 ± 14.0), or type 2 diabetes mellitus (N = 21, %female = 28.9, age = 59.8 ± 9.7) and healthy volunteers (N = 9, %female = 11.1, age = 58.0 ± 8.1).

FIELD STRENGTH/SEQUENCES

3 T, balanced steady-state free precession MOdified Look-Locker Inversion recovery (MOLLI), multi- and dual-echo gradient echo Dixon, gradient echo magnetic resonance elastography (MRE).

ASSESSMENT

T1 values were measured in phantoms to determine the respective correction factors. The correction was tested in vivo and validated by proton magnetic resonance spectroscopy (1 H-MRS). The quantification of liver T1 based on automatic segmentation was compared to the T1 values based on manual segmentation. The association of T1 with MRE-derived liver stiffness was evaluated.

STATISTICAL TESTS

Bland-Altman plots and intraclass correlation coefficients (ICCs) were used for MOLLI vs. 1 H-MRS agreement and to compare liver T1 values from automatic vs. manual segmentation. Pearson's r correlation coefficients for T1 with hepatic lipids and liver stiffness were determined. A P-value of 0.05 was considered statistically significant.

RESULTS

MOLLI T1 values after correction were found in better agreement with the 1 H-MRS-derived water T1 (ICC = 0.60 [0.37; 0.76]) in comparison with the uncorrected T1 values (ICC = 0.18 [-0.09; 0.44]). Automatic quantification yielded similar liver T1 values (ICC = 0.9995 [0.9991; 0.9997]) as with manual segmentation. A significant correlation of T1 with liver stiffness (r = 0.43 [0.11; 0.67]) was found. A marked and significant reduction in the correlation strength of T1 with liver stiffness (r = 0.05 [-0.28; 0.38], P = 0.77) was found after correction for hepatic lipid content.

DATA CONCLUSION

Imaging-based correction factors enable accurate estimation of water T1 in vivo.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Impact of fat on the apparent T1 value of the liver: assessment by water-only derived T1 mapping

OBJECTIVES

To determine the impact of fat on the apparent T1 value of the liver using water-only derived T1 mapping.

METHODS

3-T MRI included 2D Look-Locker T1 mapping and proton density fat fraction (PDFF) mapping. T1 values of the liver were compared among T1 maps obtained by in-phase (IP), opposed-phase (OP), and Dixon water sequences using paired t-test. The correlation between T1 values of the liver on each T1 map and PDFF was assessed using Spearman correlation coefficient. The absolute differences between T1 value of the liver on Dixon water images and that on IP or OP images were also correlated with PDFF.

RESULTS

One hundred sixty-two patients (median age, 70 [range, 24-91] years, 90 men) were retrospectively evaluated. The T1 values of the liver on each T1 map were significantly different (p < 0.001). The T1 value of the liver on IP images was significantly negatively correlated with PDFF (r =  - 0.438), while the T1 value of the liver on OP images was slightly positively correlated with PDFF (r = 0.164). The T1 value of the liver on Dixon water images was slightly negatively correlated with PDFF (r =  - 0.171). The absolute differences between T1 value of the liver on Dixon water images and that on IP or OP images were significantly correlated with PDFF (r = 0.606, 0.722; p < 0.001).

CONCLUSION

Fat correction for the apparent T1 value by water-only derived T1 maps will be helpful for accurately evaluating the T1 value of the liver.

CLINICAL RELEVANCE STATEMENT

Fat-corrected T1 mapping of the liver with the water component only obtained from the 2D Dixon Look-Locker sequence could be useful for accurately evaluating the T1 value of the liver without the impact of fat in daily clinical practice.

KEY POINTS

• The T1 values of the liver on the conventional T1 maps are significantly affected by the presence of fat. • The apparent T1 value of the liver on water-only derived T1 maps would be slightly impacted by the presence of fat. • Fat correction for the apparent T1 values is necessary for the accurate assessment of the T1 values of the liver.