T 1ρ mapping improvement using stretched-type adiabatic locking pulses for assessment of human liver function at 3 T

Robust cardiac T 1 ρ $$ {\mathrm{T}}_{1_{\boldsymbol{\rho}}} $$ mapping at 3T using adiabatic spin-lock preparations

PURPOSE

The aim of this study is to develop and optimize an adiabaticT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ (T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ ) mapping method for robust quantification of spin-lock (SL) relaxation in the myocardium at 3T.

METHODS

Adiabatic SL (aSL) preparations were optimized for resilience againstB 0 $$ {\mathrm{B}}_0 $$ andB 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities using Bloch simulations. OptimizedB 0 $$ {\mathrm{B}}_0 $$ -aSL, Bal-aSL andB 1 $$ {\mathrm{B}}_1 $$ -aSL modules, each compensating for different inhomogeneities, were first validated in phantom and human calf. MyocardialT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ mapping was performed using a single breath-hold cardiac-triggered bSSFP-based sequence. Then, optimizedT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ preparations were compared to each other and to conventional SL-preparedT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ maps (RefSL) in phantoms to assess repeatability, and in 13 healthy subjects to investigate image quality, precision, reproducibility and intersubject variability. Finally, aSL and RefSL sequences were tested on six patients with known or suspected cardiovascular disease and compared with LGE,T 1 $$ {\mathrm{T}}_1 $$ , and ECV mapping.

RESULTS

The highestT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ preparation efficiency was obtained in simulations for modules comprising 2 HS pulses of 30 ms each. In vivoT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ maps yielded significantly higher quality than RefSL maps. Average myocardialT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ values were 183.28± $$ \pm $$ 25.53 ms, compared with 38.21± $$ \pm $$ 14.37 ms RefSL-preparedT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ .T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ maps showed a significant improvement in precision (avg. 14.47± $$ \pm $$ 3.71% aSL, 37.61± $$ \pm $$ 19.42% RefSL, p < 0.01) and reproducibility (avg. 4.64± $$ \pm $$ 2.18% aSL, 47.39± $$ \pm $$ 12.06% RefSL, p < 0.0001), with decreased inter-subject variability (avg. 8.76± $$ \pm $$ 3.65% aSL, 51.90± $$ \pm $$ 15.27% RefSL, p < 0.0001). Among aSL preparations,B 0 $$ {\mathrm{B}}_0 $$ -aSL achieved the better inter-subject variability. In patients,B 1 $$ {\mathrm{B}}_1 $$ -aSL preparations showed the best artifact resilience among the adiabatic preparations.T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ times show focal alteration colocalized with areas of hyper-enhancement in the LGE images.

CONCLUSION

Adiabatic preparations enable robust in vivo quantification of myocardial SL relaxation times at 3T.

Magnetic resonance myocardial T1ρ mapping : Technical overview, challenges, emerging developments, and clinical applications

The potential of cardiac magnetic resonance to improve cardiovascular care and patient management is considerable. Myocardial T1-rho (T1ρ) mapping, in particular, has emerged as a promising biomarker for quantifying myocardial injuries without exogenous contrast agents. Its potential as a contrast-agent-free ("needle-free") and cost-effective diagnostic marker promises high impact both in terms of clinical outcomes and patient comfort. However, myocardial T1ρ mapping is still at a nascent stage of development and the evidence supporting its diagnostic performance and clinical effectiveness is scant, though likely to change with technological improvements. The present review aims at providing a primer on the essentials of myocardial T1ρ mapping, and to describe the current range of clinical applications of the technique to detect and quantify myocardial injuries. We also delineate the important limitations and challenges for clinical deployment, including the urgent need for standardization, the evaluation of bias, and the critical importance of clinical testing. We conclude by outlining technical developments to be expected in the future. If needle-free myocardial T1ρ mapping is shown to improve patient diagnosis and prognosis, and can be effectively integrated in cardiovascular practice, it will fulfill its potential as an essential component of a cardiac magnetic resonance examination.

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.

T1ρ magnetic resonance imaging value as a potential marker to assess the severity of liver fibrosis: A pilot study

Purpose

Assessment of liver fibrosis is essential for the management of liver disease. Although liver biopsy is the gold-standard modality for the diagnosis of liver fibrosis, it has some limitations. Thus, other methods are required to overcome the disadvantages of a liver biopsy. T1ρ magnetic resonance imaging (MRI) values are potential biomarkers for liver cirrhosis. This study aimed to assess the relationship between T1ρ MRI values and liver fibrosis severity by measuring the correlation between T1ρ values and shear wave elastography (SWE) values, which are routinely used for the diagnosis of liver fibrosis.

Methods

T1ρ imaging and SWE values were obtained from four healthy volunteers and 16 patients with chronic liver disease. The regions of interest on MR images were drawn and matched with those of the right liver lobe on SWE images.

Results

The mean T1ρ values of the right liver lobe correlated positively with the mean SWE values (Pearson’s correlation coefficient: 0.783; p < 0.0001; 95 % confidence interval: 0.623–0.880).

Conclusion

The mean T1ρ values of the right liver lobe may be correlated with the severity of liver fibrosis.

Collagen deposition in the liver is strongly and positively associated with T1rho elongation while fat deposition is associated with T1rho shortening: an experimental study of methionine and choline-deficient (MCD) diet rat model

BACKGROUND

A number of questions concerning the histological mechanism of elongated T1rho in liver fibrosis remain unanswered. Using a rat model of non-alcoholic fatty liver disease (NAFLD) induced with methionine and choline-deficient (MCD) diet, the primary aim of this study is to clarify whether collagen deposition per se causes liver T1rho elongation.

METHODS

There were 45 rats in the NAFLD model group and 8 rats in the control group. NAFLD model rats were fed MCD diet for 1, 2, 4, 6, 8, or 10 weeks, respectively. At the endpoint, the rats had in vivo MRI at 3.0 T and followed by histology. For T1rho data acquisition, a rotary echo spin-lock pulse was implemented in a three-dimensional fast field echo sequence with frequency selective fat suppression. The spin-lock frequency was set to 500 Hz, and the spin-lock times of 5, 10, 40, and 50 ms were used. Liver specimens were processed with hematoxylin-eosin staining for steatosis and inflammation evaluation, and Masson's trichrome staining for collagen visualization. The semiquantitative histopathological evaluation was based on NASH Clinical Research Network criteria. Histomorphometric analysis calculated percentages of fat and collagen accumulations in the livers.

RESULTS

A strong (r=0.82) and significant (P<0.0001) positive correlation between liver collagen content and liver T1rho was observed. Rats with no or minimal inflammation could have very long T1rho value. Among experimental rats without a positive fibrosis grading, five rats did not have an inflammation score (i.e., had minimal inflammation or no inflammation) while four had a positive inflammation score; the difference in liver T1rho between these two types of rats was minimal. Eight control rat livers and 15 stage-1 fibrosis rat livers were separated by liver T1rho completely. When four subgroups of experiment rats were selected where the liver collagen had a very narrow range within these subgroups, all these four subgroups showed a trend of negative correlation between liver fat and liver T1rho.

CONCLUSIONS

Collagen deposition in the live strongly contributes to liver T1rho elongation, while fat deposition contributes to T1rho shortening. In a well-controlled experimental setting, T1rho measure alone allows separation of healthy livers and stage-1 liver fibrosis in the MCD rat liver model.

Neural magnetic field dependent fMRI toward direct functional connectivity measurements: A phantom study

Recently, the main issue in neuroscience has been the imaging of the functional connectivity in the brain. No modality that can measure functional connectivity directly, however, has been developed yet. Here, we show the novel MRI sequence, called the partial spinlock sequence toward direct measurements of functional connectivity. This study investigates a probable measurement of phase differences directly associated with functional connectivity. By employing partial spinlock imaging, the neural magnetic field might influence the magnetic resonance signals. Using simulation and phantom studies to model the neural magnetic fields, we showed that magnetic resonance signals vary depending on the phase of an externally applied oscillating magnetic field with non-right flip angles. These results suggest that the partial spinlock sequence is a promising modality for functional connectivity measurements.

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.

On-resonance and off-resonance continuous wave constant amplitude spin-lock and T1ρ quantification in the presence of B1 and B0 inhomogeneities

Spin-lock MRI is a valuable diagnostic imaging technology, as it can be used to probe the macromolecule environment of tissues. Quantitative T_1ρ imaging is one application of spin-lock MRI that is reported to be promising for a number of clinical applications. Spin-lock is often performed with a continuous RF wave at a constant RF amplitude either on resonance or off resonance. However, both on- and off-resonance spin-lock approaches are susceptible to B₁ and B₀ inhomogeneities, which results in image artifacts and quantification errors. In this work, we report a continuous wave constant amplitude spin-lock approach that can achieve negligible image artifacts in the presence of B₁ and B₀ inhomogeneities for both on- and off-resonance spin-lock. Under the adiabatic condition, by setting the maximum B₁ amplitude of the adiabatic pulses equal to the B₁ amplitude of spin-lock RF pulse, the spins are ensured to align along the effective field throughout the spin-lock process. We show that this results in simultaneous compensation of B₁ and B₀ inhomogeneities for both on- and off-resonance spin-lock. The relaxation effect during the entire adiabatic half passage (AHP) and reverse AHP, and the stationary solution of the Bloch-McConnell equation present at off-resonance frequency offset, are considered in the revised relaxation model. We demonstrate that these factors create a direct current component to the conventional relaxation model. In contrast to the previously reported dual-acquisition method, the revised relaxation model just requires one acquisition to perform quantification. The simulation, phantom, and in vivo experiments demonstrate that the proposed approach achieves superior image quality compared with the existing methods, and the revised relaxation model can perform T_1ρ quantification with one acquisition instead of two.

Multi-modal Brain MRI in Subjects with PD and iRBD

Idiopathic rapid eye movement sleep behavior disorder (iRBD) is a condition that often evolves into Parkinson's disease (PD). Therefore, by monitoring iRBD it is possible to track the neurodegeneration of individuals who may progress to PD. Here we aimed at piloting the characterization of brain tissue properties in mid-brain subcortical regions of 10 healthy subjects, 8 iRBD, and 9 early-diagnosed PD. We used a battery of magnetic resonance imaging (MRI) contrasts at 3 T, including adiabatic and non-adiabatic rotating frame techniques developed by our group, along with diffusion tensor imaging (DTI) and resting-state fMRI. Adiabatic T_1ρ and T_2ρ, and non-adiabatic RAFF4 (Relaxation Along a Fictitious Field in the rotating frame of rank 4) were found to have lower coefficient of variations and higher sensitivity to detect group differences as compared to DTI parameters such as fractional anisotropy and mean diffusivity. Significantly longer T_1ρ were observed in the amygdala of PD subjects vs. controls, along with a trend of lower functional connectivity as measured by regional homogeneity, thereby supporting the notion that amygdalar dysfunction occurs in PD. Significant abnormalities in reward networks occurred in iRBD subjects, who manifested lower network strength of the accumbens. In agreement with previous studies, significantly longer T_1ρ occurred in the substantia nigra compacta of PD vs. controls, indicative of neuronal degeneration, while regional homogeneity was lower in the substantia nigra reticulata. Finally, other trend-level findings were observed, i.e., lower RAFF4 and T_2ρ in the midbrain of iRBD subjects vs. controls, possibly indicating changes in non-motor features as opposed to motor function in the iRBD group. We conclude that rotating frame relaxation methods along with functional connectivity measures are valuable to characterize iRBD and PD subjects, and with proper validation in larger cohorts may provide pathological signatures of iRBD and PD.

Age- and Gender-Associated Liver Physiological T1rho Dynamics Demonstrated with a Clinically Applicable Single-Breathhold Acquisition

To understand women's and men's physiological ranges of liver T1rho relaxation time measured with a single breathhold black blood sequence, this healthy volunteer study was conducted in 62 women (mean age, 38.9 y; range, 18-75 y) and 34 men (mean age, 44.7 y; range, 24-80 y). Approval from the institutional ethics committee was obtained. Magnetic resonance imaging was performed with a 3.0T scanner with six spin-lock times of 0, 10, 20, 25, 35, and 50 ms and a single breathhold of 12 s per slice acquisition. Six slices were acquired for each examination. The results demonstrated that the female liver T1rho value ranged between 35.07 and 51.97 ms and showed an age-dependent decrease, with younger women having a higher measurement. The male liver T1rho value ranged between 34.94 and 43.39 ms, with no evidential age dependence. Postmenopausal women had similar liver T1rho values as men. For women, there was a trend that the liver T1rho value could be 4% to 5% lower during the menstrual phase than during the nonmenstrual phase. For both women and men, no evidential association was seen between body mass index and liver T1rho.

Quantitative assessment of liver function with whole-liver T1rho mapping at 3.0T

OBJECTIVES

To assess the segmental liver function in healthy subjects and liver cirrhosis (LC) patients with different Child-Pugh grades using whole-liver T1rho mapping at 3.0T.

METHODS

Thirty-three healthy volunteers and 33 patients with clinically diagnosed LC were examined using a three-dimensional (3D) whole-liver coverage T1rho mapping. T1rho maps were calculated from five respiratory-triggered sequences with different spin-lock durations (0, 10, 20, 40, and 60ms). The patients were classified into group A with Child-Pugh A cirrhosis and group B with Child-Pugh B or C cirrhosis. The hepatic T1rho values in different segments of the healthy volunteers and LC patients were compared, and receiver operating characteristic curves (ROC) were plotted to determine the performance of T1rho.

RESULTS

The median T1rho value of the patients (Child-Pugh class A: 47.07ms; Child-Pugh classes B and C: 51.09ms) was significantly higher than that of the healthy volunteers (39.37ms, P<0.001). No remarkable variations among different hepatic segments in LC patients with various Child-Pugh grades were found (P>0.05). The T1rho values of the liver parenchyma were significantly correlated with albumin (r=-0.590, P<0.001) and prothrombin time (r=0.601, P<0.001). The T1rho values in patients increased with an increase in the Child-Pugh classification (r=0.574, P<0.001).

CONCLUSIONS

The whole-liver coverage T1rho sequence at 3.0T was feasible for the assessment of segmental liver function. T1rho relaxation might be a potential biomarker for the estimation of liver function in LC patients.