Magnetic Resonance Materials in Physics, Biology and Medicine最新文献

Purpose: Accurate quantification of proton density fat fraction (PDFF) and ${T_2}^{\ast }$ in the supracalvicular (SCV) fossa is critical for studying brown adipose tissue (BAT), but is challenged by respiratory motion-induced $B_0$ fluctuations. This study compares conventional Cartesian imaging to a radial stack-of-stars (SoS) trajectory, with and without retrospective temporal $B_0$ correction, in terms of PDFF and ${T_2}^{\ast }$ mapping precision.

Methods: Motion-induced $B_0$ fluctuations and tissue displacement were modeled using a digital anatomical phantom. Both Cartesian and radial SoS trajectories were simulated, with temporal $B_0$ correction, relying on oversampling of the k-space center, applied to the radial SoS data. Additionally, repeated in vivo scans were performed in four volunteers using both trajectories. PDFF and ${T_2}^{\ast }$ were quantified across repetitions.

Results: Simulations demonstrated smaller PDFF and ${T_2}^{\ast }$ errors in radial SoS compared to Cartesian imaging under the influence of simulated motion effects. In the simulations, the mean absolute PDFF error decreased from ${1.07\%}_{\text{PDFF}}$ with Cartesian to ${0.47\%}_{\text{PDFF}}$ with radial SoS, and the ${T_2}^{\ast }$ error decreased from 7.50 ms to 3.37 ms. In vivo, radial SoS provided higher repeatability for both parameters compared to Cartesian acquisitions, as measured by the inter-scan coefficient of variation. Retrospective temporal $B_0$ correction further improved the repeatability of ${T_2}^{\ast }$ quantification.

Conclusions: Radial SoS imaging improves motion robustness and repeatability of PDFF and ${T_2}^{\ast }$ quantification in the SCV fossa compared to Cartesian acquisitions. Incorporating retrospective temporal $B_0$ correction further enhances ${T_2}^{\ast }$ reliability and may strengthen the precision of BAT activation studies.

Objective: To present a wireless, batteryless, and optically powered two-dimensional (2D) electro-mechanical positioner operable inside a 3 T MRI scanner.

Methods: The system uses Lorentz force actuators, each comprising a coil connected to a monocrystalline silicon solar cell, leveraging the scanner's strong B₀ field. Six actuators form a rotor; two rotors are used to construct the 2D positioner using plastic, glass, and ceramic parts for MRI compatibility. The rotor is modeled using circuit-based analytical and numerical simulations, incorporating the solar cell's nonlinear current-voltage behavior. A custom coil is designed for 3 T to maximize mechanical power.

Results: Experimental validation includes dynamic torque measurements inside a 53 mT home-made desktop Helmholtz coil. The clinical-grade 3 T MRI scanner experiments demonstrate successful positioning in X and Y directions via remote laser diode control and power transmission through fiber optic cables. The rotor achieves 150 rotations per minute and 3.4 mN∙m torque at 6.3 mW/mm² optical intensity, amplified to 194 mN∙m by the gear train. The positioner attains a linear velocity of 2.2 mm/s with an open-loop accuracy of 1.5 mm, verified using MR images. The system shows stable behavior without imaging artifacts during in-scanner operation.

Conclusion: This is the first demonstration of a remotely controlled, optically powered 2D positioner operating wirelessly inside a clinical 3 T MRI. It enables precise marker placement or mechanical stimulation and can be extended to 5 degrees of freedom for MRI-guided interventions such as biopsies.

Background: Magnetic Resonance Spectroscopic Imaging (MRSI), also known as Chemical Shift Imaging (CSI), is a pivotal tool in both clinical and preclinical metabolic research. Traditional MRSI offers high sensitivity to weak metabolites and covers a wide spectral bandwidth. However, the large number of RF excitations required for fully sampled 3D-MRSI acquisitions renders it impractical for hyperpolarized (HP) MRI applications, especially given the rapid signal decay and non-renewable magnetization of HP agents such as [1-¹³C]pyruvate.

Purpose: This study aims to develop and validate an accelerated MRSI method that can preserve broad spectral bandwidth and weak metabolite detectability without aliasing, overcoming limitations of fast MRSI techniques such as echo-planar spectroscopic imaging (EPSI), which typically cause narrower spectral bandwidth and can suffer from spectral aliasing.

Methods: We implemented a sparsely sampled 3D-MRSI pulse sequence on an MRI scanner, acquiring data with large reduction ratios. A 4D compressed sensing (CS) reconstruction algorithm was developed to recover high-resolution spectroscopic data from undersampled measurements. The algorithm jointly reconstructs the three spatial dimensions and the frequency dimension, leveraging sparsity priors and iterative conjugate gradient optimization. The in vivo experiments were performed on a GE 3 T clinical MRI scanner (GE MR750W) using hyperpolarized [1-¹³C]pyruvate in one rat, with two acquisitions (R = 8 and R = 16) performed sequentially.

Results: Our method achieved high-quality reconstructions even at acceleration factors of R = 16 and R = 32, corresponding to 6.25 and 3.125% sampling, respectively. The normalized root-mean-square error (nRMSE) and structural similarity index (SSIM) remained low (nRMSE < 4 × 10^-3, SSIM > 0.95) even at high undersampling rates. In vivo experiments using hyperpolarized [1-¹³C]pyruvate in rat kidneys demonstrated the ability to resolve lactate, alanine, pyruvate, and bicarbonate distributions with high spatial and spectral fidelity.

Conclusion: The integration of sparse MRSI acquisition and 4D-CS reconstruction enables rapid, high-fidelity MRSI with HP ¹³C-MRSI. This approach reduces acquisition time by up to 32-fold, facilitating dynamic metabolic studies and improving feasibility for routine preclinical and future clinical use.

Objective: To develop a non-iterative method for applying elliptical field-of-view (FOV) to radial imaging and evaluate it for Stack-Of-Stars (SOS) with variable radial density in the $k_z$ direction.

Materials and methods: New analytic expressions were derived to compute the radial profile angles for an elliptical FOV with and without golden angle sampling. With a major-to-minor-axis FOV ratio of 1:0.5, anisotropic FOV and variable density SOS were evaluated, using point spread function analysis, phantom imaging, and in vivo pelvic imaging.

Results: Compared with conventional SOS, elliptical density in $k_z$ reduced scan time by 20%, while maintaining similar levels of radial aliasing artifacts. Anisotropic FOV reduced scan time by 31%, resulting in similar levels of radial aliasing artifacts at low undersampling for objects with matching in-plane anisotropy. Combining both techniques resulted in a 45% scan time reduction. Alternatively, when compared to conventional SOS using identical scan time, variable density and anisotropic FOV both displayed a lower level of radial aliasing artifacts, although for anisotropic FOV this effect was less pronounced at higher undersampling.

Discussion: Variable density and anisotropic FOV can reduce scan time and/or reduce aliasing artifacts for SOS. The new analytical expressions for elliptical FOV will facilitate future studies on anisotropic FOV radial imaging.

Objective: This study investigates the dynamic metabolic characteristics of glioblastoma (GBM) using Deuterium Metabolic Imaging (DMI) at 7 T, aiming to dynamically characterize the Warburg effect in vivo.

Material and methods: Five newly diagnosed GBM patients underwent dynamic DMI prior to any treatment. 3D ²H free-induction-decay (FID)-Magnetic resonance spectroscopy imaging (MRSI) measurements (11:44 min per scan) were performed at 7 T during ~ 100 min following [6,6'-²H₂]glucose consumption. Venous plasma glucose and plasma ²H-Glc atom percent enrichment (APE) levels were measured during the scan. Brain ²H-glucose (²H-Glc),²H-Glutamate/Glutamine (²H-Glx), ²H-Lactate (²H-Lac), ²H-Lac/²H-Glx were analyzed with a two-level (time and tissue type) Linear Mixed Model.

Results: Brain ²H-Glc levels were similar across tissue types. ²H-Glx was significantly lower in tumors compared to normal appearing brain tissue (NABT) (p < 0.01). ²H-Lac was significantly higher in tumors compared to NABT (P < 0.01). The ²H-Lac/²H-Glx ratio provided tumor-specific contrast, starting 40-50 min post [6,6'-²H₂]glucose consumption. Venous plasma glucose and ²H-Glc APE increased within 50 min and venous ²H-Glc APE stabilized at ~ 60%.

Discussion: Dynamic DMI at 7 T reveals metabolic alterations in GBM, particularly through the ²H-Lac/²H-Glx ratio. This contrast was primarily driven by decreased ²H-Glx rather than profoundly increased ²H-Lac. These findings support the utility of DMI in assessing metabolic reprogramming in brain tumors.

Objective: This study aimed to dynamically evaluate the attenuating effects of donafenib combined with carvedilol using intra-voxel incoherent motion (IVIM) MRI at different time points of disease course in a thioacetamide (TAA)-induced hepatic fibrosis rat model.

Methods: In this study, 40 male Sprague-Dawley rats received TAA for 6 weeks to induce liver fibrosis and were divided into four groups randomly (N = 10). From week 3 to week 6 of modeling, each group of rats received daily gavage of vehicle, carvedilol (CARV), donafenib (DON), and donafenib plus carvedilol (DON + CARV), respectively. IVIM MRI was used to assess the degree of liver fibrosis in the above groups at 0, 2, 4, and 6 weeks after modeling. Liver fibrosis was classified according to the METAVIR scoring system (F0-F4). IVIM parameters were calculated using a biexponential fitting model, and a least-squares fitting approach was applied for parameter estimation.

Results: The mean pathological collagen areas and the expression of α-SMA and collagen I in the CARV, DON, and DON + CARV groups were significantly less than that in the vehicle group (P < 0.001). IVIM-derived parameters (D, D^*, and f) and ADC values were negatively correlated with the fibrosis levels (D: r² = 0.594, P < 0.001; D^*: r² = 0.556, P < 0.001; f: r² = 0.737, P < 0.001; ADC: r² = 0.694, P < 0.001). At 4 and 6 weeks after modeling, the mean IVIM parameters and ADC values of the DON + CARV group were significantly higher than those of the vehicle group.

Conclusion: IVIM MRI is a noninvasive and valuable dynamic monitoring tool for liver fibrosis, and it was useful to monitor the dynamic inhibition process of donafenib and carvedilol on liver fibrosis in a TAA-induced rat model.

Objective: In the kidney, the medulla is most susceptible to damage in case of hampered perfusion or oxygenation. Due to separate regulation of cortical and medullary perfusion, measurement of both is crucial to improve the understanding of renal pathophysiology. We aim to develop and evaluate a physiologically accurate model to measure renal inner medullary (F_med) and cortical perfusion (F_cor) separately.

Materials and methods: We developed a 7-compartment model of renal perfusion and used an iterated approach to fit 10 free parameters. Model stability and accuracy were tested on both patient data and simulations. Cortical perfusion and F_T (tubular flow or glomerular filtration rate per unit of tissue volume) were compared to a conventional 2-compartment filtration model.

Results: Average (standard deviation) F_med was 37(23)mL/100 mL/min. Fitting stability as expressed by the median (interquartile range) coefficient of variation between fits was 0.0(0.0-5.8)%, with outliers up to 81%. In simulations, F_med was underestimated by around 8%. Intra-class correlation coefficients for F_cor and F_T as measured with the 2- and 7- compartment model were 0.87 and 0.63, respectively.

Discussion: We developed a pharmacokinetic model closely following renal physiology. Although the results were vulnerable for overfitting, relatively stable results could be obtained even for F_med.

Objective: To differentiate cribriform (GP4Crib+) from non-cribriform growth and Gleason 3 patterns (GP4Crib-/GP3) using MRI.

Methods: Two hundred and ninety-one operated prostate cancer men with pre-treatment MRI and whole-mount prostate histology were retrospectively included. T2-weighted, apparent diffusion coefficient (ADC) and fractional blood volume maps from 1.5/3T MRI systems were used. 592 histological GP3, GP4Crib- and GP4Crib+ regions were segmented on whole-mount specimens and manually co-registered to MRI sequences/maps. Radiomics features were extracted, and an erosion process was applied to minimize the impact of delineation uncertainties. A logistic regression model was developed to differentiate GP4Crib+ from GP3/GP4Crib- in the 465 remaining regions. The differences in balanced accuracy between the model and baseline (where all regions are labeled as GP3/GP4Crib-) and 95% confidence intervals (CI) for all metrics were assessed using bootstrapping.

Results: The logistic regression model, using the 90th percentile ADC feature with a negative coefficient, showed a balanced accuracy of 0.65 (95% CI: 0.48-0.79), receiver operating characteristic area under the curve (AUC) of 0.75 (95% CI: 0.54-0.92), a precision-recall AUC of 0.35 (95% CI: 0.14-0.68).

Conclusion: The radiomics MRI-based model, trained on Gleason sub-patterns segmented on whole-mount specimen, was able to differentiate GP4Crib+ from GP3/GP4Crib- patterns with moderate accuracy. The most dominant feature was the 90th percentile ADC. This exploratory study highlights 90th percentile ADC as a potential biomarker for cribriform growth differentiation, providing insights into future MRI-based risk assessment strategies.