Comparing the macromolecular-to-free pool size ratio and the magnetization transfer ratio for the assessment of myelin injury in early multiple sclerosis.

Background: The selective inversion recovery quantitative magnetization transfer imaging-derived macromolecular-to-free pool size ratio (PSR) and the magnetization transfer imaging-derived magnetization transfer ratio (MTR) are both indirect indicators of myelin integrity. However, it remains unknown whether the two measures perform equally in clinical studies.

Objectives: To compare the accuracy and effect size (ES) of PSR and MTR in assessing white matter (WM) injury in the brain of people with multiple sclerosis (PwMS).

Interpreting amide proton transfer-weighted imaging contrast between normal and tumor brain tissues using the asymmetry analysis method at 4.7 T.

Purpose: To provide a comprehensive analysis of the contributors to the amide proton transfer-weighted (APTw) imaging signal using an asymmetry analysis method, as well as its contrast between tumors and the contralateral normal tissues at 4.7 T.

Methods: First, a signal model was developed to demonstrate the dependence of APTw signal on various contributors, including water T, reference signal containing direct water saturation (DS) and magnetization transfer (MT), as well as APT, amine CEST, and nuclear Overhauser enhancement (NOE) effects.

Comparison of MR cytometry methods in predicting immunohistochemical factor status and molecular subtypes of breast cancer.

Background: First evaluation of the performance of MR cytometry incorporating transcytolemmal water exchange in predicting immunohistochemical factor status and molecular subtypes of breast cancer.

Patients And Methods: We prospectively enrolled 90 breast cancer patients in the study. For each participant, pulsed gradient spin-echo (PGSE) with diffusion time of 70 ms and oscillating gradient spin-echo (OGSE) diffusion-weighted imaging of 25 Hz and 50 Hz were performed on a 3T MRI scanner.

Detection of Region-specific Fiber Damage within Injured Spinal Cord Using Advanced Diffusion MRI.

This study aimed to evaluate diffusion parameters derived from diffusion tensor imaging (DTI) and spherical mean technique (SMT) for detecting region-specific, fine-grained tissue damage and white matter (WM) tract disruptions following spinal cord injury (SCI). Diffusion MRI data were acquired from the cervical spinal cord of monkeys before and after a unilateral dorsal column lesion at the C5 level, using a 9.4T scanner.

Noninvasive assessment of liver inflammation in metabolic dysfunction associated steatohepatitis using MR cytometry.

The current diagnostic gold standard for metabolic dysfunction-associated steatohepatitis (MASH) requires invasive biopsy to assess steatosis, inflammation, and ballooning. While MRI-based proton density fat fraction (PDFF) and MR elastography address steatosis and fibrosis, non-invasive methods for evaluating hepatic inflammation remain lacking. This study developed a diffusion MRI (dMRI)-based MR cytometry technique to map liver cellular properties, including MRI-derived cell size (excluding fat content) and cell density.

Comprehensive characterization of tumor therapeutic response via simultaneous mapping of cell size, density, and transcytolemmal water exchange.

The evaluation of tumor response to neoadjuvant chemotherapy is critical for the personalized management of cancer patients, aiming to minimize unnecessary toxicity, costs, and treatment delays. Current imaging techniques primarily depend on detecting tumor volume changes, which reflect downstream effects. In contrast, advanced microstructural diffusion MRI (dMRI) methods offer cellular-level insights but are limited by biased estimates of cell density due to oversimplified biophysical models.

MATI: A GPU-accelerated toolbox for microstructural diffusion MRI simulation and data fitting with a graphical user interface.

Purpose: To introduce MATI (Microstructural Analysis Toolbox for Imaging), a versatile MATLAB-based toolbox that combines both simulation and data fitting capabilities for microstructural dMRI research.

Methods: MATI provides a user-friendly, graphical user interface that enables researchers, including those without much programming experience, to perform advanced simulations and data analyses for microstructural MRI research. For simulation, MATI supports arbitrary microstructural tissues and pulse sequences.

Distinguishing Hepatocellular Carcinoma from Cirrhotic Regenerative Nodules Using MR Cytometry.

Background And Objectives: Current guidelines recommend contrast-enhanced CT/MRI as confirmatory imaging tests for diagnosing hepatocellular carcinoma (HCC). However, these modalities are not always able to differentiate HCC from benign/dysplastic nodules that are commonly observed in cirrhotic livers. Consequently, many lesions require either pathological confirmation via invasive biopsy or surveillance imaging after 3-6 months, which results in delayed diagnosis and treatment.

Evaluating the Diagnostic Performance of MR Cytometry Imaging in Differentiating Benign and Malignant Breast Tumors.

Background: MR cytometry is a class of diffusion-MRI-based methods that characterize tumor microstructures at the cellular level. It involves multicompartmental biophysical modeling of multi-b and multiple diffusion time data to generate microstructural parameters, which may improve differentiation of benign and malignant breast tumors.

Purpose: To implement MR cytometry imaging with transcytolemmal water exchange (JOINT and EXCHANGE) to differentiate benign and malignant breast tumors, and to compare the classification efficacy of IMPULSED, JOINT, and EXCHANGE.

Improving the Detection of Myelin Integrity in Multiple Sclerosis Using Selective Inversion Recovery for MRI With Quantitative Magnetization Transfer.

Background: Selective inversion recovery quantitative magnetization transfer (SIR-qMT)-derived macromolecular to free water pool size ratio (PSR) and diffusion tensor imaging (DTI)-derived radial diffusivity (RD) are potential metrics for assessing myelin integrity in multiple sclerosis (MS). However, establishing their accuracy in identifying tissue injury is essential for clinical translation.

Purpose: To compare the accuracy and Cohen's effect size (ES) of PSR and RD in detecting and quantifying tissue injury in early MS.

Watershed regions are more susceptible to tissue microstructural injury in multiple sclerosis.

Histopathologic studies report higher concentrations of multiple sclerosis white matter lesions in watershed areas of the brain, suggesting that areas with relatively lower oxygen levels may be more vulnerable to disease. However, it is unknown at what point in the disease course lesion predilection for watershed territories begins. Accordingly, we studied a cohort of people with newly diagnosed disease and asked whether (1) white matter lesions disproportionally localize to watershed-regions and (2) the degree of microstructural injury in watershed-lesions is more severe.

Improving the Assessment of Axonal Injury in Early Multiple Sclerosis.

Rationale And Objectives: Several quantitative magnetic resonance imaging (MRI) methods are available to measure tissue injury in multiple sclerosis (MS), but their pathological specificity remains limited. The multi-compartment diffusion imaging using the spherical mean technique (SMT) overcomes several technical limitations of the diffusion-weighted image signal, thus delivering metrics with increased pathological specificity. Given these premises, here we assess whether the SMT-derived apparent axonal volume (V) provides a better tissue classifier than the diffusion tensor imaging (DTI)-derived axial diffusivity (AD) in the white matter (WM) of MS brains.

Restriction-induced time-dependent transcytolemmal water exchange: Revisiting the Kӓrger exchange model.

The Kӓrger model and its derivatives have been widely used to incorporate transcytolemmal water exchange rate, an essential characteristic of living cells, into analyses of diffusion MRI (dMRI) signals from tissues. The Kӓrger model consists of two homogeneous exchanging components coupled by an exchange rate constant and assumes measurements are made with sufficiently long diffusion time and slow water exchange. Despite successful applications, it remains unclear whether these assumptions are generally valid for practical dMRI sequences and biological tissues.

Joint estimation of compartment-specific T relaxation and tumor microstructure using multi-TE IMPULSED MRI.

Purpose: This study aims to assess how T2 heterogeneity biases IMPULSED-derived metrics of tissue microstructure in solid tumors and evaluate the potential of estimating multi-compartmental T2 and microstructural parameters simultaneously.

Methods: This study quantifies the impact of T2 relaxation on IMPULSED-derived microstructural parameters using computer simulations and in vivo multi-TE IMPULSED MRI in five tumor models, including brain, breast, prostate, melanoma, and colon cancer. A comprehensive T + IMPULSED method was developed to fit multi-compartmental T and microstructural parameters simultaneously.

Comprehensive characterization of tumor therapeutic response with simultaneous mapping cell size, density, and transcytolemmal water exchange.

Early assessment of tumor therapeutic response is an important topic in precision medicine to optimize personalized treatment regimens and reduce unnecessary toxicity, cost, and delay. Although diffusion MRI (dMRI) has shown potential to address this need, its predictive accuracy is limited, likely due to its unspecific sensitivity to overall pathological changes. In this work, we propose a new quantitative dMRI-based method dubbed EXCHANGE (MRI of water Exchange, Confined and Hindered diffusion under Arbitrary Gradient waveform Encodings) for simultaneous mapping of cell size, cell density, and transcytolemmal water exchange.

Experimental demonstration of diffusion limitations on resolution and SNR in MR microscopy.

Purpose: MR microscopy is in principle capable of producing images at cellular resolution (<10 µm), but various factors limit the quality achieved in practice. A recognized limit on the signal to noise ratio and spatial resolution is the dephasing of transverse magnetization caused by diffusion of spins in strong gradients. Such effects may be reduced by using phase encoding instead of frequency encoding read-out gradients.

Detection of Treatment Response in Triple-Negative Breast Tumors to Paclitaxel Using MRI Cell Size Imaging.

Background: Breast cancer treatment response evaluation using the response evaluation criteria in solid tumors (RECIST) guidelines, based on tumor volume changes, has limitations, prompting interest in novel imaging markers for accurate therapeutic effect determination.

Purpose: To use MRI-measured cell size as a new imaging biomarker for assessing chemotherapy response in breast cancer.

Study Type: Longitudinal; animal model.

Evaluation of contributors to amide proton transfer-weighted imaging and nuclear Overhauser enhancement-weighted imaging contrast in tumors at a high magnetic field.

Purpose: The purpose is to evaluate the relative contribution from confounding factors (T weighting and magnetization transfer) to the CEST ratio (CESTR)-quantified amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) (-3.5) in tumors as well as whether the CESTR can reflect the distribution of the solute concentration (f ).

Methods: We first provided a signal model that shows the separate dependence of CESTR on these confounding factors and the clean CEST/NOE effects quantified by an apparent exchange-dependent relaxation (AREX) method.

Diffusion time dependency of extracellular diffusion.

Purpose: To quantify the variations of the power-law dependences on diffusion time t or gradient frequency of extracellular water diffusion measured by diffusion MRI (dMRI).

Methods: Model cellular systems containing only extracellular water were used to investigate the dependence of , the extracellular diffusion coefficient. Computer simulations used a randomly packed tissue model with realistic intracellular volume fractions and cell sizes.

Towards differentiation of brain tumor from radiation necrosis using multi-parametric MRI: Preliminary results at 4.7 T using rodent models.

Background: It remains a clinical challenge to differentiate brain tumors from radiation-induced necrosis in the brain. Despite significant improvements, no single MRI method has been validated adequately in the clinical setting.

Methods: Multi-parametric MRI (mpMRI) was performed to differentiate 9L gliosarcoma from radiation necrosis in animal models.

Rodent Model of Brain Radionecrosis Using Clinical LINAC-Based Stereotactic Radiosurgery.

Purpose: Our purpose was to develop a rodent model of brain radionecrosis using clinical linear accelerator based stereotactic radiosurgery.

Methods And Materials: Single fraction maximum prescription points in the mouse's left hemisphere were irradiated using linear accelerator-based stereotactic radiosurgery with multiple arcs at 60 (n = 5), 100 (n = 5), and 140 (n = 5) Gy. Rats (n = 6) were similarly treated with 140 Gy.

Selective Cell Size MRI Differentiates Brain Tumors from Radiation Necrosis.

Unlabelled: Brain metastasis is a common characteristic of late-stage lung cancers. High doses of targeted radiotherapy can control tumor growth in the brain but can also result in radiotherapy-induced necrosis. Current methods are limited for distinguishing whether new parenchymal lesions following radiotherapy are recurrent tumors or radiotherapy-induced necrosis, but the clinical management of these two classes of lesions differs significantly.

Improving MR cell size imaging by inclusion of transcytolemmal water exchange.

The goal of the current study is to include transcytolemmal water exchange in MR cell size imaging using the IMPULSED model for more accurate characterization of tissue cellular properties (e.g., apparent volume fraction of intracellular space ) and quantification of indicators of transcytolemmal water exchange.

Transcallosal and Corticospinal White Matter Disease and Its Association With Motor Impairment in Multiple Sclerosis.

Purpose: In this cross-sectional, proof-of-concept study, we propose that using the more pathologically-specific neurite orientation dispersion and density imaging (NODDI) method, in conjunction with high-resolution probabilistic tractography, white matter tract templates can improve the assessment of regional axonal injury and its association with disability of people with multiple sclerosis (pwMS).

Methods: Parametric maps of the neurite density index, orientation dispersion index, and the apparent isotropic volume fraction (IVF) were estimated in 18 pwMS and nine matched healthy controls (HCs). Tract-specific values were measured in transcallosal (TC) fibers from the paracentral lobules and TC and corticospinal fibers from the ventral and dorsal premotor areas, presupplementary and supplementary motor areas, and primary motor cortex.