Nahla M. H. Elsaid

Background: Noninvasive fetal temperature assessment could improve MRI safety monitoring and provide insight into fetal physiology. Diffusion MRI is a potential approach because water diffusivity in free fluids is temperature dependent. However, the applicability of adult‐derived diffusivity–temperature calibration to neonatal and fetal CSF remains uncertain. Purpose: To evaluate the feasibility of diffusion MRI for noninvasive estimation of a diffusion‐derived proxy of fetal temperature in cerebrospinal fluid (CSF). Study Type: Prospective feasibility study. Population/Subjects: 11 preterm neonates (postmenstrual age, 30.0–40.6 weeks; 5 male, 6 female) underwent CSF diffusion MRI for translational validation, and 11 fetuses (gestational age, 27.6–37.6 weeks) underwent CSF diffusion MRI for in utero feasibility assessment. Field Strength/Sequence: 1.5T monopolar spin‐echo echo‐planar diffusion imaging for neonatal validation; 3T monopolar spin‐echo echo‐planar diffusion MRI for fetal imaging. Assessment: Temperature was derived from CSF apparent diffusion coefficients using an established diffusivity–temperature calibration. Neonatal estimates were compared with pre and postscan axillary temperatures. Monte Carlo simulations evaluated the effects of noise, gradient‐amplitude scaling errors, and calibration uncertainty. Statistical Tests: Bland–Altman analysis, linear regression, descriptive statistics, Huber M‐estimation, and Monte Carlo simulations were performed. Statistical significance for regression analyses was defined as p < 0.05. Results: Diffusion‐derived CSF temperatures agreed with axillary measurements within approximately ±1°C in 11 preterm neonates and showed Bland–Altman biases of 0.41°C and 0.50°C for mean diffusion‐derived temperature compared with pre and postscan axillary measurements, respectively. In 11 fetuses, the CSF temperature estimates using the Huber M‐estimator were 37.13°C ± 0.41°C (mean ± SD). Monte Carlo simulations revealed a decrease in the temperature SD from about 4.5°C at SNR = 30 to 1.6°C at SNR = 80. Gradient‐amplitude scaling errors of ±8% resulted in approximately 6.5°C–7°C absolute temperature bias, which was reduced to ≤ 0.1°C after ideal effective b value correction. Data Conclusion: Diffusion MRI enables feasible estimation of a diffusion‐derived proxy of fetal temperature in CSF. Level of Evidence: 2. Technical Efficacy: Stage 1.

The National Institutes of Health (NIH) Toolbox cognition battery and Trail Making Tests (TMT) are widely used to quantify cognitive aging and to detect early cognitive vulnerability in Alzheimer’s disease and related conditions. However, these tests are often treated as interchangeable markers of global cognition, despite likely differences in their dependence on specific brain systems, limiting interpretability across studies and clinical contexts. To address this gap, we examined associations between four commonly used cognitive measures—fluid cognition, crystallized cognition, TMT-A, and TMT-B—and multimodal MRI metrics in 725 healthy volunteers aged 36 to 100 years from the Human Connectome Project–Aging. Voxel-wise diffusion MRI and vertex-wise cortical thickness and volume analyses were adjusted for age, sex, and years of education. Higher crystallized and fluid cognition scores and faster TMT-A/B completion times were generally associated with greater white matter integrity. TMT-B showed the most extensive diffusion and cortical associations, involving major projection, commissural, and association pathways and frontoparietal and temporo-occipital cortices. TMT-A and crystallized cognition demonstrated intermediate, overlapping patterns, whereas fluid cognition showed only focal brainstem and limited cortical correlates. These findings demonstrate systematic differences in the neuroanatomical substrates underlying commonly used cognitive tests and provide normative structure–cognition reference maps that can improve test selection, mechanistic interpretation, and sensitivity to brain health in studies of aging, vascular risk, and preclinical neurodegenerative disease.

Purpose: This paper reports on the technical performance of a nonlinear “inside‐out” gradient and its feasibility and safety for diffusion encoding in humans. The tested hardware is a solenoidal coil with a 10 cm diameter, positioned at the isocenter of the magnet bore, designed to generate strong gradients within the surrounding volume. Methods: Various methods were used to characterize the spatial, temporal, mechanical, and acoustic properties of the gradient coil. ADC mapping studies show the feasibility of diffusion‐weighted imaging and ADC mapping in phantoms and humans. Results: The hardware was found to generate high gradient strengths (> 200 mT/m) for expected prostate regions whilst heating, noise, and eddy currents remained within acceptable limits for human scanning. Despite its unconventional geometry and compact form factor, standard calibration methods were effective, enabling accurate ADC mapping in both phantoms and human subjects. No peripheral nerve stimulation (PNS) was reported, even at maximum slew rates and gradient amplitudes. Conclusion: Inside‐out nonlinear gradients can be calibrated with conventional techniques, and the hardware can provide a more convenient approach to strong diffusion weighting of targeted organs.

Purpose: To standardize T‐weighted images from clinical Turbo Spin Echo (TSE) scans by generating corresponding T maps with the goal of removing scanner‐ and/or protocol‐specific heterogeneity.Methods: The T map is estimated by minimizing an objective function containing a data fidelity term in a Virtual Conjugate Coils (VCC) framework, where the signal evolution model is expressed as a linear constraint. The objective function is minimized by Projected Gradient Descent (PGD).Results: The algorithm achieves accuracy comparable to methods with customized sampling schemes for accelerated T mapping. The results are insensitive to the tunable parameters, and the relaxed background phase prior produces better T maps compared to the strict real‐value enforcement. It is worth noting that the algorithm works well with challenging Tw‐TSE data using typical clinical parameters. The observed normalized root mean square error ranges from 6.8% to 12.3% over grey and white matter, a clinically common level of quantitative map error.Conclusion: The novel methodological development creates an efficient algorithm that allows for T map generated from TSE data with typical clinical parameters, such as high resolution, long echo train length, and low echo spacing. Reconstruction of T maps from TSE data with typical clinical parameters has not been previously reported.

Peripheral artery disease (PAD) is a common vascular disease that primarily affects the lower limbs and is defined by the constriction or blockage of peripheral arteries and may involve microvascular dysfunction and tissue injury. Patients with diabetes have more prominent disease of microcirculation and develop peripheral neuropathy, autonomic dysfunction, and medial vascular calcification. Early and accurate diagnosis of PAD and disease characterization are essential for personalized management and therapy planning. Magnetic resonance imaging (MRI) provides excellent soft tissue contrast and multiplanar imaging capabilities and is useful as a noninvasive imaging tool in the comprehensive physiological assessment of PAD. This review provides an overview of the current state of the art of MRI in the evaluation and characterization of PAD, including an analysis of the many applicable MR imaging techniques, describing the advantages and disadvantages of each approach. We also present recent developments, future clinical applications, and future MRI directions in assessing PAD. The development of new MR imaging technologies and applications in preclinical models with translation to clinical research holds considerable potential for improving the understanding of the pathophysiology of PAD and clinical applications for improving diagnostic precision, risk stratification, and treatment outcomes in patients with PAD.

Advanced dMRI techniques have been used to resolve the complex tongue muscle architecture. However, dMRI-derived tongue muscle architecture has not been validated with histology. In this study, we validated the dMRI-derived tongue muscle architecture with histology of a tongue specimen. dMRI was acquired for a post-mortem head and a healthy volunteer. dMRI-derived muscle fiber orientations, visualized as the tractogram, were compared against microscopic histology slices of the tongue specimen. Muscle fibers in the tractograms show good correspondence with those appearing in the histology images. The study demonstrates that dMRI can accurately reveal the complex muscle architecture of the human tongue.

Purpose The goal of the current study was to introduce a new methodology that holds a promise to be used in hippocampus-aging studies using sub-millimeter super-resolution hybrid diffusion imaging (HYDI) MRI. Methods HYDI diffusion data were acquired in two groups of older and younger healthy participants recruited from the Indiana Alzheimer’s Disease Research Center and community. These data were then transformed into super-resolution diffusion images before the hippocampal subfield analyses. We studied the correlation between the subjects’ age and the structural connectivity involving the hippocampal subfields and the connectivity between the whole hippocampus and the cerebral cortex. Results Structural integrity derived from the tractography streamlines between the hippocampal subfields was reduced in older than younger adults. Conclusion The findings offered a new promising framework, and they opened avenues for future studies to explore the relationship between the structural connectivity in the hippocampal area and different types of dementia.

Purpose: To develop an image‐based motion‐robust diffusion MRI (dMRI) acquisition framework that is able to minimize motion artifacts caused by rigid and nonrigid motion, applicable to both brain and tongue dMRI.Methods: We developed a novel prospective motion‐correction technique in dMRI using a phase image–based real‐time motion‐detection method (PITA‐MDD) with re‐acquisition of motion‐corrupted images. The prospective PITA‐MDD acquisition technique was tested in the brains and tongues of volunteers. The subjects were instructed to move their heads or swallow, to induce motion. Motion‐detection efficacy was validated against visual inspection as the gold standard. The effect of the PITA‐MDD technique on diffusion‐parameter estimates was evaluated by comparing reconstructed fiber tracts using tractography with and without re‐acquisition.Results: The prospective PITA‐MDD technique was able to effectively and accurately detect motion‐corrupted data as compared with visual inspection. Tractography results demonstrated that PITA‐MDD motion detection followed by re‐acquisition helps in recovering lost and misshaped fiber tracts in the brain and tongue that would otherwise be corrupted by motion and yield erroneous estimates of the diffusion tensor.Conclusion: A prospective PITA‐MDD technique was developed for dMRI acquisition, providing improved dMRI image quality and motion‐robust diffusion estimation of the brain and tongue.