Biology subjects

Basser, P.

Publications and source records attributed to Basser, P..

4 recordsLinked to original sources

bioRxiv2022

Novel Pore Size-Controlled, Susceptibility Matched, 3D-Printed MRI Phantoms

Diffusion magnetic resonance imaging (dMRI) methods are commonly employed to infer changes in tissue microstructure. Quantities like the apparent diffusion coefficient (mADC), and the fractional anisotropy (FA), derived from diffusion tensor imaging (DTI) data, characterize voxel-averaged diffusion properties, whereas double pulse field gradient (dPFG) or double diffusion encoded (DDE) MR methods can be used to characterize heterogeneous diffusion processes occurring within the voxel. Owing to its unique modular design, our novel 3D-printed dMRI phantom exhibits both macroscopic and microscopic anisotropy and can serve to calibrate measures of them. Our phantom susceptibility is close to that of waters, enabling fast diffusion weighted echo-planar image (DW-EPI) acquisitions to be used to scan it. 3D printed microstructures offer a new medium with which to vet and validate theoretical models of diffusion and pipelines used to estimate it. HighlightsO_LIResearch highlight 1: We report the design concept and fabrication of dimensionally stable, uniformly oriented blocks or modules that can be assembled into large-scale MRI phantoms. Waffle-like structures containing blocks of aligned microcapillaries can be stacked into even larger arrays to construct diameter distribution phantoms, or fractured, to create a "powder-averaged" emulsion of randomly oriented blocks. C_LIO_LIResearch highlight 2: This phantom can be used to vet and calibrate various MRI methods, such as DTI, AxCaliber MRI, MAP-MRI, and various multiple pulsed field gradient (PFG) or multiple diffusion-encoded microstructure imaging methods. C_LI Graphical Abstract

biophysics↗

bioRxiv2022

Water exchange rates measure active transport and homeostasis in neural tissue

For its size, the brain is the most metabolically active organ in the body. Most of its energy demand is used to maintain stable homeostatic physiological conditions. Altered homeostasis and active states are hallmarks of many diseases and disorders. Yet there is currently no reliable method to assess homeostasis and absolute basal activity or activity-dependent changes non-invasively. We propose a novel, high temporal resolution low-field, high-gradient diffusion exchange NMR method capable of directly measuring cellular metabolic activity via the rate constant for water exchange across cell membranes. Using viable ex vivo neonatal mouse spinal cords, we measure a component of the water exchange rate which is active, i.e., coupled to metabolic activity. We show that this water exchange rate is sensitive primarily to tissue homeostasis and viability and provides distinct functional information in contrast to the Apparent Diffusion Coefficient (ADC), which is sensitive primarily to tissue microstructure but not activity. SIGNIFICANCE STATEMENTDespite what physiology text-books may report, water transport across membranes is not only a passive process. However, current understanding is limited because standard techniques can only measure net flux (the difference between water moving in and water moving out). Even so, water is constantly exchanging between the inside and outside of cells and organelles without net flux during homeostasis. We developed a Magnetic Resonance method able to "see" water molecules exchanging on shorter timescales than could be observed before. In neural tissue we find most water exchange is active, that is, linked to ATP-driven processes. This method may one day be translated to clinical MRI applications for measuring cellular function and activity in the human brain and body.

neuroscience↗

bioRxiv2021

Multidimensional MRI for characterization of subtle axonal injury accelerated using an adaptive nonlocal multispectral filter

Multidimensional MRI is an emerging approach that simultaneously encodes water relaxation (T1 and T2) and mobility (diffusion) and replaces voxel-averaged values with subvoxel distributions of those MR properties. While conventional (i.e., voxel-averaged) MRI methods cannot adequately quantify the microscopic heterogeneity of biological tissue, using subvoxel information allows to selectively map a specific T1-T2-diffusion spectral range that corresponds to a group of tissue elements. The major obstacle to the adoption of rich, multidimensional MRI protocols for diagnostic or monitoring purposes is the prolonged scan time. Our main goal in the present study is to evaluate the performance of a nonlocal estimation of multispectral magnitudes (NESMA) filter on reduced datasets to limit the total acquisition time required for reliable multidimensional MRI characterization of the brain. Here we focused and reprocessed results from a recent study that identified potential imaging biomarkers of axonal injury pathology from the joint analysis of multidimensional MRI, in particular voxelwise T1-T2 and diffusion-T2 spectra in human Corpus Callosum, and histopathological data. We tested the performance of NESMA and its effect on the accuracy of the injury biomarker maps, relative to the co-registered histological reference. Noise reduction improved the accuracy of the resulting injury biomarker maps, while permitting data reduction of 35.7% and 59.6% from the full dataset for T1-T2 and diffusion-T2 cases, respectively. As successful clinical proof-of-concept applications of multidimensional MRI are continuously being introduced, reliable and robust noise removal and consequent acquisition acceleration would advance the field towards clinically-feasible diagnostic multidimensional MRI protocols.

neuroscience↗

bioRxiv2019

Magnetic Resonance measurements of sub-cellular membrane structures in live and fixed neural tissue

We develop magnetic resonance (MR) methods for measuring real-time changes of tissue microstructure and membrane permeability of live and fixed neural tissue. Diffusion and exchange MR measurements are performed using the large static gradient produced by a single-sided permanent magnet. Using tissue delipidation methods, we show that water diffusion is restricted solely by lipid membranes. Most of the diffusion signal can be assigned to water in tissue which is far from membranes. The remaining 25% can be assigned to water restricted on length scales of roughly a micron or less, near or within membrane structures at the cellular, organelle, and vesicle levels. Diffusion exchange spectroscopy measures water exchanging between membrane structures and free environments at 100 s-1.

biophysics↗