Biology subjects

Dydak, U.

Publications and source records attributed to Dydak, U..

5 recordsLinked to original sources

bioRxiv2026

Testing the reliability of novel Voxel Placement approaches for Magnetic Resonance Spectroscopy

BackgroundSingle-voxel magnetic resonance spectroscopy (MRS) is a non-invasive method for measuring clinically and cognitively relevant metabolites. Reliable measurements require precise voxel placement across sessions and participants. We developed a scanner-console-based approach to improve voxel placement precision. MethodsIn a crossover design (n=7; six sessions each), we compared test-retest reliability of three voxel placement methods in a reference benchmark (left parietal cortex) and a technically challenging region (left ventromedial prefrontal cortex). Methods included (1) conventional anatomy-based placement, (2) mask-guided real-time positioning (MGRP), and (3) semiautomated session-locked voxel repositioning (SSVR). Resting-state MRS data were acquired using PRESS and MEGA-PRESS. Within-subject reliability of voxel placement and metabolite concentrations, namely, total N-acetylaspartate (tNAA), total Creatine (tCr), GABA (gamma-aminobutyric acid), and Glx (glutamate + glutamine) are reported using the coefficient of variation (CV), the intraclass correlation coefficient (ICC), minimal detectable change (MDC), and the spatial overlap. ResultsSSVR markedly improved voxel placement reliability, increasing spatial overlap (up to 88%) and achieving near-perfect geometric reproducibility (ICC = 0.99) compared to conventional anatomy-based placement and MGRP. SSVR improved tissue composition consistency and reduced metabolite variability in the technically challenging region (variability reduction of [~]70% tCr, [~]59% tNAA, and [~]51% Glx) while further refining already stable measurements in the benchmark region (tNAA from [~]15% to [~]10%). ConclusionBoth MGRP and SSVR improved voxel placement and metabolite measurement reproducibility compared with conventional anatomy-based placement. SSVR further enhanced within-subject reproducibility across repeated sessions, particularly in the technically challenging region, providing a robust approach for longitudinal single-voxel MRS studies.

neuroscience↗

bioRxiv2021

Comparison of seven modelling algorithms for GABA-edited 1H-MRS

Edited MRS sequences are widely used for studying GABA in the human brain. Several algorithms are available for modelling these data, deriving metabolite concentration estimates through peak fitting or a linear combination of basis spectra. The present study compares seven such algorithms, using data obtained in a large multi-site study. GABA-edited (GABA+, TE = 68 ms MEGA-PRESS) data from 222 subjects at 20 sites were processed via a standardised pipeline, before modelling with FSL-MRS, Gannet, AMARES, QUEST, LCModel, Osprey and Tarquin, using standardised vendor-specific basis sets (for GE, Philips and Siemens) where appropriate. After referencing metabolite estimates (to water or creatine), systematic differences in scale were observed between datasets acquired on different vendors hardware, presenting across algorithms. Scale differences across algorithms were also observed. Using the correlation between metabolite estimates and voxel tissue fraction as a benchmark, most algorithms were found to be similarly effective in detecting differences in GABA+. An inter-class correlation across all algorithms showed single-rater consistency for GABA+ estimates of around 0.38, indicating moderate agreement. Upon inclusion of a basis set component explicitly modelling the macromolecule signal underlying the observed 3.0 ppm GABA peaks, single-rater consistency improved to 0.44. Correlation between discrete pairs of algorithms varied, and was concerningly weak in some cases. Our findings highlight the need for consensus on appropriate modelling parameters across different algorithms, and for detailed reporting of the parameters adopted in individual studies to ensure reproducibility and meaningful comparison of outcomes between different studies. HighlightsO_LIGABA-edited MRS data from 222 healthy adults across 20 research sites were analyzed C_LIO_LIData were modelled using seven different algorithms, yielding GABA+ and Glx estimates C_LIO_LIModerate agreement was seen across all the tested algorithms C_LIO_LIAdding a component to represent co-edited macromolecule signals improved concordance C_LIO_LIBaseline modelling emerged as major factor differentiating outcomes C_LI

neuroscience↗

bioRxiv2020

Fast in vivo 23Na imaging and T2* mapping using accelerated 2D-FID magnetic resonance spectroscopic imaging at 3 T: Proof of concept and reliability study

PurposeTo implement an accelerated MR-acquisition method allowing to map sodium T2* relaxation and absolute concentration within skeletal muscles at 3T. MethodsA fast-2D density-weighted concentric-ring-trajectory 23Na-MRSI technique was used to acquire 64 time-points of FID with a spectral bandwidth of 312.5 Hz from a 2.5 x 2.5 mm2 in-plane resolution within about 15 minutes. The fast relaxing 23Na signal was localized with a single-shot, inversion-recovery based, non-echo (SIRENE) OVS method. The sequence was verified using simulation and phantom studies before implementing it in human calf muscles. Within two same-day sessions, 2D-SIRENE-MRSI (UTE = 0.55 ms) and 3D-MRI (UTE = 0.3 ms) data were acquired. The T2* values were fitted voxel-by-voxel using a bi-exponential model for the 2D-MRSI data. Within-subject coefficients of variation were estimated for both acquisition methods. ResultsThe MRSI-FID data allowed for fast and slow T2* mapping of the calf muscles in vivo with minimal sensitivity reduction. The spatial-distributions of 23Na concentration for both in vivo MRSI and 3D-MRI acquisitions were significantly correlated (r = 0.7, P<0.001). The test-retest results rendered high reliability for both MRSI (CV = 5%) and 3D MRI (CV = 6%). The mean [Formula] in calf muscles was 0.7 {+/-} 0.1 (contribution fraction = 37%), while [Formula] was 13.2 {+/-} 0.2 ms (63%). The mean absolute muscle 23Na concentration calculated from the T2*-corrected data was 28.6 {+/-} 3.3 mM. ConclusionThe proposed MRSI technique is a reliable technique to map sodiums absolute concentration and T2* within a clinically acceptable scan time at 3T.

biophysics↗

bioRxiv2019

Musculoskeletal fat imaging and quantification by high-resolution metabolite cycling magnetic resonance spectroscopic imaging at 3 T: A fast method to generate separate distribution maps of lipid components

PurposeTo provide a rapid, non-invasive fat quantification technique capable of producing separate lipid component maps.\n\nMethodsThe calf muscles in 5 healthy adolescents (age 12-16 years; BMI = 20 {+/-} 3 Kg/m2) were scanned by two different fat fraction (FF) quantification methods. A high-resolution, density-weighted concentric ring trajectory (DW-CRT) metabolite cycling (MC) magnetic resonance spectroscopic imaging (MRSI) technique was implemented to collect data with 0.25 mL resolution within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity (SSIM) analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data.\n\nResultsThe proposed MRSI technique provided individual FF maps for eight musculoskeletal lipids identified by LCModel analysis (L09, L11, L13, L15, L21, L23, L53, and L55) with mean SSIM indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively compared to that of Dixons FF map. Further analysis of voxels with zero SSIM demonstrated an increased sensitivity of FF lipid maps from data acquired using this MRSI technique over the standard Dixon technique. The trend of lipid spatial distribution over calf muscles was consistent with previously published findings in adults.\n\nConclusionThe advantages of this MRSI technique make it a useful tool when individual lipid FF maps are desired within a short scanning time.

biochemistry↗

bioRxiv2019

Density-Weighted Concentric Ring Trajectory using simultaneous multi-band acceleration: 3D Metabolite-cycled Magnetic Resonance Spectroscopy Imaging at 3 T

Simultaneous multi-slice or multi-band parallel imaging is frequently used in fMRI to accelerate acquisition. In this study, we propose a new a non-water-suppressed multi-band MRSI using a density weighted concentric ring trajectory (DW-CRT) acquisition. The properties of multi-band acquisition scheme were compared against single-band acquisition in phantoms and in-vivo experiments. High-quality spectra were acquired for all simultaneously acquired three slices from a limited volume of interest with an in-plane resolution of 5 x 5 mm2 in 19.2 min. The achieved in vivo spectral quality of the multi-band method allowed the reliable metabolic mapping of four major metabolites with Cramer-Rao lower bounds below 50%, using a LCModel analysis. Metabolite maps and LCModel quality metrics were compared between multi-band and single-band acquisition schemes for both phantom and in-vivo measurements. Structural similarity (SSIM) index and conventional coefficient of variance analysis of both phantom and in-vivo measurements revealed a SSIM index higher than 0.83, corresponding to a coefficient of variance of less than 30%. These findings demonstrate that our multi-band DW-CRT MRSI demonstrate a multi-band acceleration, simultaneously acquired 3 slices, with no apparently loss in spectral quality, reducing scan time by a factor of 3 without any significant penalty.

neuroscience↗