Efficient whole-brain orientation-specific T1 mapping at 3 tesla
Bibliographic record
Abstract
Quantitative magnetic resonance imaging (qMRI) techniques such as T1 mapping are used to probe the microstructure of white matter in the human brain.However, these methods cannot disentangle the unique microstructural features of different white matter fibre populations, also called tracts, inside the voxel.This is a significant problem for qMRI because 60 to 90 % of MR image voxels in white matter contain complex configurations of multiple fibres (Jeurissen, Leemans, Tournier, Jones, & Sijbers, 2013).This calls for new qMRI methods that can disentangle the microstructure of individual tracts in a voxel.A recent MRI method combines inversion recovery (IR) and diffusion-weighted imaging (DWI) to measure tractspecific T1 relaxation times inside the voxel (De Santis, Assaf, Jeurissen, Jones, & Roebroeck, 2016; De Santis, Barazany, Jones, & Assaf, 2016).In human brain white matter, T1 is sensitive to tract myelination, and DWI is sensitive to tract geometry.IR-DWI was used at 7 tesla (T) to resolve multiple diffusion orientation-specific T1 values in phantoms (test objects) and in healthy human subjects (De Santis, Assaf, et al., 2016;De Santis, Barazany, et al., 2016).This original implementation is limited, however, by a long scan time, requiring over two hours for a wholebrain acquisition.An accelerated IR-DWI method applicable in more common 3 T MRI systems was developed in this thesis work at the McConnell Brain Imaging Centre of McGill University in collaboration with researchers at the Athinoula A. Martinos Center for Biomedical Imaging in Charlestown, Massachusetts, USA.Accelerated IR-DWI combines a slice-shuffled readout and simultaneous multi-slice imaging to enable whole-brain scanning in under 15 minutes.Accelerated IR-DWI was used to extract multiple orientation-specific T1 values in voxels with crossing fibres in a phantom and in the healthy human brain.This thesis demonstrates the feasibility of accelerated IR-DWI at 3 T and validates the technique.Future studies will use accelerated IR-DWI to examine how altered myelination in specific tracts affects structural connectivity in the brain and, ultimately, behaviour.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.012 | 0.007 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".