Separating the vascular and nonvascular sources of magnetic susceptibility in physiological MRI techniques based on the reversible transverse relaxation rate, R2’
Bibliographic record
Abstract
The blood oxygenation level-dependent (BOLD) signal is the most common functional MRI technique for mapping human brain organization. It is a qualitative measure that reflects changes in oxygen metabolism and blood flow driven by changes in brain activity. Various techniques exist to quantify physiological parameters underlying the BOLD signal, primarily based on relating them to the transverse relaxation rates. Quantitative susceptibility maps measured in subjects at rest and during a hypercapnic challenge were used to determine how much vasculature contributes to magnetic susceptibility compared to other tissues. Iso-oxygen saturation maps show the apparent oxygen saturation of blood where the susceptibility of blood and surrounding non-blood tissue would be equivalent, it is closer to 0.9. Non-blood susceptibility creates bias in quantifying oxygen metabolism in gas-free calibrated BOLD and quantitative BOLD. Iso-oxygen saturation of blood was found to be lower in deeper cortical tissue and to negatively correlate with non-heme iron concentration.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 0.004 |
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".