Reactivity of Basilar and Circle of Willis Arteries Measured Simultaneously at 7 Tesla
Bibliographic record
Abstract
The subcortical conduit vessels contribute significantly to the total cerebral vascular resistance making knowledge regarding their vasoreactivity to physiological stimuli a requirement when attempting to understand regional brain perfusion. Recent evidence points to significant dilatory and constrictor potential in the middle cerebral artery. However, reactivity of the remaining conduit arteries remains poorly understood due to a need for improved imaging methods that can assess these vessels simultaneously while each receives the same stimulus. In this study we characterize the basilar and all Circle of Willis conduit arteries' reactivity to changes in end‐tidal CO 2 (ETCO 2 ). All imaging was performed on a 7T Siemens MAGNETOM neuro‐optimized MRI using an 8‐channel transmit, 32‐channel receive head coil. Cross‐sectional area (%ΔCSA) measurements were evaluated from images collected using a T1‐weighted 3D SPACE pulse sequence, optimized to produce black‐blood and high signal contrast between vessel lumen and surrounding tissue. The acquisition was tuned to produce high‐resolution (0.5mm isotropic) information with no inflow signal (TE=8.2ms, TR=700ms, FOV=224mm sagittal, radial trajectory, iPat=2) and a whole‐brain acquisition time of 5.63 minutes. Collection of isotropic data allowed us to arbitrarily re‐orient the image data to evaluate the relative change in cross‐sectional area (%ΔCSA) of the subcortical conduit arteries perpendicular to the direction of flow. Change in ETCO 2 (ΔETCO 2, ADInstruments) and %ΔCSA data were produced from 7 healthy individuals (age range, 18–23 years). Cerebrovascular CO 2 reactivity was calculated as %ΔCSA/ΔETCO 2 . All 9 subcortical conduit arteries (basilar, right and left internal carotid, as well as the right and left posterior, middle and anterior cerebral arteries) were evaluated during normocapnia (37±6 mm Hg), hypercapnia (51±6 mmHg achieved by breathing a gas mixture of 5% CO 2 , balance oxygen), and hypocapnia (27±4 mmHg achieved by hyperventilation). Cerebral artery reactivity to hypercapnia exhibited a range of dilation from 0.27%/mm Hg in the right internal carotid artery to 2.5%/mm Hg in the left anterior cerebral artery. In response to hypocapnia, cerebral artery vasoconstriction ranged from 1.1%/mm Hg in the left anterior cerebral artery to 3.2%/mm Hg in the right posterior cerebral artery. This study demonstrated the heterogeneous cerebrovascular reactivity to hypercapnia and hypocapnia across the nine subcortical conduit arteries. Support or Funding Information Canadian Institute of Health Research (201503MOP‐342412‐MOV‐CEEA)
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".