A non-invasive hybrid PET/MR method for imaging the cerebral metabolic rate of oxygen
Bibliographic record
Abstract
1596 Introduction: Positron emission tomography (PET) is the gold standard for imaging the cerebral metabolic rate of oxygen (CMRO2); however, the technique is invasive as it requires arterial sampling and complex due to the need to correct for recirculating [15O]H2O and blood-borne activity [1]. We propose a non-invasive hybrid PET/ magnetic resonance imaging (MRI) method (PMROx) that uses MRI measurements of whole-brain (WB) CMRO2 to calibrate [15O]O2-PET. With PMROx, cerebral blood flow (CBF) images are obtained with a similar non-invasive PET/MRI approach combining [15O]H2O PET with phase-contrast MRI [2]. Alternatively, PET imaging can be reduced to just [15O]O2 inhalation by incorporating the MRI-based perfusion method, arterial spin labeling (PMROxASL) [3]. Here we present a comparison between PMROx and PMROxASL in animal experiments that also incorporated an established PET-alone method for validation [4]. The sensitivity of PMROxASL to altered metabolism was investigated by increasing the anesthetics. Methods: [15O]H2O and [15O]O2 PET data were acquired in a hybrid PET/MR scanner (3 T Siemens Biograph mMR), together with simultaneous MRI oximetry (OxFlow [5]) and perfusion (ASL), from juvenile pigs (n = 8). Animals were anesthetized with 3% isoflurane and 6 mL/kg/h propofol. Arterial sampling was performed for PET-alone measurements. Cerebral metabolism was reduced by increasing the propofol infusion to 20 mL/kg/h. Results: Significant correlations were found between regional CMRO2 measurements from PET and each of the PMROx methods (i.e. using either [15O]water or ASL to image CBF) with no significant differences between average CMRO2 from the three techniques: 1.89 ± 0.16 (PMROx), 1.88 ± 0.24 (PMROxASL) and 1.81 ± 0.10 mLO2/100g/min (PET). Moreover, PMROx and PMROxASL were sensitive to propofol-induced reduction in CMRO2 (Fig. 1). Conclusions: This study provides an initial validation of a non-invasive PET/MRI technique that circumvents many of the complexities of PET-only CMRO2 imaging. PMROx not only avoids arterial sampling, but can reduce the PET imaging procedure to [15O]O2 by incorporating ASL-CBF images. Future studies in humans are required to validate this approach. References: [1] Mintun MA, Raichle ME, Martin WR, Herscovitch P. Brain oxygen utilization measured with O-15 radiotracers and positron emission tomography. J Nucl Med. 1984;25:177-87. [2] Ssali T, Anazodo UC, Thiessen JD, Prato FS, St. Lawrence K. A noninvasive method for quantifying cerebral blood flow by hybrid PET/MRI. J Nucl Med. 2018;59:1329-1334. [3] Gunther M, Oshio K, Feinberg DA. Single-shot 3D imaging techniques improve arterial spin labeling perfusion measurements. Magn Reson Med. 2005;54:491-498. [4] Kudomi N, Hirano Y, Koshino K, et al. Rapid quantitative CBF and CMRO2 measurements from a single PET scan with sequential administration of dual 15O-labeled tracers. J Cereb Blood Flow Metab. 2013;33:440-448. [5] Jain V, Langham MC, Wehrli FW. MRI estimation of global brain oxygen consumption rate. J Cereb Blood Flow Metab. 2010;30:1598-1607. Figure 1. Group-wise CBF, OEF and CMRO2 images obtained with DBFM, PMROx and PMROxASL techniques for baseline (n = 8, top three rows). CBF and CMRO2 results from PMROx and PMROxASL for the lower metabolic condition (n = 6) are presented on the bottom two rows. MPRAGE from one animal was included for anatomical reference.
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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 | 0.000 |
| 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 | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".