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Cerebrovascular reactivity (CVR) reflects the CBF change to meet different physiological demands. The reference CVR technique is PET imaging with vasodilators but is inaccessible to most patients. DSC can measure transit time to evaluate patients suspected of stroke, but the use of gadolinium may cause side-effects. Arterial spin labeling (ASL) is a non-invasive MRI technique for CBF measurements. Here, we investigate the effectiveness of ASL with single and multiple post labeling delays (PLD) to replace PET and DSC for CVR and transit time mapping in 26 Moyamoya patients. Images were collected using simultaneous PET/MRI with acetazolamide. CVR, CBF, arterial transit time (ATT), and time-to-maximum (Tmax) were measured in different flow territories. Results showed that CVR was lower in occluded regions than normal regions (by 68 ± 12%, 52 ± 5%, and 56 ± 9%, for PET, single- and multi-PLD PCASL, respectively, all p  0.35, p

Cerebrovascular reactivity (CVR) reflects the capacity of the brain to meet changing physiological demands and can predict the risk of cerebrovascular diseases. CVR can be obtained by measuring the change in cerebral blood flow (CBF) during a brain stress test where CBF is altered by a vasodilator such as acetazolamide. Although the gold standard to quantify CBF is PET imaging, the procedure is invasive and inaccessible to most patients. Arterial spin labeling (ASL) is a non-invasive and quantitative MRI method to measure CBF, and a consensus guideline has been published for the clinical application of ASL. Despite single post labeling delay (PLD) pseudo-continuous ASL (PCASL) being the recommended ASL technique for CBF quantification, it is sensitive to variations to the arterial transit time (ATT) and labeling efficiency induced by the vasodilator in CVR studies. Multi-PLD ASL controls for the changes in ATT, and velocity selective ASL is in theory insensitive to both ATT and labeling efficiency. Here we investigate CVR using simultaneous 15O-water PET and ASL MRI data from 19 healthy subjects. CVR and CBF measured by the ASL techniques were compared using PET as the reference technique. The impacts of blood T1 and labeling efficiency on ASL were assessed using individual measurements of hematocrit and flow velocity data of the carotid and vertebral arteries measured using phase-contrast MRI. We found that multi-PLD PCASL is the ASL technique most consistent with PET for CVR quantification (group mean CVR of the whole brain = 42±19% and 40±18% respectively). Single-PLD ASL underestimated the CVR of the whole brain significantly by 15±10% compared with PET (p

Oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen (CMRO2) are key cerebral physiological parameters to identify at-risk cerebrovascular patients and understand brain health and function. PET imaging with [15O]-oxygen tracers, either through continuous or bolus inhalation, provides non-invasive assessment of OEF and CMRO2. Numerous tracer delivery, PET acquisition, and kinetic modeling approaches have been adopted to map brain oxygenation. The purpose of this technical review is to critically evaluate different methods for [15O]-gas PET and its impact on the accuracy and reproducibility of OEF and CMRO2 measurements. We perform a meta-analysis of brain oxygenation PET studies in healthy volunteers and compare between continuous and bolus inhalation techniques. We also describe OEF metrics that have been used to detect hemodynamic impairment in cerebrovascular disease. For these patients, advanced techniques to accelerate the PET scans and potential synthesis with MRI to avoid arterial blood sampling would facilitate broader use of [15O]-oxygen PET for brain physiological assessment.

Background Cerebrovascular reserve (CVR) may be measured by using an acetazolamide test to clinically evaluate patients with cerebrovascular disease. However, acetazolamide use may be contraindicated and/or undesirable in certain clinical settings. Purpose To predict CVR images generated from acetazolamide vasodilation with a deep learning network by using only images before acetazolamide administration. Materials and Methods Simultaneous oxygen 15 (15O)-labeled water PET/MRI before and after acetazolamide injection were retrospectively analyzed for patients with Moyamoya disease and healthy control participants from April 2017 to May 2019. Inputs to deep learning models were perfusion-based images (arterial spin labeling [ASL]), structural scans (T2 fluid-attenuated inversion-recovery, T1), and brain location. Two models, that is, 15O-labeled water PET cerebral blood flow (CBF) and MRI (PET-plus-MRI model) before acetazolamide administration and only MRI (MRI-only model) before acetazolamide administration, were trained and tested with sixfold cross-validation. The models learned to predict a voxelwise relative CBF change (rΔCBF) map by using rΔCBF measured with PET due to acetazolamide as ground truth. Quantitative analysis included image quality metrics (peak signal-to-noise ratio, root mean square error, and structural similarity index), as well as comparison between the various methods by using correlation and Bland-Altman analyses. Identification of vascular territories with impaired rΔCBF was evaluated by using receiver operating characteristic metrics. Results Thirty-six participants were included: 24 patients with Moyamoya disease (mean age ± standard deviation, 41 years ± 12; 17 women) and 12 age-matched healthy control participants (mean age, 39 years ± 16; nine women). The rΔCBF maps predicted by both deep learning models demonstrated better image quality metrics than did ASL (all P < .001 in patients) and higher correlation coefficient with PET than with ASL (PET-plus-MRI model, 0.704; MRI-only model, 0.690 vs ASL, 0.432; both P < .001 in patients). Both models also achieved high diagnostic performance in identifying territories with impaired rΔCBF (area under receiver operating characteristic curve, 0.95 for PET-plus-MRI model [95% confidence interval: 0.90, 0.99] and 0.95 for MRI-only model [95% confidence interval: 0.91, 0.98]). Conclusion By using only images before acetazolamide administration, PET-plus-MRI and MRI-only deep learning models predicted cerebrovascular reserve images without the need for vasodilator injection. © RSNA, 2020 Online supplemental material is available for this article.

BackgroundH2 15 O-positron emission tomography (PET) is considered the reference standard for absolute cerebral blood flow (CBF). However, this technique requires an arterial input function measured through continuous sampling of arterial blood, which is invasive and has limitations with tracer delay and dispersion.PurposeTo demonstrate a new noninvasive method to quantify absolute CBF with a PET/MRI hybrid scanner. This blood-free approach, called PC-PET, takes the spatial CBF distribution from a static H2 15 O-PET scan, and scales it to the whole-brain average CBF value measured by simultaneous phase-contrast MRI.Study typeObservational.SubjectsTwelve healthy controls (HC) and 13 patients with Moyamoya disease (MM) as a model of chronic ischemic disease.Field strength/sequences3T/2D cardiac-gated phase-contrast MRI and H2 15 O-PET.AssessmentPC-PET CBF values from whole brain (WB), gray matter (GM), and white matter (WM) in HCs were compared with literature values since 2000. CBF and cerebrovascular reactivity (CVR), which is defined as the percent CBF change between baseline and post-acetazolamide (vasodilator) scans, were measured by PC-PET in MM patients and HCs within cortical regions corresponding to major vascular territories. Statistical Tests: Linear, mixed effects models were created to compare CBF and CVR, respectively, between patients and controls, and between different degrees of stenosis.ResultsThe mean CBF values in WB, GM, and WM in HC were 42 ± 7 ml/100 g/min, 50 ± 7 ml/100 g/min, and 23 ± 3 ml/100 g/min, respectively, which agree well with literature values. Compared with normal regions (57 ± 23%), patients showed significantly decreased CVR in areas with mild/moderate stenosis (47 ± 17%, P = 0.011) and in severe/occluded areas (40 ± 16%, P = 0.016). Data Conclusion: PC-PET identifies differences in cerebrovascular reactivity between healthy controls and cerebrovascular patients. PC-PET is suitable for CBF measurement when arterial blood sampling is not accessible, and warrants comparison to fully quantitative H2 15 O-PET in future studies.Level of evidence3 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;51:183-194.

Background and Purpose- Noninvasive imaging of brain perfusion has the potential to elucidate pathophysiological mechanisms underlying Moyamoya disease and enable clinical imaging of cerebral blood flow (CBF) to select revascularization therapies for patients. We used hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI) technology to characterize the distribution of hypoperfusion in Moyamoya disease and its relationship to vessel stenosis severity, through comparisons with a normative perfusion database of healthy controls. Methods- To image CBF, we acquired [15O]-water PET as a reference and simultaneously acquired arterial spin labeling (ASL) MRI scans in 20 Moyamoya patients and 15 age-matched, healthy controls on a PET/MRI scanner. The ASL MRI scans included a standard single-delay ASL scan with postlabel delay of 2.0 s and a multidelay scan with 5 postlabel delays (0.7-3.0s) to estimate and account for arterial transit time in CBF quantification. The percent volume of hypoperfusion in patients (determined as the fifth percentile of CBF values in the healthy control database) was the outcome measure in a logistic regression model that included stenosis grade and location. Results- Logistic regression showed that anterior ( P

Rationale: Thromboembolism is a serious complication of endovascular treatment for ruptured cerebral aneurysms. The administration of antiplatelet agents before endovascular treatment for ruptured cerebral aneurysms may reduce the risk of thromboembolic complications. Aim: This study aimed to assess the safety and efficacy of preoperative aspirin administration in endovascular treatment for ruptured cerebral aneurysms. Sample size estimates: Assuming a 15% incidence rate of both intraoperative thromboembolic morbidity and symptomatic ischemic lesions on magnetic resonance imaging diffusion-weighted imaging scans assessed by an Independent Review Committee, a sample size of 484 will be required to detect a 10% improvement with aspirin administration with 90% power using the Pearson's chi-square test at a two-sided significance level of 2.5% for each primary outcome, after accounting for a 5% dropout rate. Methods and design: ASTOP is a multicenter, randomized, double-blind, placebo-controlled clinical trial. A total of 484 patients with ruptured cerebral aneurysms receiving coil embolization within 72 h of onset will be randomly assigned 1:1 to receive 200 mg of aspirin or placebo before the procedure. Study outcomes: The primary outcomes will be the incidence rates of intraoperative thromboembolic complications and symptomatic ischemic lesions on magnetic resonance imaging diffusion-weighted imaging scans evaluated by the Independent Review Committee. The secondary outcomes will be the incidence rate of cerebral ischemic events and all bleeding events within 14 days of enrollment and functional outcomes defined by the modified Rankin Scale score at 90 days. Discussion: This trial will provide valuable data on the role of antiplatelet agents during endovascular treatment for ruptured cerebral aneurysms. Trial registration: Registration: Japan Registry of Clinical Trials, Identifier: jRCTs031210421. [ABSTRACT FROM AUTHOR]

Background: Cardiac neoplasms may cause life-threatening symptoms associated with cerebral infarction, ventricular arrhythmias, and heart failure. Emergency surgery or preoperative treatment may be required for these patients. However, no study has reported the surgical outcomes in cases involving cardiac neoplasms with life-threatening complications. The current study investigated the mid- to long-term outcomes of surgery in patients with cardiac neoplasms in life-threatening conditions. Methods: This study retrospectively analyzed 36 consecutive patients who underwent resection for cardiac neoplasms with life-threatening cardiovascular, respiratory, and cerebral nervous system complications from January 2000 to December 2022. Their mean age at surgery was 54.9 years. In terms of fatal events, one patient who experienced a ventricular tachycardia storm caused by a left ventricular neoplasm was placed under deep sedation and managed with a ventilator preoperatively. Seven patients who presented with limb motor paralysis and visual defects had cerebral infarction. Two of the seven patients with cerebral infarction received cerebrovascular treatment before cardiac surgery. Results: During the follow-up period, cerebral- and cardiovascular-related deaths were not recorded. All postoperative cerebral and cardiovascular complications were new-onset cerebral infarction (n = 2) (with symptoms that improved during the long term). The mean follow-up period was 6.2 years. The 5- and 10-year survival rates of all patients were 89.8% and 78.7%, respectively. There were no significant differences in postoperative prognosis between patients with preoperative cerebral infarctions and those without. Conclusions: The long-term surgical outcome of patients with life-threatening symptomatic cardiac neoplasm was good. Thus, preoperative complications did not affect prognosis. [ABSTRACT FROM AUTHOR]

Herein, a new energy cycle called the "hydrogen iodide (HI) cycle" is proposed that involves the repeated generation of solar hydrogen and battery power. Solar hydrogen generation using an HI solution allows for the use of a narrow‐bandgap photocatalyst. It is demonstrated that the addition of single‐walled carbon nanotubes (SWCNTs) effectively enhances solar hydrogen generation from HI solution with methylammonium lead iodide. Electron microscopy observations and spectroscopic experiments reveal that SWCNTs improve hydrogen generation by adsorbing byproduct iodine molecules. Additionally, a zinc‐iodine battery, utilizing paper I@SWCNTs recovered from the photocatalyst test cell and zinc metal, operates efficiently with an initial cell voltage of approximately 1.2 V. The battery's capacity, corresponding to the amount of encapsulated iodine molecules, indicates that SWCNTs can effectively adsorb the byproduct iodine molecules within the photocatalyst test cell. It is also discussed that the electrolyte solution after the discharge experiment should include iodide ions, indicating that the solution after battery discharge returns to the starting point of the "HI cycle." Raman measurements reveal that I@SWCNTs are transformed back into empty tubes during the discharge experiment. Therefore, SWCNTs can be repeatedly used in the new cyclic energy scheme referred to as the "HI cycle." [ABSTRACT FROM AUTHOR]