Simultaneous phase‐contrast MRI and PET for noninvasive quantification of cerebral blood flow and reactivity in healthy subjects and patients with cerebrovascular disease

Abstract

Background: H 2 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. Purpose: To 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 H 2 15 O-PET scan, and scales it to the whole-brain average CBF value measured by simultaneous phase-contrast MRI. Study Type: Observational. Subjects: Twelve healthy controls (HC) and 13 patients with Moyamoya disease (MM) as a model of chronic ischemic disease. Field Strength/Sequences: 3T/2D cardiac-gated phase-contrast MRI and H 2 15 O-PET. Assessment: PC-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. Results: The mean CBF values in WB, GM, and WM in HC were 42 AE 7 ml/100 g/min, 50 AE 7 ml/100 g/min, and 23 AE 3 ml/100 g/min, respectively, which agree well with literature values. Compared with normal regions (57 AE 23%), patients showed significantly decreased CVR in areas with mild/moderate stenosis (47 AE 17%, P = 0.011) and in severe/occluded areas (40 AE 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 H 2 15 O-PET in future studies. Level of Evidence: 3 Technical Efficacy Stage: 2

Quantification of brain oxygen extraction and metabolism with [15O]-gas PET: A technical review in the era of PET/MRI

“…Furthermore, global OEF MRI measurements from the superior sagittal sinus are more widespread and have been compared to each other with some success ( Barhoum et al, 2015 ). Whole-brain OEF information from MRI could thus be used as a scaling factor ( Ishii et al, 2020 ) for simultaneous [ 15 O]-oxygen PET/MRI studies and eliminate the need for invasive arterial blood sampling. Initial simulations suggest that global scaling of PET images with MRI-derived flow and whole-brain CMRO 2 measures is robust to signal variations related to recirculating water and CBV ( Narciso et al, 2019 ).…”

Evaluation of Arterial Spin Labeling MRI—Comparison with 15O-Water PET on an Integrated PET/MR Scanner

“…In contrast, previous studies using 15 O-water PET with arterial sampling have reported CBF values in GM ranging from 37 to 67 mL/100 g/min in healthy subjects [ 11 , 28 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. Thus, current published normal-range CBF measured by 15 O-water PET with arterial blood sampling shows large variations [ 36 , 42 ]. A generally accepted and often-cited average normal whole-brain CBF value in younger adults is 50 mL/100 g/min [ 43 ].…”

Predicting 15O-Water PET cerebral blood flow maps from multi-contrast MRI using a deep convolutional neural network with evaluation of training cohort bias

“…the whole brain flow measured by phase-contrast imaging. 47,48 However, scaling methods should be used cautiously, as systematic bias has been shown between phase-contrast MRI and 15 O-water PET with arterial sampling, 43,49 especially at lower spatial resolutions and for higher flow rates. Furthermore, the validity of phase-contrast MRI in patients with steno-occlusive disorders is less well understood.…”