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Background: Perfusion imaging with multidetector CT is integral to the evaluation of patients presenting with ischemic stroke due to large-vessel occlusion. Using conebeam CT perfusion in a direct-to-angio approach could reduce workflow times and improve functional outcome., Purpose: Our aim was to provide an overview of conebeam CT techniques for quantifying cerebral perfusion, their clinical applications, and validation., Data Sources: A systematic search was performed for articles published between January 2000 and October 2022 in which a conebeam CT imaging technique for quantifying cerebral perfusion in human subjects was compared against a reference technique., Study Selection: Eleven articles were retrieved describing 2 techniques: dual-phase ( n = 6) and multiphase ( n = 5) conebeam CTP., Data Analysis: Descriptions of the conebeam CT techniques and the correlations between them and the reference techniques were retrieved., Data Synthesis: Appraisal of the quality and risk of bias of the included studies revealed little concern about bias and applicability. Good correlations were reported for dual-phase conebeam CTP; however, the comprehensiveness of its parameter is unclear. Multiphase conebeam CTP demonstrated the potential for clinical implementation due to its ability to produce conventional stroke protocols. However, it did not consistently correlate with the reference techniques., Limitations: The heterogeneity within the available literature made it impossible to apply meta-analysis to the data., Conclusions: The reviewed techniques show promise for clinical use. Beyond evaluating their diagnostic accuracy, future studies should address the practical challenges associated with implementing these techniques and the potential benefits for different ischemic diseases., (© 2023 by American Journal of Neuroradiology.)

In arterial spin labeling (ASL) a magnetic label is applied to the flowing blood in feeding arteries allowing depiction of cerebral perfusion maps. The labeling efficiency depends, however, on blood velocity and local field inhomogeneities and is, therefore, not constant over time. In this work, we investigate the ability of statistical methods used in functional connectivity research to infer flow territory information from traditional pseudo-continuous ASL (pCASL) scans by exploiting artery-specific signal fluctuations. By applying an additional gradient during labeling the minimum amount of signal fluctuation that allows discrimination of the main flow territories is determined. The following three approaches were tested for their performance on inferring the large vessel flow territories of the brain: a general linear model (GLM), an independent component analysis (ICA) and t-stochastic neighbor embedding. Furthermore, to investigate the effect of large vessel pathology, standard ASL scans of three patients with a unilateral stenosis (>70%) of one of the internal carotid arteries were retrospectively analyzed using ICA and t-SNE. Our results suggest that the amount of natural-occurring variation in labeling efficiency is insufficient to determine large vessel flow territories. When applying additional vessel-encoded gradients these methods are able to distinguish flow territories from one another, but this would result in approximately 8.5% lower perfusion signal and thus also a reduction in SNR of the same magnitude., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Background and Purpose: Impairment of the cerebral autoregulation is an important predictor of TIA and stroke in patients with an ICA stenosis. The autoregulative status can be assessed directly by measuring the vasodilatory capacity of the cerebral arteries. The aim of our study was to investigate the vasodilatory capacity of the proximal and distal cerebral vasculature in patients with an ICA stenosis and healthy control subjects by combining MRA with an acetazolamide provocation challenge., Materials and Methods: Fourteen functionally independent patients (mean age, 67.2 ± 8.7 years) with a symptomatic ICA stenosis and 19 healthy controls (mean age, 63.1 ± 7.2 years) were included. MRA was performed before and 20 minutes after intravenous administration of acetazolamide. The vasodilatory capacity of 11 proximal and distal cerebral vessels was assessed by measuring the increase in vessel diameter after acetazolamide., Results: In the hemisphere ipsilateral to the ICA stenosis, there was no increase in diameter after acetazolamide, whereas a significant increase was measured in the contralateral hemisphere for the A1 and A2 segments of the ACA, the pericallosal artery, and the BA. A significant diameter increase was measured in all except 1 vessel of the controls. The vasodilatory capacity was significantly lower ipsilateral to the ICA stenosis compared with the A1 segment of the ACA and the P2 segment of the PCA in the controls., Conclusions: MRA combined with an acetazolamide provocation challenge can measure normal and impaired vasodilatory capacity of the cerebral vasculature.

From intra-arterial angiography studies and recently developed imaging techniques capable of non-invasively visualizing the flow territories of the cerebral arteries at brain tissue level, it is known that brain regions can be fed by multiple arteries simultaneously. This indicates a mixing of blood from separate supplying arteries before reaching the brain tissue. Herein, we aim to explore the various manners blood from different arteries may mix in both healthy individuals and in patients with steno-occlusive disease. Furthermore, the impact of cerebrovascular interventions on the blood flow patterns and its effect on the mixing of the blood supply is discussed. More accurate knowledge and understanding of the vascular sources of tissue perfusion, and potential mixing, may result in more efficient vascular therapies and interventions targeted specifically to affected brain tissue areas., (Copyright © 2010 Elsevier Masson SAS. All rights reserved.)

Background: Arterial spin labeling (ASL) perfusion MRI with image acquisition at multiple delay times can be used to measure delays in the arrival of arterial blood to the brain. We assessed the effect of a symptomatic internal carotid artery (ICA) stenosis on ASL timing parameters, and evaluated the effect of collateral flow through the circle of Willis., Methods: Forty-four functionally independent patients (30 men, 69 +/- 9 years) with a recently symptomatic ICA stenosis > or =50% and 34 sex-matched and age-matched healthy volunteers were investigated. Magnetic resonance angiography and 2-dimensional phase-contrast imaging were used to assess collateral flow in the circle of Willis., Results: In the hemisphere ipsilateral to the ICA stenosis, cerebral blood flow (CBF) was lower (p < 0.01) in the anterior frontal, posterior frontal, parieto-occipital, and occipital regions than in control subjects. The transit times were prolonged (p < 0.01) in the ipsilateral anterior frontal, posterior frontal, and frontoparietal regions when compared with the control subjects. The trailing edge time was prolonged (p < 0.01) in the ipsilateral frontoparietal region when compared to the control subjects. In the 27 patients without a contralateral stenosis, the trailing edge was longer (p < 0.01) in the ipsilateral posterior frontal, frontoparietal, and parieto-occipital regions than in the contralateral regions. Collateral flow via the circle of Willis did not affect CBF and transit or trailing edge times., Conclusion: Arterial spin labeling MRI is a noninvasive tool for imaging cerebral blood flow and delays in the arrival of arterial blood to the brain, and can potentially provide valuable information on the quality of perfusion to the brain in patients with cerebrovascular disease.

Background and Purpose: Arterial spin-labeling (ASL) with image acquisition at multiple delay times can be exploited in perfusion MR imaging to visualize and quantify the temporal dynamics of arterial blood inflow. In this study, we investigated the consequences of an internal carotid artery (ICA) occlusion and collateral blood flow on regional timing parameters., Materials and Methods: Seventeen functionally independent patients with a symptomatic ICA occlusion (15 men, 2 women; mean age, 57 years) and 29 sex- and age-matched control subjects were investigated. ASL at multiple delay times was used to quantify regional cerebral blood flow (CBF) and the transit and trailing edge times (arterial timing parameters) reflecting, respectively, the beginning and end of the labeled bolus. Intra-arterial digital subtraction angiography and MR angiography were used to grade collaterals., Results: In the hemisphere ipsilateral to the ICA occlusion, the CBF was lower in the anterior frontal (31 +/- 4 versus 47 +/- 3 mL/min/100 g, P < .01), posterior frontal (39 +/- 4 versus 55 +/- 2 mL/min/100 g, P < .01), and frontal parietal region (49 +/- 3 versus 61 +/- 3 mL/min/100 g, P = .04) than that in control subjects. The trailing edge of the frontal-parietal region was longer in the hemisphere ipsilateral to the ICA occlusion compared with that in control subjects (2225 +/- 167 versus 1593 +/- 35 ms, P < .01). In patients with leptomeningeal collateral flow, the trailing edge was longer in the anterior frontal region (2436 +/- 275 versus 1648 +/- 201 ms, P = .03) and shorter in the occipital region (1815 +/- 128 versus 2388 +/- 203 ms, P = .04), compared with patients without leptomeningeal collaterals., Conclusion: Regional assessment of timing parameters with ASL may provide valuable information on the cerebral hemodynamic status. In patients with leptomeningeal collaterals, the most impaired territory was found in the frontal lobe.