Blood Flow Lateralization and Collateral Compensatory Mechanisms in Patients With Carotid Artery Stenosis

Abstract

Background and Purpose— Four-dimensional phase-contrast magnetic resonance imaging enables quantification of blood flow rate (BFR; mL/min) in multiple cerebral arteries simultaneously, making it a promising technique for hemodynamic investigation in patients with stroke. The aim of this study was to quantify the hemodynamic disturbance and the compensatory pattern of collateral flow in patients with symptomatic carotid stenosis. Methods— Thirty-eight patients (mean, 72 years; 27 men) with symptomatic carotid stenosis (≥50%) or occlusion were investigated using 4-dimensional phase-contrast magnetic resonance imaging. For each patient, BFR was measured in 19 arteries/locations. The ipsilateral side to the symptomatic carotid stenosis was compared with the contralateral side. Results— Internal carotid artery BFR was lower on the ipsilateral side (134±87 versus 261±95 mL/min; P <0.001). BFR in anterior cerebral artery (A1 segment) was lower on ipsilateral side (35±58 versus 119±72 mL/min; P <0.001). Anterior cerebral artery territory bilaterally was primarily supplied by contralateral internal carotid artery. The ipsilateral internal carotid artery mainly supplied the ipsilateral middle cerebral artery (MCA) territory. MCA was also supplied by a reversed BFR found in the ophthalmic and the posterior communicating artery routes on the ipsilateral side (−5±28 versus 10±28 mL/min, P =0.001, and −2±12 versus 6±6 mL/min, P =0.03, respectively). Despite these compensations, BFR in MCA was lower on the ipsilateral side, and this laterality was more pronounced in patients with severe carotid stenosis (≥70%). Although comparing ipsilateral MCA BFR between stenosis groups (<70% and ≥70%), there was no difference ( P =0.95). Conclusions— With a novel approach using 4-dimensional phase-contrast magnetic resonance imaging, we could simultaneously quantify and rank the importance of collateral routes in patients with carotid stenosis. An important observation was that contralateral internal carotid artery mainly secured the bilateral anterior cerebral artery territory. Because of the collateral recruitment, compromised BFR in MCA is not necessarily related to the degree of carotid stenosis. These findings highlight the importance of simultaneous investigation of the hemodynamics of the entire cerebral arterial tree.

Assessment of Intracranial Collateral Circulation Using Novel TCCS Grading System in Patients With Symptomatic Carotid Occlusion

“…Our results are in agreement with those presented in previous reports such as Zarrinkoob et al ( 10 ) who studied hemodynamic disturbance and compensatory pattern of collateral flow in patients with symptomatic carotid stenosis by studying blood flow rates (BFR) with four-dimensional phase-contrast magnetic resonance imaging and found that the ACOM was the major collateral that contributed to BFR equalization in patients with carotid artery stenosis.…”

Hemodynamic impairments within individual watershed areas in asymptomatic carotid artery stenosis by multimodal MRI

“…23 The other imaging parameters were: Label duration 1800 ms, 4 BGS pulses, segmented 3D GraSE readout (TE ¼ 7.4 ms, TR ¼ 4377 ms, a ¼ 90 , 16 slices, TSE factor 19, echo planar imaging (EPI) factor 7, acquisition voxel size 2.75 Â 2.75 Â 6.0 mm 3 ), three dynamics including a proton density weighted (PD-weighted) M 0 scan, and an acquisition time of 5:41 min. • BH-fMRI was performed according to Pillai et al 24 with five end-expiratory breath-holds of 15 33 and duplicate acquisition of the k-space center for motion correction, 37 as described previously 27 , which followed the ASFNR recommendations 38 and as described previously. 39 Contrast-enhanced angiography of the arteries of the neck and the aortic arch was also performed to exclude other relevant stenoses arteries that supply the brain.…”

“…Ipsilateral to the stenosis, we measured decreased CBF (-18% in iWSA-GM), which is in agreement with previous PET 52 and MRI studies 7,53 as well as the model of Powers et al 18 In the contralateral hemisphere, absolute CBF values were comparable to HCs, but the variability was increased (SD across subjects increased by þ22% in patients compared to HCs within iWSA-GM). This could be explained by subject specific collateralizations of blood flow, 15 that affect the contralateral hemisphere, and thereby increasing the inter-subject variability of contralateral CBF. Even though no obvious signs of arterial delay artefacts were found, CBF in watershed areas of ICAS-patients may potentially be affected by delayed blood arrival.…”

“…19 Recent MRI studies have also reported unchanged OEF with a decreased CBF. 7,11 This mismatch between the OEF and CBF changes might indicate microscopic variations of oxygen diffusivity from the capillary bed to brain tissue, as proposed by Hyder et al [20][21][22] While earlier PET studies revealed important information on ICAS-related hemodynamic impairments, the clinical applicability is restricted by limited availability, methodological complexity, radioactive tracer application and high costs of 15 O PET. Emerging MRI methods now allow a comprehensive evaluation of tissue perfusion and oxygenation, and a noninvasive measurement of up to six hemodynamic parameters within a single session.…”

A novel sequence for simultaneous measurement of whole‐brain static and dynamic MRA, intracranial vessel wall image, and T1‐weighted structural brain MRI

“…An integrated and comprehensive imaging assessment of intracranial vessels, including luminal stenosis, vessel wall, and blood flow conditions, is expected to be valuable for neurovascular disease diagnosis and to advance research. [1][2][3][4] MRI sequences are used to assess different aspects of vessel structure and blood flow. However, most existing sequences address only a single aspect of the conditions of intracranial vessels, and multiple sequences need to be performed to achieve a comprehensive assessment, which leads to prolonged total acquisition time and limits clinical application.…”