Distribution Of Cerebral Blood Flow In The Circle Of Willis: Evaluation With MR Angiography In Normal Adults

Purpose: To prospectively determine the effect of morphologic variations in thecircle of Willis on the volume flow distribution in the intracranial bilateral internalcarotid artery (ICA), basilar artery (BA) and total cerebral blood flow (TCBF) bycombinational use manifold sequences on magnetic resonance angiography (MRA)and diffusion weighted imaging (DWI).Materials and Methods: 560 patients have performed head-neck MRAexamination by clinical application in our hospital between March 2005 and January2007.The examinations were all performed with a superconductive GE 1.5TTwin-Speed Infinity with ExciteⅠsystem equipped with 8NV head and neck coil. Thefollowing sequences were performed for all the patients: DWI sequence in head, threedimensional contrast enhanced MRA (3D CE-MRA) in cervical part, threedimensional time of flight (3D TOF) and MR phase contrast-cine. 106 patients (male61, female 45, rang of age 21-82 years, mean age 51-14 years) conforming to perfectimaging and complete test sequences without brain substance process on DWIsequence, head-cervical artery stenosis-obstruct process on 3D CE-MRA were chosen as research subjects from the patients, whose main symptom is headache anddizziness without local neurology signs and pathologic reflex. 3D TOF was used forevaluating the morphology of the circle of Willis. Initial imaging data obtained by MRPC-cine was analyzed by the software of cerebral volume flow (CV flow) inAdvantage Workstation 4.0 and produced mean blood volume flow of intracranialbilateral ICA and BA. Calculated the TCBF by the equation, which equals the plus ofvolume flow in bilateral ICA and BA. Analyzed for the difference between bilateralICA in respective groups included typical subtype, variant subtype and hypoplasticsubtype in the circle of Willis typeⅡ, which referred to that anterior circulation wascomplete but the posterior circulation was incomplete; the difference of the volumeflow in the intracranial bilateral ICA, BA and the difference of TCBF, which was indifferent groups, then determined the effect of morphologic Variations in the circle ofWillis, mainly fetal-type posterior cerebral artery (PCA) or hypoplastic A1 segment ofanterior cerebral artery (ACA) on the volume flow distribution in the intracranialbilateral ICA, BA and TCBF.Results: In theⅡb subtype group with unilateral fetal-type PCA (calledⅡbunilateral fetal-type present), the volume flow in the ICA on the side of thefetal-type PCA is significantly increased compared with the volume flow in thecontralateral ICA and Compared with volume flow in the ICA inⅡa subtype withunilateral posterior cerebral communicating artery (PCOA) (calledⅡa unilateralposterior present) (p＜0.05), however the difference of the volume flow in bilateralICA inⅡa subtype group has no statistics significance (p＞0.05); the difference of thevolume flow in BA in the two groups has no statistics significance (p＞0.05), but thevolume flow in the BA inⅡb subtype group has a tend to decrease compared with thevolume flow in the BA inⅡa subtype group; the difference of the TCBF in the twogroups also has no statistics significance (p＞0.05). In theⅡc subtype group with a hypoplastic A1 segment of ACA and without bilateral PCOA (calledⅡc bilateralposterior absence), the volume flow in the ipsilateral ICA is significantly decreasedcompared with the volume flow in the contralateral ICA and compared with volumeflow in the ICA in theⅡa subtype without bilateral PCOA (calledⅡa bilateralposterior absence) (p＜0.05), however the difference of the volume flow in bilateralICA inⅡa subtype group has no statistics significance (p＞0.05); the difference ofBA, the TCBF in these two groups respectively has no statistics significance (p＞0.05).In theⅠa subtype (typical subtype) group of the circle of Willis typeⅠ, whichreferred to the circle of Willis was complete, the difference of the volume flow inbilateral ICA has no statistics significance (p＞0.05).TCBF decreased following theincreasing of age.Conclusions: The difference of distribution in intracranial volume flow ofnormal adults is partly influenced by the morphologic variations in the circle of Willis.While there is unilateral fetal-type PCA variation, the volume flow in the ipsilateralICA is significantly increased compared with the volume flow in the contralateralICA, and the volume flow in the BA decreases. While there is a hypoplastic A1segment or lack A1 segment of ACA variant, the volume flow in the ipsilateral ICA issignificantly increased compared with the volume flow in the contralateral ICA, butthe volume flow in BA has no significant variant. While PCOA is lack or incompleteinⅠa,Ⅱa type, the distribution of the volume flow in intracranial great vessels isnot effected. TCBF of normal adults is not influence by the morphologic variance inthe circle of Willis, nevertheless decrease with increasing of age. MRA can not onlydirectly display morphology of intracranial vessels, but also can provide theinformation about cerebral hemodynamics. When evaluate the hemodynamics changeof all kinds of cerebral vessels disease, combine with vascular morphologic would beobtain more accurate information.