The calculation of the physical coordinates from the image points and the sequence parameters as well as the calculation of the parameters of the new slices were done with a program written by one of the authors. The connecting line of the two outer points defined the normal of the new slices and, consequently, the new slice angels, the included third point defined the position of the following flow quantification sequence. Then, three points in the maximum intensity-projection (MIP) of the angiogram were selected, which were situated on a straight part of the target vessel, the A. First a coronal three-dimensional phase contrast angiogram of the whole rat brain was performed to detect the circle of Willis. Blood flow changes were monitored by a MRI-Scanner (Bruker PharmaScan 70/16–7.0 Tesla (300.51 MHz 16 cm) 1 d, 7 d and 14 d after surgery under controlled isoflurane anaesthesia. In the Ligature-Shunt group AV fistula-creation on the left side was performed additionally to the ligature of the right common carotid artery (n=10). In the Solo-Shunt group the common carotid artery was anastomosed end-to-side with the jugular vein, thereby creating an arterio-venous (AV) fistula on the left side (n=10). Materials and Methods: To increase blood flow in the rat circle of Willis we developed two different models. Thus, the aim of this study was to establish the quantitative MRI-based flow measurement using the example of the rat circle of Willis. Introduction: Determination of blood flow in the intracerebral collaterals is an essential step to investigate the effects of experimentally increased fluid shear stress (FSS) on the growth of cerebral collaterals in small animal models. Quantitative MRI-based measurement of blood flow in the rat-circle of Willis by Bruker PharmaScan 70/16 Abstract

Bruker apex iii 70