Technical considerations Time-of-flight magnetic resonance angiography In time-of-flight magnetic resonance angiography (TOF MRA), repetitive pulses are used to suppress stationary background tissues, while the unsuppressed protons of flowing blood create a signal. The high signal intensity in the blood vessels during TOF MRA is attributable to flow-related enhancement, and the absence of flow is characterized by reduced signal intensity [1]. The signal intensity of flowing blood depends on its velocity, the length and course of the vessel being imaged, the flow characteristics, and sequence parameters. The main lim- itations of the technique are the spin dephasing that occurs in complex or turbulent flow pattern, particularly in three-dimensional (3D) TOF, and in vessels in close proximity to tissues with short T1, such as fat or subacute hemorrhage (Table 1). Signal loss may also occur in the presence of flow resulting from the spin saturation effect, O ¨ zkan O ¨ zsarlak Johan W. Van Goethem Menno Maes Paul M. Parizel MR angiography of the intracranial vessels: technical aspects and clinical applications Received: 19 April 2004 Accepted: 6 September 2004 Published online: 4 December 2004 Ó Springer-Verlag 2004 Abstract Evaluation of the intra- cranial circulation provides valuable information in the diagnosis and prognosis of various intracranial abnormalities and may influence patient management. Technical ad- vances in magnetic resonance angi- ography (MRA) have improved the accuracy of this technique in various clinical situations, such as aneurysms, arterial and venous ste- no-occlusive diseases, vascular mal- formations, inflammatory arterial diseases, preoperative assessment of the patency of dural sinuses, and congenital vascular abnormalities. In many centers, MRA has replaced conventional digital subtraction angiography in screening for intra- cranial vascular disease, because of its non-invasive and non-ionizing character. Several MRA techniques have been developed for the imaging of the intracranial vascular system, such as time-of-flight MRA (TOF MRA), phase-contrast MRA (PC MRA), and more recently contrast- enhanced MRA (CE MRA). In the evaluation of steno-occlusive dis- ease, the three-dimensional (3D) TOF-MRA technique is recom- mended for arterial evaluation, and the 2D TOF or 2D PC-MRA tech- nique for venous evaluation. For the evaluation of aneurysms and arte- riovenous malformations (AVMs), we recommend the 3D CE-MRA technique, especially dynamic sequences in case of AVM. In this review, the technical aspects, limita- tions, and optimization of these MRA techniques will be discussed together with their indications in intracranial disease. Keywords Magnetic resonance Æ Vascular studies Æ Infarction Æ Aneurysm Æ Intracranial Æ Arteriovenous malformations Neuroradiology (2004) 46: 955–972 DOI 10.1007/s00234-004-1297-9 DIAGNOSTIC NEURORADIOLOGY O ¨ .O ¨ zsarlak (&) Æ J. W. Van Goethem M. Maes Æ P. M. Parizel Neuroradiology Section, Department of Radiology, University Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium E-mail: ozkan.ozsarlak@uza.be Tel.: +32-3-8214585 Fax: +32-3-8252026