1. MR ANGIOGRAPHY USING SPIN LABELING – DETERMINATION OF FEEDING AND DRAINING VESSELS OF ARTERIOVENOUS MALFORMATIONS C. Warmuth, C. Zimmer, A. Förschler Charité, Department of Neuroradiology, Berlin, Germany Purpose: We attempted to determine feeding and draining vessels of arteriovenous malformations completely noninvasively. Conventional time-of-flight (TOF) MRA incorporates no dynamic information about blood flow (velocity and direction). With spin-labeling it is possible to image the inflow of magnetically labeled blood into the vessel tree in a time-resolved fashion. Similar to X-ray angiography, projection angiograms of the vessels are acquired at different times after labeling. Temporal resolution is limited only by the scanner hardware and the overall duration of the measurement. With our scanner (Siemens Vision) up to 80 images per second are possible. Materials & Methods: Spin-labeling was done using the FAIR inversion scheme in combination with a segmented FLASH Look-Locker sampling strategy (1, 2). Arterial blood is labeled by alternating slice selective and nonselective adiabatic inversion pulses. After labeling, repetitive acquisition of several (n = 1..9) k-space lines is done for a period of 1-2 sec. As the label decays with T1 of blood (1200 ms), no labeled blood is left after 4 sec and acquisition is continued with the the next n k-space lines. Segmented data acquisition relies on the assumption that blood dynamics is identical for every heart beat and k-space lines from different heart beats with the same delay after inversion can be combined to an image of that delay. Cardiac triggering was used therefore whenever possible. A threefold segmentation was chosen to be appropriate, resulting in a temporal resolution of 40 ms (25 images per sec) and a measurement time of 12 min for 2 averages. Six patients with arteriovenous malformations were examined, 5 of them with prior embolization. Results: Feeding arteries could be visualized well in 5 of 6 patients, draining veins could be identified in 4 patients. Three measurements are shown in Figure 2. Thirty images were made with a temporal resolution of 40 ms. In the figure, 5 consecutive images are averaged, resulting in an inter image delay of 200 ms. Compared to TOF MRA, feeders and veins are better distinguishable. The drawback however, is the missing 3D information as it is a projection technique. It can be done in 3D too, but measurement time scales with the number of partitions. Conclusions: Noninvasive dynamic projection angiography is possible using spin-labeling. Temporal resolution is higher than that of X-ray DSA, but SNR and spatial resolution are inferior. The technique is optimally suited for planning and monitoring of gamma knife surgery. References References: 1. Kwong K, et al. MR perfusion studies with T1-weighted echo planar imaging. Magn Reson Med 1995;34:878-887 2. Guenther M, et al. Arterial spin labeling in combination with a Look-Locker sampling strategy: Inflow Turbo-Sampling EPI-FAIR (ITS- FAIR). Magn Reson Med 2001;46:974-984 Sequence scheme: 3 fold segmentation SS / NS line 1 line 2 line 3 line 1 line 2 line 3 line 1 line 2 line 3 line 1 line 2 line 3 SS / NS line 4 line 5 line 6 line 4 line 5 line 6 line 4 line 5 line 6 line 4 line 5 line 6 40 ms 25 frames/s Image 1 Temporal resolution measurement time line 1 line 2 line 3 line 4 line 5 line 6 Image 2Image 3Image 4Image 5 Labeling t=0 ms t=40 mst=80 mst=120 mst=160 mst=200 ms Next repetition after 3-4 s. 100ms300ms500ms700ms900ms1100ms DSLA-AverageTime of max. TOF-MRA DSA: Ext. LATDSA: VAG LATDSA: MCA AP DSLA 400ms600ms 800ms 1000ms 1100ms Average DSA: VAG LAT DSA: VAG AP DSLA 200ms400ms 600ms 800ms 1000ms Average DSLA DSA: VAG LAT Patient 1: AVM at the left Arteria cerebri posterior. The feeding vessel (yellow arrow) is clearly visible, also the nidus itself. The draining vein (red arrow) is hardly to be seen. Patient 2: The nidus is filled from the right posterior cerebral artery. Prolongued venous drainage by a central vein (red arrow), visible in the later images. Feeders are hard to identify.