- Compatible with GRAPPA parallel acquisition technique
- Compatible with standard 12 channel head matrix coil and 32 channel head coil
- Option of ASL 2D and ASL 3D
- ASL 2D is implemented with 3D PACE and inline calculation of relCBF maps for a quantitative evaluation of brain perfusion
- ASL 3D is implemented with inline calculation of perfusion-weighted maps for a qualitative evaluation of brain perfusion
In ASL, first, arterial blood water is magnetically labeled just below the region of interest by applying a 180 degree radiofrequency (RF) inversion pulse. The result of this pulse is inversion of the net magnetization of the blood water. In other words, the water molecules within the arterial blood are labeled magnetically. After a period of time (called the transit time), the magnetically labeled water flows into the region of interest where it exchanges with tissue water. The inflowing inverted spins within the blood water alter total tissue magnetization, reducing it and, consequently, the MR signal and image intensity. During this time, an image is taken (called the tag image). The experiment is then repeated without labeling the arterial blood to create another image (called the control image). The tagstate is alternated with the control state, in which the magnetization of the arterial blood is not inverted. The control image and the tag image are subtracted to produce a perfusion image. This image will reflect the amount of arterial blood delivered to the slice within the transit time. There are mainly two techniques for ASL; PASL (Pulsed ASL) and CASL (Continuous ASL). In PASL, the RF pulse is applied in a spatially selective manner (region-specific). Consequently the inversion of the arterial blood occurs over a specific area. PASL such as ASL 2D and ASL 3D are particularly attractive for higher field strengths as other schemes such as CASL have to deal with the challenge of high Specific Absorption Rate (SAR).