MR perfusion without contrast (Arterial Spin Labeling, ASL)

Teaching points by Dr MGK Murthy1.  So far, in the absence of better techniques for studying direct neural activity, Science has relied on Vascular supply to regions as an Index , using (a) Gadolinium MRI  (b) Radioactively labeled water (15 O water )imaged with with PET Scanner (c) BOLD techniques of MRI (using Oxygen uptake for e.g.: as in functional MRI) 2. However a new technique now using , Magnetically labeled water molecules(Arterial Spin Labeled, ASL) on MRI scanners to study Brain perfusion ( CBF ,Cerebral Blood Flow) is becoming increasingly popular due to (a) No injections or chemicals (b) No Radiation(c) Changes in ASL on activation of brain areas more than possible with BOLD techniques Disadvantage: Takes longer for acquisition/ Less slices/ Thicker slices /Inherently Noisier (as compared to BOLD) TECHNIQUE:(a) Arterial blood water labeled just below the slice of interest by applying inversion RF pulse of 180 deg ---------------Inversion of net magnetization of Blood Water (Water molecules labeled magnetically)-------------------After a period of time (Called Transit Time) ---------- paramagnetic tracer will flow in to slice or Region of interest --------------Exchanges with Tissue water ------------Results in Decrease in Total Tissue Magnetization --------------MR signal and image intensity will decrease -----Image...
Source: Sumer's Radiology Site - Category: Radiology Authors: Source Type: blogs