Perfusion weighted imaging Arterial spin labeling Basic physics and diagnosis

1. R A H M A N U D D I N
L E C T U R E R M E D I C A L
I M A G I N G
N W I H S
PWI: Arterial Spin Labeling
(ASL)

2. Introduction
 A noninvasive method
 To assess tissue perfusion
 No exogenous contrast agent injection or radiation
Venous
Angioma

3. Procedure
 Arterial flow toward ROI tagged by magnetic
inversion pulses
 Phase of protons changed
 After delay, allow tagged blood to enter in Slice of
interest (SOI), image is acquired
 Such image is called tagged image
 Second image, same SOI again acquired without in-
flowing tagged blood, image is called control image
 The tagged is subtracted from control
 Results in perfusion image representing tagged
blood that flowed into the image slice

4. ASL procedure

7. Procedure Cont…
 ASL involves T1-w imaging
 Has poor SNR ratio
 However, ASL has better spatial and temporal
resolution than PET
 Poor SNR and sensitivity to abnormally long transit
delay of tagged protons have limited its application
in clinical practice

8. Resolution of SPECT vs. ASL