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British Journal of Radiology (2006) 79, 688-701
© 2006 British Institute of Radiology
doi: 10.1259/bjr/67705974
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Non-invasive measurement of perfusion: a critical review of arterial spin labelling techniques

E T Petersen, MSc1, I Zimine, PhD1, Y-C L Ho, MSc1 and X Golay, PhD1,2

1 Department of Neuroradiology, National Neuroscience Institute, 2 Singapore Bioimaging Consortium, A*STAR, Singapore


Figure 1
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  		Figure 1. Schematic description of a perfusion weighted image({Delta}M) obtained by subtraction of the labelled images from the control images.

 

Figure 2
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  		Figure 2. (a) Continuous arterial spin labelling (ASL) multislice experiment, using double adiabatic inversion for the control experiment, where labels get inverted during the passage of the first plane and returned to equilibrium during the subsequent passage of the second plane. (b) The EPISTAR pulsed ASL sequence, which labels everything at once and uses two 180° + 180° = 0° pulses for the control images.

 

Figure 3
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  		Figure 3. Full brain continuous arterial spin labelling(CASL) {Delta}M images acquired using double adiabatic inversion [22] in a healthy 27-year-old female. These images were acquired on a 1.5 T scanner of the F.M. Kirby Research Center for Functional Brain Imaging at Kennedy Krieger Institute.

 

Figure 4
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  		Figure 4. Full brain pulsed arterial spin labelling(PASL) using EPISTAR/PULSAR [32]. Images are the average of 30 control-label pairs acquired in 3 min using a TR of 3 s and TI of 1.7 s.

 

Figure 5
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  		Figure 5. Diagram on an arterial spin labelling(ASL) time course. In this graph, an example of two voxels having the same flow (60 ml 100 g–1 min–1) and relaxation characteristics, but different arrival time, is presented. The measured signal at a single inversion time of 1.5 s would result in a 12% lower {Delta}M signal in a voxel with delayed arrival of 500 ms (open square) as compared with a voxel with an arrival time of 200 ms (closed square).

 

Figure 6
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  		Figure 6. Dynamic perfusion characterization. In this time-course diagram, the black triangles show an example of repeated acquisition at multiple inversion time points. Usually, a three-parameter fit model is applied [37] to estimate cerebral blood flow (CBF) when multiple inversion times arterial spin labelling (ASL) sequences are used, which reveal additional information about arrival time and bolus duration. The second time-course (white triangles) has been calculated with identical perfusion parameters, while taking into account a Look-Locker readout method [43, 45, 124] (flip angle = 30°). The advantage of this method is a higher signal to noise ratio (SNR) as per acquisition time.

 

Figure 7
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  		Figure 7. Regional perfusion image(RPI) acquired using QUASAR [124] on a 23-year-old healthy female subject.

 




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