fMRI: Biological Basis and Experiment DesignLecture 15: CBF and Localization II

• CBF techniques• Big veins and big voxels

1 light year = 5,913,000,000,000 miles?

Harrison, Harel et al., Cerebral Cortex 12:225 (2002)

100m

Perfusion techniques

• FAIR – Flow-sensitive Alternating Inverstion Recovery • MOTIVE – MOdulation of TIssue and VEssel signal• QUIPSS – QUantitative Imaging of Perfusion using a

Single Subtraction• QUIPSS-II – QUIPSS ... 2nd version• CASL – Continuous Arterial Spin Labeling• PASL – Pulsed Arterial Spin Labeling

Perfusion (ASL) – general idea

• Water in blood is used as a tracer• Two images are measured

– With inversion of incoming blood• Longitudinal magnetization of incoming

blood is inverted, and subtracts from total voxel signal

– Without inversion of incoming blood

• Difference image indicates

CASL vs. PASL

• Continuous ASL– long pulse is applied to neck arteries, so all blood coming into

the head is inverted– After an appropriate delay (~1 – 2s) for that blood to get to the

volume of interest, image is acquired– Reference image is taken without inversion pulse– Subtraction provides perfusion map

• Pulsed ASL– Inversion is done in slab surrounding slices of interest– The rest is the same ...

Low res SE

High res SE