For reduced refocusing flip angles, the peak of the vessel size sensitivity curve is shifting towards larger radii with increasing echo time. The BOLD sensitivity is largely independent of the refocusing flip angle down to about 40°. CPMG or GRASE can be used with low refocusing flip angles without significant loss of sensitivity to BOLD and without the need for centric reordering. Signals acquired before or after the spin echo time point show contributions from larger vessels similar to gradient echo sequences. This effect is reduced for longer echo times.
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