Subtraction of arterial spin-labeling magnetic resonance perfusion images acquired at dual post-labeling delay: Potential for evaluating cerebral hyperperfusion syndrome following carotid endarterectomy.

Arterial spin-labeling magnetic resonance perfusion imaging is a promising tool for the diagnosis of cerebral hyperperfusion syndrome after carotid endarterectomy. However, arterial spin-labeling with a single post-labeling delay has been reported to show a higher incidence of increased arterial spin-labeling signals in the bilateral hemisphere, probably due to a shortening of the arterial transit time or an arterial transit artifact caused by intravascular stagnant magnetically-labeled spin. To overcome these shortcomings, we used two post-labeling delay settings (1.0 and 1.5 s) in 8 patients who had undergone carotid endarterectomy. In addition, we created a subtraction image between the mean perfusion maps at post-labeling delays of 1.0 and 1.5 s. This also decreased arterial transit artifacts, as these appeared in nearly the same configuration in both post-labeling delay settings. In all eight cases examined, increased arterial spin-labeling signals were observed bilaterally on both dual post-labeling delay settings. Subtraction images revealed that these increased signals were attributable to arterial transit artifacts in seven cases. However, in one patient who developed clinical symptoms, the subtraction method demonstrated post-carotid endarterectomy hyperperfusion. This preliminary study demonstrates that the subtraction method might decrease arterial transit artifacts and yield a map that can better represent true perfusion, thus enabling the detection of post-carotid endarterectomy hyperperfusion.