Tracer delay correction of cerebral blood flow with dynamic susceptibility contrast-enhanced MRI.

Cerebral blood flow (CBF) and vascular mean transit time (MTT) can be determined by dynamic susceptibility contrast-enhanced magnetic resonance imaging and deconvolution with an arterial input function. However, deconvolution by a singular value decomposition (SVD) method is sensitive to the tracer delay that often occurs in patients with cerebrovascular disease. We investigated the effect of tracer delay on CBF determined by SVD deconvolution. Simulation study showed that underestimation of CBF due to tracer delay was larger for shorter MTTs. We developed a delay correction method that determines tracer delay by means of least-squares fitting pixel-by-pixel. The corrected CBF was determined by SVD deconvolution after time-shifting of the measured concentration curve. The simulations showed that the corrected CBF was insensitive to tracer delay irrespective of the vascular model, although CBF fluctuation increased slightly. We applied the delay correction to the CBF and MTT images acquired for nine patients with hyperacute stroke and unilateral occlusion of the middle cerebral artery. We found in some patients that the delay correction modulated the contrast of CBF and MTT images. For hyperacute stroke patients, tracer delay correction is essential to obtain reliable perfusion image when SVD deconvolution is used.