A standardized method of generating time-to-peak perfusion maps in dynamic-susceptibility contrast-enhanced MR imaging

BACKGROUND AND PURPOSE: Perfusion MR imaging, performed as dynamic-suscepti bility contrast-enhanced MR imaging, is sensitive to hemodynamic risks for patients with cerebrovascular disease. We sought to define a quantitative p arameter for perfusion MR imaging, which shows brain areas at hemodynamic r isk and enables direct comparison of different perfusion MR imaging examina tions. METHODS: A new standardization procedure for the time-to-peak (TTP) paramet er, standardized time to peak (stdTTP), was introduced. The stdTTP automati cally calculates a time offset correlated to the earliest enhancing voxels in a section and rescales all TTP values accordingly. Because of a close re lation between this offset and stdTTP of early enhancing voxels in central vascular territories (CVTs), stdTTP provides an estimate of the bolus run t ime between CVTs and related border zones (BZs). The stdTTP in CVTs and BZs was measured in 11 patients without hemodynamic impairment by using high t emporal resolution dynamic-susceptibility contrast-enhanced perfusion MR im aging. RESULTS: An excellent comparability of different dynamic susceptibility con trast-enhanced MR imaging studies was found. The stdTTP in CVTs was 0.4 +/- 0.5 s (minimum, 0 s; maximum, 1.3 s) for the anterior, 0.5 +/- 0.3 s (mini mum, 0 s; maximum, 1.0 s) for the middle, and 1.4 +/- 0.5 s (minimum, 0.4 s ; maximum, 2.4 s) for the posterior cerebral artery. In the anterior BZ, st dTTP was 2.3 +/- 0.4 s (minimum, 1.6 s; maximum, 3.2 s), and in the posteri or BZ, stdTTP was 2.8 +/- 0.4 s (minimum, 2.0 s; maximum, 3.4 s). CONCLUSION: The results suggest a limit for stdTTP of approximately 3.5 s i n the anterior and posterior BZs. The stdTTP could serve as a quantitative measure for the hemodynamic risk assessment of patients with cerebrovascula r disease. Because stdTTP can be directly derived from the measured curves, the hemodynamic situation of a patient can be judged with a minimum of com putational effort.