Background and purpose: Standardized time to peak (stdTTP) enables a quick quantification of time to peak measurements. An stdTTP </=3.5 seconds is reported to be regular, and evidence suggests that an stdTTP >/=7 seconds indicates critically perfused tissue. We verified this stdTTP in acute ischemia (within the first 6 hours after the onset of symptoms), when perfusion is critical, and after 24-72 hours.
Methods: Combined diffusion-weighted imaging (DWI) and perfusion MR imaging was performed in 20 consecutive patients with acute cerebral ischemia. Distributions of stdTTP >/=7 and </=3.5 seconds were analyzed in corresponding regions with (ischemic injury) or without (no ischemic injury) substantial hyperintensity on DWI in both hemispheres. Follow-up examinations were available in 11 patients.
Results: About 80% of voxels in regions with ischemic injury showed an stdTTP >/=7 seconds. StdTTP of about 80% of voxels was </=3.5 seconds in regions without ischemic injury. In both conditions, 14% of stdTTP values were between 3.5 and 7 seconds. We found a strong correlation between areas with stdTTP >/=7 seconds and resulting infarct (r(2)=0.86).
Conclusion: StdTTP is reciprocal in regions with and without ischemic injury. An stdTTP >/=7 seconds (regular range) is strongly correlated with resulting infarct and reflects critical perfusion with a high probability of ischemic tissue injury in acute ischemia, whereas this is unlikely in regions with stdTTP </=3.5 seconds (regular range). An stdTTP of 3.5-7 seconds is equivocal concerning ischemic injury and may indicate a tolerable perfusion condition.