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AJNR - American Journal of Neuroradiology

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American Journal of Neuroradiology 25:945-950, June-July 2004
© 2004 American Society of Neuroradiology

BRAIN

Standardized Time to Peak in Ischemic and Regular Cerebral Tissue Measured with Perfusion MR Imaging

Christian Nael^a, Nicole Kronsteiner^a, Erwin Schindler^a, Sören Kreuzer^a and Stephan Gentzsch^a

^a From the Division of Neuroradiology, Department of Radiology, University of Vienna, Austria

Address reprint requests to C. Nael, MD, Division of Neuroradiology, Department of Radiology, University of Vienna, AKH-Wien, Währingergürtel 18–20, A–1090 Vienna, Austria

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 (r²=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.