Acute stroke evaluated by time-to-peak mapping during initial and early follow-up perfusion CT studies

Abstract

Background and purpose: Early diagnosis of perfusion deficits in patients with acute stroke could guide treatment decisions and improve prognosis. We investigated the sensitivity of perfusion CT studies using parametric time-to-peak maps to assess ischemic brain tissue with respect to early infarct signs on native CT scans.

Methods: First-pass, single-section perfusion CT was performed in 20 patients who presented with symptoms of acute stroke within 6 hours of onset. Initial CT perfusion studies were compared with follow-up studies within 30 hours in 10 patients. A manual, region of interest (ROI)-based, local evaluation procedure was performed to determine delayed time-to-peak values and diminished peak amplitudes. In addition, time-to-peak parameter maps were processed off-line from the dynamic CT data sets to identify areas of perfusion deficits, which were expressed as hemispheric lesion areas (HLAs). Evolution of the ischemic regions was assessed by comparing the HLA on the initial and follow-up studies as well as on the native CT scan of the follow-up studies.

Results: Diagnostic time-to-peak maps were generated in 19 of 20 initial and in nine of 10 follow-up perfusion CT studies. The initial time-to-peak map showed perfusion deficits in 14 of 20 patients. Hemispheric territorial infarcts were diagnosed with a sensitivity of 93%. Perfusion deficits in two patients with brain stem infarctions and three patients with lacunar strokes were missed. Follow-up time-to-peak maps showed the extent of reperfusion after various therapeutic strategies.

Conclusion: Perfusion CT is potentially useful for detecting cerebral perfusion deficits in acute ischemic stroke before morphologic changes are observable on native CT scans. Compared with a locally restricted ROI-based evaluation, time-to-peak maps provide sensitive, global indications of malperfused brain areas, facilitate lesion localization, and allow assessment of the evolution of the infarction during follow-up.

fig 1.

Patient 6. A, Initial native CT scan shows standardized circular ROIs, which were manually placed in both hemispheres in the vascular territories of the ACA, MCA, PCA, the basal ganglia region, and the thalamus. B, Enhancement-versus-time curves of ROIs 1 and 2 located symmetrically in the anterior vascular territory of the MCA in the ischemic and healthy areas, respectively. Note the strong enhancement peak indicating the passage of the compact contrast bolus in the normal area (ROI 2). Conversely, the time course of the contralateral ROI (ROI 1) shows a markedly delayed and slow enhancement, indicating hypoperfusion.

fig 2.

Initial native CT scans and corresponding time-to-peak parameter maps. The maps are color-coded with values ranging from 5 to 40 seconds. A, Patient 6: 62-year-old woman who presented 40 minutes after onset of left hemiparesis. The CT scan is normal. Note the clear demarcation of the diseased area in the right hemisphere, corresponding to the right ACA and MCA territories, including the basal ganglia on the parameter map. B, Patient 17: 77-year-old woman who presented 40 minutes after onset of somnolence and left hemiparesis. The native CT scan is normal. The parameter map shows an area of delayed perfusion in the territory of the right MCA. C, Patient 1: 60-year-old man who had a normal CT scan 2.8 hours after onset. The time-to-peak map depicts a large perfusion deficit in the left MCA territory, including the basal ganglia.

fig 3.

Patient 10: initial and follow-up examinations. A, 2 hours 50 minutes after onset. B, 30 hours after onset, during therapy with heparin. The patient suffered from a large infarct in the left hemisphere with global aphasia and right hemiparesis. The first native CT scan (A) reveals only discrete cortical hypodensity and effacement of cortical sulci in the ischemic hemisphere. In contrast, the time-to-peak map clearly shows the extent of the affected brain area, which corresponds strongly to the hypodensity seen on the CT scan in the follow-up study (B). The time-to-peak map shows tissue reperfusion 30 hours later. A large MCA infarction developed despite recanalization.