(15)O-Gas PET is useful for evaluating hemodynamic status in patients with ischemic cerebrovascular disease. To reduce examination time and exposure to radioactive gas, we assessed a count-based method with shorter continuous (15)O(2) gas inhalation.
Methods: Twenty-five patients (66 +/- 13 [mean +/- SD] y old) with unilateral cerebrovascular stenoocclusive disease were examined by use of measurements of asymmetric oxygen extraction fraction (OEF) elevation. Dynamic PET scans of 1 min per frame were obtained starting 2 min after the beginning of (15)O(2) inhalation at a constant flow rate (740 MBq/min). Each subject also underwent C(15)O and H(2)(15)O PET with the bolus administration method. To evaluate the effects of different scan start times and durations during (15)O(2) inhalation, we extracted and summed individual (15)O(2) PET data from the dynamic (15)O(2) dataset. Count-based OEF (cbOEF) images were calculated from (15)O(2) and H(2)(15)O PET images. The asymmetric indices (AI) of cbOEF (cbOEF-AI) were obtained from regions of interest drawn on territories of the bilateral middle cerebral artery. These AI were compared with the AI of quantitative OEF (qOEF-AI).
Results: The slopes of the regression lines and the coefficients of correlation between qOEF-AI and cbOEF-AI were close to 1.00 and greater than 0.79, respectively, regardless of different scan start times and durations. The cbOEF-AI obtained with a longer scan duration were closer to the qOEF-AI than those obtained with a shorter scan duration. Longer scan durations also provided better coefficients of correlation between cbOEF-AI and qOEF-AI regardless of scan start times. The coefficients of correlation between cbOEF-AI and qOEF-AI were greater than 0.90, except for cbOEF-AI obtained from (15)O(2) images at 2-3 min after (15)O(2) inhalation.
Conclusion: The cbOEF obtained by (15)O(2) imaging from 4 min after (15)O(2) inhalation to 7 min or longer can correctly diagnose misery perfusion. The less invasive count-based PET method used in this study will be able to reduce examination time, exposure time, and stress for patients with ischemic cerebrovascular disease.