Fmdamentl alld Cliuical investigation of rCBF Measurement by single Photou Emission CTg (HEADTOME)

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The purpose of our stude was to improve image quality and reliability in measurement of tomographic regional cerebral blood flow (rCBF). Image quality was mostly affected by the window level of the pulse height analyzer (PHA). As asymmetric window level should be set as 75-110 KeV for 81 KeV photon energy of Xe-133. To avoid mismatching between the head data and the respiratory air curve, the interval of data acquisition timing was standardized. To minimize loss of Xe-133 gas and discrepancy between the air curve and the arterial activity curve, suitable volume setting of spiro- bag and breath-synchronized control of the inhalation system were required. For the Xe-133 gas inhalation, a mouthpiece was superior to a face mask because of less scattered radiation from the nasal cavity. to improve the reliability of the rCBF value, a correction of the rCBF data for end- tidal CO2 concentration was attempted. Mean rCBF increased by 14% for each 1% increase in end-tidal CO2 concentration. We introduced the correction of rCBF data by normalizing the end-tidal CO2 concentration around 5.8% corresponding to 41mmHg PaCO2. After these improvements, the quality of the rCBF image and the reliability of measured rCBF value were markedly elevated.As a clinical application, demented patiensts were examined. A temporo-parietal reduction in the distribution of the rCBF characteristic in the Alzheimer's disease and a patchy whole brain reduction characteristic in the multi infarct dementia were detected. The severity of dementia correlated with the degree of rCBF reduction especially at the temporo-parietal region in the case of Alzheimer's disease. The ability of our improved SPECT makes it a promising tool for research or routine examination of demented patients.