Measurement of the evoked vascular response (EVR) to cerebral activation due to vibro-tactile stimulation using gated ¹¹C-CO PET acquisition

Conventional positron emission tomography (PET) activation studies are performed using multiple injections of ¹⁵O water and subtraction of base-line from activation studies. These studies are acquired over 30 to 60 seconds and can be repeated every ten to 15 minutes, so their temporal resolution is poor. The authors report on a much more rapid technique to measure cerebral activation with PET. In their first successful studies the subject inhaled a tracer quantity (750 MBq) of ¹¹C carbon monoxide mixed in medical air. A pulsed vibrator taped to the fingers of the right hand provided a stimulus in 8 five-second phases (four on, four off) over a period of 20 minutes. PET images were acquired with a Scanditronix PC2048-15B whose data acquisition system had been modified to allow cyclic acquisitions similar to gated cardiac studies. In a series of four subjects the evoked vascular response (EVR) was clearly identified. When the subjects data is pooled a clear pattern of activation is easily seen, and the phase of the on-set is measurable. When analyzing the data from individual subjects the authors found the studies with higher count-rates give the most conspicuous activation. It is anticipated that single subject activation studies would yield improved image quality on a scanner capable of 3D acquisitions