PET measurement of regional cerebral blood flow changes during noise stimulation

Abstract

Positron emission tomographic (PET) studies of regional cerebral blood flow (rCBF) using the steady‐state 0–15 carbon dioxide (CO2) method allows within‐subject stimulation and control studies to be performed in the same session. Using this technique, we previously reported data suggesting that broadband white noise increased rCBF significantly. In the present study, we examined the temporal course of these changes. Six normal volunteers were studied with eyes covered while CO2 was inhaled through nasal prongs. Fourteen serial 1‐min images were acquired in the following sequence: 2‐min quiet, 6‐min auditory stimulation, 6‐min quiet. Arterial blood was automatically sampled every 18 s. The stimulation protocols replicated conditions used previously to study the physiological effects of noise [J. Meyer‐Delius, Automobile Tech. J. 59, 293 (1957)], with broadband white noise presented binaurally through earphones at 90 dBA with an on/off cycle of 30 s. Region of interest (ROI) data were obtained for at least 30 regions across 9 planes for each of the 14 time frames using a thresholding technique. Transient rCBF increases occurred in most ROI's within the first 1–3 min. Increased rCBF was also observed after the stimulation period ended, most consistently in cerebellum and paracentral regions where 10%–30% increases were seen in all subjects. These results suggest that rCBF changes with auditory stimulation have a significant temporal component that is not uniform across brain regions. This component must be defined when regional brain response to auditory stimulation is studied.