Positron Imaging Laboratories, McConnell Brain Imaging Center, Montreal Neurological Institute, Montreal, Canada

Correspondence: Ernst Meyer, WB 211. Webster Pavillion, Montreal Neurological Institute, 3801 University, Montreal, Quebec, H3A 2B4, Canada.

Received 30 June 1994; Revised 21 June 1996; Accepted 21 June 1996.

Abstract

When used to measure blood flow, water leaves a residue in the vascular bed, which may contribute to the calculation of increased blood flow during functional activation of brain tissue. To assess the magnitude of this contribution with the two-compartment positron emission tomography (PET) method, we mapped the water clearance (K₁) of the brain as an index of cerebral blood flow (CBF) and the apparent vascular distribution of nonextracted H₂¹⁵O (V_o). The latter map represented mainly the cerebral arterial and arteriolar volume. We also prepared subtraction maps (K₁, V_o) of the response to vibrotactile stimulation of the fingertips of the right hand of six normal volunteers. Using magnetic resonance (MR) images of all subjects, the data were rendered into Talairach's stereotaxic coordinates and the averaged subtraction images (activation minus baseline) merged with the corresponding averaged MRI image. The K₁ map revealed the expected response in the primary sensory hand area; the V_o response was located about 13 mm more anteriorly, close to the central fissure, most likely reflecting changes of the arteries feeding the primary sensory hand area. We conclude that cerebral perfusion and cerebrovascular responses to vibrotactile stimulation may occur in disparate locations that can be identified separately by using the two-compartment method.