1. ¹Department of Radiology and Nuclear Medicine, Akita Research Institute of Brain and Blood Vessels, Akita, Japan
2. ²Department of Nuclear Medicine and Radiology, Division of Brain Sciences, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan

Correspondence: Dr Hiroshi Ito, Department of Nuclear Medicine and Radiology, Division of Brain Sciences, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-Machi, Aoba-Ku, Sendai 980-8575, Japan. E-mail: hito@idac.tohoku.ac.jp

Received 10 June 2004; Revised 22 October 2004; Accepted 3 November 2004; Published online 19 January 2005.

Abstract

The discrepancy between the increases in cerebral blood flow (CBF) and CMRO₂ during neural activation causes an increase in venous blood oxygenation and, therefore, a decrease in paramagnetic deoxyhemoglobin concentration in venous blood. This can be detected by functional magnetic resonance imaging (fMRI) as blood oxygenation level-dependent (BOLD) contrast. In the present study, changes in the cerebral oxygen extraction fraction (OEF) that corresponds to the ratio of CMRO₂ to CBF, and in the BOLD signal during neural activation, were measured by both positron emission tomography (PET) and fMRI in the same human subjects. C¹⁵O, ¹⁵O₂, and H₂¹⁵O PET studies were performed in each subject at rest (baseline) and during performance of a right-hand motor task. Functional magnetic resonance imaging studies were then performed to measure the BOLD signal under the two conditions. During performance of the motor task, a significant increase in CBF and a significant decrease in OEF were observed in the left precentral gyrus, left superior frontal gyrus, right precentral gyrus, right cingulate gyrus, and right cerebellum. A significant positive correlation was observed between changes in the CBF and the BOLD signal, and a significant negative correlation was observed between changes in the OEF and the BOLD signal. This supports the assumption on which BOLD contrast studies during neural activation are based.