Introduction
Recently, dual-head coincidence gamma camera (DHC) has been developed. This system has sodium-iodine detectors and a coincidence detection mode. Although the DHC system has been used for the qualitative assessment of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) whole body distribution in nuclear oncology, to the best of our knowledge, there have been no studies on the quantitative measurement of regional cerebral metabolic rate of glucose (CMRglc). The purpose of this study was to measure regional CMRglu by using the DHC.
Methods
We studied seven healthy male volunteers who showed no clinical evidences of cognitive and neurological deficits. Their mean age was 30.2±5.8 years (range:25-39 years). Data acquisition was performed by use of VERTEX Plus MCD (ADAC Laboratories, Milpitas, CA). This system has in-plane spatial resolution of 10 mm (FWHM) and a sensitivity of 3.0 cps/Bq/ml. The brain scanning was started 30 or 70 min after injection of 185 or 111 MBq of FDG. The emission data were collected for 30 min. Sixty four projections of coincidence detection were obtained at 50 seconds per projections every 5.6 for 360 (180×2), in a 128×128 matrix. Frame-by-frame decay correction was performed before image reconstruction using a Butterworth filter (cut-off frequency 1.20 cycles/cm, order 10). The Chang's postreconstruction attenuation correction was applied to the slices by fitting an ellipse to the scalp contour for the entire brain with an attenuation coefficient of 0.08 cm−1. The final reconstructed axial image was generated from 4.0 mm-thick slices with ordered subset expectation maximization algorithm (subset: 8, iteration: 4). Serial arterial blood samplings were done from a catheter placed in the radial artery to measure plasma radioactivity and glucose. Regional CMRglc was calculated according to the autoradiographic method 1 originally developed by Sokoloff et al 2 . The incorporated metabolic rate constants were K1=0.102, k2=0.130, and k3 =0.062, and the lumped constant was 0.42.
Results
The mean value of regional CMRglc for the frontal, temporal, parietal, occipital cortexes, thalamus and cerebellum was 4.5±0.8, 4.7±0.8, 4.5±0.8, 4.3±0.8, 3.7±0.6 and 4.8±0.8, respectively. The mean CMRglc for global cerebral cortexes was 4.5±0.7 mg/100 g/min. These values were slightly lower than the published values of the CMRglc on normal volunteers measured by positron emission tomography.
Conclusion
By taking influences of attenuation correction, dead time correction and scatter fraction into account, the quantitative measurement of brain glucose metabolism is possible by the DHC.