Use of short-lived 18F and long-lived 14C in double tracer autoradiography for simultaneous measurement of LCBF and LCGU.

We have developed a quantitative autoradiographic technique for the simultaneous measurement of local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU) using a combination of 14C-long-lived and 18F-short-lived radionuclides as labels. To obtain the LCGU image, a 50-fold greater radioactivity of 18F than of 14C was administered and the first exposure was done for 2 hours. Three days later, when most of the 18F had decayed, a second exposure was done for 5 to 6 days to obtain the LCBF image. 18F standards were prepared in each experiment. The technique provides, for the first time, the local glucose flow ratio (LGFR). LGFR, obtained by dividing the LCGU by the LCBF image, was expressed as percent mumol/ml (multiplied by 100). Measurement of these three values in the same animal is expected to prove useful in the investigation of the pathophysiology of the brain. The advantages of this method are that cross contamination is less than 4%, chemical or physical manipulation of the slices is unnecessary, and final results can be obtained within a week.