SUMMARY We have developed an autoradiographic technique for tbe simultaneous measurement of local cerebral blood flow (LCBF) and local cerebral metabolic rate for glucose (LCMRgl) using '"Modoantipyrioe and "C-2-deoxyglucose respectively. By exploiting tbe different half-lives of "I and "C, 13.0 hours versus 5730 years, we produce 2 autoradiographic images. The first is predominantly a result of the "*I and the second is predominantly from the U C. Because of the Impracticality of making m I standards, it was necessary to determine the constant which relates the ability of 1M I, with respect to "C, to expose Kodak SB-54 fllm, so that tbe '"I exposure could be quantified using "C standards. Subtraction equations can then be used to solve for the local 1MI and "C concentrations. The technique was validated in conditions simulating a 12-fold decoupling of flow and metabolism and the standard deviation of error in measuring tracer concentrations was less than 6%. It was then used to measure these parameters in the normal awake rats and values obtained agreed well with published values from single radionudide studies. The technique is expected to be useful in the simultaneous measurement of LCBF and LCMRgl in various physiologic or pathologic states, including those with significant decoupling of flow and metabolism. In addition, by using other tracers labelled with '"I and "C, other parameters can be measured concurrently. Stroke, Vol 12, No 5, 1981INTEREST in autoradiographic techniques which can differentiate between 2 radionuclides has risen sharply. This enthusiasm is a result of the recent development of radiopharmaceuticals which can be used for in vivo measurement of various physiologic and metabolic states of organs in laboratory animals. Local cerebral blood flow (LCBF) 1 ' * and local cerebral metabolic rate for glucose (LCMRgl) 1 have been studied using the tracers u C-iodoantipyrine and u C-2-deoxyglucose respectively. The ability to measure such parameters simultaneously would be of value in determining their interrelationships in various physiological and pathological states.Various non-quantitative methods are presently employed to separate autoradiographically radionuclides with different energy spectra or decay rates. The isotopes can be separated by selective filtration with inert absorbers when the emission energy spectra differ significantly, or by time dependent means when the half-life of one isotope is considerably shorter than the other. No technique described allows measurement of 2 parameters with fine spatial detail. An ex-

A comparison of local cerebral blood flow estimates with the microsphere and the 4-[N-methyl-14C]iodoantipyrine ([14C]IAP) techniques has been performed in cats. Good correlation of [14C]IAP with microsphere flow estimates in the gray matter was found. In the white matter, however, [14C]IAP flow estimates were consistently lower than microsphere flow estimates. Error analysis of both techniques and comparison with previous studies suggest that peculiarities of white matter arterial vasculature with preferential microsphere accumulation may lead to this discrepancy. Microspheres did not interfere with flow as shown by the normal appearance of subsequent [14C]IAP autoradiograms. The number of microspheres seen on autoradiograms was used for an estimate of microvessels blocked by spheres and found to be negligible. The study also demonstrates that [14C]IAP is not diffusion limited up to the observed flow values of 2 ml.g-1.min-1. Both techniques might be used together for a combination of their respective advantages, which are temporal and spatial resolution for microsphere and [14C]IAP, respectively.