The Measurement of Local Blood Flow in the Cerebral Cortex from the Clearance of Xenon-133.

Recently Lassen and Ingvar (1961) devised a technique for measuring local blood flow through the cerebral cortex. Their method, derived from the Fick principle, entailed the injection of the radioactive gas krypton85 into the carotid artery and the subsequent measurement of the rate of clearance from the brain of the beta emissions of the isotope. As these have an average range in tissue of 0-7 mm., measurements of local blood flow can be made only on the exposed brain cortex. A more recent report describes the measurement of regional cerebral blood flow in man by monitoring the low incidence gamma emissions of krypton85 with a scintillation detector placed over the scalp and Ingvar, 1963). However, in that study uncolli-mated detectors were used in most patients, and the clearance of krypton85 was recorded from almost one hemisphere of the brain. Recently we reported the substitution of the gamma-emitting isotope xenon133 for Kr85 and the measurement of local blood flow in a fairly small area of the cerebral cortex by external counting through the intact skull using a depth-focusing collimator (Glass and Harper, 1963). This paper describes measurements made in several patients who were undergoing cerebral angiography. METHOD Xenon133 was received in 100 mc. doses in a sealed glass ampoule, which was connected to a glass reservoir which had been previously evacuated with a vacuum pump. On breaking the seal the gas entered the reservoir and the remaining space was filled with normal saline. Aliquots of the solution, each of 20 ml., were withdrawn into syringes. Each syringe contained approximately 0-5-1 mc. of radioactivity. Measurements of cortical blood flow were made on anaesthetized patients undergoing cerebral angio-graphy for suspected intracranial lesions. Anaesthesia was induced with thiopentone and maintained with 75 % N2O and oxygen. D-tubocurarine (15-25 mg.) was administered and additional doses of 10 mg. were given as required. The patients were ventilated with intermittent positive pressure on a Barnett ventilator. An open circuit was used and the expired gases led to the outside atmosphere through a thick-walled plastic tube. The detector consisted of a focusing collimator, a 5-in. diameter sodium iodide crystal, and a photomultiplier. The last was connected to a ratemeter and direct writing recorder. The focusing collimator was mounted in front of the crystal and localized the area of cortex under view. The collimator was lowered by a special stand on to the patient's scalp, when the centre of …