Clinical investigation of the measurement of brain transit time by intravenous injection of technetium-99m

Abstract

The measurement of brain transit time by intravenous radioisotope administration had had an advantage as a clinical examination, because of its technical simplicity and little loading to the patient. This method, however, had been encountered with the difficulties to measure a precise brain transit time, since radioisotope bolus administered intravenously was dispersed, mainly through cardiopulmonary circulation. This progress report will describe a method for studying cerebral hemispheric circulation which eliminates above problem. Oldendorf had estimated the period between two inflection points of ascending and descending limbs of radioencephalogram (REG) as to be expressed brain transit time. The recognition of these two points was obscured because of statistical error of measuring radioactivities. By using gamma scintillation camera with data processing system, we tried to get a precise recognition of these inflection points in REG. Method and Results 1) Computation of frequency function of brain transit time distribution The mathematical function which characterizes the motion of tracer within a monitored region is called the frequency function of transit times, g(t). The frequency function [g(t)] of brain hemisphere was obtained by a computation of the dilution curves coupling from aorta [a(t)] with from brain hemisphere [h(t)] after intravenous injection of Tc-99m. After computing [h(t)] by convolution of [a(t)] and arbitrary frequency function of the brain [g(t)], the determination of correct frequency function [computed g(t)] can be assumed only when the computed h(t) was well coincided with original h(t). A well fit was obtained between computed REG and original REG. 2) The measurement of brain transit time by using gamma scintillation camera with data ' processing system REG presented radioactivity versus time in selected regions after intravenous injection of Tc-99m was smoothed and then differenciated by a data processing system. The two peaks of the first derivatives were clearly displayed on CRT and X-Y recorder. Brain transit times obtained by the procedure state above were 6.8, 5.0, 5.8 seconds in three cases with A-V malformation and 12.0, 11.0, 9.2 seconds in three cases in the advanced cerebral arteriosclerosis. Conclusion and Comment The frequency function of the brain transit times was computed by convolution of the radio- activities versus time from the brain hemisphere and the aorta. By using gamma scintillation camera with data processing system, brain transit times were obtained and the procedures had the advantages of clinical application for technical simplicity, rapidity to get results and its reliability. Among the clinical examinations of cerebral circulation, the measurement of brain transit time is worthy to obtain a correct diagnosis, especially using together with brain scintigraphy.