Regional pulmonary function evaluation using xenon 133, a scintillation camera, and computer.

Abstract

FOR THE PAST three years, xenon 133 and a scintillation (Anger) camera have been used extensively in our Nuclear Medicine Clinic to evaluate pulmonary function and measure regional blood flow (1–3). This report is a follow-up of these studies in selected patients with pulmonary disease, including our experience with the use of a computer2 for data processing. Materials and Methods One-curie ampules of 133Xe are received at weekly intervals from Oak Ridge National Laboratories. The gas is transferred into sterile saline solution in concentrations up to 5 mCi Xe/ml. Details of the technic involved have been discussed elsewhere (1,2). Our scintillation camera is equipped with bi-alkali cathode photomultiplier tubes which have a relatively low work function for electron release; for this reason, acceptable statistical information concerning the positioning of individual scintillations is obtainable despite the relatively low energy of the gamma rays emitted by 133Xe (81 keY). These cathode tubes, together with a multichannel collimator designed for use with low-energy gamma emitters, provide a resolution of approximately 15 mm as measured in a manner similar to that of Westerman and Glass (4). The camera crystal may be divided electronically into halves or quadrants so that data occurring in these sectors may be recorded separately. Thus it has been possible to obtain data on ventilation and perfusion in each hemilung or in each upper and lower lung field bilaterally. For the past year, data have also been recorded on magnetic tape for computer evaluation. This was made possible through the use of interface equipment consisting of an analog-to-digital converter, a 1,600-channel memory system, and a magnetic tape controller. The controller transfers data from the memory system onto the magnetic tape at preselected time intervals (Fig. 1).3 The tape deck contains seven tracks and travels at a speed of 36 inches/second. The 1,600-word memory provides a 40 X 40 matrix for recording in digital form the distribution of scintillation events occurring in the camera crystal. For evaluating rapidly changing dynamic processes such as pulmonary function, data are usually transferred from the memory system to tape at three-second intervals. The time required to transfer each collection of data from the 1,600-channel memory system to tape is two-tenths of one second when the total counts accumulated per channel (characters per word) is maintained below 1,000 for each data transfer. Each set of data transferred to the magnetic tape is given one number in sequence and a second number to identify the patient. It is possible to play back any or all records for review on an oscilloscope which is also part of the interface equipment, thus permitting studies of the distribution of radioactive xenon in the lungs at particular times and selection of regions of interest to be programmed into the computer.