Transverse section and rectilinear brain scanning with Tc-99-m pertechnetate.

Abstract

This communication reports our initial twelve-month experience with Tc99m pertechnetate, using it for both rectilinear and transverse section brain scanning. The scanning agent Tc99m pertechnetate was chosen to keep radiation exposure low, even when we gave large doses of radionuclide to increase the count rate (1). With the high count rate, multiple pictures of good quality were obtained in an acceptable period of scanning time. Transverse section scanning (2–5) was employed to improve the description of lesion extent in three dimensions and to test the premise that the method should improve diagnostic accuracy. We predicted that the transverse section scan would be less influenced by those normal images of muscle and blood which can obscure information in the rectilinear scan. If this were true, we expected diagnostic accuracy to be improved for lesions of the base of the cranial vault and posterior fossa. Method Rectilinear scanning was performed with either of two instruments, a commercial scanner or a research scanner. The commercial scanner had a detector crystal 5.1 cm thick and 7.6 cm in diameter, a collimator with a 3.0 cm diameter of view at a focal length of 6.8 cm, and a mechanically coupled photorecorder.2 Count rate over the head was 400–2,000 counts per second. The scan speed was 1.5 cm per second, and the line spacing was 0.3 cm. Each view of the head was completed in ten to fifteen minutes of scanning time. The research scanner has been described in detail elsewhere (4, 5). For rectilinear scanning, two opposed scintillation detectors scanned both sides of the head simultaneously. Each detector had a crystal 5.1 cm thick and 7.6 cm in diameter and a low-energy collimator with a 1.25 cm diameter of view at a focal length of 7.6 cm (6). Count rate over the head was 100–500 counts per second. Counting and position data were recorded on perforated paper tape at the time of scanning and replayed later for generation of scan pictures on Polaroid film (7). Scan speed was 2 cm per second, and the line spacing was 0.25 cm, Two views of the head were completed in ten to fifteen minutes of scanning time. Transverse section scanning with the research instrument displayed the radioactivity in a cross section of brain approximately 1 or 2 cm thick. For section scanning, each collimatorhad a 1.25 cm diameter of view at a focal length of 11.4 cm (6). A section image resulted when the pair of detectors completed a sequential series of 24 tangential scan lines (7.5° angular interval) around the complete circumference of the patient's head. The scan speed was 2 cm per second. All counting and position data were recorded on perforated paper tape, and the section image was generated later on the film of an oscilloscope camera. Each complete transverse section image required approximately ten minutes of scanning time.