Total body scanner for high energy gamma rays.

Abstract

In order to facilitate metabolic studies in man with certain radioactive isotopes, a special scintiscanner has been designed, constructed, and placed in operation. This has been particularly designed to be used with isotopes with high-energy gamma rays, such as calcium 47, zinc 65, etc., and to permit scanning of any portion of the body conveniently. Some of the special features are reported here. The region scanned is 6 × 2.5 feet in a horizontal plane. A more limited vertical plane can also be accommodated. Two scanning heads were designed: one to move above the patient on an elevated track, and the other to move below the patient on a floor-mounted track. The scanner has been placed in operation with only the upper unit completed. A thin Lucite platform supports the patient, and folds away when a bed or stretcher is preferred. The scanning heads can move with either continuous or step-wise motion. The speed can be adjusted from 0.1 to 10 cm./sec. in orthogonal directions in the horizontal plane. The vertical positions of the heads are also controlled by motors and the upper head can be rotated through a complete hemisphere. Each head is provided with 4 × 4-inch crystal with a 4-inch diameter photomultiplier tube. The crystal and tube are surrounded by a combination lead and tungsten shield 12 inches in diameter. A focusing collimator of tungsten with 19 holes and a focal length of 3 1/2 inches beyond its face is employed. The total weight of each collimator and shield assembly is 600 lb. A linear amplifier, single channel pulse height analyzer, and decade scaler are used to accumulate the pulse counts before printing. The data are displayed with a unique system which permanently records all the information received by the crystal. When the head is used with a step-wise motion, counts are accumulated during its stationary interval and printed while it advances to its next counting position. The distance between counting positions may be adjusted from 3/16 to 3 inches and the time interval may be adjusted from 1 to 60 seconds. A specially built electrical output-writing typewriter prints the counts accumulated at each position at a corresponding point on a roll of paper 2 feet wide. A 3-digit print-out is employed, with the use of two-colored ribbon with shift to accommodate large numbers. Identifying marks can also be printed as desired for any particular count. The synchronization between the scanner head and print-out position is accomplished by having the typewriter carriage driven by synchromotors which are controlled by the motion of the scanner.