A High-Contrast Photographic Recorder for Scintillation Counter Scanning

Abstract

During the past four years, in the Hospital of the University of Pennsylvania, external scintillation counter scanning has been used to provide information relative to the distribution of radioactive isotopes in patients. Attention has been centered largely on representation of the thyroid gland, detection of functioning metastases of thyroid carcinoma, and the outlining of intraperitoneal and intrapleural radioactive colloidal gold distributions. We have been dissatisfied with the standard mechanical relay recording systems, such as those which print marks on paper to indicate the. rate of counting gamma-ray activity. Recently, there have been described several recording devices which attempt to provide better representation of radioactive distributions (1-4). While differing in construction, these instruments are alike in that, with constant scanner speed, the spacing of marks produced on paper or film is proportional to the time required to accumulate a pre-set number of counts. Such a recorder will outline an area whose count rate differs several-fold from the count rate of its surroundings. With smaller differences, however, the change in spacing is not sufficient to be noticed, and the area of activity may be overlooked. Because of this, it was felt that a photographic method of recording might be advantageously employed for converting count rate data into contrasting visual images. The recording system to be described here is thought to offer an improvement in the scanning technic because the method of presenting the count rate data makes possible visualization of relatively small differences in activity. A permanent record is produced and, since the film base is transparent, the recorded image may be superimposed on a roentgenogram to permit better anatomical reference of the area under study. A block diagram of the external scanning equipment is shown in Figure 1. The scintillation counter is driven over the patient by two motors. The signal from the photomultiplier is amplified, passed through a discriminator, and counted with a scaler. A signal from the scaler drives a conventional mechanical recording system2 and, after electronic modification, energizes the light source for the photographic recorder. The light source is enclosed with the recording film in a light-proof box. Design of Scanner and Recorder Mechanical Apparatus: The scanner framework (Fig. 2) is suspended so that it can be positioned in height or rotated about an axis between its supporting columns. Such flexibility is desirable, since it makes possible scanning from above, below, or from the side without change in the position of the patient. This feature is particularly useful in scanning fluids which may shift within the body.