An Automatic Method of Studying the Distribution of Activity in a Source of Ionizing Radiation

Abstract

Many attempts have been made to determine the distribution of radioactive materials in the human body by means of highly directional counting systems. In many instances in clinical practice, use is made of a Geiger counter in a lead shield having a narrow aperture through which the detector “sees” the radioactive material. This counter may be held in the hand, moved mechanically, or perhaps placed in succession in a number of positions aginst the flat surface of a mould worn by the patient. The observed counting-rates may be displayed in a diagram of lines of equal counting rates (“equinumerals”) and an attempt thus made to deduce the distribution of activity in the patient (Mayneord, 1950). After some experience of these methods it seemed that they were often clumsy and inadequate. It appears that a mechanical scanning system coupled to a display which presents a visual image of the distribution of counting-rate would have great advantages. By an obvious extension a permanent photographic record might be obtained for subsequent study and comparison. Preliminary experiments (Mayneord, Turner, Newbery, and Hodt, 1951) soon showed that there was no difficulty in causing a single pulse from a Geiger counter to modulate the brightness of the spot of a cathoderay tube, raising it from a very low level of brightness to its maximum value. Imagine now a detector receiving radiation only from a small angular region and moving in front of a source so as to scan it.