The Instrumentation for the Medical Use of Radioisotopes Diagnosis

Radioisotopes diagnosis technique helps in obtaining image of the body anatomy and functions. The images are obtained by detecting energy emitted from the radioactive substance injected in the patient either intravenously or by mouth.

The radiation emitted from the patient is similar to that emerging during radiography or CT scanning. The radioisotopes images help in diagnosing diseases; tumours, infections and disorders in organ functioning while CT scan, ultrasound and magnetic resonance provide anatomic or structural information. The primary purpose of radioisotope imaging is to provide functional data.

The radioisotopes are treated by the body like the normal substances. With the help of the emitted radiation, however, the path of the radioisotope can be traced and its concentration in various parts of the organ can be determined. If this procedure is performed in vivo, the radioisotopes emit gamma radiation that penetrates the surrounding tissues and comes out of the body to be measured by the detector.

When radioactive material is introduced into the human body for diagnosis purposes, it must be ensured that the radiation dose in the body is at a safe level. In order to ensure the removal of the source radiation after measurement, radioisotopes with a short half-life must be used.

Operation of a radioactive measurement instrumentation system

A small dose of radioactive compound is given to the patient, usually intravenously but sometimes orally, so that the radioactive material (tracer) can be localized in the specified body organ system. The radioactive compound eventually accumulates in the organ and starts emitting gamma rays. The imaging detector is made of sodium iodide crystal where gamma radiation gets absorbed and it causes scintillation (tiny flashes of light). These are amplified with a photomultiplier. The pulses from the photomultiplier are amplified and shortened before they pass through the pulse height analyzer. A timer and gate allow the pulses that occur in a specified time interval to be counted by means of a scaler which is a counter with readout. A rate or frequency meter is used to show the rate of pulses.