Development of Various Catheter Semiconductor Radiation Detectors and Their Application to Clinical Medicine

A catheter semiconductor radiation detector (CASRAD) probe which can be placed safely inside a human body for the measurement of beta-ray activity was developed. To fulfill specific requirements arising from medical purposes, the detector element of the CASRAD probe is made by a silicon p-n junction diode of single-ended coaxial structure, 2.3 mm in diameter and 1-4 mm long. Difficulties of electronic noise caused by vibration of a long cable approximately 120 cm in length was solved by using a subminiature noiseless coaxial cable. The overall noise level of the CASRAD probe at 20 V bias and 40°C is less than about 40 keV beta rays equivalent. Therefore, the probe can be used to detect beta rays from 14C, 85Kr, 32P etc., provided window thickness of the probe is chosen properly. The beta-ray sensitivity of a CASRAD probe type TCK-2 is about 5,000 cpm/μCi/ml of 32P solution. The CASRAD probe type TCK-2 has been used to hemodynamic studies including measurement of circulation time, detection of left-to-right intracardiac shunt, continuous measurement of cardiac output and measurement of coronary blood flow. Pulmonary function also has been studied by using a CASRAD probe with a collimator and 85Kr as an indicator. Malignancies of various organs such as the esophagus, stomach, lung , uterus and breast have been diagnosed by means of 32P and the CASRAD probe.