CATHETER SEMICONDUCTOR RADIATION DETECTOR FOR CONTINUOUS MEASUREMENT OF CARDIAC OUTPUT.

Summary The catheter semiconductor radiations detector (CASRAD) was developed for in vivo measurements of beta radiation in blood and tissue. The detector element is a silicon p-n junction diode which is 2.3 mm in dia and 1 mm thick. The specially developed subminiature noiseless coaxial cable, approximately 120 cm long, is connected to the detector head. The entire probe is covered with a polyethylene tube to make it watertight. The maximum outer diameter of the probe is about 3.2 mm, and a completely transistorized low-noise charge sensitive preamplifier was developed to eliminate microphonic noise. The following are some of the important characteristics of the detector: A low operating voltage of 10–40 volts with constant sensitivity in this range; lineality between counting rate and radioisotope concentration; sufficient noise discrimination and good spatial resolution. It was proved that this detector can be safely inserted into the body and is suitable for measuring localized beta activity in vivo. The CASRAD probe was used to continuously measure the right cardiac output based on flow dilution relationship with 85Kr saline solution used as an indicator. In the studies performed on anesthetized dogs, the probe was placed in the outflow tract of the right ventricle where it detected the 85Kr radioactivity infused at a constant rate into the femoral vein. Changes in the cardiac output caused by epinephrine injections were recorded continuously by this method. Comparison of the CASRAD method with IHSA dilution and electromagnetic flowmeter methods in the determination of cardiac output revealed good agreement between the results.