PERFORMANCE OF A COINCIDENCE BASED BLOOD ACTIVITY MONITOR

A new device has been constructed that measures the positron emitting radio-tracer concentration in arterial blood by extracting blood with a peristaltic pump, then measuring the activity concentration by detecting coincident pairs of 511 keV photons with a pair of heavy inorganic scintillators attached to photomultiplier tubes. The sensitivity of this device is experimentally determined to be 610 counts/second per µCi/ml, and has a paralyzing dead time of 1.2 µs, so is capable of measuring blood activity concentrations as high as 1 mCi/ml. Its performance is compared to two other blood monitoring methods: discrete blood samples counted with a well counter and a device that uses a plastic scintillator to directly detect positrons. The positron detection efficiency of this device for 18F is greater than the plastic scintillation counter, and also eliminates the radioisotope dependent correction factors necessary to convert count rate to absolute concentration. Coincident photon detection also has the potential of reducing the background compared to direct positron detection, thereby increasing the minimum detectable isotope concentration. Copyright © 1990 by The Institute of Electrical and Electronics Engineers, Inc.