Abstract: A blood counting device comprises a capillary conduit for drawing from a subject in which a radiotracer has previously been injected a quantity of blood in the micro-liter range to produce in the capillary conduit a flow of blood from which beta radiation is emitted. At least one direct beta radiation detector is placed closely adjacent to the capillary conduit. The direct beta radiation detector consists of a semiconductor photodiode which detects the beta radiation from the flow of blood when directly hit by this beta radiation.

Abstract: The present invention relates to a detector assembly, comprising at least one beta radiation detector, and a conduit for drawing from a subject blood in which a radiotracer has been injected, at least a portion of the conduit extending adjacent to the beta radiation detector to detect beta radiation from the blood drawn through the conduit. The present invention further relates to a blood counting method and device using a beta radiation detector assembly. A conduit has a first end for connection to a blood vessel of a subject in which a radiotracer has been injected, at least a portion of the conduit extending adjacent to the beta radiation detector assembly. A blood pump connects to a second end of the conduit for drawing blood through the conduit and produce a flow a blood through that conduit. The beta radiation detector assembly senses beta radiation from the blood in the above mentioned portion of the conduit.