Feasibility of using beta-gamma coincidence for 3D PET attenuation correction

Better attenuation correction is needed in 30 PET in order to reduce image noise. It is well known that positrons must lose an appreciable amount of e nergy before annihilation with an electron can occur. If this energy is los t in a plastic scintillator or PIN photo-diode, this could provide a pulse to a coincidence circuit, while the conventional PET detectors provide a se cond pulse identifying the line of response. Cheaper, non-positron emitting isotopes, which decay by beta-gamma cascade, (eg Co-60) could also be used . We have shown that the energy loss of positrons emitted from F-18 can be de tected with a PIN diode. The recorded energy is above the noise for most ev ents, and the timing spectrum from a PIN diode detecting the positron and a n LSO crystal detecting the gamma ray show excellent timing resolution. A n arrow coincidence window allows high count rates. Multiple sources and post -injection scans-can be used. Based on preliminary data presented here it s hould be possible to adapt this technique to modern PET scanners which now use 2D acquisitions, and extended septa only for performing transmission sc ans.