High Energy Slit Aperture Spect and Simplified Invitro Methods for the Dosimetryof Positron Emitting Radiotracers

摘要

The dosimetry of new positron emitting radiopharmaceuticals is initiallyestimated using animal tissue and organ biodistributions assessed invitro. Such methods are time and labor intensive and can have limited accuracy. This research investigated two alternative methods by which biodistribution can be obtained from the laboratory rat: invitro organ measurements using a reduced sacrifice technique, and invivo measurements using single photon emission computed tomography (SPECT). As an alternative to a four time-point sacrifice method, a two time-point method was evaluated as a means to determine the organ cumulated activity of C labeled radiopharmaceuticals. Residence times calculated using two time-points acquired during the first half-life of C were either equivalent or larger than those resulting from using four sacrifice times. Correction factors were required for the urinary bladder and gallbladder when using this simplified technique due to delayed uptakes. Invivo assessments were performed with SPRINT, a full ring detector SPECT system using a slit aperture to obtain a 3-to-1 object to image magnification ratio. Acceptable resolution for 511 keV photons was achieved using a high energy parallel slice collimator and a novel technique to correct for penetration of the slit aperture by high energy photons. The resulting system resolution was approximately 4.5 mm axially and transaxially. System sensitivity was approx. 55 cpm/micronCi, a consequence of high resolution collimation and poor intrinsic detector efficiency.