High-energy slit aperture SPECT and simplified in vitro methods for the dosimetry of positron-emitting radiotracers

The dosimetry of new positron emitting radiopharmaceuticals is initially estimated using animal tissue and organ biodistributions assessed in vitro. 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: in vitro organ measurements using a reduced sacrifice technique, and in vivo 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 ;In vivo 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 ;Qualitative and quantitative high energy imaging was performed using two-dimensional and three-dimensional phantoms and live rats injected with (;Analysis of animal biodistributions using a reduced sacrifice protocol provides results in good agreement with and generally conservative to results using all sacrifice intervals. Animal biodistributions assessed in vivo with slit aperture SPECT can show good accuracy for organs with substantial uptakes, but the method is hindered by very poor system sensitivity.