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High energy slit aperture SPECT and simplified in vitro methods for the dosimetry of positron emitting radiotracers
Author(s) -
Wrobel Mark Christopher
Publication year - 1997
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597977
Subject(s) - imaging phantom , collimator , nuclear medicine , dosimetry , collimated light , single photon emission computed tomography , image resolution , physics , optics , positron emission tomography , spect imaging , iterative reconstruction , materials science , medicine , radiology , laser
The dosimetry of new positron emitting radiopharmaceuticals is initially estimated using animal organ biodistributions assessed in vitro . This research investigated the accuracy of in vivo assessments using single photon emission computed tomography (SPECT). Measurements 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 FWHM was approximately 4.5 mm axially and transaxially. System sensitivity was 25 cps/MBq (∼55 cpm/μCi), a consequence of high resolution collimation and poor intrinsic detector efficiency. Qualitative and quantitative high energy imaging was performed using two‐ and three‐dimensional phantoms and live rats injected with [ 18 F ] fluorodeoxyglucose. Three mm μJaszczak phantom objects were well resolved, and rat images showed good contrast of the brain and heart regions. Hot phantom regions and animal organs were quantified with an accuracy of ±8% (S.D. ±15%). Accurate determination of region activity required concentrations up to 3.7 MBq/ml (∼100 μCi/ml) and imaging times of one hour. In summary, animal biodistributions assessed with slit aperture SPECT can show good accuracy for organs with substantial uptakes, but poor sensitivity limits temporal resolution.