Ionizing radiation constitutes a health risk to imaging scientists and study animals. Therefore Both PET and CT produce ionizing radiation. CT doses in pre-clinical in vivo imaging typically range from 50 to 1,000 mGy and biological effects in mice at this dose range have been previously described. Because [18F]FDG body doses in mice have been estimated to be in the range of 100 mGy for [18F]FDG. Yearly, the average whole body doses due to handling of activity by PET technologists are report to be 3–8 mSv.
Health risk to imaging
A preclinical PET/CT system is present with design features which make it suitable for small animal low-dose imaging. The CT subsystem uses a X-source power that is optimize for small animal imaging. The system design incorporates a spatial beam sharper coupled with a highly sensitive flat-panel detector and very fast acquisition (<10 s) which allows for whole body scans with doses as low as 3 mGy.
The mouse total-body PET subsystem uses a detector architecture based on continuous crystals, coupled to SiPM arrays and a readout based in rows and columns. The PET field of view is 150 mm axial and 80 mm transaxial. The high solid-angle coverage of the sample and the use of continuous crystals achieve a sensitivity of 9% (NEMA) that can be leveraged for use of low tracer doses and/or performing rapid scans.
Continuous crystals achieve
The low-dose imaging capabilities of the total-body PET subsystem are test with NEMA phantoms, in tumor models, a mouse bone metabolism scan and a rat heart dynamic scan. The CT imaging capabilities were tested in mice and in a low contrast phantom. The PET low-dose phantom and animal experiments provide evidence that image quality suitable for preclinical PET studies is achieve.
Furthermore, CT image contrast using low dose scan settings is suitable as a reference for PET scans. Total-body mouse PET/CT studies could be complete with total doses of <10 mGy. Both positron emission tomography (PET) and compute
tomography (CT) imaging involves ionizing radiation producing deleterious effects on study animals and constitutes a health
risk for researchers.
Dose reduction efforts are important in pre-clinical imaging for animal care and study integrity considerations, especially where repeat scans will be performed in longitudinal studies. Further, dose reduction efforts can also help limit the exposure to human system operators. In humans, acute radiation dose effects like skin redness, hair loss, radiation burns, or acute radiation syndrome occur when doses exce 1 Sv and are deliver at high dose rates.
Nevertheless, it is the increase in cancer risk with low but continuous dose exposure that is relevant in radiation exposed workers. Epidemiological studies in humans point to a significant cancer risk increase for doses above 100 mSv (1). The regulation applied in more than ten European countries prescribes the following dose limits: