Hybrid MicroPET Imaging for Dosimetric Applications in Mice: Improvement of Activity Quantification in Dynamic MicroPET Imaging for Accelerated Dosimetry Applied to 6-[ 18 F] Fluoro- L -DOPA and 2-[ 18 F]Fluoro- L -Tyrosine

Purpose:
Dynamic microPET imaging has advantages over traditional organ harvesting, but is
pronetoquantificationerrorsinsmallvolumes.Hybridimaging,wheremicroPETactivitiesarecross-
calibrated using post scan harvested organs, can improve quantification. Organ harvesting,
dynamic imaging and hybrid imaging were applied to determine the human and mouse radiation
dosimetry of 6-[18 F]fluoro-L-DOPA and 2-[18 F]fluoro-L-tyrosine and compared.
Procedures:
Two-hour dynamic microPET imaging was performed with both tracers in four
separate mice for 18 F-FDOPA and three mice for 18 F-FTYR. Organ harvesting was performed
at 2, 5, 10, 30, 60 and 120 min post tracer injection with n=5 at each time point for 18 F-FDOPA
and n=3 at each time point for 18 F-FTYR. Human radiation dosimetry projected from animal
data was calculated for the three different approaches for each tracer using OLINDA/EXM. S-
factors for the MOBY phantom were used to calculate the animal dosimetry.
Results:
Correlations between dose estimates based on organ harvesting and imaging was
improved from r=0.997 to r=0.999 for 18 F-FDOPA and from r=0.985 to r=0.996 (p<0.0001 for
all) for 18 F-FTYR by using hybrid imaging.
Conclusion:
Hybrid imaging yields comparable results to traditional organ harvesting while
partially overcoming the limitations of pure imaging. It is an advantageous technique in terms of
number of animals needed and labour involved.