Performance Measurement of the microPET Focus 120 Scanner

¹ Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul, Korea; Interdisciplinary Programs in Radiation Applied Life Science Major, Seoul National University College of Medicine, Seoul, Korea
² Department of Nuclear Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea

^* To whom correspondence should be addressed. E-mail: jaes{at}snu.ac.kr.

	Abstract

The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. Methods: A ⁶⁸Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a ²²Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an ¹⁸F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250750 keV or 350650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. Results: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250750 keV, 10 ns), 6.7% (250750 keV, 6 ns), 4.0% (350650 keV, 10 ns), and 3.8% (350650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. Conclusion: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.

Key Words: small-animal PET, performance measurement, instrumentation, molecular imaging, small-animal imaging

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