We describe a newly developed ultra-high resolution SPECT system using four pinhole collimators for small animal studies.
Methods: The system utilizes a clinical four-head SPECT scanner with specially designed pinhole collimators. Four types of pinholes with different configurations were designed with different effective aperture sizes (1.0, 2.0 and 4.0 mm) and rotating radii (40 mm and 50 mm). The distance from the axis of rotation to the scintillator was fixed to 180 mm. A filtered backprojection algorithm was used to reconstruct SPECT images after fanbeam-to-parallel-beam data conversion.
Results: The system provided a reconstructed spatial resolution of 1.65 mm (FWHM) and sensitivity of 4.3 kcps/microCi/ml with the best type of pinholes, respectively. The 99mTc-HMPAO SPECT image in rat studies clearly visualized small brain structures, and the left ventricular myocardium and cardiac cavity were clearly separated with 99mTc-MIBI. Dynamic SPECT imaging of rat brain with [123I]iomazenil was also feasible.
Conclusion: This ultra-high resolution SPECT system can be used to measure the regional distribution of radiolabeled tracers in small animals in vivo and may play a significant role in the development of new radiopharmaceuticals and in studies of various disease models using living animals.