Slit-slat collimator geometrical calibration for a PET/SPECT dual modality animal scanner

As part of our continued effort on developing a dual modality PET/SPECT imaging device based on an animal PET scanner, we studied two new techniques for calibrating the geometrical parameters of the slit-slat collimator insert based SPECT system. The collimator´s slat-to-crystal position (SCP) in axial direction was determined from the cyclic pattern of the sensitivity profile of a series of ⁹⁹mTc point source measurements in the axial direction. To calibrate the center of rotation (COR) and slit aperture centers (SACs), a ¹⁸F line source was first attached along one of the slits and imaged in PET mode at multiple rotational positions of the slit. The COR and SAC values were then estimated from the PET images of the line source. The calibration techniques were assessed with Monte Carlo simulated and experimental studies. The calibrated geometrical parameters were used in analytical calculation to generate the system matrix for SPECT image reconstruction. Phantom and animal studies were performed to demonstrate the imaging performance. The proposed new calibration methods were found effective in enabling slit-slat SPECT imaging on a PET scanner.