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

We developed a cost-effective dual modality PET/SPECT imaging device based on an animal PET scanner. To achieve a large axial field of view (FOV) in the SPECT imaging mode, a slit-slat collimator insert was used. The objective of this work was to assess a method that used the PET imaging capability of the scanner to calibrate the geometrical parameters of the slit-slat collimator, including the slit aperture centers (SACs), axis of rotation (A OR), and slat center positions (SCPs). To calibrate the SAC and AOR values, the inner wedge surfaces of the slit apertures were painted with a ¹⁸F solution. The slit cylinder was mounted in its SPECT setup and imaged in PET mode at multiple rotational positions. The SAC and AOR values were then estimated from the reconstructed PET images. To calibrate the SCP values, the slat assembly was mounted in its SPECT setup, with a ¹⁸F capillary line source attached to its inner tube wall and along the scanner´s axial direction, and imaged in PET mode. The axial sectional profile of the reconstructed PET image was used to estimate the SCPs. The calibrated geometrical parameters were used to generate the system matrix for SPECT image reconstruction. Phantom studies were performed. It was found that the proposed PET calibration method was easy to setup, fast to perform, and reliable.