Abstract
The use of multi-pinhole collimation has enabled ultra-high-resolution imaging of SPECT and PET tracers in small animals. Key for obtaining high-quality images is the use of statistical iterative image reconstruction with accurate energy-dependent photon transport modelling through collimator and detector. This can be incorporated in a system matrix that contains the probabilities that a photon emitted from a certain voxel is detected at a specific detector pixel. Here we introduce a fast Monte-Carlo based (FMC-based) matrix generation method for pinhole imaging that is easy to apply to various radionuclides. The method is based on accelerated point source simulations combined with model-based interpolation to straightforwardly change or combine photon energies of the radionuclide of interest. The proposed method was evaluated for a VECTor PET-SPECT system with (i) a HE-UHR-M collimator and (ii) an EXIRAD-3D 3D autoradiography collimator. Both experimental scans with 99mTc, 111In, and 123I, and simulated scans with 67Ga and 90Y were performed for evaluation. FMC was compared with two currently used approaches, one based on a set of point source measurements with 99mTc (dubbed traditional method), and the other based on an energy-dependent ray-tracing simulation (ray-tracing method). The reconstruction results show better image quality when using FMC-based matrices than when applying the traditional or ray-tracing matrices in various cases. FMC-based matrices generalise better than the traditional matrices when imaging radionuclides with energies deviating too much from the energy used in the calibration and are computationally more efficient for very-high-resolution imaging than the ray-tracing matrices. In addition, FMC has the advantage of easily combining energies in a single matrix which is relevant when imaging radionuclides with multiple photopeak energies (e.g. 67Ga and 111In) or with a continuous energy spectrum (e.g. 90Y). To conclude, FMC is an efficient, accurate, and versatile tool for creating system matrices for ultra-high-resolution pinhole SPECT.
Highlights
Statistical iterative image reconstruction is prominently used in SPECT and PET (Hutton et al 1997, Qi and Leahy 2006)
FMC has the advantage of combining energies in a single matrix which is relevant when imaging radionuclides with multiple photopeak energies (e.g. 67Ga and 111In) or with a continuous energy spectrum (e.g. 90Y)
The presented point spread functions (PSFs) corresponds to photons from a point source at the collimator’s centre going through three different pinholes
Summary
Statistical iterative image reconstruction is prominently used in SPECT and PET (Hutton et al 1997, Qi and Leahy 2006). The first approach is based on analytical modelling of the scanner with some pre-determined geometrical information obtained from a calibration measurement (Feng et al 2010, Aguiar et al 2014, Bitar et al 2014) This method requires a very precise calibration, especially for high-resolution pinhole systems because such systems are susceptible to small parameter variations. A practical way is to measure only a small number of PSFs, and interpolate to estimate the missing PSFs (van der Have et al 2008, Miller et al 2012) This is time-efficient and has been used in preclinical pinhole SPECT systems to produce both highly quantitative (Wu et al 2010) and highresolution images, currently with resolutions down to 0.12 mm (Nguyen et al 2020b). The drawback is that MCS is computationally demanding; it is time-consuming and may even be infeasible to obtain noiseless PSFs for very-high-resolution pinhole SPECT
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
