Depth-of-interaction Reconstruction in NeuroEXPLORER

Abstract

The NeuroEXPLORER (NX) system has recently been proposed for a high-resolution and high-sensitivity PET scanner dedicated for brain research. A long axial field-of-view (FOV) of 50cm was used for maximizing the sensitivity in brain region. Depth-of-interaction (DOI) modelling of NX system is necessary for generating high-resolution images and compensate for the large angle effects caused by long axial FOV.To minimize the modifications on the existing reconstruction algorithm and to minimize computational cost, a listmode-based DOI compensation method (DOI mashing) was developed. For detected event with non-zero DOI value, a new virtual detector pair was calculated along the incidence angle. The virtual detector pair has DOI value 0 and therefore has minimal DOI effect. Monte Carlo simulations were used to calculate the point-spread-functions (PSF) with the DOI effect with and without mashing. Analytical simulations were carried out with the acquired PSFs to simulate reconstructions with and without DOI corrections.The full-width-half-maximum (FWHM) of the PSF in the axial direction was 2.8mm with 0 incidence angle and was 8mm with the maximum incidence angle. With DOI mashing, the maximum FWHM reduced to 4mm. The residual blurring was found to be caused by inter-crystal scatters. Similar trend was found in the transaxial PSFs, where a large FWHM was observed in off-center locations. Image reconstruction without DOI mashing showed that without DOI mashing, image resolution degrades in off-center locations. With DOI mashing, image resolution was preserved in off-center locations.In conclusion, we proposed a DOI mashing approach that can compensate the DOI effects on the listmode data with minimal modifications of existing reconstruction methods.