Optimisation of the event-based TOF filtered back-projection for online imaging in total-body J-PET

TL;DR

This paper presents an optimized time-of-flight filtered back-projection algorithm for real-time total-body J-PET imaging, demonstrating significant improvements in spatial resolution and image quality through parametric studies and Monte Carlo simulations.

Contribution

It introduces a novel parametric optimization of the TOF FBP algorithm tailored for J-PET scanners, enhancing spatial resolution and image quality for real-time imaging.

Findings

Axial spatial resolution increased by 1.5 times with TOF FBP.

Gaussian TOF kernel and median filtering improve image quality.

Optimized parameters outperform non-TOF FBP in image quality.

Abstract

We perform a parametric study of the newly developed time-of-flight (TOF) image reconstruction algorithm, proposed for the real-time imaging in total-body Jagiellonian PET (J-PET) scanners. The asymmetric 3D filtering kernel is applied at each most likely position of electron-positron annihilation, estimated from the emissions of back-to-back $\gamma$-photons. The optimisation of its parameters is studied using Monte Carlo simulations of a 1-mm spherical source, NEMA IEC and XCAT phantoms inside the ideal J-PET scanner. The combination of high-pass filters which included the TOF filtered back-projection (FBP), resulted in spatial resolution, 1.5 $\times$ higher in the axial direction than for the conventional 3D FBP. For realistic $10$-minute scans of NEMA IEC and XCAT, which require a trade-off between the noise and spatial resolution, the need for Gaussian TOF kernel components, coupled with median post-filtering, is demonstrated. The best sets of 3D filter parameters were obtained by the Nelder-Mead minimisation of the mean squared error between the resulting and reference images. The approach allows training the reconstruction algorithm for custom scans, using the IEC phantom, when the temporal resolution is below 50 ps. The image quality parameters, estimated for the best outcomes, were systematically better than for the non-TOF FBP.