Parameterizing the Angular Distribution of Emission: A Model for TOF-PET Low-Count Reconstruction

TL;DR

This paper introduces PADE, a novel model for low-count TOF-PET reconstruction that explicitly parameterizes emission angular distribution, showing potential for less noisy solutions compared to classical models in ultra-fast TOF scenarios.

Contribution

The paper proposes PADE, a new reconstruction approach that extends the classical model by including the projection domain with greater degrees of freedom, suitable for ultra-fast TOF-PET.

Findings

PADE achieves similar contrast recovery as MLEM for larger structures.

PADE converges to less noisy solutions than MLEM.

Potential for improved low-count PET reconstruction with ultra-fast TOF.

Abstract

Low-count reconstruction remains a challenge for Positron Emission Tomography (PET) even with the recent progress in time-of-flight (TOF) resolution. In this context, the bias between the acquired histogram, consisting of low values or zeros, and the expected histogram, obtained from the forward projector, is propagated to the image, resulting in a biased reconstruction. This situation could be exacerbated with finer resolution of the TOF information, which further sparsifies the acquired histogram. We propose a new approach to circumvent this limitation of the classical reconstruction model. It consists of extending the description of the reconstruction scheme to also explicitly include the projection domain by Parameterizing the Angular Distribution of Emission (PADE). This parametrization has greater degrees of freedom than the log-likelihood model, which can not be harnessed in classical circumstances. We hypothesize that with ultra-fast TOF this new approach would not only be viable for low-count reconstruction, but also more adequate than the classical reconstruction model. As a proof of concept, an implementation of this approach is compared to the log-likelihood model by investigating two-dimensional simulations of a hot spots phantom. The proposed model achieves similar contrast recovery coefficients as MLEM except for the smallest structures where the low-count nature of the simulations makes it difficult to draw conclusions. However, this new model seems to converge toward less noisy solutions than MLEM. These results suggest that the PADE approach has potential for low-count reconstruction with ultra-fast TOF.