Simultaneous Multi-Bed MAP Reconstruction with CT-Guided Directional TV Prior for Y-90 PET SIRT

Abstract

Text Yttrium-90 (Y-90) microspheres are used clinically for selective internal radiation therapy (SIRT) for unresectable liver cancers and have been proposed for glioblastoma^1,2. Accurate dosimetry is critical but remains challenging due to low-count PET data arising from Y-90’s low positron branching ratio, as well as accurate treatment of bremsstrahlung for SPECT. Anatomically guided edge-preserving regularisation has shown promise for improving reconstruction quality under such conditions³. Whole-organ PET scans often exceed the axial field-of-view, requiring acquisition across multiple, partially overlapping bed positions (BPs). A common approach reconstructs each BP separately and merges them via sensitivity-weighted averaging. However, in overlap regions, low counts and edge-preserving priors can interact to produce intensity discontinuities that obscure image features. We introduce a maximum-a-posteriori (MAP) framework that reconstructs all BPs jointly, with a CT-guided directional total variation (DTV) prior function applied over a combined image volume⁴. We evaluate this method for Y-90 PET following SIRT.

Y-90 SIRT PET data was acquired on a GE Discovery 690 using two BPs, with overlap centred on the liver. We compared two workflows:

1. Separate + Fuse – independent reconstructions with sensitivity-weighted merging post-reconstruction.
2. Joint – Simultaneous reconstruction of both bed positions using a combined image volume, with separate updates computed for the data-fit terms per bed position and a single joint update for the prior term.

Visual assessment shows that Separate + Fuse obtains abrupt changes in intensity in the overlap region due to noise. The Joint method suppresses these artefacts and yields a smoother, anatomically consistent distribution (Figure 1).

Simultaneous reconstruction of multiple bed positions with a CT-guided DTV prior reduces overlap artefacts and enhances qualitative fidelity in Y-90 SIRT PET.

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