arXiv subjects

Kristof Baete

Publications and source records attributed to Kristof Baete.

2 recordsLinked to original sources

arXiv2026

Multicenter Comparison of Radionuclide Calibrators and SPECT/CT Protocols for Quantitative 177Lu Imaging in Clinical Practice

Purpose: Following the clinical success of 177Lu-based therapies, accurate quantification of 177Lu using radionuclide calibrators (RNCs) and SPECT/CT is gaining importance as prerequisite for accurate treatment delivery and dosimetry. However, the lack of standardization can introduce inter-system variability, compromising multi-center clinical trials. This study aimed to assess the accuracy and variability of 177Lu measurements using RNCs and SPECT/CT across different systems and hospitals. Methods: A uniform cylindrical phantom and a NEMA phantom with hot spheres were prepared using traceable activities and imaged at 8 different hospitals using 13 SPECT/CT systems (9 conventional and 4 3D CZT). Acquisitions and reconstructions were performed using both site-specific and standardized protocols. The cylindrical phantom images were used to evaluate the system calibration and establish image calibration factors (ICFs), the NEMA images to evaluate effective resolution by calculating recovery coefficients (RCs). In parallel, two vials were measured to test RNC accuracy. Results: RNC measurements differed up to 11% between centers, while SPECT quantification of the cylindrical phantom differed up to 20%. While ICFs were consistent for systems of the same type, image quality varied strongly when using clinical protocols (36% difference in RCs in the largest sphere). Standardized reconstruction reduced variability in RCs for each system type (maximum 12% difference), regardless of acquisition protocol, but differences between system types persisted when standardizing acquisition and reconstruction (33% difference). Conclusion: Current 177Lu measurement practices yield significant variability in quantification and image quality. Harmonization efforts should prioritize standardized calibration and reconstruction protocols to improve multicenter reproducibility of quantitative 177Lu-SPECT/CT.

physics.med-ph↗

arXiv2025

Improved energy-based scatter estimation by incorporating local energy spectra and accelerating the parametric fitting

PET requires accurate, precise, and efficient scatter correction techniques. Conventional scatter estimation typically relies on tail-fitted single-scatter simulation (SSS) strategy. However, the accuracy of tail-fitted SSS is limited, for example, by mismatches between the attenuation image and the PET emission data or by the presence of activity outside the FOV. These shortcomings can be addressed using energy-based scatter estimation (EBSE), as recently proposed by Efthimiou et al. and Hamill et al. The aim of this work is to 1. improve the accuracy of EBSE by accounting for the LOR dependence of the energy spectrum of unscattered photons, 2. improve the computational speed of EBSE through better initialization and a more efficient optimization algorithm. The proposed improved EBSE method models the energy probability density function (PDF) of both single and multiple scattered photons, and incorporates a position-dependent energy PDF for unscattered photons. These energy PDFs form the basis of two forward models used for scatter estimation based on 2D energy histograms. The performance of these models were evaluated using GATE Monte Carlo simulations and a NEMA phantom acquisition on a GE SIGNA PET/MR scanner. Furthermore, we assessed the stability of EBSE across the forward models by varying the number of counts in the 2D energy histograms via data mashing. EBSE outperformed tail-fitted SSS, particularly in regions near out-of-FOV activity. Our GATE simulations showed that incorporating a local energy for unscattered photons improves off-center regional quantification by approximately 2% points. Additionally, improved initialization combined with the NEGML optimizer enabling execution on a mashed TOF sinogram in 12 minutes on six-core CPU. The proposed method enhances both the accuracy and computational efficiency of EBSE, making it well-suited for clinical applications.

physics.med-ph↗