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Quantitative performance and optimal regularization parameter in block sequential regularized expectation
Edwin E G W Ter Voert1,2, Urs J Muehlematter3, Gaspar Delso4
1Department of Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, CH-8091, Zurich, Switzerland. Edwin.terVoert@usz.ch.
EJNMMI Research
|July 29, 2018
Summary
Block sequential regularized expectation maximization (BSREM) PET imaging offers improved image quality over ordered subset expectation maximization (OSEM). Optimal regularization (β) for 68Ga-PSMA PET/MR is between 400-550, balancing noise reduction and lesion detection.
Area of Science:
- Nuclear Medicine
- Medical Imaging
- Radiochemistry
Background:
- Block sequential regularized expectation maximization (BSREM) offers improved convergence and image quality compared to ordered subset expectation maximization (OSEM) in positron emission tomography (PET).
- Previous studies with 18F-FDG PET and BSREM demonstrated enhanced signal-to-noise ratios and standardized uptake values (SUV).
Purpose of the Study:
- To determine the optimal regularization parameter (β) for time-of-flight (TOF) BSREM reconstruction in 68Ga-PSMA PET/MR imaging of the pelvic region.
- To compare TOF BSREM reconstructions with TOF OSEM in terms of image quality and lesion detectability.
Main Methods:
- Retrospective reconstruction of 2-minute pelvic emission data from 25 patients undergoing 68Ga-PSMA PET/MR.
- Utilized TOF BSREM with 15 β values (150-1200) and TOF OSEM (28 subsets, 2 iterations) as reference.
- Analyzed background noise (SUVstd) and lesion uptake (SUVmax) in defined regions of interest.
Main Results:
- Increasing β values in BSREM reduced background noise (SUVstd) and lesion SUVmax.
- BSREM reconstructions with β < 400 showed significantly higher background noise than OSEM (p < 0.01).
- BSREM reconstructions with β > 600 resulted in lower lesion SUVmax (p < 0.05), potentially obscuring small, low-uptake lesions.
Conclusions:
- TOF BSREM with 68Ga-PSMA PET/MR yields lower background noise and potentially higher lesion SUVmax compared to TOF OSEM.
- An optimal β value between 400 and 550 is suggested to balance reduced noise and maintained lesion detectability.
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