Evaluation of block-sequential regularized expectation maximization reconstruction of 68Ga-DOTATOC, 18F-fluoride, and 11C-acetate whole-body examinations acquired on a digital time-of-flight PET/CT scanner

Abstract

Background: Block-sequential regularized expectation maximization (BSREM) is a fully convergent iterative image reconstruction algorithm. We hypothesize that tracers with different distribution patterns will result in different optimal settings for the BSREM algorithm. The aim of this study was to evaluate the image quality with variations in the applied β-value and acquisition time for three positron emission tomography (PET) tracers. NEMA image quality phantom measurements and clinical whole-body digital time-of-flight (TOF) PET/computed tomography (CT) examinations with 68 Ga-DOTATOC (n = 13), 18 Ffluoride (n = 10), and 11 C-acetate (n = 13) were included. Each scan was reconstructed using BSREM with β-values of 133, 267, 400, and 533, and ordered subsets expectation maximization (OSEM; 3 iterations, 16 subsets, and 5-mm Gaussian post-processing filter). Both reconstruction methods included TOF and point spread function (PSF) recovery. Quantitative measures of noise, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR) were analysed for various acquisition times per bed position (bp). Results: The highest β-value resulted in the lowest level of noise, which in turn resulted in the highest SNR and lowest SBR. Noise levels equal to or lower than those of OSEM were found with β-values equal to or higher than 400, 533, and 267 for 68 Ga-DOTATOC, 18 Ffluoride, and 11 C-acetate, respectively. The specified β-ranges resulted in increased SNR at a minimum of 25% (P < 0.0001) and SBR at a maximum of 23% (P < 0.0001) as compared to OSEM. At a reduced acquisition time by 25% for 68 Ga-DOTATOC and 18 F-fluoride, and 67% for 11 C-acetate, BSREM with β-values equal to or higher than 533 resulted in noise equal to or lower than that of OSEM at full acquisition duration (2 min/bp for 68 Ga-DOTATOC and 18 Ffluoride, 3 min/bp for 11 C-acetate). The reduced acquisition time with β 533 resulted in increased SNR (16-26%, P < 0.003) and SBR (6-18%, P < 0.0001 (P = 0.07 for 11 C-acetate)) compared to the full acquisition OSEM.

Can a penalized-likelihood estimation algorithm be used to reduce the injected dose or the acquisition time in 68Ga-DOTATATE PET/CT studies?

“…Therefore, a direct comparison between present results and those of [ 13 ] is challenging. Recently Lindström et al [ 15 ] showed that for 68 Ga-DOTATOC PET/CT studies β values equal to or higher than 400 result in noise levels equal to or lower than those of OSEM (2 min/bp) with improved SNR and SBR. The OSEM reconstruction algorithm used in [ 15 ] corresponds to the algorithm recommended by the manufacturer, i.e.…”

“…For 68 Ga-DOTA, one preliminary study by Lantos et al [ 13 ] in 10 patients suggested using a β factor between 350 and 450 in clinical practice for all the studied radiopharmaceuticals while the study conducted by ter Voert et al [ 14 ] concluded that, for 68 Ga-PSMA, a β value between 400 and 550 could be optimal. A recent study conducted by Lindström et al [ 15 ] on thirteen 68 Ga-DOTATOC studies concluded that β values equal to or higher than 400 result in noise levels equal to or lower than those of OSEM (3 iterations, 16 subsets, 5-mm post-filter) with improved SNR and SBR.…”

Moving the goalposts while scoring―the dilemma posed by new PET technologies

“…• Image noise [75][76][77][78] • Subjective image quality [73,77,[79][80][81][82][83][84] • Prediction of subjective image quality from objectified measures [85] • Lesion SUV [75,86,87] • Conspicuity of pulmonary lesions [69,77,86] • Detection rate in pulmonary lesions [88] • Lesion detectability in pelvic PSMA PET/MRI at low activity [89] • Detection rate of lymph nodes in fluorocholine PET [90] • Normal databases for brain PET in neurodegenerative disease [91,92] • Acquisition time reduction [81,84,89,93] Level 2:…”

Image reconstruction methods affect software-aided assessment of pathologies of [18F]flutemetamol and [18F]FDG brain-PET examinations in patients with neurodegenerative diseases

“…Studies addressing whole body [ 18 F]FDG on various PET/CT scanners have shown for BSREM to reduce image noise without impeding the tumor detectability, or vice versa, to improve tumor detectability at similar noise levels as ordered-subsets expectation maximization (OSEM) ( Teoh et al, 2016 , Sah et al, 2017 , Lindström et al, 2018 , Trägårdh et al, 2019 , Bjöersdorff et al, 2019 ). Other studies have also shown the need to adjust the setting of β depending on the tracer and application being used ( Lindström et al, 2019 , Lindström et al, 2020 ).…”