Standardisation of conventional and advanced iterative reconstruction methods for Gallium-68 multi-centre PET-CT trials

Abstract

Purpose To assess the applicability of the Fluorine-18 performance specifications defined by EANM Research Ltd (EARL), in Gallium-68 multi-centre PET-CT trials using conventional (ordered subset expectation maximisation, OSEM) and advanced iterative reconstructions which include the systems’ point spread function (PSF) and a Bayesian penalised likelihood algorithm (BPL) commercially known as Q.CLEAR. The possibility of standardising the two advanced reconstruction methods was examined. Methods The NEMA image quality phantom was filled with Gallium-68 and scanned on a GE PET-CT system. PSF and BPL with varying post-reconstruction Gaussian filter width (2–6.4 mm) and penalisation factor (200–1200), respectively, were applied. The average peak-to-valley ratio from six profiles across each sphere was estimated to inspect any edge artefacts. Image noise was assessed using background variability and image roughness. Six GE and Siemens PET-CT scanners provided Gallium-68 images of the NEMA phantom using both conventional and advanced reconstructions from which the maximum, mean and peak recoveries were drawn. Fourteen patients underwent 68Ga-PSMA PET-CT imaging. BPL (200-1200) reconstructions of the data were compared against PSF smoothed with a 6.4-mm Gaussian filter. Results A Gaussian filter width of approximately 6 mm for PSF and a penalisation factor of 800 for BPL were needed to suppress the edge artefacts. In addition, those reconstructions provided the closest agreement between the two advanced iterative reconstructions and low noise levels with the background variability and the image roughness being lower than 7.5% and 11.5%, respectively. The recoveries for all methods generally performed at the lower limits of the EARL specifications, especially for the 13- and 10-mm spheres for which up to 27% (conventional) and 41% (advanced reconstructions) lower limits are suggested. The lesion standardised uptake values from the clinical data were significantly different between BPL and PSF smoothed with a Gaussian filter of 6.4 mm wide for all penalisation factors except for 800 and 1000. Conclusion It is possible to standardise the advanced reconstruction methods with the reconstruction parameters being also sufficient for minimising the edge artefacts and noise in the images. For both conventional and advanced reconstructions, Gallium-68 specific recovery coefficient limits were required, especially for the smallest phantom spheres.

Positron Range Corrections and Denoising Techniques for Gallium-68 PET Imaging: A Literature Review

“…Two different approaches were identified for reducing the noise in 68 Ga PET images and enabling low-count 68 Ga PET measurements. The first approach reduces the noise during the image reconstruction process (reconstruction-based noise reduction approaches, n = 11) [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], whereas the second approach is based on neural networks (deep learning approaches for noise reduction, n = 5) [ 37 , 38 , 39 , 40 , 41 ], as seen in Figure 2 .…”

“…A literature search including both BSREM and Q.Clear revealed multiple studies on the optimal use of Q.Clear for different 68 Ga-labeled radiotracers using both patient and phantom studies. These studies demonstrated that increasing the β value resulted in a reduction in the image noise [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], an improvement in the signal-to-noise ratio (SNR) [ 26 , 27 , 29 , 30 , 32 ], and a reduction in Gibbs artifacts [ 33 ] at the cost of a reduction in the maximum standardized uptake value (SUV max ) [ 26 , 28 , 29 , 31 ], CR [ 26 , 28 , 30 ], RC [ 33 ], and signal-to-background ratio (SBR) [ 27 , 29 , 32 ]. Additionally, the mean standardized uptake value (SUV mean ) was almost identical for different β values [ 26 , 27 , 28 , 29 ].…”

Optimization of Bayesian penalized likelihood reconstruction for 68Ga-prostate-specific membrane antigen-11 PET/computed tomography

“…While Rijnsdorp S et al suggested β 600 based on the evaluation of multiple reconstructions with different β of phantom scans and only semi-quantitative assessment [20], we assessed our β values using reconstructed clinical data and both semi-quantitative and qualitative assessment. Krokos G et al looked into harmonizing PSF and BPL for Gallium-68 multicentre PET-CT trials and found that β values of 800-1000 were needed to suppress the edge artefacts and for BPL to provide images with lower noise levels when compared to PSF [21]. The focus of their study was to harmonize the reconstruction rather than optimizing BPL, also the GE Discovery 710 scanner was used for clinical data.…”

“…Krokos G et al . looked into harmonizing PSF and BPL for Gallium-68 multicentre PET-CT trials and found that β values of 800–1000 were needed to suppress the edge artefacts and for BPL to provide images with lower noise levels when compared to PSF [21]. The focus of their study was to harmonize the reconstruction rather than optimizing BPL, also the GE Discovery 710 scanner was used for clinical data.…”

Eligibility for177Lu-PSMA Therapy Depends on the Choice of Companion Diagnostic Tracer: A Comparison of68Ga-PSMA-11 and99mTc-MIP-1404 in Metastatic Castration-Resistant Prostate Cancer

“…A low-dose CT scan (140 kV, mA 15-100, noise index 40, 0.5s rotation time, and 40 mm collimation) was performed at the start of imaging to provide attenuation correction and an anatomical reference. PET image reconstruction used a Bayesian Penalized Likelihood Algorithm (Q.CLEAR, GE Healthcare, Chicago, USA) with a  penalization factor of 800 as previously described (15,16).…”