Background Fully integrated PET/MR systems are being used frequently in clinical research and routine. National Electrical Manufacturers Association (NEMA) characterization of these systems is generally done with 18 F which is clinically the most relevant PET isotope. However, other PET isotopes, such as 68 Ga and 90 Y, are gaining clinical importance as they are of specific interest for oncological applications and for follow-up of 90 Y-based radionuclide therapy. These isotopes have a complex decay scheme with a variety of prompt gammas in coincidence. 68 Ga and 90 Y have higher positron energy and, because of the larger positron range, there may be interference with the magnetic field of the MR compared to 18 F. Therefore, it is relevant to determine the performance of PET/MR for these clinically relevant and commercially available isotopes. Methods NEMA NU 2–2007 performance measurements were performed for characterizing the spatial resolution, sensitivity, image quality, and the accuracy of attenuation and scatter corrections for 18 F, 68 Ga, and 90 Y. Scatter fraction and noise equivalent count rate (NECR) tests were performed using 18 F and 68 Ga. All phantom data were acquired on the GE Signa integrated PET/MR system, installed in UZ Leuven, Belgium. Results 18 F, 68 Ga, and 90 Y NEMA performance tests resulted in substantially different system characteristics. In comparison with 18 F, the spatial resolution is about 1 mm larger in the axial direction for 68 Ga and no significative effect was found for 90 Y. The impact of this lower resolution is also visible in the recovery coefficients of the smallest spheres of 68 Ga in image quality measurements, where clearly lower values are obtained. For 90 Y, the low number of counts leads to a large variability in the image quality measurements. The primary factor for the sensitivity change is the scale factor related to the positron emission fraction. There is also an impact on the peak NECR, which is lower for 68 Ga than for 18 F and appears at higher activities. Conclusions The system performance of GE Signa integrated PET/MR was substantially different, in terms of NEMA spatial resolution, image quality, and NECR for 68 Ga and 90 Y compared to 18 F. But these differences are compensated by the PET/MR scann...

PurposeQ.Clear is a block sequential regularized expectation maximization (BSREM) penalized-likelihood reconstruction algorithm for PET. It tries to improve image quality by controlling noise amplification during image reconstruction. In this study, the noise properties of this BSREM were compared to the ordered-subset expectation maximization (OSEM) algorithm for both phantom and patient data acquired on a state-of-the-art PET/CT.MethodsThe NEMA IQ phantom and a whole-body patient study were acquired on a GE DMI 3-rings system in list mode and different datasets with varying noise levels were generated. Phantom data was evaluated using four different contrast ratios. These were reconstructed using BSREM with different β-factors of 300–3000 and with a clinical setting used for OSEM including point spread function (PSF) and time-of-flight (TOF) information. Contrast recovery (CR), background noise levels (coefficient of variation, COV), and contrast-to-noise ratio (CNR) were used to determine the performance in the phantom data. Findings based on the phantom data were compared with clinical data. For the patient study, the SUV ratio, metabolic active tumor volumes (MATVs), and the signal-to-noise ratio (SNR) were evaluated using the liver as the background region.ResultsBased on the phantom data for the same count statistics, BSREM resulted in higher CR and CNR and lower COV than OSEM. The CR of OSEM matches to the CR of BSREM with β = 750 at high count statistics for 8:1. A similar trend was observed for the ratios 6:1 and 4:1. A dependence on sphere size, counting statistics, and contrast ratio was confirmed by the CNR of the ratio 2:1. BSREM with β = 750 for 2.5 and 1.0 min acquisition has comparable COV to the 10 and 5.0 min acquisitions using OSEM. This resulted in a noise reduction by a factor of 2–4 when using BSREM instead of OSEM. For the patient data, a similar trend was observed, and SNR was reduced by at least a factor of 2 while preserving contrast.ConclusionThe BSREM reconstruction algorithm allowed a noise reduction without a loss of contrast by a factor of 2–4 compared to OSEM reconstructions for all data evaluated. This reduction can be used to lower the injected dose or shorten the acquisition time.

NEMA characterization of PET systems is generally based on 18 F because it is the most relevant radioisotope for the clinical use of PET. 18 F has a half-life of 109.7 min and decays into stable 18 O via β+ emission with a probability of over 96% and a maximum positron energy of 0.633 MeV. Other commercially available PET radioisotopes, such as 82 Rb and 68 Ga have more complex decay schemes with a variety of prompt gammas, which can directly fall into the energy window and induce false coincidence detections by the PET scanner. Methods: Aim of this work was threefold: (A) Develop a GATE model of the GE Signa PET/MR to perform realistic and relevant Monte Carlo simulations (B) Validate this model with published sensitivity and Noise Equivalent Count Rate (NECR) data for 18 F and 68 Ga (C) Use the validated GATE-model to predict the system performance for other PET isotopes including 11 C, 15 O, 13 N, 82 Rb, and 68 Ga and to evaluate the effect of a 3T magnetic field on the positron range. Results: Simulated sensitivity and NECR tests performed with the GATE-model for different radioisotopes were in line with literature values. Simulated sensitivities for 18 F and 68 Ga were 21.2 and 19.0 /kBq, respectively, for the center position and 21.1 and 19.0 cps/kBq, respectively, for the 10 cm off-center position compared to the corresponding measured values of 21.8 and 20.0 cps/kBq for the center position and 21.1 and 19.6 cps/kBq for the 10 cm off-center position. In terms of NECR, the simulated peak NECR was 216.8 kcps at 17.40 kBq/ml for 18 F and 207.1 kcps at 20.10 kBq/ml for 68 Ga compared to the measured peak NECR of 216.8 kcps at 18.60 kBq/ml and 205.6 kcps at 20.40 kBq/ml for 18 F and 68 Ga, respectively. For 11 C, 13 N, and 15 O, results confirmed a peak NECR similar to 18 F with the effective activity concentration scaled by the inverse of the positron fraction. For 82 Rb, and 68 Ga, the peak NECR was lower than for 18 F while the corresponding activity concentrations were higher. For the higher energy positron emitters, the positron range was confirmed to be

Background: Increased throughput in small animal preclinical studies using positron emission tomography leads to reduced costs and improved efficiency of experimental design, however the presence of multiple off-centre subjects, as opposed to a single centered one, may affect image quality in several ways.Methods: We evaluated the count rate performance using a NEMA scatter phantom. A Monte Carlo simulation of the system was validated against this dataset and used to simulate the count rate performance for dual scatter phantoms. NEMA NU4 image quality phantoms were then scanned in the central and offset positions, as well as in the offset position next to a uniform activity phantom. Uniformity, recovery coefficients and spillover ratios were then compared, as were two time frames for acquisition.Results: Count rate performance assessed with a single NEMA scatter phantom was in line with previous literature, with simulated data in good agreement. Simulation of dual scatter phantoms showed an increase in scatter fraction. For the NEMA Image Quality phantom, uniformity and Recovery coefficients were degraded in the offset, and dual phantom cases, while spillover ratios were increased, notably when the chamber was placed nearest the gantry. Image quality metrics were comparable between the 20- and 10 min timeframes.Conclusion: Dual animal scanning results in some loss of image quality on the Sedecal Argus PET scanner; however, this degradation is within acceptable limits.

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Iterative image reconstruction methods are widely used in PET due to their better image quality when compared to analytical methods. However, inaccurate quantification occurs in low activity concentration regions, which leads to biased quantification of PET images. The diagnosis of some neurodegenerative diseases, such as Alzheimer’s disease, is based on identifying such low-uptake regions. Furthermore, PET imaging in these populations should be as short as possible to limit head movements and improve patient comfort. This work aims to identify optimized reconstruction parameters of [18F]FDG PET brain images aiming to reduce image acquisition time with minimal impact on quantification. For this, [18F]FDG PET images of a Hoffman 3-D brain phantom were acquired. Analytical and iterative reconstruction methods were compared utilizing image quality and quantitative accuracy metrics. OSEM reconstruction algorithm was optimized (4 iterations and 32 subsets). It resulted in remarkably similar images compared to the current clinical settings, with a 50% reduction in scan time (5 min with a post-reconstruction filter of 4 mm). Future clinical studies are needed to confirm the results presented here.

Aim: To demonstrate the clinical capability of ultra-fast whole body PET acquisition enabled by digital photon counting PET (dPET) and to assess and compare its diagnostic and quantitative characteristics to current clinical PET acquisition. Methods: Twenty-five patients scheduled for FDG whole body PET/ CT were imaged using three separate acquisitions as part of intraindividual comparison study with a pre-commercial release dPET/CT (Vereos) and cPET/CT (Gemini, Philips, Cleveland). Standard cPET imaging was performed at~75 min p.i. of~450 MBq FDG with investigational dPET imaged at~55 min p.i. The first dPET acquisition was performed using 90s/bed position, immediately followed by a 9s/bed position. Acquisition which lead to average table times of~15 and~2 min. These were compared with standard-of-care 90s/bed position cPET. The 9s/bed dPET listmode data were reconstructed using a previously optimized methodology. All other aspects of image acquisition were kept identical. Three blinded reviewers evaluated the data sets regarding visual characteristics, diagnostic confidence and semiquantitative readouts. Results: Visual assessment scores were significantly higher for 90s/bed dPET whole body (p<0.01) with no difference between 9s/bed dPET and 90s/bed cPET. Quantitatively, the 9s/bed dPET images presented slightly increased background noise, however there was no significant impact on diagnostic confidence or SUV measures of FDG-avid lesions. Conclusion: Next generation digital photon counting PET detector technology enables a new capability of Ultra-Fast (~2min) wholebody acquisition with comparable diagnostic confidence and quantitative precision to current generation cPET acquisitions taking 10 times longer. This allows for new PET workflow concepts, improved patient comfort, minimized patient motion and whole-body pseudo-dynamic imaging of tracer uptake. Aim: Detection of the extent of local recurrence and of metastases in biochemical recurrence (BCR) of prostate cancer facilitates selection of appropriate treatment. The FALCON trial (NCT02578940) assessed the impact of 18F-fluciclovine PET/CT on the clinical management of men with BCR of prostate cancer following initial radical therapy. Methods: Men being considered for curative-intent salvage therapy following first BCR were recruited at 6 UK sites. Management plans were documented prior to and following 18F-fluciclovine PET/CT imaging. Post-scan changes to treatment modality such as salvage radiotherapy [RT] to systemic therapy were classed as 'major' , while changes within a modality (e.g. modified RT fields) were classed as 'other'. A pre-planned interim analysis of the first 85 patients was conducted; recruitment was to be stopped for efficacy if the number of treatment changes was > 45 (52.9%; 97.5% CI: 40.3-62.3%), or for futility if ≤ 8 (9.4%, 97.5% CI: 3.6-18.9%). Results: The 85 enrolled patients were a mean 4.8 y post-initial diagnosis, with a median age of 67 y and median PSA of 0.63ng/mL. Twelve (14.1%) had a Gleason score ≤ 6, 60 (70.6%) had ...