Effects of Respiratory Motion on Y-90 PET Dosimetry for SIRT

Respiratory motion degrades the quantification accuracy of PET imaging by blurring the radioactivity distribution. In the case of post-SIRT PET-CT verification imaging, respiratory motion can lead to inaccuracies in dosimetric measures. Using an anthropomorphic phantom filled with 90Y at a range of clinically relevant activities, together with a respiratory motion platform performing realistic motions (10–15 mm amplitude), we assessed the impact of respiratory motion on PET-derived post-SIRT dosimetry. Two PET scanners at two sites were included in the assessment. The phantom experiments showed that device-driven quiescent period respiratory motion correction improved the accuracy of the quantification with statistically significant increases in both the mean contrast recovery (+5%, p = 0.003) and the threshold activities corresponding to the dose to 80% of the volume of interest (+6%, p < 0.001). Although quiescent period gating also reduces the number of counts and hence increases the noise in the PET image, its use is encouraged where accurate quantification of the above metrics is desired.

Perspectives of brain imaging with PET systems

In this partial review and partial attempt at vision of what may be the future of dedicated brain PET scanners, the key implementations of the PET technique, we postulate that we are still on a development path and there is still a lot to be done in order to develop optimal brain imagers. Optimized for particular imaging tasks and protocols, and also mobile, that can be used outside the PET center, in addition to the expected improvements in sensitivity and resolution. For this multi-application concept to be more practical, flexible, adaptable designs are preferred. This task is greatly facilitated by the improved TOF performance that allows for more open, adjustable, limited angular coverage geometries without creating image artifacts. As achieving uniform very high resolution in the whole body is not practical due to technological limits and high costs, hybrid systems using a moderate-resolution total body scanner (such as J-PET) combined with a very high performing brain imager could be a very attractive approach. As well, as using magnification inserts in the total body or long-axial length imagers to visualize selected targets with higher resolution. In addition, multigamma imagers combining PET with Compton imaging should be developed to enable multitracer imaging.

The effect of modern PET technology and techniques on the EANM paediatric dosage card

Aim Recent advancements in PET technology have brought with it significant improvements in PET performance and image quality. In particular, the extension of the axial field of view of PET systems, and the introduction of semiconductor technology into the PET detector, initially for PET/MR, and more recently available long-field-of-view PET/CT systems (≥ 25 cm) have brought a step change improvement in the sensitivity of PET scanners. Given the requirement to limit paediatric doses, this increase in sensitivity is extremely welcome for the imaging of children and young people. This is even more relevant with PET/MR, where the lack of CT exposures brings further dose reduction benefits to this population. In this short article, we give some details around the benefits around new PET technology including PET/MR and its implications on the EANM paediatric dosage card. Material and methods Reflecting on EANM adult guidance on injected activities, and making reference to bed overlap and the concept of MBq.min bed−1 kg−1, we use published data on image quality from PET/MR systems to update the paediatric dosage card for PET/MR and extended axial field of view (≥ 25 cm) PET/CT systems. However, this communication does not cover the expansion of paediatric dosing for the half-body and total-body scanners that have recently come to market. Results In analogy to the existing EANM dosage card, new parameters for the EANM paediatric dosage card were developed (class B, baseline value: 10.7 MBq, minimum recommended activity 10 MBq). The recommended administered activities for the systems considered in this communication range from 11 MBq [18F]FDG for a child with a weight of 3 kg to 149 MBq [18F]FDG for a paediatric patient weight of 68 kg, assuming a scan of 3 min per bed position. The mean effective dose over all ages (1 year and older) is 2.85 mSv. Conclusion With this, recommendations for paediatric dosing are given for systems that have not been considered previously.

Convolutional Neural Networks for Automatic Image Quality Control and EARL Compliance of PET Images

Background: Machine learning studies require a large number of images often obtained on different PET scanners. When merging these images, the use of harmonized images following EARL-standards is essential. However, when including retrospective images, EARL accreditation might not have been in place. The aim of this study was to develop a convolutional neural network (CNN) that can identify retrospectively if an image is EARL compliant and if it is meeting older or newer EARL-standards. Materials and Methods: 96 PET images acquired on three PET/CT systems were included in the study. All images were reconstructed with the locally clinically preferred, EARL1, and EARL2 compliant reconstruction protocols. After image pre-processing, one CNN was trained to separate clinical and EARL compliant reconstructions. A second CNN was optimized to identify EARL1 and EARL2 compliant images. The accuracy of both CNNs was assessed using 5-fold cross validation. The CNNs were validated on 24 images acquired on a PET scanner not included in the training data. To assess the impact of image noise on the CNN decision, the 24 images were reconstructed with different scan durations.Results: In the cross-validation, the first CNN classified all images correctly. When identifying EARL1 and EARL2 compliant images, the second CNN identified 100% EARL1 compliant and 85% EARL2 compliant images correctly. The accuracy in the independent dataset was comparable to the cross-validation accuracy. The scan duration had almost no impact on the results. Conclusion: The two CNNs trained in this study can be used to retrospectively include images in a multi-center setting by e.g. adding additional smoothing. This method is especially important for machine learning studies where the harmonization of images from different PET systems is essential.

Combined BNCT and PET for theranostics

This short review summarizes the issue of boron distribution monitoring in boron neutron capture therapy (BNCT), which remains a serious drawback of this powerful oncological treatment. Here we present the monitoring methods that are presently used with particular emphasis on the positron emission tomography (PET) which has the highest potential to be used for the real-time monitoring of boron biodistribution. We discuss the possibility of using present PET scanners to determine the boron uptake in vivo before the BNCT treatment with the use of p-boronphenylalanine (BPA) labeled with 18F isotope. Several examples of preclinical studies and clinical trials performed with the use of [18F]FBPA are shown. We also discuss shortly the perspectives of using other radiotracers and boron carriers which may significantly improve the boron imaging with the use of the state-of-the-art Total-Body PET scanners providing a theranostic approach in the BNCT.

Adoption of large-scale medical equipment: the impact of competition in the German inpatient sector

The availability of large-scale medical equipment such as computed tomography (CT), magnet resonance imaging (MRI) and positron emission tomography (PET) scanners has increased rapidly worldwide over the last decades. Among OECD countries, Germany ranks high according to the number of imaging technologies and their applications per inhabitant. In contrast to other countries, there is no active governmental planning of large-scale medical equipment. We therefore investigated whether and how the adoption and distribution of CT, MRI and PET scanners in the German inpatient sector is subject to competition. Using a linear-probability model, we additionally examined the impact of regional, hospital- and population-based factors. In summary, our results indicate that the adoption rate by hospital sites decreases with the number of other sites being already equipped with the respective device and their proximity. However, the effect presumably depends on the technologies’ stage within the diffusion process. No influence regarding the amount of state subsidies could be identified. Furthermore, hospital size and university status strongly affect the adoption.

Role of 18F-FDG PET/CT Radiomics Features in the Differential Diagnosis of Solitary Pulmonary Nodules: Diagnostic Accuracy and Comparison between Two Different PET/CT Scanners

The aim of this retrospective study was to investigate the ability of 18 fluorine-fluorodeoxyglucose positron emission tomography/CT (18F-FDG-PET/CT) metrics and radiomics features (RFs) in predicting the final diagnosis of solitary pulmonary nodules (SPN). We retrospectively recruited 202 patients who underwent a 18F-FDG-PET/CT before any treatment in two PET scanners. After volumetric segmentation of each lung nodule, 8 PET metrics and 42 RFs were extracted. All the features were tested for significant differences between the two PET scanners. The performances of all features in predicting the nature of SPN were analyzed by testing three classes of final logistic regression predictive models: two were built/trained through exploiting the separate data from the two scanners, and the other joined the data together. One hundred and twenty-seven patients had a final diagnosis of malignancy, while 64 were of a benign nature. Comparing the two PET scanners, we found that all metabolic features and most of RFs were significantly different, despite the cross correlation being quite similar. For scanner 1, a combination between grey level co-occurrence matrix (GLCM), histogram, and grey-level zone length matrix (GLZLM) related features presented the best performances to predict the diagnosis; for scanner 2, it was GLCM and histogram-related features and metabolic tumour volume (MTV); and for scanner 1 + 2, it was histogram features, standardized uptake value (SUV) metrics, and MTV. RFs had a significant role in predicting the diagnosis of SPN, but their accuracies were directly related to the scanner.

Evaluation of a Method Combining Physical Experiment and Data Insertion For the Assessment of PET-CT Systems

Background: To evaluate and compare Positron Emission Tomography (PET) devices among them, tests are performed on phantoms that generally consist in simple geometrical objects, fillable with radiotracers. On one hand, those tests bring a control over the experiment through the operator preparation but on the other hand, they are limited in terms of reproducibility, repeatability and are time-consuming, in particular, if several replications are required. To overcome these restrictions, we designed a method combining physical experiment and data insertion that aims to avoid experimental repetitions while testing multiple configurations for the performance evaluation of PET scanners.Methods: Based on the National Electrical Manufacturers Association Image Quality standard, four experiments, with different spheres-to-background ratios: 2:1, 4:1, 6:1 and 8:1, were performed. An additional acquisition was done with a radioactive background and no activity within the spheres. It was created as a baseline to artificially simulate the radioactive spheres and reproduce initial experiments. Standard sphere set was replaced by smaller target sizes (4, 5, 6, 8, 10 and 13 mm) to match current detectability performance of PET scanners. Images were reconstructed following standard guidelines, i.e. using OSEM algorithm, and an additional BPL reconstruction was performed. We visually compared experimental and simulated images. We measured the activity concentration values into the spheres to calculate the mean and maximum recovery coefficient (RCmean and RCmax ) which we used in a quantitative analysis.Results: No significant visual discrepancies were identified between experimental and simulated series. Mann-Whitney U tests comparing simulated and experimental distributions showed no statistical differences for both RCmean (P value = 0.611) and RCmax (P value = 0.720). Spearman tests revealed high correlation for RCmean (ρ = 0.974, P value < 0.001) and RCmax (ρ = 0.974, P value < 0.001) between both datasets. According to Bland-Altman plots, we highlighted slight shifts in RCmean and RCmax of respectively 2.1 ± 16.9 % and 3.3 ± 22.3 %.Conclusions: The method produced realistic results compared to experimental data. Known synthesized information fused with original data allows full exploration of the system's capabilities while avoiding the limitations associated with repeated experiments.