Projection Space Implementation of Deep Learning-Guided Low-Dose Brain PET Imaging Improves Performance over Implementation in Image Space

Purpose: To assess the performance of full dose (FD) positron emission tomography (PET) image synthesis in both image and projection space from low-dose (LD) PET images/sinograms without sacrificing diagnostic quality using deep learning techniques. Methods: Clinical brain PET/CT studies of 140 patients were retrospectively employed for LD to FD PET conversion. 5% of the events were randomly selected from the FD list-mode PET data to simulate a realistic LD acquisition. A modified 3D U-Net model was implemented to predict FD sinograms in the projection-space (PSS) and FD images in image-space (PIS) from their corresponding LD sinograms/images, respectively. The quality of the predicted PET images was assessed by two nuclear medicine specialists using a five-point grading scheme. Quantitative analysis using established metrics including the peak signal-to-noise ratio (PSNR), structural similarity index metric (SSIM), region-wise standardized uptake value (SUV) bias, as well as first-, second- and high-order texture radiomic features in 83 brain regions for the test and evaluation dataset was also performed. Results: All PSS images were scored 4 or higher (good to excellent) by the nuclear medicine specialists. PSNR and SSIM values of 0.96 ± 0.03, 0.97 ± 0.02 and 31.70 ± 0.75, 37.30 ± 0.71 were obtained for PIS and PSS, respectively. The average SUV bias calculated over all brain regions was 0.24 ± 0.96% and 1.05 ± 1.44% for PSS and PIS, respectively. The Bland-Altman plots reported the lowest SUV bias (0.02) and variance (95% CI: -0.92, +0.84) for PSS compared with the reference FD images. The relative error of the homogeneity radiomic feature belonging to the Grey Level Co-occurrence Matrix category was -1.07 ± 1.77 and 0.28 ± 1.4 for PIS and PSS, respectively Conclusion: The qualitative assessment and quantitative analysis demonstrated that the FD PET prediction in projection space led to superior performance, resulting in higher image quality and lower SUV bias and variance compared to FD PET prediction in the image domain

Predictive value of 99mTc-MAA-based dosimetry in personalized 90Y-SIRT planning for liver malignancies

[EN] Background: Selective internal radiation therapy with 90Y radioembolization aims to selectively irradiate liver tumours by administering radioactive microspheres under the theragnostic assumption that the pre-therapy injection of 99mTc labelled macroaggregated albumin (99mTc-MAA) provides an estimation of the 90Y microspheres biodistribution, which is not always the case. Due to the growing interest in theragnostic dosimetry for personalized radionuclide therapy, a robust relationship between the delivered and pre-treatment radiation absorbed doses is required. In this work, we aim to investigate the predictive value of absorbed dose metrics calculated from 99mTc-MAA (simulation) compared to those obtained from 90Y post-therapy SPECT/CT. Results: A total of 79 patients were analysed. Pre- and post-therapy 3D-voxel dosimetry was calculated on 99mTc-MAA and 90Y SPECT/CT, respectively, based on Local Deposition Method. Mean absorbed dose, tumour-to-normal ratio, and absorbed dose distribution in terms of dose-volume histogram (DVH) metrics were obtained and compared for each volume of interest (VOI). Mann-Whitney U-test and Pearson's correlation coefficient were used to assess the correlation between both methods. The effect of the tumoral liver volume on the absorbed dose metrics was also investigated. Strong correlation was found between simulation and therapy mean absorbed doses for all VOIs, although simulation tended to overestimate tumour absorbed doses by 26%. DVH metrics showed good correlation too, but significant differences were found for several metrics, mostly on non-tumoral liver. It was observed that the tumoral liver volume does not significantly affect the differences between simulation and therapy absorbed dose metrics. Conclusion: This study supports the strong correlation between absorbed dose metrics from simulation and therapy dosimetry based on 90Y SPECT/CT, highlighting the predictive ability of 99mTc-MAA, not only in terms of mean absorbed dose but also of the dose distributionEURATO

Differential privacy preserved federated transfer learning for multi-institutional 68Ga-PET image artefact detection and disentanglement.

PURPOSE Image artefacts continue to pose challenges in clinical molecular imaging, resulting in misdiagnoses, additional radiation doses to patients and financial costs. Mismatch and halo artefacts occur frequently in gallium-68 (68Ga)-labelled compounds whole-body PET/CT imaging. Correcting for these artefacts is not straightforward and requires algorithmic developments, given that conventional techniques have failed to address them adequately. In the current study, we employed differential privacy-preserving federated transfer learning (FTL) to manage clinical data sharing and tackle privacy issues for building centre-specific models that detect and correct artefacts present in PET images. METHODS Altogether, 1413 patients with 68Ga prostate-specific membrane antigen (PSMA)/DOTA-TATE (TOC) PET/CT scans from 3 countries, including 8 different centres, were enrolled in this study. CT-based attenuation and scatter correction (CT-ASC) was used in all centres for quantitative PET reconstruction. Prior to model training, an experienced nuclear medicine physician reviewed all images to ensure the use of high-quality, artefact-free PET images (421 patients' images). A deep neural network (modified U2Net) was trained on 80% of the artefact-free PET images to utilize centre-based (CeBa), centralized (CeZe) and the proposed differential privacy FTL frameworks. Quantitative analysis was performed in 20% of the clean data (with no artefacts) in each centre. A panel of two nuclear medicine physicians conducted qualitative assessment of image quality, diagnostic confidence and image artefacts in 128 patients with artefacts (256 images for CT-ASC and FTL-ASC). RESULTS The three approaches investigated in this study for 68Ga-PET imaging (CeBa, CeZe and FTL) resulted in a mean absolute error (MAE) of 0.42 ± 0.21 (CI 95%: 0.38 to 0.47), 0.32 ± 0.23 (CI 95%: 0.27 to 0.37) and 0.28 ± 0.15 (CI 95%: 0.25 to 0.31), respectively. Statistical analysis using the Wilcoxon test revealed significant differences between the three approaches, with FTL outperforming CeBa and CeZe (p-value < 0.05) in the clean test set. The qualitative assessment demonstrated that FTL-ASC significantly improved image quality and diagnostic confidence and decreased image artefacts, compared to CT-ASC in 68Ga-PET imaging. In addition, mismatch and halo artefacts were successfully detected and disentangled in the chest, abdomen and pelvic regions in 68Ga-PET imaging. CONCLUSION The proposed approach benefits from using large datasets from multiple centres while preserving patient privacy. Qualitative assessment by nuclear medicine physicians showed that the proposed model correctly addressed two main challenging artefacts in 68Ga-PET imaging. This technique could be integrated in the clinic for 68Ga-PET imaging artefact detection and disentanglement using multicentric heterogeneous datasets

L’impact du phénomène de réserve cognitive dans le diagnostic de la maladie d’Alzheimer

Le concept de réserve dans la maladie d’Alzheimer (MA) a été introduit suite à l’observation que certains facteurs, notamment l’éducation, peuvent moduler l’expression clinique des lésions neuropathologiques, grâce au développement de ressources et réseaux alternatifs, qui fournissent une capacité compensatoire. Les biomarqueurs d’imagerie moléculaire, parmi lesquels le PET au 18F-Fluorodesoxyglucose (FDG-PET), contribuent au diagnostic de la MA en permettant d’estimer in vivo la dysfonction neuronale associée aux lésions neuropathologiques. Pour une validation systématique des biomarqueurs dans la pratique clinique il est crucial de mesurer l’impact des différents facteurs modulateurs sur la performance diagnostique. Dans cette étude, nous avons pu démontrer que le niveau d’éducation des patients module la relation entre la dysfonction neuronale mesurée au FDG-PET et la sévérité clinique, en démontrant donc une réserve associée à l’éducation, toutefois sans diminuer la performance diagnostique du FDG-PET, qui reste excellente chez l’ensemble des patients

Intra-vagal parathyroid adenoma on digital PET/CT with 18F-fluorocholine

Parathyroid adenoma within or adjacent to the vagus nerve is a rare ectopia, with only 21 cases reported in the literature [1,2,3]. A plausible explanation described by Gilmour in 1937 is that parathyroid elements, destined for the inferior parathyroid glands, may segregate and attach to the nerve during embryogenesis [4, 5]

Dopaminergic imaging separates normal pressure hydrocephalus from its mimics

Idiopathic normal pressure hydrocephalus (iNPH) and iNPH mimics (i.e., Parkinson's disease, progressive supranuclear palsy or dementia with Lewy bodies) share similar clinical features, and discrimination between both conditions relies on invasive time-consuming investigations. This study aims to compare [123I]FP-CIT SPECT imaging-visual rating and semiquantitative values-between iNPH and iNPH mimics

Increased Petrous Bone Uptake on ¹⁸F-PSMA-1007 PET/CT Due to Otospongiosis

We report the case of a 74-year-old man who had undergone radical prostatectomy for prostatic cancer 6 months earlier. Elevated prostate-specific antigen during follow-up prompted 18F–prostate-specific membrane antigen (PSMA) ligand PET/CT (18F-PSMA-1007 PET/CT) to search for new manifestations of prostate cancer, revealing an increased focal uptake (SUVmax, 5.9) in the left cochlear/pericochlear temporal bone and equivocal PSMA-RADS-3a external iliac nodes. Comparison with cone-beam CT and MRI showed that the focal temporal bone uptake corresponded to the typical morphological features of active otospongiosis (otosclerosis) in the context of a previously known long-standing otospongiosis

The Clinical Added Value of Breast Cancer Imaging Using Hybrid PET/MR Imaging

Dedicated MR imaging is highly performant for the evaluation of the primary lesion and should regularly be added to whole-body PET/MR imaging for the initial staging. PET/MR imaging is highly sensitive for the detection of nodal involvement and could be combined with the high specificity of axillary second look ultrasound for the confirmation of the N staging. For M staging, with the exception of lung lesions, PET/MR imaging is superior to PET/computed tomography, at half the radiation dose. The predictive value of multiparametric imaging with PET/MR imaging holds promise to improve through radiomics and artificial intelligence

Scintigraphic Identification of Gastric Tissue in a Mediastinal Mass

We present a Tc pertechnetate scintigraphy performed in a 64-year-old woman to investigate a mediastinal cystic mass in search of residual gastric mucosa after gastrectomy. She had a history of esophagectomy and gastric pull-up for esophageal cancer. Postoperative leakage necessitated ablation of the gastric pull-up and reconstruction using part of the colon. Oral realimentation resulted in mediastinal pain and brownish discharge within the trachea, raising the suspicion of residual gastric pouch. SPECT/CT demonstrated increased tracer uptake in the median part of the mediastinal cyst, and a biopsy confirmed the presence gastric mucosa

High protracted (99m)Tc-HDP uptake in synthetic bone implants - a potentially misleading incidental finding on bone scintigraphy

We report the case of a 56-year-old male with bilateral total knee prostheses suffering from bilateral knee pain mainly on the right side and referred for bone scintigraphy. The medical history of the patient revealed an opening wedge high tibial osteotomy performed nine years earlier, with insertion of two blocks of ceramic made of hydroxyapatite and tricalcium phosphate in a wedge configuration as synthetic bone substitutes. The porous structure of these implants is analogous to the architecture of cancellous bone and permits fibrovascular and bone ingrowth, promoting the healing process. Planar scintigraphy and SPECT/CT showed an intense uptake within those implants in the early phase as well as in the late phase of the bone scan. It also showed bilateral patellofemoral arthritis. A (99m)Tc-labeled antigranulocyte antibody scintigraphy was negative for infection or inflammation. Bilateral patellar resurfacing led to complete symptom regression, confirmed at 10 months follow-up. To the best of our knowledge, this scintigraphic pattern with such a high tracer uptake reflecting bone substitute osteointegration has not yet been published. This should be considered in patients with such bone replacement materials that are increasingly used, in order to avoid false diagnosis of inflammation or infection