Monte Carlo simulation of the system performance of a long axial field-of-view PET based on monolithic LYSO detectors.

BACKGROUND: In light of the milestones achieved in PET design so far, further sensitivity improvements aim to optimise factors such as the dose, throughput, and detection of small lesions. While several longer axial field-of-view (aFOV) PET systems based on pixelated detectors have been installed, continuous monolithic scintillation detectors recently gained increased attention due to their depth of interaction capability and superior intrinsic resolution. As a result, the aim of this work is to present and evaluate the performance of two long aFOV, monolithic LYSO-based PET scanner designs. METHODS: Geant4 Application for Tomographic Emission (GATE) v9.1 was used to perform the simulations. Scanner designs A and B have an aFOV of 36.2 cm (7 rings) and 72.6 cm (14 rings), respectively, with 40 detector modules per ring each and a bore diameter of 70 cm. Each module is a 50 × 50 × 16 mm3 monolithic LYSO crystal. Sensitivity, noise equivalent count rate (NECR), scatter fraction, spatial resolution, and image quality tests were performed based on NEMA NU-2018 standards. RESULTS: The sensitivity of design A was calculated to be 29.2 kcps/MBq at the centre and 27 kcps/MBq at 10 cm radial offset; similarly, the sensitivity of design B was found to be 106.8 kcps/MBq and 98.3 kcps/MBq at 10 cm radial offset. NECR peaks were reached at activity concentrations beyond the range of activities used for clinical studies. In terms of spatial resolution, the values for the point sources were below 2 mm for the radial, tangential, and axial full width half maximum. The contrast recovery coefficient ranged from 53% for design B and 4:1 contrast ratio to 90% for design A and 8:1 ratio, with a reasonably low background variability. CONCLUSIONS: Longer aFOV PET designs using monolithic LYSO have superior spatial resolution compared to current pixelated total-body PET (TB-PET) scanners. These systems combine high sensitivity with improved contrast recovery.

68Ga-DOTATATE PET in Restaging and Response to Therapy in Neuroblastoma: A Case Series and a Mini Review.

68Ga-DOTATATE PET/CT is widely used for the evaluation of neuroendocrine tumors. Some reports exist on its use in the management of neuroblastoma. Building on the prior reports as well as our previous experience in using this technique for initial staging, we propose to describe its practical benefits in restaging and response to therapy. We describe different aspects including supply logistics, preparation, spatial resolution, and other practical applications. Methods: We reviewed the medical records for 8 patients who were evaluated with 68Ga-DOTATATE PET/CT at our institution over 2 y. A note was made of the patient and disease characteristics and the indication for PET imaging, and the results were retrospectively analyzed for feasibility, logistics, radiation exposure, and utility in answering the clinical question. Results: Eight children (5 girls and 3 boys; age range, 4-60 mo; median age, 30 mo) diagnosed with neuroblastoma were imaged with 68Ga-DOTATATE PET/CT and 5 with 123I-metaiodobenzylguanidine (123I-MIBG) SPECT/CT over 2 y. Three 68Ga-DOTATATE PET scans were done for staging, 10 for response evaluation, and 2 for restaging. 68Ga-DOTATATE PET accurately identified neuroblastoma lesions suspected or seen on anatomic imaging. It has been shown to be more specific and more sensitive than 123I-MIBG and at times also MRI. It had better spatial and contrast resolution than 123I-MIBG. 68Ga-DOTATATE PET was better than 123I-MIBG SPECT/CT, CT, and MRI in the detection of early progression and viable tumor delineation for response assessment, as well as in target volume definition for external-beam radiotherapy and proton-beam radiotherapy. 68Ga-DOTATATE PET was also better at assessing bony and bone marrow disease changes with time. Conclusion: 68Ga-DOTATATE PET/CT offers added value and a superior edge to other imaging modalities in restaging and response assessment in neuroblastoma patients. Further multicenter evaluations in larger cohorts are needed.

The potential of a medium-cost long axial FOV PET system for nuclear medicine departments.

PURPOSE: Total body positron emission tomography (TB-PET) has recently been introduced in nuclear medicine departments. There is a large interest in these systems, but for many centers, the high acquisition cost makes it very difficult to justify their current operational budget. Here, we propose medium-cost long axial FOV scanners as an alternative. METHODS: Several medium-cost long axial FOV designs are described with their advantages and drawbacks. We describe their potential for higher throughput, more cost-effective scanning, a larger group of indications, and novel research opportunities. The wider spread of TB-PET can also lead to the fast introduction of new tracers (at a low dose), new methodologies, and optimized workflows. CONCLUSIONS: A medium-cost TB-PET would be positioned between the current standard PET-CT and the full TB-PET systems in investment but recapitulate most advantages of full TB-PET. These systems could be more easily justified financially in a standard academic or large private nuclear medicine department and still have ample research options.

A Review of Radiomics and Artificial Intelligence and Their Application in Veterinary Diagnostic Imaging.

Great advances have been made in human health care in the application of radiomics and artificial intelligence (AI) in a variety of areas, ranging from hospital management and virtual assistants to remote patient monitoring and medical diagnostics and imaging. To improve accuracy and reproducibility, there has been a recent move to integrate radiomics and AI as tools to assist clinical decision making and to incorporate it into routine clinical workflows and diagnosis. Although lagging behind human medicine, the use of radiomics and AI in veterinary diagnostic imaging is becoming more frequent with an increasing number of reported applications. The goal of this paper is to provide an overview of current radiomic and AI applications in veterinary diagnostic imaging.

177Lu-PSMA Therapy for Metastatic Castration-Resistant Prostate Cancer: A Mini-Review of State-of-the-Art.

BACKGROUND: Prostate specific membrane antigen (PSMA) ligand labeled with Lutetium-177 (177Lu) is a promising therapeutic option for metastatic castration-resistant prostate cancer (mCRPC). Several prospective and retrospective studies as well as clinical trials are completed or underway. This has ultimately led to the approval of this therapy by the US Food and Drug Administration (FDA) on March 23 2022. Our work aims to present a mini-review of the most recent research performed and the potential future directions of 177Lu-PSMA-radioligand therapy (RLT) for mCRPC patients. MAIN BODY: For patients with mCRPCwho have met the eligibility criteria for 177Lu-PSMA RLT, numerous studies and trials are either ongoing or have been completed. The studies included in this review have reported overall biochemical response, defined as a prostate-specific antigen (PSA) decline of at least 50%, in at least 44% of patients with mCRPC. The median ranges of overall survival (OS) and radiographic progression-free survival (rPFS) were reported within 10.7-56 and 3.6-16 months, respectively. With data from several retrospective and prospective studies published, the safety of 177Lu-PSMA RLT in mCRPC has been confirmed and demonstrated by its low toxicity profile. Various studies have published pharmacokinetic/pharmacodynamic models to better understand the absorption, distribution, metabolism, and excretion of the RLT in this patient population. Findings have been published for 177Lu-PSMA RLT alone and in combination with other agents. We summarize their findings in our review. CONCLUSIONS: The efficacy of 177Lu-PSMA RLT for patients with mCRPC has been proven thus far with promising results: PSA response, OS and rPFS when used alone or in combination with other treatment options, relative to the standard treatment options alone. The low toxicity profile noted also proves the safety of 177Lu-PSMA RLT in these patients.

First-principles studies of defect behaviour in bismuth germanate.

Intrinsic defects are known to greatly affect the structural and electronic properties of scintillators thereby impacting performance when these materials are in operation. In order to overcome this effect, an understanding of the defect process is required for the design of more stable materials. Here we employed density functional theory calculations and the PBE0 hybrid functional to study the structural, electronic,defect process and optical properties of [Formula: see text] (BGO), a well know material used as scintillator. We examined possible intrinsic defects and calculated their formation energy and their impact on the properties that affect the scintillation process. Furthermore, we investigated the effect and role of rare earth element (REE = Nd, Pr, Ce and Tm) doping on the properties of the BGO system. While the PBE functional underestimated the band gap, the PBE0 was found to adequately describe the electronic properties of the system. Out of all the defects types considered, it was found that [Formula: see text] antisite is the most favourable defect. Analysis of the effect of this defect on the electronic properties of BGO revealed an opening of ingap states within the valence band. This observation suggests that the [Formula: see text] could be a charge trapping defect in BGO. We found that the calculated dopant substitution formation energy increases with increase in the size of the dopant and it turns out that the formation of O vacancy is easier in doped systems irrespective of the size of the dopant. We analyzed the optical spectra and noted variations in different regions of the photon energy spectra.

Amino Acid PET Imaging with 18F-DOPA in the evaluation of Pediatric Brain Tumors.

Although MRI is the workhorse of brain tumor initial evaluation and follow-up, there is a growing amount of data recommending the incorporation of amino-acid PET imaging at different stages of the management of these patients. Recent nuclear medicine and neuro-oncology clinical practice recommendations support the use of amino-acid imaging in brain tumor imaging. Considering 18F-DOPA is FDA approved for the evaluation of parkinsonian syndromes, it could be used clinically for other valuable clinical indications such as brain tumor evaluations. This value seems to be well established in adults and has growing evidence for its use in pediatrics as well. We offer to present four pediatric brain tumor cases imaged with 18F-DOPA and review the literature.

Clinical Management of End-Stage Renal Disease Patients on Dialysis Receiving Radioactive Iodine Treatment.

PURPOSE: Radioactive iodine (RAI) is used to treat thyroid cancer patients with a clear paradigm for most patients. End-stage renal disease (ESRD) patients pose several challenges when undergoing RAI treatment, primarily due to the lack of renal clearance. We retrospectively report our experience with RAI treatment in a cohort of patients with ESRD and provide a set of recommendations on aspects such as the need for adjusted dose activity, balancing scheduling between RAI therapy and dialysis, and radiation safety precautions. PATIENTS AND METHODS: In this study, we report on 5 patients (6 cases), with ESRD on dialysis, treated with RAI for thyroid cancer. Retention measurements to determine individual biological clearance of RAI from the patient's body before and after dialysis sessions were assessed using external exposure dose rates measured at 1 m. RESULTS: Delayed biological clearance of RAI, after the first hemodialysis session, resulted in a longer RAI effective half-life as a consequence of longer retention periods, consistent with observations reported in scientific literature. To achieve a much closer radiation exposure compared with a nondialysis patient, one would recommend administering ~20%-30% of the dose activity normally administered to a thyroid cancer patient based on their medical history, histopathology, and uptake with the appropriate dialysis schedule. CONCLUSIONS: Special precautions should be taken with the administration of RAI in ESRD patients by adjusting the prescribed dose activity, dialysis sessions, and paying special attention to wastes. Pooling data from multiple centers may be useful to build a consensus and substantiated recommendations.

Simulation study of a coincidence detection system for non-invasive determination of arterial blood time-activity curve measurements.

BACKGROUND: Arterial sampling in PET studies for the purposes of kinetic modeling remains an invasive, time-intensive, and expensive procedure. Alternatives to derive the blood time-activity curve (BTAC) non-invasively are either reliant on large vessels in the field of view or are laborious to implement and analyze as well as being prone to many processing errors. An alternative method is proposed in this work by the simulation of a non-invasive coincidence detection unit. RESULTS: We utilized GATE simulations of a human forearm phantom with a blood flow model, as well as a model for dynamic radioactive bolus activity concentration based on clinical measurements. A fixed configuration of 14 and, also separately, 8 detectors were employed around the phantom, and simulations were performed to investigate signal detection parameters. Bismuth germanate (BGO) crystals proved to show the highest count rate capability and sensitivity to a simulated BTAC with a maximum coincidence rate of 575 cps. Repeatable location of the blood vessels in the forearm allowed a half-ring design with only 8 detectors. Using this configuration, maximum coincident rates of 250 cps and 42 cps were achieved with simulation of activity concentration determined from 15O and 18F arterial blood sampling. NECR simulated in a water phantom at 3 different vertical positions inside the 8-detector system (Y = - 1 cm, Y = - 2 cm, and Y = -3 cm) was 8360 cps, 13,041 cps, and 20,476 cps at an activity of 3.5 MBq. Addition of extra axial detection rings to the half-ring configuration provided increases in system sensitivity by a factor of approximately 10. CONCLUSIONS: Initial simulations demonstrated that the configuration of a single half-ring 8 detector of monolithic BGO crystals could describe the simulated BTAC in a clinically relevant forearm phantom with good signal properties, and an increased number of axial detection rings can provide increased sensitivity of the system. The system would find use in the derivation of the BTAC for use in the application of kinetic models without physical arterial sampling or reliance on image-based techniques.

Influence of surface vacancy defects on the carburisation of Fe 110 surface by carbon monoxide.

Adsorption and dissociation of gaseous carbon monoxide (CO) on metal surfaces is one of the most frequently occurring processes of carburisation, known as primary initiator of metal dusting corrosion. Among the various factors that can significantly influence the carburisation process are the intrinsic surface defects such as single surface vacancies occurring at high concentrations due to their low formation energy. Intuitively, adsorption and dissociation barriers of CO are expected to be lowered in the vicinity of a surface vacancy, due to the strong attractive interaction between the vacancy and the C atom. Here the adsorption energies and dissociation pathways of CO on clean and defective Fe 110 surface are explored by means of density functional theory. Interestingly, we find that the O adatom, resulting from the CO dissociation, is unstable in the electron-deficit neighbourhood of the vacancy due to its large electron affinity, and raises the barrier of the carburisation pathway. Still, a full comparative study between the clean surface and the vacancy-defected surface reveals that the complete process of carburisation, starting from adsorption to subsurface diffusion of C, is more favourable in the vicinity of a vacancy defect.

Mechanisms behind the immediate effects of Roux-en-Y gastric bypass surgery on type 2 diabetes.

BACKGROUND: The most common bariatric surgery, Roux-en-Y gastric bypass, leads to glycemia normalization in most patients long before there is any appreciable weight loss. This effect is too large to be attributed purely to caloric restriction, so a number of other mechanisms have been proposed. The most popular hypothesis is enhanced production of an incretin, active glucagon-like peptide-1 (GLP-1), in the lower intestine. We therefore set out to test this hypothesis with a model which is simple enough to be robust and credible. METHOD: Our method involves (1) setting up a set of time-dependent equations for the concentrations of the most relevant species, (2) considering an "adiabatic" (or quasi-equilibrium) state in which the concentrations are slowly varying compared to reaction rates (and which in the present case is a postprandial state), and (3) solving for the dependent concentrations (of e.g. insulin and glucose) as an independent concentration (of e.g. GLP-1) is varied. RESULTS: Even in the most favorable scenario, with maximal values for (i) the increase in active GLP-1 concentration and (ii) the effect of GLP-1 on insulin production, enhancement of GLP-1 alone cannot account for the observations. I.e., the largest possible decrease in glucose predicted by the model is smaller than reported decreases, and the model predicts no decrease whatsoever in glucose ×insulin, in contrast to large observed decreases in homeostatic model assessment insulin resistance (HOMA-IR). On the other hand, both effects can be accounted for if the surgery leads to a substantial increase in some substance that opens an alternative insulin-independent pathway for glucose transport into muscle cells, which perhaps uses the same intracellular pool of GLUT-4 that is employed in an established insulin-independent pathway stimulated by muscle contraction during exercise. CONCLUSIONS: Glycemia normalization following Roux-en-Y gastric bypass is undoubtedly caused by a variety of mechanisms, which may include caloric restriction, enhanced GLP-1, and perhaps others proposed in earlier papers on this subject. However, the present results suggest that another possible mechanism should be added to the list of candidates: enhanced production in the lower intestine of a substance which opens an alternative insulin-independent pathway for glucose transport.