Frontiers in nuclear medicine (Lausanne, Switzerland)最新文献

Background: Comparative patient dosimetry for diagnostic PET/CT can guide radiation-safety procedures and tracer selection in prostate cancer. We compared [^68Ga]Ga-PSMA-11 and ^18F-choline PET/CT and examined whether kidney SUVmax predicts patient effective dose (ED).

Methods: Prospective single-center study of consecutive men undergoing clinically indicated PET/CT: 70 ^68Ga-PSMA-11 and 70 ^18F-choline examinations (Jan 2022-Dec 2023). Dose-rate measurements were recorded at the injection site and at 1 m, immediately post-injection and at 1 h. ED was derived from literature-based tracer coefficients (h_PSMA-11 = 0.0169 mSv/MBq; h_F-choline = 0.0173 mSv/MBq). Kidney SUVmax was extracted in a subset (n = 40 per tracer) to test ED-SUVmax associations (Pearson's r).

Results: Mean surface dose rate was higher with ^68Ga-PSMA vs. ^18F-choline (4.9 ± 0.8 vs. 4.5 ± 0.7 µSv·h^{- 1}; p = 0.004). At 1 m, the difference persisted but was smaller (1.9 ± 0.3 vs. 1.7 ± 0.3 µSv·h^{- 1}; p = 0.02). Effective dose (ED) was similar between tracers (21.3 ± 3.6 vs. 20.7 ± 3.4 mSv; p = 0.28). SUVmax correlated with ED for ^68Ga-PSMA (r = 0.71; p < 0.001), but not for ^18F-choline (r = -0.12; p = 0.46).

Conclusions: ^68Ga-PSMA yields slightly higher dose-rate readings than ^18F-choline, while overall ED is comparable. These exploratory correlations do not support SUVmax as a stand-alone safety surrogate or outcome predictor.

Purpose: The physical properties of ⁴⁴Sc, combined with its imminent clinical application, position it as a prime candidate for in vivo positronium lifetime imaging. In this study, we investigate the count statistics for ortho-positronium (oPs) measurements with ⁴⁴Sc on a commercial long-axial field-of-view (LAFOV) PET/CT.

Method: A NEMA image quality phantom was filled with 41.7 MBq of ⁴⁴Sc dissolved in water and scanned on a LAFOV PET/CT. Three-photon events were identified using a prototype feature of the scanner and dedicated software. The lifetime of oPs was determined in the phantom spheres and in $4\times 4\times 4$ mm³ voxels.

Results: All measured oPs lifetimes are compatible, within the uncertainties, with the literature values for water. The oPs lifetime is $2.65\pm 0.50$ , $1.39\pm 0.20$ and $1.76\pm 0.18$ ns in the three smallest spheres of the phantom and $1.79\pm 0.57$ ns for a single voxel in the central region of the largest sphere. The relative standard deviation in the background regions of the time difference distributions, i.e., for time differences smaller than $-2.7$ ns, is above 20%-even for voxels inside the phantom spheres.

Conclusions: Despite the favorable physical properties of ⁴⁴Sc, the count statistics of three-photon events remains a challenge. The high prompt-photon energy causes a significant amount of random three-photon coincidences with the given methodology and, therefore, increases the statistical uncertainties on the measured oPs lifetime.

Introduction: Brown tumours (BTs), also known as osteitis fibrosa cystica, are benign osteolytic lesions associated with hyperparathyroidism (HPT). BTs are cured by correcting the hypercalcaemia and HPT, which often requires surgical resection of the parathyroid adenoma. ¹⁸F-fluorocholine (FCH) PET/CT is becoming an effective tool for detecting parathyroid adenomas in cases of hyperparathyroidism. This study aims to evaluate the role of FCH PET/CT in detecting brown tumours in patients with hyperparathyroidism.

Clinical cases: Three cases are presented to demonstrate the effectiveness of FCH PET/CT in detecting BTs in patients presenting with clinical and biochemical signs of HPT with suspicion of BTs.

Literature review: A literature review aimed to summarize the bibliographic evidence on the use of this technique in this setting, which is relatively innovative.

Conclusion: FCH PET/CT appears to be a useful tool for detecting BTs, and further prospective studies are needed to confirm this.

Parathyroid disorders profoundly affect bone metabolism, often long before structural damage is apparent on conventional imaging. Positron emission tomography/computed tomography (PET/CT) has emerged as a transformative tool in dysparathyroidism, enabling visualization of early metabolic bone changes and accurate localization of parathyroid pathology. This review explores the pathophysiology of bone disease in hyper- and hypoparathyroidism and highlights the role of key PET radiotracers: fluorine-18 sodium fluoride ([18F]NaF), fluorine-18 fluorodeoxyglucose ([18F]FDG), fluorine-18 fluorocholine ([18F]FCH), gallium-68 prostate-specific membrane antigen ([68Ga]PSMA). Distinct imaging patterns, such as the [18F]NaF "superscan" in secondary hyperparathyroidism and focal uptake in brown tumors, are discussed alongside tracer-specific strengths. Clinical applications including diagnosis, monitoring response to therapy, and prognostication are examined. We also consider emerging technologies such as artificial intelligence (AI)-assisted interpretation and positron emission tomography/magnetic resonance imaging (PET/MRI) fusion imaging. As PET/CT becomes more accessible, it is likely to play an increasingly central role in the early detection and personalized management of parathyroid-related bone disease.

The ⁶⁴Cu/⁶⁷Cu pair is an ideal set of theranostic radionuclides for treating patients based on their genetic profiles. We propose a novel production route for this radionuclide pair using accelerator-generated neutrons. We report experimental measurements of the absolute activity and radionuclide purity of ⁶⁴Cu and ⁶⁷Cu, produced by irradiating ⁶⁴Zn and ⁶⁸Zn with these neutrons. The measured results were consistent with simulated values. ⁶⁴Cu and ⁶⁷Cu were separated from the irradiated natural Zn and ⁶⁸Zn using sublimation and column separation techniques. The production methods for ⁶⁴Cu and ⁶⁷Cu developed in this study are expected to enhance their availability in an economically sustainable manner.

Population pharmacokinetic (PopPK) has emerged as a robust framework for characterizing inter-individual variability in the absorbed dose estimates in radiopharmaceutical therapy (RPT). By enabling the analysis of biokinetic data from heterogeneous patient populations, PopPK allows individualized absorbed dose estimates while simultaneously leveraging population-level information. This review presents and evaluates the current applications of PopPK, such as nonlinear mixed-effects modeling (NLMEM) and Bayesian fitting methods in RPT, emphasizing its advantages over traditional individual-based modeling approaches. We summarize key studies that have implemented PopPK for modeling radiopharmaceutical biokinetics, with a focus on time-integrated activity (TIA) estimation, including single-time-point (STP) dosimetry, uncertainty analysis, as well as pharmacodynamic (PD) analysis. The flexibility of PopPK in handling sparse and irregularly sampled data makes it particularly relevant for clinical scenarios where comprehensive imaging schedules are impractical. However, despite its potential, the widespread adoption of PopPK in RPT remains limited due to challenges such as computational complexity and the need for specialized expertise. This review discusses critical aspects of PopPK implementation while emphasizing the importance of interdisciplinary collaboration in translating PopPK methodologies into clinical practice. Future directions include integrating PopPK into adaptive dosimetry frameworks and applying it in STP dosimetry and PD modeling to optimize treatment personalization. By providing a comprehensive overview of PopPK applications in RPT, this review aims to facilitate the integration of advanced modeling techniques into routine clinical workflows, ultimately supporting the development of accurate and precise RPTs.

We investigated subset-based optimization methods for positron emission tomography (PET) image reconstruction incorporating a regularizing prior. PET reconstruction methods that use a prior, such as the relative difference prior (RDP), are of particular relevance because they are widely used in clinical practice and have been shown to outperform conventional early-stopped and post-smoothed ordered subset expectation maximization. Our study evaluated these methods using both simulated data and real brain PET scans from the 2024 PET Rapid Image Reconstruction Challenge (PETRIC), where the main objective was to achieve RDP-regularized reconstructions as fast as possible, making it an ideal benchmark. Our key finding is that incorporating the effect of the prior into the preconditioner is crucial for ensuring fast and stable convergence. In extensive simulation experiments, we compared several stochastic algorithms-including stochastic gradient descent (SGD), stochastic averaged gradient amelioré (SAGA), and stochastic variance reduced gradient (SVRG)-under various algorithmic design choices and evaluated their performance for varying count levels and regularization strengths. The results showed that SVRG and SAGA outperformed SGD, with SVRG demonstrating a slight overall advantage. The insights gained from these simulations directly contributed to the design of our submitted algorithms, which formed the basis of the winning contribution to the PETRIC 2024 challenge.

Platinum group metals (PGMs) consist of six transition metals: platinum (Pt), palladium (Pd), rhodium (Rh), osmium (Os), iridium (Ir), and ruthenium (Ru). PGMs have been used notably in industrial, electronic, and medical applications. For example, Ir-192 is often utilized in industry to detect structural defects in metal and assess pipeline integrity. Pd-104 is irradiated to produce Pd-103 seeds, used for prostate cancer treatment. Other isotopes of elements in this group can be sourced to facilitate critical applications, discussed in this review. Due to their unique chemical and nuclear properties, these metals may be promising candidates for various nuclear medicine applications, including diagnostic imaging via Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT) and Targeted Radionuclide Therapy (TRT). This review will explore PGMs in nuclear medicine, focusing on their production routes, nuclear characteristics, and suitability for past and future development of radiopharmaceuticals. We will highlight methods for radiochemical separation and purification of each radionuclide, discussing potential challenges and emphasizing the need for further research to ensure sustainability. As the demand for advanced nuclear medicine techniques continues to grow, PGMs may play a significant role in addressing current challenges in the field. We will discuss several radionuclides of interest to nuclear medicine including ¹⁹¹Pt, ^193mPt, ^195mPt, ¹⁰³Pd, ¹⁰⁹Pd, ^103mRh, ¹⁰⁵Rh, ¹⁹¹Os, ¹⁹²Ir, ⁹⁷Ru, and ¹⁰³Ru.

Background: In this study, we investigate the impact of MR-derived attenuation maps and limited detector resolution on the quantification of positron emission tomography (PET) activity uptake in the spinal cord during PET/MRI. This was performed by simulating [ ${}^{18}$ F]FDG PET data in the neck and thorax and then modifying the attenuation map to remove bone features. We then compared Ordered Subset Expectation Maximisation-reconstructed images to those with full attenuation correction. This simulation was performed at two detector resolutions of 2.1 and 4.4 mm. Acquisitions from a clinical study were then used to assess the ability of point spread function (PSF) modelling and time-of-flight (TOF) corrections, as implemented on the SIGNA PET/MR scanner (GE HealthCare), to correct for these quantification errors. For comparison, mean uptake was measured in regions of interest at each vertebral position along the spinal cord.

Results: Simulation results showed a decreasing pattern of uptake from the cervical to the thoracic spinal cord. When bone was not included in attenuation correction, the mean uptake decreased by 3%-10.4%. This difference in measured uptake was 6.4%-23.9% in images simulated at a detector resolution representative of a clinical PET/MRI scanner. At a detector resolution of 4.4 mm, a 32.2% decrease in uptake was measured compared to the 2.1 mm simulation. In patient data, introducing vertebral bone to the attenuation correction pseudo-CT led to a 1.8%-18.3% difference in ${\mathrm{SUV}}_{\mathrm{mean}}$ in the spinal cord. Applying PSF modelling did not lead to any statistically significant changes. TOF correction reduces the difference in ${\mathrm{SUV}}_{\mathrm{mean}}$ between data attenuation corrected with and without vertebral bone to 4.3%-7%. TOF Q.Clear images with beta = 100 showed the smallest difference between attenuation correction approaches at 0.6%-5.2%.

Conclusion: Ignoring bone during image reconstruction in PET/MRI reduces the activity measured during quantification of the spinal cord; however, the partial volume effect has a greater impact on reducing measured uptake in lower-resolution data. While time-of-flight correction goes somewhat resolves these quantification errors, further research is needed into partial volume correction.