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

Introduction: Accurate PET reconstruction in spinal cord PET/MRI is challenging due to the small size of the structure and interference from background activity. The aim of this study was to establish whether MR-guided PET reconstruction can improve the accuracy of measured uptake in the spinal cord.

Methods: The hybrid kernel expectation maximisation (HKEM) algorithm was evaluated on a digital anthropomorphic phantom (XNAT), and an implementation of a modified asymmetric Bowsher's prior incorporating both PET and MR data was evaluated on clinical test cases. The methods were compared against commonly used algorithms OSEM and Q.Clear.

Results: The results demonstrated that the two algorithms lead to an increase in measured [₁₈ F]FDG PET tracer uptake in the spinal cord. Comparison to ground truth indicates that the improvement is insufficient to remove the bias in this small structure.

Discussion: With care taken to optimise for the desired application, novel PET image reconstruction algorithms using PET and MR data to inform iterative image updates lead to improved quantification and improved image quality compared to OSEM. Further work is needed to investigate the optimal parameters and identify strategies to reduce residual bias.

Background: Neuroinflammation plays an important role in progression of Parkinson disease (PD). [¹⁸F]SMBT-1 is a promising novel radiotracer for in vivo evaluation of reactive astrogliosis.

Methods: The automated radiosynthesis of [¹⁸F]SMBT-1 was optimized and performed production by using the Synthra RNplus synthesizer module, and the quality of the labeled tracer was evaluated. Total 5 participants, 2 PD and 3 Healthy Control were enrolled. Cognitive assessments were performed in all participants while H&Y scales and MDS-UPDRS were performed only in PD. All participants underwent [¹⁸F]SMBT-1 PET/MRI and [¹⁸F]FDOPA PET/CT within 2-week intervals. Demographic and imaging data were collected. The correlation between [¹⁸F]FDOPA uptake and [¹⁸F]SMBT-1 uptake was analyzed by Spearman's correlation.

Results: [¹⁸F]SMBT-1 was successfully synthesized via nucleophilic substitution of a tosylate precursor, followed by a deprotection step. After purification and formulation, [¹⁸F]SMBT-1 was obtained with an average decay-corrected radiochemical yield of 36.56 ± 11.55% and molar activity as 396 Gbq/μmol at the end of synthesis (n = 7). Moderate PD defined by the [¹⁸F]FDOPA showed increased [¹⁸F]SMBT-1 in prefrontal cortex, temporal lobes, striatum, thalamus, pons, medullar, and midbrain while severe PD showed globally increased [¹⁸F]SMBT-1. Healthy control also showed globally increased [¹⁸F]SMBT-1 uptake. There was no significant correlation between the degree of [¹⁸F]FDOPA uptake and [¹⁸F]SMBT-1 uptake in any brain region.

Conclusion: The automated radiosynthesis of [¹⁸F]SMBT-1 are suitable for routine production without any immediate complication reported after administration. Moderate PD shows decreased astrocyte function as they lose neuroprotective astrocytes while severe PD shows increased astrocyte function as increased neurotoxic astrocytes.

Fibroblast activation protein (FAP) is a type II transmembrane serine protease predominantly expressed by cancer-associated fibroblasts (CAFs) in more than 90% of epithelial malignancies. The advent of FAP inhibitor (FAPI)-based positron emission tomography (PET) imaging has established FAP as a promising pan-tumor target for radioligand therapy (RLT). This review summarizes the current clinical landscape of FAP-targeted RLT in solid tumors, while also discussing existing challenges and future directions in this rapidly evolving field.

Introduction: The positron emission tomography (PET) problem with Poisson log-likelihood is notoriously ill-conditioned. This stems from its dependence on the inverse of the measured counts and the square of the attenuation factors, causing the diagonal of the Hessian to span over 5 orders of magnitude. Optimization is, therefore, slow, motivating decades of research into acceleration techniques. In this paper, we propose a novel preconditioner tailored for maximum a posteriori (MAP) PET reconstruction priors that is designed to achieve approximately uniform spatial resolution.

Methods: Our approach decomposes the Hessian into two components: one diagonal and one circulant. The diagonal term is the Hessian expectation computed in an initial solution estimate. As the circulant term, we use an apodized 2D ramp filter. We evaluated our method on the PET Rapid Image reconstruction Challenge dataset that includes a wide range of phantoms, scanner models, and count levels. We also varied the regularization strengths. Our preconditioner was implemented in a conjugate gradient descent algorithm without subsets or stochastic acceleration.

Results: We show that the proposed preconditioner consistently achieves convergence in fewer than 10 full iterations-each consisting of just one forward and one backward projection. We also show that the circulant component, despite its crude 2D approximation, provides very meaningful acceleration beyond the diagonal-only case.

Discussion: These results demonstrate that decomposing the Hessian into diagonal and circulant components is an effective strategy for accelerating MAP PET reconstruction. The proposed preconditioner significantly improves convergence speed in challenging, ill-conditioned Poisson PET inverse problems.

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.