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

Purpose: Routine oncological whole-body 18F-1-fluoro-2-deoxyglucose (FDG) PET/CT in the majority of institutions is performed from the base of the skull to the mid-thigh. However, at our institution, the brain is included. The aim of this study was to identify the prevalence of unsuspected intracranial findings in patients undergoing oncological 18F-FDG PET/CT examinations with inclusion of the brain in the field of view.

Methods: A total of 3,523 patients who underwent oncological limited whole-body 18F-FDG PET/CT scans between February 2019 and December 2021 were retrospectively reviewed. The study variables included the patient's age, sex, type of malignancy, disease stage, and clinical presentation and the presence of clinically unsuspected intracranial findings. The intracranial findings were correlated with brain MRI findings in a subset of patients. Clinical significance, defined by a change in disease stage and/or patient management informed by the identification of unsuspected intracranial findings, was assessed.

Results: In total, 132/3,523 (3.7%) oncological whole-body 18F-FDG PET/CT scans had unsuspected intracranial findings, of which clinically significant unsuspected intracranial findings were found in 62 cases (1.4%). The most common intracranial findings were metastasis, followed by subclinical vascular findings. Moreover, 22/62 cases underwent follow-up brain MRI, and the sensitivity and specificity of the 18F-FDG PET/CT scans were 94.7% and 66.7%, respectively. Data on post-PET/CT management were available for 32/132 patients. A change in management was observed in 25/32 (78%) cases.

Conclusion: The inclusion of the brain in the field of view in oncological whole-body 18F-FDG PET/CT may lead to the early detection of unsuspected intracranial metastases and changes in patient management. This is especially true for breast and lung cancers, which have a greater propensity to metastasize to the brain.

In this case report, we describe an unusual case of PET-avid muscle enlargement in the right tensor fascia lata (TFL) muscle mimicking metastatic disease during lung cancer staging. The patient, a 67-year-old woman, had a history of left Achilles tendon rupture, which had been managed non-operatively. A PET/CT scan revealed focal fluorodeoxyglucose (FDG) uptake in a markedly expanded right TFL muscle. The presence of concurrent ipsilateral pelvic lymphadenopathy on the scan initially raised concern for muscle metastasis in this context. However, subsequent MRI of the hip showed diffuse muscle enlargement without a discrete mass, favoring benign muscle hypertrophy, particularly given the presence of a concurrent chronic Achilles tendon rupture that altered the patient's gait. A follow-up surveillance PET/CT and subsequent CT scans obtained over several years showed stability of the muscle abnormality, supporting the diagnosis of benign muscle hypertrophy and preventing an unnecessary biopsy. This case highlights the importance of correlating imaging findings with prior biomechanical injuries that can impact muscle architecture, particularly in a malignancy workup where FDG uptake in muscle may be misleading.

Background: Assessing muscle tissue perfusion in patients with peripheral arterial occlusive disease (PAOD) is challenging, as conventional techniques such as computed tomography angiography and transcutaneous oxygen pressure (TcPO₂) do not capture perfusion within deeper muscle compartments, which are clinically relevant because symptoms such as claudication manifest in the muscles. [¹⁵O]H₂O positron emission tomography computed tomography (PET-CT) enables quantitative measurement of tissue blood flow but has not yet been systematically applied in PAOD. This exploratory study investigated the feasibility and reproducibility of using long axial field of view (LAFOV) [¹⁵O]H₂O PET-CT to quantify calf muscle perfusion in PAOD patients, comparing two VOI selection strategies and generating hypotheses for future studies.

Methods: Patients with Rutherford stage 3-6 PAOD undergoing endovascular revascularization underwent [¹⁵O]H₂O PET-CT imaging before and after treatment. Muscle perfusion (K1 in mL/100 cm³/min) was calculated using a 1-tissue compartment model and image-derived input functions. VOIs were defined using either full muscle contours or standardized spherical volumes. Ten legs from five scanning sessions (each including pre- and post-treatment imaging) were analyzed twice by two observers. Agreement and variability between methods and observers were assessed.

Results: K₁ values ranged from 1.54 to 5.22 mL/100 cm³/min. Both VOI methods enabled reproducible quantification of calf muscle perfusion. Intrarater intraclass correlation coefficients (ICCs) were ≥0.94 for both methods; interrater ICCs were 0.90 for spherical VOIs and 0.96 for muscle contours. Bland-Altman analysis showed no systematic bias. Muscle contours showed slightly higher reproducibility, likely due to anatomical accuracy.

Conclusions: [¹⁵O]H₂O LAFOV PET-CT enables robust quantification of muscle perfusion in PAOD. This method is promising for future studies on treatment response and pathophysiology in vascular disease.

Introduction: In our previous studies, we demonstrated that nimesulide derivatives bearing iodine at the para-position of the phenyl ring exhibit potent inhibitory activity against cyclooxygenase-2 (COX-2). In the present study, we investigated whether radioiodinated derivatives of nimesulide could serve as COX-2 imaging agents for single-photon emission computed tomography (SPECT), with a particular focus on their potential to visualize COX-2 expression in the brain.

Methods: ¹²⁵I-labeled derivatives substituted at the para- or meta-positions were synthesized from the corresponding tributyltin precursors with satisfactory radiochemical yields and purities. Biodistribution studies and ex vivo autoradiography in normal mice revealed that [¹²⁵I]para-I nimesulide exhibited limited brain penetration and did not accurately reflect the distribution of COX-2 in the brain, suggesting it is unsuitable as a brain-targeted imaging agent.

Results: In contrast, biodistribution and blocking experiments in a mouse model of inflammation demonstrated selective accumulation of [¹²⁵I]para-I nimesulide in inflamed regions, which was significantly inhibited by COX-2-selective inhibitors. Moreover, [¹²⁵I]para-I nimesulide exhibited high radiochemical purity and persistent in vivo stability, but strong plasma albumin binding likely restricted its brain uptake.

Discussion: These findings indicate that while [¹²⁵I]para-I nimesulide has limited potential for brain-targeted COX-2 imaging, it may serve as a promising tracer for detecting COX-2 expression in peripheral tissues. Importantly, this study also highlighted that the electronic properties of substituents strongly influence metabolic stability, providing valuable insights for the design of future COX-2-targeted molecular imaging agents.

[This corrects the article DOI: 10.3389/fnume.2025.1702390.].

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.