A guideline proposal for mice preparation and care in 18F-FDG PET imaging

Timing performance evaluation of a dual-Axis rotational PET system according to NEMA NU 4-2008 standards: A simulation study

Introduction:Positron Emission Tomography (PET) imaging's diagnostic accuracy is dependent on the scanner design and image quality, which is affected by several factors including the coincidence timing window (CTW). NEMA NU 4-2008 procedures are commonly used to assess and compare PET systems performance, including dual rotation technologies like easyPET.3D, known for high-spatial resolution and reduced parallax contribution.Aim:This study aims to identify easyPET.3D's optimal performance based on NEMA standards. In addition, explores the impact of different CTWs on PET image quality by comparing simulated electronics capable of a 300 ps CTW with a 40 ns CTW.Results:When the data is filtered by a 40 ns CTW, a sub-millimetre resolution at the field-of-view (FoV) centre and a constant behaviour in the radial direction are achieved. The absolute sensitivity was 0.18% with a maximum value of 0.31%, for a 15 mm transverse FoV. The noise equivalent count rate peaked at 18 MBq with 249 cps. Recovery coefficients ranged from 17% to 90%, and spilled-over ratios were 0.32 (water) and 0.41 (air).Conclusions:A shorter 300 ps CTW primarily impacted PET dynamic range, allowing higher activity acquisitions, with no significant changes in resolution and sensitivity under NEMA test conditions. As for the image quality test, the 300 ps CTW images have less background, better SOR values, and similar RC values when comparing the 40 ns CTW.

Selective PET imaging of CXCR4 using the Al18F-labeled antagonist LY2510924

BACKGROUND

[68Ga]PentixaFor detects C-X-C chemokine receptor type 4 (CXCR4) overexpression in various malignancies, such as multiple myeloma and non-Hodgkin lymphomas, as well as in endocrine and inflammatory disorders. This study aimed to develop an Al18F-labeled radiotracer derived from LY2510924 for CXCR4-targeted imaging, leveraging the physical and logistical advantages of fluorine-18.

METHODS

We designed a CXCR4-specific radioprobe, [18F]AlF-NOTA-SC, based on LY2510924 by incorporating a triglutamate linker and NOTA chelator to enable Al18F-labeling. The in vitro CXCR4 affinity was assessed using cell-based binding assays. Subsequently, in vivo pharmacokinetics and tumor uptake of [18F]AlF-NOTA-SC were assessed in naïve mice and mice with xenografts derived from U87.CD4/U87.CD4.CXCR4 and MM.1 S cells. Finally, biodistribution was determined in a non-human primate using PET-MR.

RESULTS

Compared to Ga-PentixaFor, AlF-NOTA-SC demonstrated similar in vitro affinity for human CXCR4. [18F]AlF-NOTA-SC was produced with a decay-corrected radiochemical yield of 21.0 ± 7.1% and an apparent molar activity of 16.4 ± 3.6 GBq/µmol. In [18F]AlF-NOTA-SC binding assays on U87.CD4.CXCR4 cells, the total bound fraction was 7.1 ± 0.5% (58% blocking by AMD3100). In naïve mice, the radiotracer did not accumulate in any organs; however, it showed a significant CXCR4-specific uptake in xenografted tumors (SUVmeanU87.CD4 = 0.04 ± 0.00 (n = 3); SUVmeanU87.CD4.CXCR4 = 3.04 ± 0.65 (n = 3); SUVmeanMM.1 S = 1.95 ± 0.11 (n = 3)). In a non-human primate, [18F]AlF-NOTA-SC accumulated in CXCR4 expressing organs, such as the spleen and bone marrow.

CONCLUSION

[18F]AlF-NOTA-SC exhibited CXCR4-specific uptake in vitro and in vivo, with fast and persistent tumor accumulation, making it a strong candidate for clinical translation as an 18F-alternative to [68Ga]PentixaFor.

Illuminating Cardiac Remodeling: Insights From [18F]-Fluorodeoxyglucose Positron Emission Tomography Imaging in Plakoglobin-Associated Arrhythmogenic Cardiomyopathy

BACKGROUND

Arrhythmogenic cardiomyopathy (ACM) is a genetic heart muscle disease, which presents with arrhythmias and sudden cardiac death, along with progressive cardiac remodeling and myocardial inflammation. This study aims to elucidate the patterns of [18F]-fluorodeoxyglucose ([18F]-FDG) uptake in a mouse model of plakoglobin-associated cardiac disease to better understand its diagnostic potential.

METHODS AND RESULTS

Plakoglobin (Jup) knockout mice developed a cardiomyopathy that presented an ACM-like phenotype at 6 weeks of age. Flow cytometry experiments showed a significant increase of immune cells, for example, an expansion of proinflammatory and tissue-injury macrophages. In vivo positron emission tomography and ex vivo autoradiography showed increased [18F]-FDG uptake in genotype positive hearts. A correlative analysis between [18F]-FDG positivity and macrophage infiltration using CD68 and CD206 staining did not show colocalization. CD68 and CD206 positivity was primarily observed within the fibrotic scar, whereas [18F]-FDG uptake was predominantly identified in CD68 and CD206-negative tissue areas. Instead, [18F]-FDG signal seemed to originate from cardiomyocytes adjacent to areas of fibrotic remodeling. Morphometric analysis revealed hypertrophy of these cardiomyocytes, which may reflect metabolic remodeling as a compensatory response.

CONCLUSIONS

In our murine model of Jup-related ACM, strong cardiac [18F]-FDG uptake was detected, which colocalized with regional hypertrophic cardiomyocytes rather than inflammatory cells. These findings indicate that [18F]-FDG positron emission tomography is a valuable tool for identifying and localizing hypermetabolic areas associated with cardiac remodeling in ACM, providing insights into disease mechanisms and potential diagnostic strategies.

Optimisation of Animal Handing and Timing of 2-deoxy-2-[18F]fluoro-D-glucose PET Tumour Imaging in Mice

PURPOSE

In humans, 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) tumour-to-background contrast continues to increase long after a typical uptake period of 45 - 60 min. Similar studies have not been performed in mice and the static imaging time point for most studies is arbitrarily set at 30 - 60 min post-injection of [18F]FDG. Ideally, static PET imaging should be performed after the initial period of rapid uptake but this period has not been defined in mice, with previous dynamic studies in mice being limited to 60 min. This study aimed to define the kinetics of [18F]FDG biodistribution over periods of 3 - 4 h in different murine tumour models, both subcutaneous and autochthonous, and to further refine fasting and warming protocols used prior to imaging.

PROCEDURES

Dynamic [18F]FDG PET-CT scans lasting 3 or 4 h were performed with C57BL/6 J and Balb/c nude mice bearing subcutaneous EL4 murine T-cell lymphoma and Colo205 human colorectal tumours, respectively, and with transgenic Eμ-Myc lymphoma mice. Prior to [18F]FDG injection, four combinations of different animal handling conditions were used: warming for 1 h at 31 °C; maintenance at room temperature (20 - 24 °C), fasting for 6 - 10 h and a fed state.

RESULTS

Tumour mean standardised uptake value (SUVmean) peaked at 147 ± 48 min post injection in subcutaneous tumours and 74 ± 31 min in autochthonous Eμ-Myc lymphomas. The tumour-to-blood ratio (TBR) peaked at 171 ± 57 and 83 ± 33 min in subcutaneous and autochthonous Eμ-Myc tumours, respectively. Fasting increased tumour [18F]FDG uptake and suppressed myocardial uptake in EL4 tumour-bearing mice. There was a good correlation between tumour SUVmean and Ki calculated using an input function (IDIF) derived from the inferior vena cava.

CONCLUSIONS

Delayed static [18F]FDG-PET imaging (> 60 min) in both autochthonous and subcutaneous tumours in improved tumour-to-background contrast and increased reproducibility.

Dissociable Roles of the mPFC-to-VTA Pathway in the Control of Impulsive Action and Risk-Related Decision-Making in Roman High- and Low-Avoidance Rats

BACKGROUND

Impulsive action and risk-related decision-making (RDM) are associated with various psychiatric disorders, including drug abuse. Both behavioral traits have also been linked to reduced frontocortical activity and alterations in dopamine function in the ventral tegmental area (VTA). However, despite direct projections from the medial prefrontal cortex (mPFC) to the VTA, the specific role of the mPFC-to-VTA pathway in controlling impulsive action and RDM remains unexplored.

METHODS

We used positron emission tomography with [18F]-fluorodeoxyglucose to evaluate brain metabolic activity in Roman high- (RHA) and low-avoidance (RLA) rats, which exhibit innate differences in impulsive action and RDM. Notably, we used a viral-based double dissociation chemogenetic strategy to isolate, for the first time to our knowledge, the role of the mPFC-to-VTA pathway in controlling these behaviors. We selectively activated the mPFC-to-VTA pathway in RHA rats and inhibited it in RLA rats, assessing the effects on impulsive action and RDM in the rat gambling task.

RESULTS

Our results showed that RHA rats displayed higher impulsive action, less optimal decision-making, and lower cortical activity than RLA rats at baseline. Chemogenetic activation of the mPFC-to-VTA pathway reduced impulsive action in RHA rats, whereas chemogenetic inhibition had the opposite effect in RLA rats. However, these manipulations did not affect RDM. Thus, by specifically targeting the mPFC-to-VTA pathway in a phenotype-dependent way, we reverted innate patterns of impulsive action but not RDM.

CONCLUSION

Our findings suggest a dissociable role of the mPFC-to-VTA pathway in impulsive action and RDM, highlighting its potential as a target for investigating impulsivity-related disorders.

Characterization of a Syngeneic Orthotopic Model of Cholangiocarcinoma by [18F]FDG-PET/MRI

Cholangiocarcinoma (CCA) is a type of primary liver cancer originating from the biliary tract epithelium, characterized by limited treatment options for advanced cases and low survival rates. This study aimed to establish an orthotopic mouse model for CCA and monitor tumor growth using PET/MR imaging. Murine CCA cells were implanted into the liver lobe of male C57BL/6J mice. The imaging groups included contrast-enhanced (CE) MR, CE-MR with static [18F]FDG-PET, and dynamic [18F]FDG-PET. Tumor volume and FDG uptake were measured weekly over four weeks. Early tumor formation was visible in CE-MR images, with a gradual increase in volume over time. Dynamic FDG-PET revealed an increase in the metabolic glucose rate (MRGlu) over time. Blood analysis showed pathological changes in liver-related parameters. Lung metastases were observed in nearly all animals after four weeks. The study concludes that PET-MR imaging effectively monitors tumor progression in the CCA mouse model, providing insights into CCA development and potential treatment strategies.

Engineering Nanoplatforms for Theranostics of Atherosclerotic Plaques

Atherosclerotic plaque formation is considered the primary pathological mechanism underlying atherosclerotic cardiovascular diseases, leading to severe cardiovascular events such as stroke, acute coronary syndromes, and even sudden cardiac death. Early detection and timely intervention of plaques are challenging due to the lack of typical symptoms in the initial stages. Therefore, precise early detection and intervention play a crucial role in risk stratification of atherosclerotic plaques and achieving favorable post-interventional outcomes. The continuously advancing nanoplatforms have demonstrated numerous advantages including high signal-to-noise ratio, enhanced bioavailability, and specific targeting capabilities for imaging agents and therapeutic drugs, enabling effective visualization and management of atherosclerotic plaques. Motivated by these superior properties, various noninvasive imaging modalities for early recognition of plaques in the preliminary stage of atherosclerosis are comprehensively summarized. Additionally, several therapeutic strategies are proposed to enhance the efficacy of treating atherosclerotic plaques. Finally, existing challenges and promising prospects for accelerating clinical translation of nanoplatform-based molecular imaging and therapy for atherosclerotic plaques are discussed. In conclusion, this review provides an insightful perspective on the diagnosis and therapy of atherosclerotic plaques.