Advances in Preclinical PET

Therapeutic evaluation of [212Pb]Pb-AB001 and [177Lu]Lu-PSMA-617 in a mouse model of disseminated prostate cancer

BACKGROUND

Metastatic castration-resistant prostate cancer (mCRPC) frequently leads to bone and soft tissue metastases, leading to poor prognosis. The beta-emitting radioligand [177Lu]Lu-PSMA-617 targets the prostate-specific membrane antigen (PSMA) and may be less efficient against micrometastatic disease. The alpha-emitting radioligand [212Pb]Pb-AB001 could offer enhanced treatment by delivering high energy over a short range. This study compared the efficacy of [212Pb]Pb-AB001 and [177Lu]Lu-PSMA-617 in a mouse model of disseminated prostate cancer.

METHODS

Binding and internalisation of radioligands were evaluated in PC-3 PIP-luc cells. A mouse model was established by intracardiac injection of these cells. Treatments with 0.24‒1.0 MBq [212Pb]Pb-AB001 or 22‒66 MBq [177Lu]Lu-PSMA-617 were initiated 7 d post-cell inoculation. Metastatic burden was measured using bioluminescence imaging, and PSMA-targeted uptake was determined with [18F]F-PSMA-1007 µPET/µCT. Gamma-autoradiography evaluated [212Pb]Pb-AB001 distribution, and bone metastases were identified by radiography.

RESULTS

Both radioligands displayed comparable in vitro binding. In vivo studies revealed metastatic formation in clinically relevant organs. µPET/µCT demonstrated increased [18F]F-PSMA-1007 uptake in metastases, matching the bioluminescence imaging results. Focal [212Pb]Pb-AB001 distribution in the metastatic xenograft indicated heterogeneously distributed micrometastases in the organs. A median survival up to 47 d was achieved with [212Pb]Pb-AB001, compared to 25 d for controls and 27 d for [177Lu]Lu-PSMA-617. An activity-dependent reduction in bone metastases was observed for [177Lu]Lu-PSMA-617, while no bone lesions were detected in [212Pb]Pb-AB001-treated mice.

CONCLUSION

[212Pb]Pb-AB001 showed significant efficacy against micrometastases and advantages over [177Lu]Lu-PSMA-617 in preventing or treating early bone metastases for the investigated injected activities. This implies clinical potential for treating mCRPC, including patients at risk of early metastatic disease, but further studies including dosimetry and toxicity analyses are required with regards to activity levels.

A pre-clinical PET scanner based on a monolithic annulus of scintillator (AnnPET): construction and NU4-2008 performance testing

Objective.In the past several decades, numerous positron emission tomography (PET) scanners of various designs have been constructed for use in pre-clinical studies. Our group is investigating use of a monolithic annulus of scintillator, instead of the traditional arrays of discrete scintillator elements or individual detectors that utilize continuous blocks of scintillator, to construct a novel pre-clinical PET scanner.Approach.This scanner, called AnnPET, is based on a fourteen-faceted annulus of lutetium yttrium orthosilicate with an inner diameter of 6 cm and length of 7.2 cm. Each facet is populated with four specially constructed 4 × 4 arrays of 4 mm × 4 mm multi-pixel photon counters .To cool and temperature stabilize these devices, the scanner gantry is immersed in dielectric fluid. Positioning of events in the scintillator is accomplished with the application of deep-residual convolutional neural network. The scanner's performance was assessed using the NEMA NU4-2008 protocols.Results.Full-width-at-half-maximum (FWHM) of the images of a point source reconstructed with the single slice rebinned filtered backprojection (SSRB-FBP) algorithm at 5 mm from the center of the scanner are: 1.40 mm (radial), 1.38 mm (tangential) and 1.40 mm (axial). At 18 mm from scanner center (edge of the scanner's inner bore) the FWHMs are: 1.62 mm (radial), 1.43 mm (tangential) and 1.48 mm (axial) FWHM. Peak detection sensitivity is 9.5% (0.086 cps Bq-1). Peak noise equivalent count rate is 234 kcps at 14.4 MBq.Significance.Overall, testing of the AnnPET system demonstrated very promising performance results for a pre-clinical PET scanner based on a single, cooled annulus of monolithic scintillator used with neural networks. Continued development of the system is planned.

The effects of music and darkness on radionuclide distribution during mice FDG-PET scan

Background

There is growing interest in the therapeutic potential of music or light in different human disorders.

Aims

This study aimed to evaluate the effects of music as well as darkness on FDG uptake in 4T1 tumor-bearing BALB/c mice using a PET scan.

Methods

The music, darkness, and music plus darkness groups were subjected to either song or darkness and their combination, respectively, 30 min before the radiopharmaceutical injection until the end of the experiments. The control group was imaged in silence under ambient conditions.

Results

Our results revealed that music did not significantly alter the range of tumor SUVmean, but showed a slight increase in brain SUVmean (18.2%) and about 100% increase in brain percentage of injected dose per gram (%ID/g) in ex vivo analysis. In contrast, heart SUVmean and heart %ID/g were approximately half those of the silence group. The muscle SUVmean and blood activity measurements showed a decrement upon music exposure. Also, results showed a significant difference in tumor-to-muscle ratio (85% increment) and brain-to-muscle ratio (105% increment) between the silence and music groups. The muscle SUVmean decreased by 50%, and tumor-to-muscle and brain-to-muscle ratios were observed to increase by 44% and 60% in the group exposed to darkness, respectively.

Conclusion

Our results suggest that music and environmental factors may influence FDG uptake in small-animal PET imaging, and provide important insights into the reliability of FDG-PET imaging for music intervention research and may aid researchers in investigating the effects of music on brain changes and tissue metabolism.

Preclinical magnetic resonance imaging and spectroscopy in the fields of radiological technology, medical physics, and radiology

Magnetic resonance imaging (MRI) is an indispensable diagnostic imaging technique used in the clinical setting. MRI is advantageous over X-ray and computed tomography (CT), because the contrast provided depends on differences in the density of various organ tissues. In addition to MRI systems in hospitals, more than 100 systems are used for research purposes in Japan in various fields, including basic scientific research, molecular and clinical investigations, and life science research, such as drug discovery, veterinary medicine, and food testing. For many years, additional preclinical imaging studies have been conducted in basic research in the fields of radiation technology, medical physics, and radiology. The preclinical MRI research includes studies using small-bore and whole-body MRI systems. In this review, we focus on the animal study using small-bore MRI systems as "preclinical MRI". The preclinical MRI can be used to elucidate the pathophysiology of diseases and for translational research. This review will provide an overview of previous preclinical MRI studies such as brain, heart, and liver disease assessments. Also, we provide an overview of the utility of preclinical MRI studies in radiological physics and technology.

A look at radiation detectors and their applications in medical imaging

The effectiveness and precision of disease diagnosis and treatment have increased, thanks to developments in clinical imaging over the past few decades. Science is developing and progressing steadily in imaging modalities, and effective outcomes are starting to show up as a result of the shorter scanning periods needed as well as the higher-resolution images generated. The choice of one clinical device over another is influenced by technical disparities among the equipment, such as detection medium, shorter scan time, patient comfort, cost-effectiveness, accessibility, greater sensitivity and specificity, and spatial resolution. Lately, computational algorithms, artificial intelligence (AI), in particular, have been incorporated with diagnostic and treatment techniques, including imaging systems. AI is a discipline comprised of multiple computational and mathematical models. Its applications aided in manipulating sophisticated data in imaging processes and increased imaging tests' accuracy and precision during diagnosis. Computed tomography (CT), positron emission tomography (PET), and Single Photon Emission Computed Tomography (SPECT) along with their corresponding radiation detectors have been reviewed in this study. This review will provide an in-depth explanation of the above-mentioned imaging modalities as well as the radiation detectors that are their essential components. From the early development of these medical instruments till now, various modifications and improvements have been done and more is yet to be established for better performance which calls for a necessity to capture the available information and record the gaps to be filled for better future advances.

Innovations in Small-Animal PET Instrumentation

Biomedical research has long relied on small-animal studies to elucidate disease process and develop new medical treatments. The introduction of in vivo functional imaging technology, such as PET, has allowed investigators to peer inside their subjects and follow disease progression longitudinally as well as improve understanding of normal biological processes. Recent developments in CRISPR, immuno-PET, and high-resolution in vivo imaging have only increased the importance of small-animal, or preclinical, PET imaging. Other drivers of preclinical PET innovation include new combinations of imaging technologies, such as PET/MR imaging, which require changes to PET hardware.

Preclinical Imaging Studies: Protocols, Preparation, Anesthesia, and Animal Care

Today preclinical PET imaging connects laboratory research with clinical applications. Here PET clearly bridges the gap, as nearly identical imaging protocols can be applied to both animal and humans. However, some hurdles exist and researchers must be careful, partly because the animals are usually anesthetized during the scans, while human volunteers are awake. This review is based on our own experiences of some of the most important pitfalls and how to overcome them. This includes how studies should be designed, how to select the right anesthesia and monitoring. The choice of anesthesia is quite crucial, as it may have a greater influence on the results than the effect of the tested procedures. Monitoring is necessary, as the animals cannot fully maintain homeostasis during anesthesia, and reliable results are dependent on a stable physiology. Additionally, it is important to note that rodents, in particular, are prone to rapidly becoming hypothermic. Thus, the selection of an appropriate anesthetic and monitoring protocol is crucial for both obtaining accurate results and ensuring animal welfare. Prior to imaging, catheters for tracer administration and, if necessary, blood sampling should be implanted. The administration of tracers should be done in a manner that minimizes interference with the scans, and the same applies to any serial blood sampling. The limited blood volume and organ size of rodents should also be taken into consideration when planning experiments. Finally, if the animal needs to be awakened after the scan, proper care must be taken to ensure their welfare.