Imaging Cardiovascular and Lung Macrophages With the Positron Emission Tomography Sensor 64Cu-Macrin in Mice, Rabbits, and Pigs.

BACKGROUND: Macrophages, innate immune cells that reside in all organs, defend the host against infection and injury. In the heart and vasculature, inflammatory macrophages also enhance tissue damage and propel cardiovascular diseases. METHODS: We here use in vivo positron emission tomography (PET) imaging, flow cytometry, and confocal microscopy to evaluate quantitative noninvasive assessment of cardiac, arterial, and pulmonary macrophages using the nanotracer 64Cu-Macrin-a 20-nm spherical dextran nanoparticle assembled from nontoxic polyglucose. RESULTS: PET imaging using 64Cu-Macrin faithfully reported accumulation of macrophages in the heart and lung of mice with myocardial infarction, sepsis, or pneumonia. Flow cytometry and confocal microscopy detected the near-infrared fluorescent version of the nanoparticle (VT680Macrin) primarily in tissue macrophages. In 5-day-old mice, 64Cu-Macrin PET imaging quantified physiologically more numerous cardiac macrophages. Upon intravenous administration of 64Cu-Macrin in rabbits and pigs, we detected heightened macrophage numbers in the infarcted myocardium, inflamed lung regions, and atherosclerotic plaques using a clinical PET/magnetic resonance imaging scanner. Toxicity studies in rats and human dosimetry estimates suggest that 64Cu-Macrin is safe for use in humans. CONCLUSIONS: Taken together, these results indicate 64Cu-Macrin could serve as a facile PET nanotracer to survey spatiotemporal macrophage dynamics during various physiological and pathological conditions. 64Cu-Macrin PET imaging could stage inflammatory cardiovascular disease activity, assist disease management, and serve as an imaging biomarker for emerging macrophage-targeted therapeutics.

Development of an anatomically correct mouse phantom for dosimetry measurement in small animal radiotherapy research.

Significant improvements in radiotherapy are likely to come from biological rather than technical optimization, for example increasing tumour radiosensitivity via combination with targeted therapies. Such paradigms must first be evaluated in preclinical models for efficacy, and recent advances in small animal radiotherapy research platforms allow advanced irradiation protocols, similar to those used clinically, to be carried out in orthotopic models. Dose assessment in such systems is complex however, and a lack of established tools and methodologies for traceable and accurate dosimetry is currently limiting the capabilities of such platforms and slowing the clinical uptake of new approaches. Here we report the creation of an anatomically correct phantom, fabricated from materials with tissue-equivalent electron density, into which dosimetry detectors can be incorporated for measurement as part of quality control (QC). The phantom also allows training in preclinical radiotherapy planning and cross-institution validation of dose delivery protocols for small animal radiotherapy platforms without the need to sacrifice animals, with high reproducibility. Mouse CT data was acquired and segmented into soft tissue, bone and lung. The skeleton was fabricated using 3D printing, whilst lung was created using computer numerical control (CNC) milling. Skeleton and lung were then set into a surface-rendered mould and soft tissue material added to create a whole-body phantom. Materials for fabrication were characterized for atomic composition and attenuation for x-ray energies typically found in small animal irradiators. Finally cores were CNC milled to allow intracranial incorporation of bespoke detectors (alanine pellets) for dosimetry measurement.