Sub-0.5-mm Resolution PET Versus Autoradiography: Comparison of mGluR1 Concentrations in Mouse Brain

For mouse brain PET imaging with high quantification accuracy, ultrahigh resolution is essential. Metabotropic glutamate receptors are important molecular targets, linked to various neurologic diseases. Here, we report the comparison of in vivo mouse brain images obtained with sub-0.5-mm resolution PET and those obtained with autoradiography using 4-¹⁸F-fluoro-N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-N-methylbenzamide (¹⁸F-FITM) that binds to metabotropic glutamate receptor subtype 1. Methods: We recently developed a sub-0.5-mm resolution PET scanner having an axial coverage of 23.4 mm and an inner diameter of 48 mm. The PET scanner comprises 32 depth-of-interaction detectors, each of which has staggered 3-layer lutetium-yttrium-orthosilicate crystal arrays with a pitch of 0.8 mm. A resolution phantom was used to evaluate the imaging performance of the PET scanner. Dynamic PET imaging was performed to evaluate the concentration changes of ¹⁸F-FITM at various mouse brain regions. In vivo metabotropic glutamate receptor imaging of a mouse brain was performed using ¹⁸F-FITM and the PET scanner. Subsequently, autoradiography images of the same mouse brain were obtained using ¹⁸F-FITM. Results: The 0.45-mm rod structure was resolved with the PET scanner. Time-activity curves of various mouse brain regions were obtained. The sub-0.5-mm resolution PET visualized ¹⁸F-FITM uptake in the mouse brain with high correlation to the autoradiography images. Conclusion: The sub-0.5-mm resolution PET opens up new opportunities for translational neuroscience research using mice models.