An MR-based brain template and atlas for optical projection tomography and light sheet fluorescence microscopy

Optical projection tomography (OPT) and light sheet fluorescence microscopy (LSFM) are high resolution optical imaging techniques operating in the mm-cm range, ideally suited for ex vivo 3D whole mouse brain imaging. Although these techniques exhibit high sensitivity and specificity for antibody labeled targets, the provided anatomical information remains limited. To allow anatomical mapping of fluorescent signal in whole brain, we developed a novel magnetic resonance (MR) based template with its associated tissue priors and atlas labels, specifically designed for brains subjected to tissue processing protocols required for 3D optical imaging. We investigated the effect of tissue preprocessing and clearing on brain size and morphology and developed optimized templates for BABB/Murrays clear (OCUM) and DBE/iDISCO (iOCUM) cleared brains. By creating optical (i)OCUM fusion images using our mapping procedure, we localized dopamine transporter and translocator protein expression and tracer innervation from the eye to the lateral geniculate nucleus of thalamus and superior colliculus. These fusion images allowed for precise anatomical identification of fluorescent signal in discrete brain areas. As such, these templates enable applications in a broad range of research areas integrating optical 3D brain imaging by providing an MR template for cleared brains. ### Competing Interest Statement The authors have declared no competing interest.