The current study aims to develop a simplified SPECT neuroimaging approach for simultaneous dual-isotope imaging of the central nervous system's dopaminergic D2/D3 and serotoninergic 5-HT2A receptors. A full quantitative method using a multi-injection procedure will be used to evaluate simplified approaches based on a reference region and a Scatchard analysis. Simplifying current SPECT imaging methods will significantly limit and reduce technique drawbacks, such as its invasive nature (i.e. multiple radioisotope injections, blood samplings) and its long scan durations, commonly attributed to current nuclear imaging techniques used to visualise a single target per scan. Furthermore, simplified methods will improve the ability and efficacy with which SPECT neuroimaging visualizes complex pathologies' interconnected effects and properties, through simultaneous dual-isotope imaging. Simultaneous representation of numerous targets, known to being implicated in complex physiopathological mechanisms, is key to the better understanding and management of today's numerous complex neuropsychiatric disorders.