IntroductionAssessment of decision-making capacity (DMC) is essential in daily life as well as for defining a person-centred care plan. Nevertheless, in ageing, especially if signs of dementia appear, it becomes difficult to assess decision-making ability and raises ethical questions. Currently, the assessment of DMC is based on the clinician’s evaluation, completed by neuropsychological tests. Functional MRI (fMRI) could bring added value to the diagnosis of DMC in difficult situations.Methods and analysisIMAGISION is a prospective, monocentric, single-arm study evaluating fMRI compared with clinical assessment of DMC. The study will begin during Fall 2021 and should be completed by Spring 2023. Participants will be recruited from a memory clinic where they will come for an assessment of their cognitive abilities due to decision-making needs to support ageing in place. They will be older people over 70 years of age, living at home, presenting with a diagnosis of mild dementia, and no exclusion criteria of MRI. They will be clinically assessed by a geriatrician on their DMC, based on the neuropsychological tests usually performed. Participants will then perform a behavioural task in fMRI (Balloon Analogue Risk Task) to analyse the activation areas. Additional semistructured interviews will be conducted to explore real life implications. The main analysis will study concordance/discordance between the clinical classification and the activation of fMRI regions of interest. Reclassification as ‘capable’, based on fMRI, of patients for whom clinical diagnosis is ‘questionable’ will be considered as a diagnostic gain.Ethics and disseminationIMAGISION has been authorised by a research ethics board (Comité de Protection des Personnes, Bordeaux, II) in France, in accordance with French legislation on interventional biomedical research, under the reference IDRCB number 2019-A00863-54, since 30 September 2020. Participants will sign an informed consent form. The results of the study will be presented in international peer-reviewed scientific journals, international scientific conferences and public lectures.Trial registration numberNCT03931148