The invention implements a digital twin to provide e.g. estimated measurements of one or more physiological or anatomical parameters in a way that requires less local storage space and local processing capacity. Embodiments are based on constructing and implementing a lean digital twin model or dataset by storing results of a number of full digital model simulations in advance and then using these pre-stored simulation results (42) to provide physiological parameter estimations, in place of the full digital twin model (32).