1. An interactive touchscreen system comprising a conductive panel having a surface portion adapted to receive touch interactions, and a tomograph operatively connected to said conductive panel, said tomograph configured for determining conductivity of said conductive panel by generating and tomographically processing energy signals received from said conductive panel, said tomograph being further configured for updating a reconstruction image obtained from the output of a tomographic reconstruction algorithm having as an input change data having elements derived from current projection data and reference projection data each obtained from said energy signals as being subject to change due to touch at said surface portion, said reconstruction image being representative of said panel conductivity properties at locations spatially correlated to a plurality of regions notionally defined over said surface portion and therefrom indicative of said touch interactions, and said tomograph further configured for processing and outputting at each iteration of an interactive loop said reconstruction image and an indication thereof, wherein the count of elements selected as the input to said tomographic reconstruction algorithm depends on a condition evaluated during said interactive loop and which ones of said elements are selected depends on said condition evaluated during said interactive loop.