Abstract: A medical apparatus includes a scanner for generating raw image data of internal tissue structures of a patient, and a computer operatively connected to the scanner and programmed to derive a three-dimensional electronic map or model of the internal tissue structures from the raw data. An image reproduction device is operatively connected to the computer for reproducing the map or model in a visually readable format. The computer controls the image reproduction device to reproduce the map or model. The visually readable format includes graphical representations of the tissue structures alignable on a skin surface of the patient with the tissue structures. In use, a medical practitioner inserts a sharp instrument into a patient through the reproduced map, using the map as a locator assist.