Abstract: The disclosure is directed to an apparatus and method for imaging radiation pattern from within a body. In accordance with the preferred method of the invention, there is provided a technique for imaging internal structure of a body which includes the following steps: a radiation-emitting substance is introduced into the body. A miniaturized probe is inserted into the body, the probe being coupled to a cable and including at least one radiation detector surrounded by a coded aperture. Signals are received from the detector via the cable for a series of positions of the probe and for different orientations of the coded aperture with respect to the body. The signals from the detector are processed to obtain an image of the radiation pattern within the body. The imaging hereof allows both the position and the strength of a source (e.g. a tumor) to be determined in the presence of background radiation.