Tomographic image reconstruction from limited projections using coherent feedback

Coherent optical feedback is used to obtain improved tomographic images from projections when the number of projections is small or the angular range of projections is limited. The technique consists of performing repeated Fourier transformations between image and transform spaces by using coherent optical feedback and applying a priori information in the feedback loop. A similar but computer-based technique of iteratively forcing the image to conform to a priori object data, such as the known boundaries of the object, has been described in a previous paper. The optical analog of this approach is described here and effectively carries out an infinite number of these iterations in an instantaneous fashion. Experimental results clearly show the improvements obtained with the optical method.