<title>Digital Coded Images</title>

Abstract

The recent progress on digital radiographic imaging systems with high speed acquisition will allow, in a near future, studies of moving organs such as the beating heart. Even obtained at a high rate, these images remain conventional radiographic images giving inte-grated informations of the organ. We consider a technique using coded sources wl,r,1:e the resulting radiographic coded image would contain all informations necessary for the 3-D dynamic reconstruction of the object. In the recording step the organ is imaged by a planar-array of X-rays sources arranged according to an appropriate code. Sources are flashed simultaneously during a fraction of second. The coded picture results from the superposition of the elementary radiographs that would be obtained with X-rays sources separately flashed. An adapted decoding process of this image allows the spatial reconstruction of the 3-D radiographied organ. In fact, during the reconstruction process artifacts generally occur. These artifacts are due to side-peaks in the cross-correlation between coding and decoding functions. We present here a method allowing perfect decoding of the image within an arbitrarily large region. Founded onthis method a computer simulation is used to decode a 3-D object made of two separated plans. This method is interesting because it may be used for any code of sources even if side peaks occur in the correlation. It can also be used for non perfect decoding of objects more complex than two separated plans. In this case the improvement of the decoded image depends mainly on the cross-correlation properties of the code. In conclusion it is stated that it would be interesting to look for an optimal code producing both good spatial resolution of the object and proper characteristics for the decoding procedure.