Tomosynthesis and coded aperture imaging: new approaches to three-dimensional imaging in diagnostic radiography

Imaging with X-radiation is one of the most important diagnostic methods in medicine. The present use of shadow projection results in the information on depth in three-dimensional objects being lost. Structures in different depth are superimposed generating a confusing image which is difficult to interpret. These problems are partly solved by the well-known method of tomography. It, however, generates only one layer, whose location in depth cannot exactly be settled beforehand, and is rather time and radiation dose-consuming. These problems are overcome by tomosynthesis which utilizes a conventional tomographic equipment to record a set of radiographs each taken from a different position of the X-ray source. Arbitrary layers of the X-ray object can then be synthesized under visual control by reconstructing the projection geometry with holographic or electronic methods. Since about 3 s are required to record the individual radiographs, this method is still restricted to slowly moving parts of the human body. The recording time can be reduced to a few milliseconds by coded aperture imaging. It employs a small number of simultaneously operated, point-like X-ray sources to record a correspondingly coded X-ray image of the patient. Images of layers in deliberately chosen depth can then be generated by post-processing. The paper will describe the theory and various optic and electronic systems for implementing the algorithms involved. Experimental results will be demonstrated.