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A new nonlinear reconstruction method for tomosynthesis is described. This method is suited for "dilute" objects, i.e., objects in which most of the voxels have negligibly small absorption. Images of blood vessels filled with contrast material approximate this condition if the background is subtracted. The technique has been tested experimentally using a wire phantom and a prepared human heart. The results show significantly less artifacts than the well-known back projection. It is possible to get diagnostic image quality with a few projections. The reconstruction algorithm can be realized with dedicated real-time hardware.

In X-ray image intensifier (II)/TV-camera systems geometric distortions occur, e.g. due to the curved input screen of the II. For methods which are based on a pixelwise comparison of images, e.g. digital angio-tomosynthesis, an accurate correction of these geometric distortions is absolutely necessary. For the application of tomosynthesis to coronary angiography the correction in addition has to be done in real-time, because the reconstruction of the three dimensional structure of the blood vessels has to be done while the patient is undergoing catheterization. This paper describes a digital correction unit which allows a large variety of geometric distortions to be corrected. It consists of an input memory for storing the distorted image, an output memory for storing the corrected image and a special address memory which will serve as an address table during the correction step. For each element of the output image the location of the corresponding element of the distorted input image is determined in a preprocessing step and stored in the address memory. The actual correction of an image is then done while the image is copied from the input into the output memory. In this way 512 x 512 images can be corrected in real-time by a 32-bit 680X0-based microprocessor system. Presented as Poster at the 3rd International Symposium CAR '89 Computer Assisted Radiology, Berlin, June 25-28, 1989.

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