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.

Digital flashing tomosynthesis (D-FTS) investigations have been performed using a new nonlinear reconstruction algorithm. It is called extreme-value decoding and produces significantly less artefact than back projection used commonly in tomosynthesis. The reduction of artefact allows the use of tomosynthesis based on only four projections in the case of dilute objects, i.e. objects with only a small number of high absorbing voxels. This condition can be realized in angiography by cancelling soft-tissue and bones by subtraction (e.g. DSA technique). The new technique has been carried out in 10 patients with coronary artery disease after investigation with standard 35 mm cineangiography. For the recording step of the D-FTS images we have used a multiple X-ray source. For the digital nonlinear reconstruction step we have used a VAX 11/780 computer. The estimated degree of stenosis found by D-FTS tomograms shows good accordance with the cineangiographic studies. The amount of contrast medium, the X-ray dose, and the investigation time are significantly reduced, because D-FTS requires only a single pre- and post-injection multiple perspective-image for each coronary artery.

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Digital Flashing Tomosynthesis (DFTS) represents a technique for three-dimensional (3D) coronary angiography. Four ECG-gated simultaneously flashed X-ray tubes generate a multiperspective digital substraction image as DFTS multiangiogram for 3D reconstruction and visualization. Computerized morphologic and morphometric quantitative analysis can be performed including videodensitometry. Postmortem coronary angiography of 30 human hearts with suspected coronary artery disease was performed by 35-mm cine technique and by DFTS. The results of angiographic measurements in 50 stenotic arterial segments were compared with the histologic reference and show excellent regression results with correlation coefficients of more than 0.95 (p less than or equal to 0.0001). No significant differences in standard errors of estimates between the techniques were found. DFTS yields an accuracy in depiction of the coronary arteries and angiographic estimation of arterial lumen equivalent to 35-mm cineangiography. DFTS images can be directly used for visual interpretation and for computerized morphologic and morphometric quantitative analysis. DFTS technology reduces the amount of radiation exposure, the amount of contrast medium, and the time of the procedure. DFTS offers the possibility to obtain 3D images of the coronary artery tree.