A method has been developed in which cineradiography is used for the assessment of the opening angle of implanted Bjork-Shiley prosthetic valves. The method is based on the fact that the ring and the disc, which are known to be circular, appear to be elliptical on x-ray films. The spatial position of the valve can be retrieved from the characteristics of these ellipses when vectoranalysis is applied. The method's accuracy does not depend on the position of the patient with respect to the direction of the x-ray beam. pecially if films of one projection only are available (see figure 2, bottom x-ray image), estimation of the short axis and the corresponding opening angle may lead to errors. We developed a method to assess opening and closing characteristics of Bjork-Shiley disc valves for each frame of a cineradiographic run, independent of the position of the patient with respect to the direction of the x-ray beam. This method is based on the fact that projections of circular objects such as the ring and the disc of the implant are, in an arbitrary spatial position, ellipsoidal and that the spatial orientation of the valve can be retrieved from the characteristics of these projected ellipses when vectoranalysis is applied. This method will be discussed and some preliminary results that show good reproducibility and accuracy -and have important clinical implications will be presented. MethodsPrinciple of assessment of the opening angle. The disc of a Bjork-Shiley prosthesis is supported by two struts, the positions of which can be easily identified on a projected frame of a cineradiographic film. From this information the motion axis

Evaluation of the function of implanted prosthetic valves is important in early diagnosis of valve dysfunction. Bjork-Shiley valves contain two radiopaque rings, which are projected as ellipses in cineradiography. From these ellipses the actual valve opening angle can be calculated. A computer-aided method was developed that enables measurement of ellipse characteristics reliably, independent of projection angle and valve opening. It is demonstrated that calculated and real opening angles differ fess than 2" with this method. Using the same technique the tilting angle of the valve ring during the cardiac cycle is computed for evaluation of progression of valve dehiscense in case of a paravalvular leak. Application of the method to patient data is illustrated by three cases. The method is suitable for use by technicians. It can be implemented on a small microprocessor system. The method proved to be a powerful tool in the evaluation of patients with implanted Bjork-Shiley valves.