An adaptive gating approach for X-ray dose reduction during cardiac interventional procedures

The increasing number of cardiac interventional procedures has resulted in a tremendous increase in the absorbed X-ray dose by radiologists as well as patients. A new method is presented for X-ray dose reduction which utilizes adaptive tube pulse-rate scheduling in pulsed fluoroscopic systems. In current pulsed systems, the X-ray tube is pulsed at a fixed rate of 30 pulses/sec (or higher) and an image is formed at the end of each pulse. In the proposed system, pulse-rate scheduling depends on the heart muscle activity phase determined through continuous guided segmentation of the patient's electrocardiogram (ECG). Displaying images generated at the proposed adaptive nonuniform rate is visually unacceptable; therefore, a frame-filling approach is devised to ensure a 30 frame/sec display rate. The authors adopted two approaches for the frame-filling portion of the system depending on the imaging mode used in the procedure. During cine-mode imaging (high X-ray dose), collected image frame-to-frame pixel motion is estimated using a pel-recursive algorithm followed by motion-based pixel interpolation to estimate the frames necessary to increase the rate to 30 frames/sec. The other frame-filling approach is adopted during fluoro-mode imaging (low X-ray dose), characterized by low signal-to-noise ratio images. This approach consists of simply holding the last collected frame for as many frames as necessary to maintain the real-time display rate. Results of simulated system performance on an image sequence from a diagnostic study of left ventricular volume produced an average of approximately 3:1 dose reduction without compromising the diagnostic quality of the generated images. The adaptive pulsed-progressive system concept is viewed as the next evolutionary step in X-ray fluoroscopic systems.