First-pass radionuclide angiography (RNA) of the human heart is performed during peak treadmill exercise using a Multiwire Gamma Camera (MWGC) and an intravenous injection of ultra-short-lived radionuclide Tantalum-178. The study focuses on left ventricular function during treadmill exercise and the use of this technique in patients with coronary artery disease (CAD) is significant compared with other methods such as echocardiography. However, patient motion and resulting image blurring during treadmill exercise can significantly degrade resolution and introduce serious image distortion. To help eliminate the effects of patient motion, we have adopted an electro-magnetic motion tracking system that can monitor the movement of patient's left ventricle (LV), based on the real-time six-dimensional position and orientation of a sensor attached to the patient's back, and the location of LV in the patient's chest contour. This system implements a motion correction algorithm which significantly reduces the effects of motion artifact incurred in treadmill exercise RNA.
The motion correction algorithm is evaluated using dynamic phantom simulations, where an external radioactive marker is attached to a volunteer, who exercises at several different Bruce levels on treadmill. Correction accuracy is assessed by calculating the root mean square (RMS) error of the locations of the maximum activity pixel (centroid) in corrected and uncorrected images. These initial test results using a dynamic phantom show that the motion artifacts can be removed. The algorithm was also evaluated on patients undergoing treadmill exercise RNA. In evaluating clinical data, one must be careful to select the correct lung background beat, and find the proper LV beats to form representative cycle, which yields reliable LV ejection fraction (EF) values. Motion-corrected images are superior with regard to the determination of ventricular wall motion and the calculation of regional ejection fraction images. In the uncorrected images, these are severely distorted and may result in an improper diagnosis.
The success of motion-corrected treadmill research points to a revolutionary new approach to stress imaging, which can potentially benefit millions of patients entering the health care system with chest pain symptoms by improving the accuracy of diagnosis, as well as, the cost-effectiveness of front-line methods of detecting cardiac dysfunction.