We have developed a technique that estimates the 3D orientations and position of thin objects using the information from a single projection image and a known model of the object. The 3D orientations and positions of catheters were determined by use of this technique, which iteratively aligns points in the model with their respective image positions. Studies were done to evaluate the sensitivity of the technique to errors in the model and image data. These studies included generating image and model data and adding Gaussian-distributed errors to these data, adding Gaussian distributed pixel value nose to x-ray images of a catheter phantom to simulate noisy fluoroscopic images, and simulating flexes, or bends, in the tip of a catheter. Results indicate that orientations and positions of a catheter of diameter 0.18 cm can be calculated by use of the technique with mean accuracies of approximately 1 degree and 0.3 cm, respectively, for errors of approximately 0.03 cm and 0.005 cm in the image and model data, respectively. Results also indicate that the technique is robust to typical levels of quantum noise in fluoroscopic images, and may be made robust to changes in the catheter's shape. !120
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