Improvement of manual 2D/3D registration by decoupling the visual influence of the six degrees of freedom

For instrument guidance in X-ray-based interventional procedures, 2D/3D registration is an important method to fuse pre-op 3D images with live X-ray images. The user modifies the six degrees of freedom (DOF) of the 3D image and thereby aligns a projection of it to the given X-ray images. Because of the projective geometry of X-ray, the classic handling of the six DOF during manual registration has side effects. Changing a specific parameter can visually influence the setting of other parameters and affect already adjusted registrations in other X-ray views. We propose an improved DOF handling such that the visual appearance of the object is consistent with the parameter changes by the user. Our evaluation shows that our method is superior to the classic approach for manually registering an ultrasound probe on biplane X-ray images.