Long Bone X-Ray Image Stitching Using Camera Augmented Mobile C-Arm

Abstract

X-ray images are widely used during surgery for long bone fracture fixation. Mobile C-arms provide X-ray images which are used to determine the quality of trauma reduction, i.e. the extremity length and mechanical axis of long bones. Standard X-ray images have a narrow field of view and can not visualize the entire long bone on a single image. In this paper, we propose a novel method to generate panoramic X-ray images in real time by using the previously introduced Camera Augmented Mobile C-arm [1]. This advanced mobile C-arm system acquires registered X-ray and optical images by construction, which facilitates the generation of panoramic X-ray images based on first stitching the optical images and then embedding the X-ray images. We additionally introduce a method to reduce the parallax effect that leads to the blurring and measurement error on panoramic X-ray images. Visual marker tracking is employed to automatically stitch the sequence of video images and to rectify images. Our proposed method is suitable for intra-operative usage generating panoramic X-ray images, which enable metric measurements, with less radiation and without requirement of fronto-parallel setup and overlapping X-ray images. The results show that the panoramic X-ray images generated by our method are accurate enough (errors less than 1%) for metric measurements and suitable for many clinical applications in trauma reduction.

Parallax-Free Long Bone X-ray Image Stitching

“…However, very limited feature information and high noise in the bone X-ray images make similarity measurements unreliable. This is the reason why others have employed the ruler [2] or video images [3] for X-ray image stitching. We constructed a phantom composed of spherical X-ray markers on three different planes (see figure 3(b)) and attached it to the operating table.…”

“…The mobile C-arm will be positioned in the common setup, in which the X-ray source is below the operating table (see figure 2(a)). In the method proposed by Wang et al [3], the marker pattern was placed above the patient and could occlude the view onto the operation situs. Compared to their solution, our system setup does not only make the marker pattern visible to the camera for pose estimation, but also let the marker pattern be smoothly integrated into the surgical procedure without disturbing the physician's view.…”

“…the ruler plane must be parallel to the detector plane of the C-arm. Wang et al [3] presented a method to generate panoramic X-ray images intra-operatively using a C-arm, to which a video camera was attached. This method does not require overlapping X-ray images or special X-ray markers.…”

“…Although methods for reducing parallax effects on the bone plane were described in [2,3], they require the bone segments to be on the same plane and parallel to the plane used for estimating the transformation. In practice, it is unlikely that the plane of the bone is exactly parallel to the plane of the ruler (or marker pattern) due to the soft tissue around bones.…”

“…Bone segments furthermore may be on different plane levels due to fracture or inability to fully extend the joints. For these complex situations, completely removing the parallax effects in the panoramic images is impossible by using the early introduced methods [2,3]. This will finally restrict the stitching approaches within clinical routine to a limited number of cases.…”