Due to their complementary information content, both X-ray
computed tomography (CT) and magnetic resonance (MR) imaging are
employed in certain clinical cases to improve the understanding of
the pathology. To spatially relate the two datasets,
image-registration and image fusion is employed. However,
registration errors, either global or local, are common and are
non-uniform within the image volume. In this paper, we propose a
new algorithm, which assesses the quality of the registration
locally within the CT-MR volume and provides visual, color-coded
feedback to the user about the location and extent of good/bad
correspondence between the two images.
The proposed registration assessment algorithm is based on a
correspondence analysis of bone structures in the CT and MR
images. For that purpose, a custom segmentation algorithm for bone
in MR images has been developed, which is based on a stochastic
threshold computation method. This segmentation method for MR
images and the CT-MR registration assessment algorithm were
validated on simulated MR datasets and real CT-MR image pairs of
the head. Some partial-volume effects occur at the borders of the
bone structures and at the bone interfaces with air, which cannot
be separated from bone in the MR image.
The presented assessment method of CT-MR image registration offers
the user a new tool to evaluate the overall and local quality of
the registration. With this information, the user does not have to
blindly trust the fused CT-MR datasets but can easily identify
areas of inaccurate correspondence. The application of the
algorithm is so far limited to T1-weighted MR and CT images of the
head area.
In this paper we describe a system for corrective and reconstructive CMF surgery that allows planning of bone segment relocations in 3D and transfer of the goal positions into an intra-operative navigation module, which provides guidance to realize the planned movement. In addition, the pre-operative planning module offers functions of mirroring and allows insertion of distraction devices. We present three clinical cases of CMF surgical procedures planned a posteriori with our application: bimaxillary realignment, involving subcondylar osteotomy of the mandible and LeFort I osteotomy, secondary orbital reconstruction and mandibular reconstruction.
Handling objects in the microworld requires a set of abilities and tools which differ from the ones used to interact with objects in the macro world. A whole new set of handling limitations is present, as well as an array of new possibilities. Due to the small dimensions, the operator has no direct access to the objects and must assemble them by teleoperation. Therefore a user interface to interact with the micro world must be specifically designed. Thus, this paper presents the implementation of a graphical user interface for a high precision robot operating on the micro world developed at the Swiss Federal Institute of Technology. In this interface the operator is provided with a set of visualization and manipulation tools on a workstation. The visualization tools are: live microscope video images with top and side view, and a 3D virtual solid model of the robot with perspective as well as orthogonal views available at the same time. The manipulation tools are: a control panel used to check the status and to operate both the camera and the robot itself and an interface wit ha 6 degree of freedom joystick-like manipulator. Several combinations of visualization and manipulation tools have been tested, as well as several manipulation strategies. The user interface and the results of this investigation are presented in this paper, as well as a description of the robot system.
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