Hans-Florian Zeilhofer

JULIUS - An Extendable Software Framework for Surgical Planning and Image-Guided Navigation

In this paper we introduce the extendable and cross-platform software framework JULIUS, which will become public available by the end of this year. JULIUS consists of three conceptual layers and provides diverse assistance for medical visualization, surgical planning and image-guided navigation. The system features a modular and portable design and combines both pre-operative planning and intra-operative assistance within one single environment.

3D osteotomy planning in cranio-maxillofacial surgery: experiences and results of surgery planning and volumetric finite-element soft tissue prediction in three clinical cases

In this paper we present the current status of our work on the development of an integrated 3D osteotomy planning system for cranio-maxillofacial surgery. Besides the demonstration of recent finite-element simulations for soft tissue prediction, as a result of an osteotomy planning, we introduce a novel technique for an improved planning of the osteotomy itself. In contrast to common approaches that concentrate on bone rearrangements only, neglecting the actual planning of bone cuts, a free-hand osteotomy planning method for arbitrarily shaped cuts is presented. Thus, sagittal split osteotomies of the mandible according to Obwegeser-Dal Pont can be planned correctly under consideration of vulnerable structures, as for instance the mandibular nerve

Segmentation and visualization of the inner structure of craniofacial hard tissue

Abstract In the biomedical context, image segmentation is the process of dividing an image into different subregions, usually different organs or tissue types. But mostly, the gray values of the inner voxels and, by this, the major part of the information remain unused. The purpose of this work is a new way of segmentation and visualization of these voxels. Concerning treatment planning for clinical cases, we deliver a macroscopic view of bone respective tissue quality. For the simulation branch, we contribute to an improved individual inhomogeneous and anisotropic description of the material law.

Three-dimensional cephalometric evaluation of maxillary growth following in utero repair of cleft lip and alveolar-like defects in the mid-gestational sheep model.

Objective: To evaluate maxillary growth following in utero repair of surgically created cleft lip and alveolar (CLA)-like defects by means of three-dimensional (3D) computer tomographic (CT) cephalometric analysis in the mid-gestational sheep model. Methods: In 12 sheep fetuses a unilateral CLA-like defect was created in utero (untreated control group: 4 fetuses). Four different bone grafts were used for the alveolar defect closure. After euthanasia, CT scans of the skulls of the fetuses, 3D reconstructions, and a 3D-CT cephalometric analysis were performed. Results: The comparisons between the operated and nonoperated skull sides as well as of the maxillary asymmetry among the experimental groups revealed no statistically significant differences of the 12 variables used. Conclusions: None of the surgical approaches used for the in utero correction of CLA-like defects seem to affect significantly postsurgical maxillary growth; however, when bone graft healing takes place, a tendency for almost normal maxillary growth can be observed.

Computer-assisted selection of donor sites for autologous grafts

A new method is proposed for a precise planning of autologous bone grafts in cranio- and maxillofacial surgery. In patients with defects of the facial skeleton, autologous bone transplants can be harvested from various donor sites in the body. The preselection of a donor site depends i.a. on the morphological fit of the available bone mass and the shape of the part that is to be transplanted. A thorough planning and simulation of the surgical intervention based on 3D CT studies leads to a geometrical description and the volumetric characterization of the bone part to be resected and transplanted. Both, an optimal fit and a minimal lesion of the donor site are guidelines in this process. We use surface similarity and voxel similarity measures in order to select the optimal donor region for an individually designed transplant.

Diagnostic possibilities with multidimensional images in head and neck area using efficient registration and visualization methods

For several diseases in the head and neck area different imaging modalities are applied to the same patient.Each of these image data sets has its specific advantages and disadvantages. The combination of different methods allows to make the best use of the advantageous properties of each method while minimizing the impact of its negative aspects. Soft tissue alterations can be judged better in an MRI image while it may be unrecognizable in the relating CT. Bone tissue, on the other hand, is optimally imaged in CT. Inflammatory nuclei of the bone can be detected best by their increased signal in SPECT. Only the combination of all modalities let the physical come to an exact statement on pathological processes that involve multiple tissue structures. Several surfaces and voxel based matching functions we have tested allowed a precise merging by means of numerical optimization methods like e.g. simulated annealing without the complicated assertion of fiducial markers or the localization landmarks in 2D cross sectional slice images. The quality of the registration depends on the choice of the optimization procedure according to the complexity of the matching function landscape. Precise correlation of the multimodal head and neck area images together with its 2D and 3D presentation techniques provides a valuable tool for physicians.

Computer simulation of orthognathic surgery with video imaging

Patients with extreme jaw imbalance must often undergo operative corrections. The goal of therapy is to harmonize the stomatognathic system and an aesthetical correction of the face profile. A new procedure will be presented which supports the maxillo-facial surgeon in planning the operation and which also presents the patient the result of the treatment by video images. Once an x-ray has been digitized it is possible to produce individualized cephalometric analyses. Using a ceph on screen, all current orthognathic operations can be simulated, whereby the bony segments are moved according to given parameters, and a new soft tissue profile can be calculated. The profile of the patient is fed into the computer by way of a video system and correlated to the ceph. Using the simulated operation the computer calculates a new video image of the patient which presents the expected postoperative appearance. In studies of patients treated between 1987-91, 76 out of 121 patients were able to be evaluated. The deviation in profile change varied between .0 and 1.6mm. A side effect of the practical applications was an increase in patient compliance.

Computer-based planning of optimal donor sites for autologous osseous grafts

Bone graft surgery is often necessary for reconstruction of craniofacial defects after trauma, tumor, infection or congenital malformation. In this operative technique the removed or missing bone segment is filled with a bone graft. The mainstay of the craniofacial reconstruction rests with the replacement of the defected bone by autogeneous bone grafts. To achieve sufficient incorporation of the autograft into the host bone, precise planning and simulation of the surgical intervention is required. The major problem is to determine as accurately as possible the donor site where the graft should be dissected from and to define the shape of the desired transplant. A computer-aided method for semi-automatic selection of optimal donor sites for autografts in craniofacial reconstructive surgery has been developed. The non-automatic step of graft design and constraint setting is followed by a fully automatic procedure to find the best fitting position. In extension to preceding work, a new optimization approach based on the Levenberg-Marquardt method has been implemented and embedded into our computer-based surgical planning system. This new technique enables, once the pre-processing step has been performed, selection of the optimal donor site in time less than one minute. The method has been applied during surgery planning step in more than 20 cases. The postoperative observations have shown that functional results, such as speech and chewing ability as well as restoration of bony continuity were clearly better compared to conventionally planned operations. Moreover, in most cases the duration of the surgical interventions has been distinctly reduced.

Model-based surgery simulation and intraoperational guidance

The transfer of the result of the surgical planning and simulation performed on an individual anatomical, CT based model onto the operation field is accomplished by fusing a live video image of the situs and a video image of the planning model, recorded rom the same relative camera location towards the anatomical structure. The surgeon can replicate the previously done simulation by guiding instruments like scalpels, bone saws, drills etc. along the markings left in the model. The visual superposition of the real and the synthetic world offers the surgeon an intuitively usable, tight link between the simulation stage and the real surgery. Osteotomy lines, the location of repositioned bone segments, implant positions and other relevant information are easily transferred in a non- invasive, non-tactile manner, thus reducing the risk of infection by reducing the count of foreign matter objects like templates, calipers, etc. brought into the situs.

High-resolution arthrosonography of the temporomandibular joint with video and computer support

Ultrasound imaging of the temporomandibular joint has been problematic due to the lower frequency of the transducers used up to the present time. Imaging of temporomandibular joint structures being utilizable for diagnosis and therapy was only possible through time-consuming and expensive radiological image yielding procedures (computertomography, magnetic resonance imaging). 84 temporomandibular joints in 42 patients were examined clinically, radiologically, by axiographic tracing, magnetic resonance imaging and ultrasound imaging. An ultrasound unit was used with a high- frequency 13MHz transducer. The temporomandibular joint was examined preauricularily; by this the lateral section of the joint could be represented. The image sequences in functional condylus movements were taped via a video output into a film recorder. Selected ultrasound images from the beginning to the end of the movement could then be digitalized and read into a personal computer to be evaluated. The computer then calculated a line of movement and the angle of the joints course. By ultrasound imaging the joint space could be represented and measured clearly. Compared with the space measured in the magnetic resonance image the value determined by ultrasonography was a tenth power more exact. The computer-supported image analysis of the condylus movements led to an exact presentation of the condylus course. The sonographically determined condylar guidance corresponded to the value traced by axiography with high significance within a range of 3 degrees. The temporomandibular joints disc could be localized just as exactly as with the magnetic resonance imaging. The use of a 13MHz transducer offers a new low-cost method of noninvasive dynamic imaging of important temporomandibular joint structures. The possibility of video and computer support enables movement analysis and opens new possibilities in the morphological and functional evaluation of the temporomandibular joint.