Erwin Keeve

RapidSplint: virtual splint generation for orthognathic surgery – results of a pilot series

Abstract Background: Within the domain of craniomaxillofacial surgery, orthognathic surgery is a special field dedicated to the correction of dentofacial anomalies resulting from skeletal malocclusion. Generally, in such cases, an interdisciplinary orthodontic and surgical treatment approach is required. After initial orthodontic alignment of the dental arches, skeletal discrepancies of the jaws can be corrected by distinct surgical strategies and procedures in order to achieve correct occlusal relations, as well as facial balance and harmony within individualized treatment concepts. To transfer the preoperative surgical planning and reposition the mobilized dental arches with optimal occlusal relations, surgical splints are typically used. For this purpose, different strategies have been described which use one or more splints. Traditionally, these splints are manufactured by a dental technician based on patient-specific dental casts; however, computer-assisted technologies have gained increasing importance with respect to preoperative planning and its subsequent surgical transfer. Methods: In a pilot study of 10 patients undergoing orthognathic corrections by a one-splint strategy, two final occlusal splints were produced for each patient and compared with respect to their clinical usability. One splint was manufactured in the traditional way by a dental technician according to the preoperative surgical planning. After performing a CBCT scan of the patient’s dental casts, a second splint was designed virtually by an engineer and surgeon working together, according to the desired final occlusion. For this purpose, RapidSplint®, a custom-made software platform, was used. After post-processing and conversion of the datasets into .stl files, the splints were fabricated by the PolyJet procedure using photo polymerization. During surgery, both splints were inserted after mobilization of the dental arches then compared with respect to their clinical usability according to the occlusal fitting. Results: Using the workflow described above, virtual splints could be designed and manufactured for all patients in this pilot study. Eight of 10 virtual splints could be used clinically to achieve and maintain final occlusion after orthognathic surgery. In two cases virtual splints were not usable due to insufficient occlusal fitting, and even two of the traditional splints were not clinically usable. In five patients where both types of splints were available, their occlusal fitting was assessed as being equivalent, and in one case the virtual splint showed even better occlusal fitting than the traditional splint. In one case where no traditional splint was available, the virtual splint proved to be helpful in achieving the final occlusion. Conclusions: In this pilot study it was demonstrated that clinically usable splints for orthognathic surgery can be produced by computer-assisted technology. Virtual splint design was realized by RapidSplint®, an in-house software platform which might contribute in future to shorten preoperative workflows for the production of orthognathic surgical splints.

Computer-aided manufacturing technologies for guided implant placement.

Implant treatment increasingly focuses on the reduction of treatment time and postoperative impairment. The improvement of 3D dental diagnosis by ConeBeam computed tomography allows detailed preparation for the surgical placement of dental implants under prosthetic considerations. While the first generation of implant planning software used high-contrast multislice computed tomography, software that has been specifically designed for ConeBeam computed tomography is now available. Implant placement can be performed using surgical guides or under the control of optical tracking systems. Surgical guides are more commonly used in private office owing to their availability. The accuracy for both techniques is clinically acceptable for achieving implant placement in critical anatomical indications. When using prefabricated superstructures and in flapless surgery, special abutments or an adjusted workflow are still necessary to compensate misfits of between 150 and 600 µm. The proposition to ensure proper implant placement by dentists with limited surgical experience through the use of surgical guides is unlikely to be successful, because there is also a specific learning curve for guided implant placement. Current and future development will continue to decrease the classical laboratory-technician work and will integrate the fabrication of superstructures with virtual treatment planning from the start.

Stereoscopic augmented reality system for computer-assisted surgery.

Abstract A first architecture for an augmented reality system in computer-assisted surgery is presented in this paper. Like in “X-ray vision” systems, a stereoscopic overlay is visually superimposed on the patient. The main purpose of our approach is user-friendliness for the surgeon: no additive wearing equipment is required. Registration, rigid body location and 3D volume computation are proven to respect real-time processing, thanks to an optical navigation system and our integrated software framework. Studies are undertaken to replace our actual monitor display by an upcoming holographic screen.

Efficient Point-Based Isosurface Exploration Using the Span-Triangle

We introduce a novel span-triangle data structure, based on the span-space representation for isosurfaces. It stores all necessary cell information for dynamic manipulation of the isovalue in an efficient way. We have found that using our data structure in combination with point-based techniques, implemented on graphics hardware, effects in real-time rendering and exploration. Our extraction algorithm utilizes an incremental and progressive update scheme, enabling smooth interaction without significant latency. Moreover, the corresponding visualization pipeline is capable of processing large data sets by utilizing all three levels of memory: disk, system and graphics. We address practical usability in actual medical applications, achieving a new level of interactivity.

Overlay visualization in endoscopic ENT surgery.

PurposeIn endoscopic ENT surgery, the identification and localization of target structures is challenging—depth information is missing, relevant tissues could be hidden behind opaque material and image distortion affects the instrument handling. In this paper, a novel overlay visualization is presented that supports the surgeon by superimposing planning and navigation information on the endoscopic image.MethodTarget regions, which have been identified in preoperative CT data, are superimposed on the endoscopic image, allowing the use of guiding lines for distance visualization. To match the overlay information with the geometrically distorted endoscopic images, a new intraoperative calibration procedure has been developed.ResultsThe accuracy of this new method has been verified by cadaver studies. Clinical evaluation in three paranasal sinus interventions was performed to show the intraoperative assistance and practicability with promising results.ConclusionThe new techniques safely support the surgeon in locating target structures in the paranasal sinuses with little change in the actual workflow.

Craniomaxillofacial surgery planning based on 3D models derived from Cone-Beam CT data

Abstract Introduction: Individual planning of complex maxillofacial corrections may require 3D models which can be manufactured based on DICOM datasets. The gold standard for image acquisition is still high-resolution multi-slice computed tomography (MSCT). However, appropriate datasets for model fabrication can be acquired by modern Cone-Beam CT (CBCT) devices that have been developed specifically for maxillofacial imaging. The clinical utility of individual models fabricated on the basis of CBCT datasets was assessed. Methods: In five patients affected by different deficiencies of the maxillofacial skeleton, preoperative imaging was performed with ILUMA CBCT. Segmentation of hard tissues was performed manually by thresholding. Corresponding STL datasets were created and exported to an industrial service provider (Alphaform, Munich, Germany) specializing in rapid prototyping, and 3D models were fabricated by the selective laser sintering (SLS) technique. For variance analysis, landmark measurements were performed on both virtual and 3D models. Subsequently, maxillofacial surgery was performed according to the model-based planning. Results: All CBCT-based DICOM datasets could be used for individual model fabrication. Detailed reproduction of individual anatomy was achieved and a topographic survey showed no relevant aberrance between the virtual and real models. The CBCT-based 3D models were therefore used for planning and transfer of different maxillofacial procedures. Conclusions: CBCT-based datasets can be used for the fabrication of surgical 3D models if the correct threshold is set. Preoperative workflow and patient comfort is improved in terms of the fast-track concept by using this “in-house” imaging technique.

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 Markov Random Fields and Region Growing for Interactive Segmentation of MR Data

Segmenting medical structures is mandatory in any computer assisted surgery system. This major field must be addressed in order to build realistic and accurate 3D models of patient individual anatomical structures.Magnetic Resonance Imaging (MRI) is becoming part of daily routine in clinical work. Whereas scanning speed and slice numbers increase each year, segmenting such data is still a challenging problem. Moreover, the segmentation stage remains time limiting in pre-operative planning and intra-operative guidance. Indeed, interactive tools, like live wire or intensity-based thresholding, requires a pre or post-filtering to homogenize areas. Common medical filters, such as median or morphology-based, are actually non adapted for MR noise removal. Their main side effect is to remove boundaries when applied on Gaussian corrupted data. Next, numerous steps spend efforts in reconstructing lost information and current approaches are therefore non interactive.

An open software framework for medical applications

In this paper we introduce the extendible and cross-platform software framework Julius. Julius combines both pre-operative planning and intraoperative assistance within one single environment. In this paper we discuss three aspects of Julius: the medical data processing, the visualization pipeline and the interaction. Each aspect provides interfaces that allow to extend the application with own algorithms and to build complex applications. We believe that this approach facilitates the development of image guided navigation and simulation procedures for computer-aided-surgery.

SURGERY PLANNING TOOLS FOR THE OSSEOUS GRAFTING TREATMENT

This paper presents a method for computer assisted selection of optimal donor sites for autologous grafts in the craniofacial surgery planning. The method consists of two stages. The non-automatic graft design step is followed by a fully automatic procedure to find the best harvesting site in the predefined donor region. The main idea of the proposed method is based on the registration paradigm. The optimal donor site is identified by performing an optimization of the surface based similarity measure between the donor region and the designed graft template. An efficient optimization method based on the Levenberg-Marquardt algorithm has been implemented. It enables, once the preprocessing step has been performed, selection of the optimal donor site in time less than one minute.