Advances in interactive craniofacial surgery planning by 3D simulation and visualization

Laser-scan-based navigation in cranio-maxillofacial surgery

BACKGROUND

In computer-assisted surgery, a correlation between a volume data set and the surgical site is required in order to localize the patient's head on the operating table. Registration markers are commonly used for this procedure. However, the marker registration is associated with high logistics, since the markers have to be placed prior to data set acquisition and have to be kept in their position until the patient enters the operating room. This study deals with a new markerless registration method in cranio-maxillofacial surgery that is based on a high-resolution laser-scan of the patient's (relaxed) skin surface.

PATIENTS

20 patients with tumours, bone malformations or foreign bodies, scheduled for computer-assisted surgery, were involved in the study.

STUDY DESIGN

The clinically applied accuracy of the laser-scan-based registration was measured through additionally placed registration markers. The inherent precision of the laser-scan registration system was controlled in phantom studies.

RESULTS

The clinically applied accuracy of the new laser-scan-based registration technique ranged between 0.2 and 1.8 mm with a mean deviation of 1.1mm and a standard deviation of 0.3 mm.

CONCLUSION

The facial skin surface can serve as a sufficiently stable and invariable reference base in order to register patients for computer-assisted cranio-maxillofacial surgery.

Validation of in vivo assessment of facial soft-tissue volume changes and clinical application in midfacial distraction: a technical report

The purpose of this study was to validate the assessment of visible volume changes of the facial soft tissue with an optical three-dimensional sensor and to introduce new parameters for the evaluation of the soft-tissue shape achieved from three-dimensional data of selected cases of midfacial distraction. Images of a truncated cone of known volume were assessed repeatedly with an optical three-dimensional sensor based on phase-measuring triangulation to calculate the volume. Two cubic centimeters of anesthetic solution was injected into the right malar region of 10 volunteers who gave their informed consent. Three-dimensional images were assessed before and immediately after the injections for the assessment of the visible volume change. In five patients who underwent midfacial distraction after a high quadrangular Le Fort I osteotomy, three-dimensional scans were acquired before and 6 and 24 months after the operation. The visible soft-tissue volume change in the malar-midfacial area and the mean distance of the accommodation vector that transformed the preoperative into the postoperative surface were calculated. The volume of the truncated cone was 235.26 +/- 1.01 cc, revealing a measurement uncertainty of 0.4 percent. The injections of anesthetic solution into the malar area resulted in an average visible volume change of 2.06 +/- 0.06 cc. The measurement uncertainty was 3 percent. In the five patients, the average distance of maxillary advancement was 6.7 +/- 2.3 mm after 6 months and 5.4 +/- 3.0 mm after 2 years. It was accompanied by a mean visible volume increase of 8.92 +/- 5.95 cc on the right side and 9.54 +/- 4.39 cc on the left side after 6 months and 3.54 +/- 3.70 cc and 4.80 +/- 3.47 cc, respectively, after 2 years. The mean distance of the accommodation vector was 4.41 +/- 1.94 mm on the right side and 4.74 +/- 1.32 mm on the left side after 6 months and 1.62 +/- 1.96 mm and 2.16 +/- 1.52 mm, respectively, after 2 years. The assessment of visible volume changes by optical three-dimensional images can be carried out with considerable accuracy. The determination of volume changes and accompanying accommodation vectors completes the cephalometric analysis during the follow-up of patients undergoing midfacial distraction. The new parameters will help to assess normative soft-tissue data on the basis of three-dimensional imaging with a view to an improved three-dimensional prediction of the operative outcome of orthognathic surgery.

Craniofacial applications of three-dimensional laser surface scanning

Recent innovations in technology have generated a variety of techniques for medical imaging. One of these initially developed for industry is laser surface scanning. Laser surface scanning is a noninvasive method for acquiring three-dimensional (3D) images. In this article, the technology of 3D laser surface scanning is described, and a few applications are reported as it relates to craniofacial research and clinical practice. Advantages and disadvantages of this imaging modality are discussed. Three-dimensional laser surface scanning holds great promise as it relates to the documentation, analysis, and evaluation of treatment results in craniofacial anomalies.

Optimizing presurgical orthodontic planning by means of the transverse coordinate simulation system (TCSS)

INTRODUCTION

When planning bilateral sagittal split osteotomies according to Obwegeser and Dal Pont, inaccuracies in the presurgical prediction of the transverse osteotomy gaps may occur. This is due to limitations of plaster models when simulating surgery on an articulator.

AIM

This paper demonstrates the transverse coordinate simulation system which allows presurgical prediction of the transverse discrepancy between the tooth bearing and the proximal segment after displacement, thus minimizing uncertainty for the surgeon.

METHOD

Diagnostic landmarks (taken from lateral and frontal cephalograms) and clinical data describing mandibular dimensions are transferred to a two-dimensional coordinate diagram. A mandibular model is then constructed using the anterior arch form, the temporomandibular joint distance and the prospective incision pattern.

RESULT

Movements in the horizontal plane and displacement of the three segments (two condylar and one mandibular arch segment) can be simulated and measured.

CONCLUSION

Transverse coordinate simulation system effectively increases the accuracy of presurgical planning without additional CT data or three-dimensional jaw models. This technique may decrease the number of additional surgical manoeuvres resulting from unexpectedly wide transverse discrepancies at the osteotomy site, which often increase surgery time, necessitate additional bone grafting, and entail the risk of healing disturbances and of malrotation or dislocation of the condyle.

First experience with a public domain computer-aided surgical system

The outcome of complex craniofacial operations is critically dependent on careful and accurate preoperative planning. Recent advances in computer technology enable the surgeon to do surgical simulations directly on to a computer terminal. We describe the clinical application of a public domain-based computer-aided system in craniofacial surgery. Operation planning was based on clinical investigations and radiological images, with particular use of a virtual three-dimensional surgical simulation. Three patients with complex craniofacial malformations were admitted for orbital correction. Surgical simulation defined numerically the extent of bone movements and the extent of resection areas. Operations were guided by the virtual planning. The outcome was compared with the planning to assess the accuracy of the operative correction. Our first experience confirms that computer-assisted simulation is a reliable and useful tool that improves surgical planning and helps to evaluate the surgical outcome.

Preshaped hydroxyapatite tricalcium-phosphate implant using three-dimensional computed tomography in the reconstruction of bone deformities of craniomaxillofacial region

We prepared solid life-sized models and templates of implants based on three-dimensional computed tomography data in six cases with a bone deformity of the craniomaxillofacial region. After simulation surgery using these models and templates, the preshaped hydroxyapatite-tricalcium phosphate (HAP-TCP) implants were prepared to fill in the facial bone defects, and implantation was performed. Consequently, implants fitted the individual bone defects, and satisfactory facial contouring was obtained in five cases. In one case with severe cutaneous scarring in the grafted site, it was necessary to reduce the volume of the preshaped HAP-TCP implant during surgery. In conclusion, the three-dimensional, solid, life-sized model and template are useful for preoperative detailed simulation, and the use of preshaped HAP-TCP implants based on the template probably contributes to successful reconstruction of complex facial bone deformities and to the reduction of surgical invasion, resulting in achievement of better results.

Interactive 3-dimensional segmentation of MRI data in personal computer environment

We describe a method of interactive three-dimensional segmentation and visualization for anatomical magnetic resonance imaging (MRI) data in a personal computer environment. The visual feedback necessary during 3-D segmentation was provided by a ray casting algorithm, which was designed to allow users to interactively decide the visualization quality depending on the task-requirement. Structures such as gray matter, white matter, and facial skin from T1-weighted high-resolution MRI data were segmented and later visualized with surface rendering. Personal computers with central processing unit (CPU) speeds of 266, 400, and 700 MHz, were used for the implementation. The 3-D visualization upon each execution of the segmentation operation was achieved in the order of 2 s with a 700 MHz CPU. Our results suggest that 3-D volume segmentation with semi real-time visual feedback could be effectively implemented in a PC environment without the need for dedicated graphics processing hardware.

Computer-aided 3-D simulation and prediction of craniofacial surgery: a new approach

BACKGROUND

In plastic and reconstructive craniofacial surgery, careful preoperative planning is essential. In complex cases of craniofacial synostosis, rapid prototyping models are used to simulate the surgery and reduce operating time. Recently, 3-D CT model surgery has been introduced for presurgical planning and prediction of the postoperative result.

OBJECTIVE

For simulation of craniofacial surgery a computer-based system was developed that allows visualization and manipulation of CT-data using computer graphics techniques. Surgical procedures in all areas of the bony skull can be performed interactively.

RESULTS

The case of a child with scaphocephalus is presented. Surgery is planned using the craniofacial surgery simulator described above.

CONCLUSION

The computer-based interactive surgery simulation systems presented here allow precise visualization of craniofacial surgery. The accurate computer-aided 3-D simulation of bone displacements is also the prerequisite for transfer of the simulated surgery using a navigation system for surgery. Thus the preoperatively planned procedure could be transferred directly to the operating table.

Computer assisted oral and maxillofacial surgery--a review and an assessment of technology

Advances in the basic scientific research within the field of computer assisted oral and maxillofacial surgery have enabled us to introduce features of these techniques into routine clinical practice. In order to simulate complex surgery with the aid of a computer, the diagnostic image data and especially various imaging modalities including computer tomography (CT), magnetic resonance imaging (MRI) and Ultrasound (US) must be arranged in relation to each other, thus enabling a rapid switching between the various modalities as well as the viewing of superimposed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft and hard tissues are required. We must develop ergonomic and user friendly interactive methods for the surgeon, thus allowing for a precise and fast entry of the planned surgical procedure in the planning and simulation phase. During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today and within this article we present a review of the development of this rapidly evolving technique. Future intraoperative assistance takes the form of such passive tools for the support of intraoperative orientation as well as so-called 'tracking systems' (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. The techniques of virtual reality and computer assisted surgery are increasingly important in their medical applications. Many applications are still being developed or are still in the form of a prototype. It is already clear, however, that developments in this area will have a considerable effect on a surgeon's routine work.

Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism

OBJECTIVE

To observe changes in the pharyngeal airway and the hyoid bone position after mandibular setback osteotomy in 30 patients with mandibular prognathism by means of 3-dimensional computed tomography (3DCT).

STUDY DESIGN

Preoperative and postoperative computed tomography (CT) examinations were performed on 17 patients treated by sagittal split ramus osteotomy with rigid osteosynthesis and on 13 patients treated by intraoral vertical ramus osteotomy without osteosynthesis. The amount of mandibular setback was measured by the preoperative to postoperative difference of the mandibular position in axial CT images. The sizes of the preoperative and postoperative pharyngeal airway were evaluated from semitransparent and crosscut 3DCT images. Postoperative displacement of the hyoid bone was evaluated by a technique to superimpose a postoperative hard tissue 3DCT image on the preoperative image. The helical scan technique was used in the CT examination. The volume rendering technique was used to create 3DCT images.

RESULTS

The mean mandibular setback was 7.8 +/- 2.1 mm with a range of 5 to 11 mm. Three months after surgery, the lateral and frontal widths of the pharyngeal airway had decreased significantly in comparison with the preoperative width. The mean reduction rates of the lateral and frontal width were 23.6% and 11.4%, respectively. The diminished airway did not recover by either 6 months or 1 year after surgery in most cases. Downward and posterior displacement of the hyoid bone was seen postoperatively. There were positive correlations between the amount of mandibular setback and reduction of the lateral width of the pharyngeal airway (r = 0.54) and the amount of hyoid bone displacement (r = 0.42). There were no significant differences between the two surgical techniques.

CONCLUSION

Three-dimensional computed tomography was a practical imaging technique to evaluate the morphologic airway changes. The pharyngeal airway may have irreversible narrowing after mandibular setback surgery.

Fabricating auricular prostheses using three-dimensional soft tissue models

This article describes a method for fabricating an auricular prosthesis. This procedure uses the contours of the soft tissue surface from computerized tomography scans to fabricate a computer-generated, side-inverted 3-dimensional soft tissue model from a solid block of polyurethane using an Endoplan milling machine. The resultant 3-dimensional soft tissue model can then be used as the basis for a wax sculpture. This procedure facilitates the planning of the prosthesis; symmetrical modeling, especially for large, hemifacial defects; and the impression, which can be made on the model itself.

The clinical application of computerized three-dimensional mimic operation for maxillofacial bone tumor

Facial bone, as the frame to support maxillofacial region and with several sinuses and cavities, is structurally complicated and the maxillofacial tumors, benign or malignant, in this region usually grows into the deep tissues, sinus-cavities and orbit and destroys the bone. In this study, the maxillofacial tumors were subjected to a mimic operation on a computer following CT scanning and 3-dimensional reconstruction. The data similar to those of real operation were obtained, which could be used for developing operative plans. As compared with data on the basis of conditions in the real operation, computerized mimic operation reflected the real conditions during operation. Computerized mimic operation is valuable for the preoperative planning and the prediction of probable intraoperative events.

Application of combined three-dimensional bone and soft tissue model. A case report

This article describes a new application in three-dimensional modelling. By adding the contours of important soft tissue structures to the bone contours, it is possible to produce a combined bone and soft tissue model. The advantages of this technique are shown in a patient suffering from a parapharyngeal tumour. The model not only enabled the precise localisation of the tumour in relation to the surrounding bone, but also identified important structures like the internal carotid artery in relation to the tumour.

Preoperative planning and intraoperative navigation in skull base surgery

Experience with the commercially available, 3-D navigation systems Viewing Wand (ISG, Mississauga, Ontario, Canada) and SPOCS (Aesculap, Germany) in skull base surgery is presented. Having meanwhile been tested in over 60 clinical trials, the systems achieved an accuracy of < or = 2.7 mm which, at the moment, we deem sufficiently acceptable to proceed with their clinical evaluation. There was no difference in intraoperative accuracy between the mechanical and the optical navigation systems. The systems proved to be very helpful in identifying the extent of the tumours and in visualizing the proximity of vital structures. 3-D-planning, simulation and intraoperative navigation especially facilitates surgery in anatomically complicated situations, without risk of damaging neighbouring structures. The SPOCS (Surgical Planning and Orientation Computer System) revealed a considerably improved flexibility in handling and a better integration into the surgical procedure in comparison with the relatively inflexible and space-demanding Viewing Wand arm. Especially, the 'offset' function of the SPOCS offers the possibility of a virtual elongation of the instrument and thus, in combination with the on-line visualization of the corresponding images, of a 'look ahead' operation. By using computer-assisted simulation and navigation systems, we can expect quality improvement and risk reduction. More extensive and radical interventions seem possible.

Virtual otoscopy

Imaging techniques assist the surgeon in diagnosis of disease, surgical planning, and providing image guidance during surgery. Endoscopy has the drawback of being a minimally invasive procedure and limiting visualization to the inner surface of the lumen. Ultrasound, CT, and MR imaging show volumes of tissue beyond the lumen wall; however, their planar, two-dimensional representations require mental reconstruction of anatomic structures, which often proves difficult with the small, complex structures within the temporal bone. To improve three-dimensional visualization of the inner ear, we successfully completed a virtual model that can be displayed as a contiguous, three-dimensional luminal view, known as virtual otoscopy, which emulates traditional endoscopy. A concomitant global view and a view of the related CT slice adds a distinct advantage in the presentation and study of this complex organ. Advances in computer and software technology may overcome the time and cost factors that, at present, limit widespread use of virtual otoscopy. Overall, virtual otoscopy stands as a promising new visualization technique for elucidation of the middle ear, inner ear, and temporal bone structures.

[Robotics in oral and maxillofacial surgery. Possibilities, chances, risks]

Robot systems are being tested in stereotactic neurosurgical interventions, orthopedic surgery of the hip or knee and advancal endoscopic systems for minimally invasive surgery. In contrast to most industrially manufactured products, objects for medical treatment are characterized by plasticity as well as by complex and individual forms. Thus, features of robots in this field have to be further developed in terms of advanced sensory and specific micromotoric systems. Safety and cooperation between surgeon and robot on the patient in the operating room have to be guaranteed. Extensive three-dimensional diagnosis, computer-aided planning and simulation of the intervention as well as sensory systems that monitor the actual performance of the operation are mandatory parts of this concept. In our interdisciplinary study, we aim to examine whether a robot-given a complete preoperative planning and simulation procedure-is able to perform certain surgical operations more precisely than the surgeon. Examples are drilling with depth control, shaping of bone surface by milling, sawing with defined depth in cranial osteotomies, defined preparation of implant sites and the positioning and insertion of dental and other surgical implants, whereby autonomous employment of the robot is not that which is aspired to in these interventions but rather the interactive support of the surgeon.