The evaluation of a novel haptic-enabled virtual reality approach for computer-aided cephalometry
Introduction
Cephalometric analysis is a standard auxiliary diagnostic tool used in oral and maxillofacial surgery. Conventionally it is performed on the 2D lateral radiograph of a patient's head. However, this only represents a composite of the patient's skull on the sagittal plane. Most patients with congenital and acquired cranio-maxillofacial deformities are asymmetric and, as a consequence, the deformity is three-dimensional [1]. Therefore, conventional 2D cephalometry is not ideal for deformity analysis, diagnosis and treatment. It is also time-consuming and with accuracy depending on the specialist's ability to locate landmarks and measure all of the cephalometric variables consistently.
Research suggests that 3D cephalometry has the potential to achieve more precise diagnosis and analysis of cranio-maxillofacial deformities over conventional 2D radiographic approaches [1], [2], [3], [4]. Other work comparing 2D and 3D cephalometry [5], [6], [7], [8], [9], [10], [11] reports that tracing a 3D model is both difficult and time consuming as some landmarks are hard to identify on 3D models. Also, there is no standard set of cephalometric variables or standards that exist for 3D cephalometric measurement and diagnosis. Therefore, new landmark selection methods are required to both improve diagnosis and to facilitate the establishment of new reference norms and standards [12]. The literature also highlights that there is a need to improve modern computer-based interactive cephalometric system usability, user friendliness and intuitiveness to facilitate easier and more accurate 2D and 3D cephalometric analyses.
This research attempts to resolve the issue of providing effective 3D cephalometric analysis through the use of haptic technologies in order to overcome many of the difficulties and disadvantages of current landmarking methods. Using the sense of touch in this way to enhance the user experience could potentially enrich the usability and intuitiveness of cephalometric computer-based systems.
Therefore the aim of this study was to evaluate the feasibility and effectiveness of using haptics in computer-aided cephalometric analysis.
Section snippets
Related work
Key general issues associated with conventional radiographic cephalometric analysis are: (i) errors in manual methods are multi-factorial with low reproducibility; (ii) landmark accuracy is highly dependent on the analyst's experience and knowledge, a key source of error [13]; (iii) some 2D cephalometric analysis variables do not exist in 3D; (iv) 3D projections errors exist when 3D objects are projected onto 2D; (v) most patients are asymmetric and the measurements distorted in the presence of
System description
OSSys (Orthognathic Surgery System) is a haptic-enabled virtual platform designed for planning, simulation and training of orthognathic surgeries. The system architecture (Fig. 1) comprises eight modules, namely: an input data module, a visualization module, a haptic module (handling module), a cephalometric module, an osteotomy module, a surgical template module, a training and evaluation module, and a data export module.
The OSSys system uses the Microsoft Foundation Classes (MFC) of Visual
Haptic-enabled cephalometry
OSSys’ cephalometric module allows haptic-enabled cephalometric analysis in a virtual environment. The user can freely explore and touch the virtual scene and 3D objects via the haptic device and are able to identify and mark the cephalometric points on a 3D model of the patient's skull. Although OSSys has been designed for 3D haptics, the system also supports 2D and 2½D and non-haptic 3D analysis with 2D used by orthognathic surgery medical practitioners in the experiments as a reference point
Evaluation
To evaluate the feasibility and effectiveness of OSSys an experimental methodology incorporating a set of trials and associated metrics was designed, conducted and analyzed as follows: (i) training session, (ii) 2D cephalometry and questionnaire, (iii) 2½D cephalometry and questionnaire, (iv) 3D cephalometry and questionnaire; (v) analysis of results.
Results
The participants performed the OSSys 2D and 3D cephalometric case studies as shown in Fig. 2. The experimental results were analyzed in terms of the cephalometric values and positional errors and then compared with benchmark values achieved by an expert using the traditional manual approach. The results were also analyzed in terms of the average TCT for the three groups, namely: Novice (N), Semi-experts (S) and Experts (E).
The haptic-enabled 2D cephalometry results are given in Table 2 and show
Discussion of results
The TCT to manually complete a conventional 2D cephalometry varies from 10 to 25 min depending on the specialist's experience, the case under consideration and the cephalometric methodology used; however, the OSSys 2D cephalometry achieved an average completion time of less than 2 min. This large reduction in the completion time is associated with the elimination of manual measurements and the rapid calculations carried out by the system.
For the full 3D cephalometry, the average task completion
Conclusions
A novel haptic-based approach to enhance the landmarking selection process in digital cephalometric analysis has been presented and evaluated. This provides the user with a sense of touch while interacting with the virtual environment to identify cephalometric landmarks. The proposed approach was justified in a series of experimental trials involving a range of users. The results demonstrated that a haptic-enabled approach is feasible in 2D, 2½D and 3D environments and that benefits were
Conflict of interest
None declared.
Acknowledgments
This research was supported by CONACYT (National Science and Technology Council of Mexico), research grant CB-2010-01-154430. The second author would like to thank CONACYT for the scholarship during his PhD studies.
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