Three-dimensional localization of cochlear implant electrodes using epipolar stereophotogrammetry

Biomechanical Morphing for Personalized Fitting of Scoliotic Torso Skeleton Models

The use of patient-specific biomechanical models offers many opportunities in the treatment of adolescent idiopathic scoliosis, such as the design of personalized braces. The first step in the development of these patient-specific models is to fit the geometry of the torso skeleton to the patient’s anatomy. However, existing methods rely on high-quality imaging data. The exposure to radiation of these methods limits their applicability for regular monitoring of patients. We present a method to fit personalized models of the torso skeleton that takes as input biplanar low-dose radiographs. The method morphs a template to fit annotated points on visible portions of the spine, and it relies on a default biomechanical model of the torso for regularization and robust fitting of hardly visible parts of the torso skeleton, such as the rib cage. The proposed method provides an accurate and robust solution to obtain personalized models of the torso skeleton, which can be adopted as part of regular management of scoliosis patients. We have evaluated the method on ten young patients who participated in our study. We have analyzed and compared clinical metrics on the spine and the full torso skeleton, and we have found that the accuracy of the method is at least comparable to other methods that require more demanding imaging methods, while it offers superior robustness to artifacts such as interpenetration of ribs. Normal-dose X-rays were available for one of the patients, and for the other nine we acquired low-dose X-rays, allowing us to validate that the accuracy of the method persisted under less invasive imaging modalities.

Femoral neck anteversion measurement using linear slot scanning radiography

Measurements between anatomical landmarks on radiographs are useful for diagnosis and treatment planning in the orthopedic field. Direct measurement on single radiographic images, however, does not truly reflect spatial relationships, as depth information is lost. We used stereo images from a slot scanning X-ray machine to estimate coordinates of three-dimensional (3D) bony landmarks for femoral neck anteversion (FNA) measurement. A set of 7 landmarks consisting of the centre of the femoral head; the centre of the base of the femoral neck; the medial and lateral condyles; the medial and lateral posterior condyles; and finally the centre of the knee; were found to be identifiable and suitable for radiographic measurement. The reconstructed 3D coordinates were then used to define the 3D geometry of the anatomical axes required to estimate FNA. Stereophotogrammetric measurements on a sample of 30 dry right adult femurs were compared to reference values obtained using the Kingsley Olmstead method applied to photographic images. A strong positive correlation (0.998) was found and the mean ± standard deviation of the stereophotogrammetric approach (13.08 ± 6.87)° was comparable to that of the Kingsley Olmstead method (13.14 ± 6.88)°. Intra- and inter-observer reliability were high, with the lower bound of the 95% confidence interval above 0.98 for the intra-class correlation coefficient. The results merit further validation against three dimensional imaging technology such as computed tomography, to confirm stereophotogrammetry as a suitable alternative for FNA measurement.

Three-dimensional models of cochlear implants: A review of their development and how they could support management and maintenance of cochlear implant performance

Three-dimensional (3D) computational modeling of the auditory periphery forms an integral part of modern-day research in cochlear implants (CIs). These models consist of a volume conduction description of implanted stimulation electrodes and the current distribution around these, coupled with auditory nerve fiber models. Cochlear neural activation patterns can then be predicted for a given input stimulus. The objective of this article is to present the context of 3D modeling within the field of CIs, the different models, and approaches to models that have been developed over the years, as well as the applications and potential applications of these models. The process of development of 3D models is discussed, and the article places specific emphasis on the complementary roles of generic models and user-specific models, as the latter is important for translation of these models into clinical application.

High-resolution in situ imaging of cochlear implant electrode arrays in cat temporal bones using Tuned Aperture Computed Tomography (TACT)

OBJECTIVE

To determine the suitability of Tuned Aperture Computed Tomography (TACT) to generate high-resolution images of intracochlear electrode arrays, in situ, with sufficient anatomic and electrode detail to relate the location of individual electrode contacts to important anatomic landmarks in cat cadaveric temporal bones. The ultimate objective is to develop an imaging technology whereby variations in electrode location, relative to the target neural tissues, can be accurately determined and related to variations in performance with the cochlear implant.

DESIGN

Cat temporal bones were implanted with an experimental scala tympani electrode array and an external fiducial landmark. A series of conventional 2D digital radiographs were collected from a variety of x-ray source projection angles and served as for generation of 3D volume renderings using the TACT software toolbox. The 3D renderings were then reoriented and resliced interactively to view the cochlear and electrode features of interest.

RESULTS

Significant electrode and anatomical details could be visualized including the course of the electrode wires (<40 microm diameter), the location of all electrode contacts and the outline of the scala tympani.

CONCLUSIONS

TACT generates high-resolution 3D images from 2D conventional radiographs. With TACT, the 3D renderings can be interactively reoriented and resectioned to permit visualization of any cochlear or electrode feature. In the present study, this aspect of TACT affords the opportunity to view of the location of each electrode contact relative to the adjacent cochlear features, such as the scalar walls. Because TACT uses conventional radiographic images to generate the volume renderings, the quality and resolution of the resulting 2D images do not suffer from artifacts characteristic of CT. These findings suggest that TACT may be a powerful tool for understanding the contribution of electrode placement to perceptual performance with the cochlear implant.

Three-Dimensional Modeling From Endoscopic Video Using Geometric Constraints Via Feature Positioning

The endoscope is a popular imaging modality used in many preevaluations and surgical treatments, and is also one of the essential tools in minimally invasive surgery. However, regular endoscopes provide only 2-D images. Even though stereoendoscopy systems can display 3-D images, the real anatomical structure of the observed lesion is unavailable and can only be judged by the surgeon's imagination. In this paper, we present a constraint-based factorization method for reconstructing 3-D structures registered to the patient, from 2-D endoscopic images. The proposed method incorporates the geometric constraints from the tracked surgical instrument into the traditional factorization method based on frame-to-frame feature motion on the endoscopically viewed scene. Experiments with real and synthetic data demonstrate good real-scale 3-D extraction, with greater accuracy than is available from traditional methods. The reconstruction process can also be accomplished in a few seconds, making it suitable for on-line surgical applications to provide surgeons with additional 3-D shape information, critical distance monitoring and warnings.