Virtual otoscopy

Virtual otoscopy for evaluating the inner ear with a fluid-filled tympanic cavity in dogs

The feasibility of virtual otoscopy (VO) imaging was evaluated in five dogs with experimentally induced otitis media, two control dogs, and two canine patients with otitis media. VO images of the tympanic cavity and ossicles were generated with commercially available software using raw computed tomography (CT) data. Eight out of 10 ears inoculated with pathogen exhibited obvious clinical signs associated with otitis externa. CT images revealed soft tissue density material occupying the tympanic bulla compatible with otitis media in three dogs with experimentally induced otitis media and two patients. No remarkable features were observed on the radiographs. Four different VO views (ear canal, tympanic bulla, eustachian tube, and ossicular chain) were created. Promontory, cochlea window, tympanic, and septum bulla as well as ossicles were easily and clearly distinguished except for the incus and stapes of the clinical patients. VO images were not more suitable than images created with conventional CT for accurately diagnosing otitis media in this study. However, it appears that VO could be more feasible for assessing the complex structure of the inner ear in dogs with fluid-filled tympanic cavities since fluid accumulation within the tympanic bulla did not affect the evaluation of bony tissue in the middle ear on VO images.

Virtual endoscopic imaging of the spine

STUDY DESIGN

Prospective trial of virtual endoscopy in spinal surgery.

OBJECTIVE

To investigate the utility of virtual endoscopy of the spine in conjunction with spinal surgery.

SUMMARY OF BACKGROUND DATA

Several studies have described clinical applications of virtual endoscopy to visualize the inside of the bronchi, paranasal sinus, stomach, small intestine, pancreatic duct, and bile duct, but, to date, no study has described the use of virtual endoscopy in the spine.

METHODS

Virtual endoscopy is a realistic 3-dimensional intraluminal simulation of tubular structures that is generated by postprocessing of computed tomographic data sets. Five patients with spinal disease were selected: 2 patients with degenerative disease, 2 patients with spinal deformity, and 1 patient with spinal injury.

RESULTS

Virtual endoscopy software allows an observer to explore the spinal canal with a mouse, using multislice computed tomographic data. Our study found that virtual endoscopy of the spine has advantages compared with standard imaging methods because surgeons can noninvasively explore the spinal canal in all directions.

CONCLUSION

Virtual endoscopy of the spine may be useful to surgeons for diagnosis, preoperative planning, and postoperative assessment by obviating the need to mentally construct a 3-dimensional picture of the spinal canal from 2-dimensional computed tomographic scans.

Is virtual endoscopy of the middle ear useful?

Virtual endoscopy is a relatively new imaging technology in otology, and therefore data on its efficacy in clinical situations are limited. We conducted a prospective study to evaluate the clinical relevance of radiologic diagnoses based on virtual endoscopy of the middle ear. Our patient population was made up of 30 adults who were scheduled to undergo surgery to correct conductive hearing loss of unknown etiology. Virtual endoscopy was performed on three-dimensional images that were constructed from images obtained with conventional two-dimensional computed tomography (CT). Findings on virtual endoscopy were then compared with the subsequent surgical findings. Virtual endoscopy suggested a middle ear pathology in 19 patients and a normal middle ear in 11 patients. Postoperatively, we found that the virtual diagnoses correlated moderately well with the surgical findings in the group of patients with predicted pathology; 13 of these 19 patients were found to have middle ear problems such as ossicular chain anomalies, otosclerosis, and cholesteatoma (positive predictive value: 68%). However, among the 11 patients whose middle ear structures were radiologically predicted to be normal, only 2 had negative middle ear findings on surgical exploration; of the remaining 9 patients, 8 had otosclerosis and 1 had malleus fixation (negative predictive value: 18%). Thus, the sensitivity and specificity of virtual endoscopy were 59 and 25%, respectively. Virtual endoscopy provides images from a surgeon's perspective, and so it has the potential to be useful in the preoperative evaluation of the middle ear cavity. With ongoing advancements in computer systems and imaging techniques, the cost, reliability, and efficacy of virtual endoscopy may improve. However, further clinical validation and cost-benefit analysis are required before we can determine if it has any additional advantages over conventional two-dimensional CT.

Interactive computer-based simulator for training in blade navigation and targeting in myringotomy

A virtual-reality simulator was developed for the training of Otolaryngology (Ear-Nose-Throat) surgical residents to perform myringotomy, a relatively common surgical procedure in which an incision is made in the eardrum mainly to treat middle-ear infections. The simulator presents the trainee with a three-dimensional (3D) virtual model of the ear that can be viewed through a mock surgical microscope consisting of a stereo visor mounted on a custom-designed stand. The trainee interacts with the virtual ear using a real myringotomy blade, the movements of which are tracked in real time using a stereo optical tracker. Interactions of the blade with virtual tissues are calculated and rendered on the visor using freely available physics and graphics software engines. Six experienced surgical residents and surgeons assessed the effectiveness of the simulator as a viable training tool by completing a questionnaire designed specifically for this study after using the simulator. Surgeons and residents were positively impressed by the simulator as a training tool and would recommend its use as part of training.

Is there a role for virtual otoscopy in the preoperative assessment of the ossicular chain in chronic suppurative otitis media? Comparison of HRCT and virtual otoscopy with surgical findings

The aim of this study was to assess the role of virtual otoscopy and 3D ossicular reconstruction in the preoperative assessment of the ossicles in chronic suppurative otitis media. Thirty three patients of chronic suppurative otitis media with conductive deafness (air-bone gap > 35 dB) were included in this prospective study. All patients underwent axial multidetector CT. The axial CT data set was utilized for multiplanar 2D reformations as well as virtual otoscopy (VO) and 3D reconstructions. The imaging findings on these two techniques were read independently by two radiologists with respect to different parts of the ossicular chain by using a three-point scoring system and were compared with surgical findings. Both imaging techniques had comparable accuracy for evaluation of larger ossicular parts. However, for evaluation of stapes superstructure, VO/3D images were more accurate (85.29%) than 2D images (76.97%). Assessment of the lenticular process and incudostapedial joint by HRCT and 2D reformatted images was not reliable (P > 0.1); however, significant correlation (P < 0.001) was present between VO/3D and the operative findings. Virtual otoscopy improves evaluation of the ossicular chain particularly that of smaller structures such as the lenticular process, incudostapedial joint and stapes superstructure which may influence decisions regarding planning of ossiculoplasty.

Pathology of the ossicular chain: comparison between virtual endoscopy and 2D spiral CT-data

OBJECTIVE

The purpose of this study was to assess the value of virtual endoscopy (VE) in the diagnosis of lesions of the ossicular chain and to compare virtual endoscopy and two-dimensional (2D) spiral computed tomography (CT) data.

STUDY DESIGN

Retrospective study.

SETTING

A university hospital.

PATIENTS

Fifty-eight patients with suspected ossicular chain lesions underwent a high-resolution CT of the temporal bone with both 2D data and VE before surgery.

MAIN OUTCOME MEASURES

Two views were chosen for VE. The CT data obtained (2D, VE, and both 2D and VE) were compared with the lesions noted during surgery.

RESULTS

In the diagnosis of dislocation of the ossicles or prostheses, VE seemed to be a better technique than 2D CT. Views chosen for the VE proved to be ineffective for diagnosing epitympanic fixations. VE was not adapted to the study of otosclerosis. We found it necessary to use the data provided by the addition to 2D CT data in the diagnosis of ossicular lysis and minor aplasia. Radiologic analysis of the lesions of the long process of the incus and the incudostapedial joint was improved by performing both 2D CT and VE. VE reconstruction of the stapes proved to be difficult, especially in cases of inflammation of the middle ear.

CONCLUSION

This study demonstrates the value of VE in the diagnosis of dislocation of the ossicles and ossicular prostheses. VE was less effective in diagnosing other pathologies of the ossicular chain.

Visualization of the temporal bone of the Chinese Visible Human

Temporal bone anatomy is very difficult to understand. After dataset acquisition of the first Chinese Visible Human, we processed the two-dimensional images to build a digitized visible model of the temporal bone and explore the role of virtual endoscopy in the inner ear. On a SGI workstation three-dimensional computer reconstructions of the ear were generated from the Chinese visible human dataset, viewing the middle and inner ear imitating the traditional otoscopy. The three-dimensional data of the temporal bone were then converted to STL format, and the temporal bone replica were fabricated with rapid prototyping by laminated object manufacturing. The virtual model of the ear was successfully completed, and the virtual endoscopy improved three-dimensional visualization of the middle and inner ear. Physical replica of the temporal bone were built with paper; the accuracy was +/-0.2 mm. The reconstructed model and the replica of the temporal bone can be used to make preoperative plans in the complicated otoneurosurgical operations, allowing various surgical exercises to be carried out on the three-dimensional stereophysical model. The virtual endoscopy stands as a promising new visualization technique for elucidation of the middle and inner ear and reveals a tremendous potential in both clinical and educational settings, providing morphological data for the image diagnosis and otoneurosurgery.

Evaluation of the internal auditory canal with virtual endoscopy

OBJECTIVE

Three-dimensional imaging can improve the understanding and comprehension of complex anatomy. Recent advances in software development allow the construction of a virtual endoscopic view of anatomic structures. This report applies virtual endoscopic capabilities to imaging of the internal auditory canal.

STUDY DESIGN, SETTING, AND PATIENTS

We conducted a retrospective case review at a tertiary referral center of patients with abnormal internal auditory canal anatomy on computed tomography.

INTERVENTIONS

Computed tomography images were obtained using conventional clinical algorithms involving multiple, 1-mm-thick slices through the temporal bone. Three-dimensional reconstructions were made using General Electric Advantage Windows Navigator software. The virtual endoscopic image-processing algorithm used selected image intensity threshold levels to visualize internal auditory canal anatomy from an endoscopic perspective.

RESULTS

Eleven cases of abnormalities of the internal auditory canal were retrospectively identified. Clinical applications using the virtual endoscopic images are presented. The virtual endoscopic images supported prior clinical decision making in 6 of the 11 cases evaluated.

CONCLUSION

This technique shows promise for the diagnosis, surgical planning, and teaching of temporal bone anatomy. Usefulness is dependent on acquisition parameters and clinical indications for examination.

Technical innovation of cardiac multirow detector CT using multisector reconstruction

Multisector reconstruction is a newly developed algorithm for multirow detector CT in cardiac study. Using volume data sets obtained by ECG-gated scanning, we can reconstruct cardiac images at any desired phase of the cardiac cycle retrospectively. In retro-processing multiplanar and three-dimensional images, thin-slice images with overlapping increment have a great advantage due to increasing z-axis resolution. In this article, we present principles of the algorithm, a phantom study, clinical applications and perspectives for the future.

Usefulness of virtual endoscopic three-dimensional reconstructions of the middle ear

This work uses a new programme for producing 3D radiological images acquired by means of CT which enables the internal surfaces of the examined structures to be visualized. This new method, which is able to navigate inside organs in a similar way to fibreoptic endoscopy, is known as virtual endoscopy. CT examinations of the temporal bone were carried out using spiral equipment and endoscopic 3D processing was carried out on a separate workstation equipped with a volume-rendering programme. Once the technical parameters necessary for obtaining a representation of the internal surfaces had been defined, a simulation of a virtual otoscopy was conducted by moving the virtual endoscope from the external auditory canal through the annulus to the tympanic cavity. The simulation can be obtained either by moving the endoscope by hand, using the mouse, or by defining a path along which the software automatically creates an endoscopic 3D reconstruction. The images thus obtained are projected sequentially to give a "movie" effect, i.e. a continuous progression of the endoscope. The average time required to conduct the procedure ranges from 20 to 30 min. A virtual endoscopic visualization of the middle ear was obtained which, in particular, generated images of the tympanic cavity with the ossicular chain. In our experience, virtual otoscopy shows the anatomy of the structures of the tympanic cavity in excellent detail and may be considered complementary to CT, providing useful images enabling better visual representation and understanding of this complex structure. Although clinical applications of the technique remain to be defined it may have a role to play in presurgical diagnostic evaluation of the ossicular chain, epitympanum and retrotympanum.

Virtual endoscopy of the tympanic cavity based on high-resolution multislice computed tomographic data

OBJECTIVE

This study was designed to assess the value of high-resolution multislice computed tomography (MSCT) data of the petrous bone for the virtual endoscopic visualization of the tympanic cavity.

BACKGROUND

The recently introduced MSCT technology has improved spatial resolution in the z axis as well as scan speed in computed tomography. Three-dimensional rendering of high-resolution MSCT data of the petrous bone may be expected to provide endoluminal views of superior image quality, thus competing with transtympanic endoscopy (otoendoscopy).

SETTING

This study was conducted at a university teaching hospital.

MATERIALS AND METHODS

Cadaveric phantom studies in a MSCT scanner were performed to define a data acquisition protocol, combining adequate detail resolution with low tube current. Subsequently, the cadaveric phantom underwent otoendoscopy. The postprocessing parameters of the three-dimensional rendering protocol were chosen to produce views closely resembling the corresponding otoendoscopic images. High-resolution data from 18 patients with pathologic conditions of the middle ear, as suggested by clinical findings and assessment of cross-sectional data, were postprocessed using the volume rendering technique to generate standardized virtual endoscopic views. A total of 36 virtual endoscopic scans of the tympanic cavity were generated.

RESULTS

With regard to intermediate and high-density structures, virtual endoscopic images, based on MSCT data, yielded endoluminal views closely resembling corresponding otoendoscopic views. Virtual endoscopy seems useful for imaging ossicular pathologic conditions such as dysplasia and chain disruption as well as for assessing patient status before and after otosurgery.

CONCLUSION

MSCT data sets allow for generating virtual endoscopic views closely resembling otoendoscopic images. The technique is especially useful when ossicular pathologic changes are present as well as for preoperative and postoperative imaging of otologic procedures.

Virtual endoscopic evaluation of labyrinthine fistulae resulting from cholesteatoma

OBJECTIVES/HYPOTHESIS

Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is valuable in limiting intraoperative morbidity. Three-dimensional virtual endoscopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the feasibility and efficacy of this technique in detecting labyrinthine fistulae caused by cholesteatoma.

STUDY DESIGN

Retrospective case study.

METHODS

Fifteen patients with surgically confirmed lateral semicircular canal fistula and preoperative CT scan were included. Scans meeting inclusion criteria were imported into a software program for production of virtual endoscopic images. Dehiscent and normal lateral semicircular canals were navigated while varying threshold values for surrounding bone. Changes in threshold values produce the effect of thickening or thinning the bone enveloping the semicircular canal. Threshold parameters that produced easy circumnavigation ("open") and intact inner surface of the lateral canal ("closed") were recorded.

RESULTS

The fistula group demonstrated a significantly lower "closed" threshold level and, consequently, a greater range of navigation between "open" and "closed" thresholds. Intrasubject absolute differences in threshold values between normal and abnormal ears appeared to be the most accurate method for detecting a fistula. The suggested imaging parameters displayed an overall sensitivity for fistula detection of 67% with a specificity of 93%.

CONCLUSIONS

The three-dimensional virtual endoscopic algorithm shows promise as a method for confirmation of otic capsule dehiscences. Sensitivity for detection is suboptimal but can be improved by alterations in image acquisition parameters.

Virtual CT endoscopy of ossicles in the middle ear

The purpose of this study is to evaluate how virtual computed tomography (CT) endoscopy may help in assessing ossicles in the middle ear. Our series consisted of 96 ears of 68 consecutive patients with conducting hearing loss. All examinations were performed with a high-resolution spiral CT using axial and direct coronal planes of the temporal bone. Perspective virtual endoscopy was processed using the virtual endoscopic software. Superstructure of the stapes was difficult to evaluate on the virtual endoscopy; however, virtual endoscopy of the middle ear provides further information on the pathological conditions including congenital anomaly, posttraumatic, and inflammatory processes.

Virtual endoscopy of the labyrinth, using a 3D-FastASE sequence

Virtual endoscopy (VE) of the labyrinth was performed using three-dimensional (3D)-fast asymmetric spin-echo MR imaging. The spatial resolution requirements and the usefulness of zero-fill interpolation (ZIP) were evaluated, and VE was used to examine three patients. The (0.6-mm) voxel data with ZIP satisfies the minimum requirements for VE for evaluation of the complex 3D anatomy and pathology of the labyrinth. J. Magn. Reson. Imaging 2001;13:792-796.

Virtual endoscopy

Virtual endoscopy is a technique in which three-dimensional viewing of hollow structures is conducted through the utilization of high-resolution imaging and unique computer processing methods. The basic components of this technique and its applications for urology and other clinical disciplines are reviewed.

Computer-aided surgical planning for implantation of hearing aids based on CT data in a VR environment

A study was undertaken to assess the feasibility of a preoperative fitting test for an implantable hearing aid in a virtual reality (VR) environment. High-resolution spiral computed tomography (CT) of the mastoid bone was performed, and the results of a mastoidectomy were simulated with manual segmentation on a standard medical workstation. CT was also performed on a temporal bone specimen obtained at real mastoidectomy, and the bone margins were segmented automatically with threshold-based techniques. A triangulated surface representation of the bone structures including the mastoid cavity was generated. These data as well as the computer-aided design (CAD) files of the medical devices were transferred into a VR environment. The CAD components of the hearing aid were manipulated to simulate the surgical implantation procedure. Merging CAD data of an implantable hearing aid with CT data of the temporal bone in a VR environment was shown to be a feasible method of providing three-dimensional information for the presurgical determination of fit and mountability. Advances in hardware and software are expected to improve the usability of this method. Although clinical studies are needed, these results may serve as an impetus for exploring the use of low-cost, widely available VR computer equipment in a potentially broad field of clinical applications.

MRI of the inner ear: comparison of axial T2-weighted, three-dimensional turbo spin-echo images, maximum-intensity projections, and volume rendering

RATIONALE AND OBJECTIVES

To compare the ability of axial T2-weighted, three-dimensional, turbo spin-echo (3D TSE) images, targeted maximum-intensity projections (MIPs), and 3D volume reconstructions to depict anatomic details of the labyrinth.

METHODS

In 24 volunteers, 3D TSE images were obtained. MIPs and 3D volume reconstructions were performed from the acquired data. All images were evaluated by three radiologists independently regarding the visualization of the different anatomic structures.

RESULTS

In the axial slices, most anatomic details were visible in comparison with observations by the other modalities. The 2.5 windings of the cochlea were best depicted on the MIPs. Volume reconstructions rendered excellent spatial information regarding the vestibule and semicircular canals and were the only technique that demonstrated all three ampullae in all cases.

CONCLUSIONS

Axial TSE images, MIPs, and 3D volume reconstructions are complementary modalities that provide different information. Our results suggest that improved diagnostic information can be obtained by applying these volume visualization reconstruction techniques.

Virtual labyrinthoscopy: visualization of the inner ear with interactive direct volume rendering

Computed tomography (CT) is the modality of choice for detailed imaging of the bony labyrinth. Usually, information about the complex three-dimensional anatomic structures of the inner ear is presented as two-dimensional section images. Interactive direct volume rendering is a powerful method for visualization of the labyrinth. Unlike other visualization methods, direct volume rendering enables direct visualization of the bony labyrinth without explicit segmentation prior to the visualization process. Direct volume rendering was applied to visualization of the structures of the temporal bone in five patients without pathologic conditions and four patients with pathologic conditions. In all cases, clear representations of the bony labyrinth and the facial canal were provided. Because standard CT examinations combined with interactive visualization based on direct volume rendering are used, the method is fast and flexible. Therefore, this approach is applicable in routine clinical work. Problems occur in patients with effusion in the temporal bone because adjustment of imaging parameters for proper delineation of the target structures is difficult in this situation. However, direct volume rendering can produce meaningful images of high quality even in these problematic cases. The term virtual labyrinthoscopy is suggested for visualization of the labyrinth by using direct volume rendering.

Head and neck computed tomography virtual endoscopy: evaluation of a new imaging technique

OBJECTIVE

To evaluate a new radiographic imaging technique: computed tomography virtual endoscopy (CTVE) for head and neck tumors.

STUDY DESIGN

Twenty-one patients presenting with head and neck masses who underwent axial computed tomography (CT) scan with contrast were evaluated by CTVE. Comparisons were made with video-recorded images and operative records to evaluate the potential utility of this new imaging technique.

METHODS

Twenty-one patients with aerodigestive head and neck tumors were evaluated by CTVE. One patient had a nasal cylindrical cell papilloma; the remainder, squamous cell carcinomas distributed throughout the upper aerodigestive tract. Patients underwent complete head and neck examination, flexible laryngoscopy, axial CT with contrast, CTVE, and in most cases, operative endoscopy. Available clinical and radiographic evaluations were compared and correlated to CTVE findings.

RESULTS

CTVE accurately demonstrated abnormalities caused by intraluminal tumor, but where there was apposition of normal tissue against tumor, inaccurate depictions of surface contour occurred. Contour resolution was limited, and mucosal irregularity could not be defined. There was very good overall correlation between virtual images, flexible laryngoscopic findings, rigid endoscopy, and operative evaluation in cases where oncological resections were performed. CTVE appears to be most accurate in evaluation of subglottic and nasopharyngeal anatomy in our series of patients.

CONCLUSION

CTVE is a new radiographic technique that provides surface-contour details. The technique is undergoing rapid technical evolution, and although the image quality is limited in situations where there is apposition of tissue folds, there are a number of potential applications for this new imaging technique.

Virtual CT intravascular endoscopy of the aorta: pierced surface and floating shape thresholding artifacts

Two types of artifacts may appear in virtual computed tomographic endoscopic views of the aorta rendered at different threshold levels: pierced surface and floating shape artifacts. A positive correlation was found between mean attenuation of the aorta and the threshold levels at which these artifacts appeared. The correlation was statistically significant (0.71 < or = r < or = 0.86) for floating shape. An artifact-free threshold range can be predicted on the basis of aortic enhancement.

Virtual laryngoscopy

Virtual endoscopy enables computer-generated 3-dimensional visualization of a cavity by reconstructing 2-dimensional computed tomographic or magnetic resonance data. The technique has been used experimentally to study the colon, bronchi, ears, and other structures. Here, virtual laryngoscopies were created from the cross-sectional image data of 3 patients. The cases represented a normal airway, a squamous cell carcinoma of the glottic fold, and a posterior glottic stenosis. These reconstructions included extraluminal anatomy that is not typical of current virtual endoscopic techniques. The 2-dimensional computed tomographic and magnetic resonance images of the patients underwent post-processing for 3-dimensional reconstruction. The resulting models were imported into an experimental virtual endoscopy program for 1) airway lumen generation and 2) interactive viewing. Though they could not be used for biopsy, the virtual laryngoscopies provided, in a noninvasive fashion, good simulation of endoscopy. Virtual endoscopy also gave the added benefits of the ability to assess the transmural extent of disease and view the airway distal to areas of luminal compromise. This technology may well provide clinical benefit in preoperative planning, staging, and intraprocedural guidance for head and neck disease and merits further study.

Computer-assisted three-dimensional reconstruction of head and neck tumors

OBJECTIVE

Because head and neck tumors reside in a complex area, having a three-dimensional (3-D) model of the patient's unique anatomical features may assist in the delineation of pathology. The authors describe a new computer technique of 3-D anatomical reconstruction from two-dimensional computed tomography (CT) and magnetic resonance (MR) data and discuss how it represents a step forward in the continuing evolution of 3-D imaging.

STUDY DESIGN

The authors selected three patients with solitary head and neck tumors and reconstructed their anatomy in a 3-D format for study. The tumors represented locations in the nose and central skull base (patient 1), temporal bone (patient 2), and neck (patient 3).

MATERIALS AND METHODS

MR and CT images from the individual patients were electronically transferred to workstations in the Surgical Planning Laboratory of the authors' institution. Registration (or fusion) was carried out between the MR and CT images. The desired anatomic components underwent segmentation (identification and isolation). Assembly of the segmented images was performed and the resulting structures were integrated to produce a 3-D model.

RESULTS

3-D models of the following were constructed and displayed in an interactive format on high-capacity computer workstations: 1) a skull base sarcoma with extension into the nasopharynx and nose; 2) an acoustic neuroma with internal auditory canal involvement; and 3) a metastatic recurrence of a tongue base squamous cell carcinoma in the posterior triangle of the right side of the neck with extension to the skull base.

CONCLUSION

The authors' Surgical Planning Laboratory has developed a 3-D reconstruction technique that has several new features. The models provided a very good 3-D interactive representation of the tumors and patient anatomy. The need now exists to develop this method of 3-D reconstruction of head and neck tumors for potential applications in treatment, research, and medical education.