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

Anatomical Variations of the Epitympanum and the Usable Space for Middle Ear Implants Analyzed With CT-assisted Imaging Using a Tablet-based Software

OBJECTIVE

To evaluate interindividual anatomical variations of the epitympanum and the usable space for implantation of active middle ear implants (AMEI) as well as the usefulness of a tablet-based software to assess individual anatomy on computed tomography (CT) scans.

PATIENTS

CT scans of 126 patients, scheduled for cochlea implantation (50.8% men; 0.6-90.0 yr) without middle ear malformations or previous middle ear surgery and with slice thickness ≤0.7 mm were analyzed.

MAIN OUTCOME MEASURES

Since no standardized measurements to assess the size of the epitympanum are available, relevant distances were defined according to anatomical landmarks. Three independent raters measured these distances using a tablet-based software. Interrater correlation was computed to evaluate the quality of the measurement process. Descriptive data were analyzed for validation and for evaluation of interindividual anatomical variations. Influence of age and sex on the taken measurements was assessed.

RESULTS

No relevant correlation between age or sex and the anatomy of the epitympanum was found. Interrater correlation ranged from Spearman's ρ = 0.3-0.9 and there were significant differences between individual rater results for various combinations. Descriptive data revealed high interindividual anatomical variance of the epitympanum, especially regarding the distance between incus and skull base.

CONCLUSION

The reported descriptive data regarding the anatomy of the epitympanum emphasizes the importance of preoperative planning, especially since the height of the epitympanum showed great interindividual variance potentially limiting implantation of AMEIs. The herein used tablet-based software seems to be convenient for preoperative assessment of individual anatomy in the hand of otosurgeons.

Comparative use of the computer-aided angiography and rapid prototyping technology versus conventional imaging in the management of the Tile C pelvic fractures

INTRODUCTION

Computed tomography (CT) scan with three-dimensional (3D) reconstruction has been used to evaluate complex fractures in pre-operative planning. In this study, rapid prototyping of a life-size model based on 3D reconstructions including bone and vessel was applied to evaluate the feasibility and prospect of these new technologies in surgical therapy of Tile C pelvic fractures by observing intra- and perioperative outcomes.

MATERIALS AND METHODS

The authors conducted a retrospective study on a group of 157 consecutive patients with Tile C pelvic fractures. Seventy-six patients were treated with conventional pre-operative preparation (A group) and 81 patients were treated with the help of computer-aided angiography and rapid prototyping technology (B group). Assessment of the two groups considered the following perioperative parameters: length of surgical procedure, intra-operative complications, intra- and postoperative blood loss, postoperative pain, postoperative nausea and vomiting (PONV), length of stay, and type of discharge.

RESULTS

The two groups were homogeneous when compared in relation to mean age, sex, body weight, injury severity score, associated injuries and pelvic fracture severity score. Group B was performed in less time (105 ± 19 minutes vs. 122 ± 23 minutes) and blood loss (31.0 ± 8.2 g/L vs. 36.2 ± 7.4 g/L) compared with group A. Patients in group B experienced less pain (2.5 ± 2.3 NRS score vs. 2.8 ± 2.0 NRS score), and PONV affected only 8 % versus 10 % of cases. Times to discharge were shorter (7.8 ± 2.0 days vs. 10.2 ± 3.1 days) in group B, and most of patients were discharged to home.

CONCLUSIONS

In our study, patients of Tile C pelvic fractures treated with computer-aided angiography and rapid prototyping technology had a better perioperative outcome than patients treated with conventional pre-operative preparation. Further studies are necessary to investigate the advantages in terms of clinical results in the short and long run.

Measurement error of 3D cranial landmarks of an ontogenetic sample using Computed Tomography

BACKGROUND/AIM

Computed Tomography (CT) is a powerful tool in craniofacial research that focuses on morphological variation. In this field, an ontogenetic approach has been taken to study the developmental sources of variation and to understand the basis of morphological evolution. This work aimed to determine measurement error (ME) in cranial CT in diverse developmental stages and to characterize how this error relates to different types of landmarks.

MATERIAL AND METHODS

We used a sample of fifteen skulls ranging from 0 to 31 years. Two observers placed landmarks in each image three times. Measurement error was assessed before and after Generalized Procrustes Analysis.

RESULTS

The results indicated that ME is larger in neurocranial structures, which are described mainly by type III landmarks and semilandmarks. In addition, adult and infant specimens showed the same level of ME. These results are specially relevant in the context of craniofacial growth research.

CONCLUSION

CT images have become a frequent evidence to study cranial variation. Evaluation of ME gives insight into the potential source of error in interpreting results. Neural structures present higher ME which is mainly associated to landmark localization. However, this error is irrespective of age. If landmarks are correctly selected, they can be analyzed with the same level of reliability in adults and subadults.

Computer-assisted virtual surgical procedure for acetabular fractures based on real CT data

OBJECTIVE

To develop and evaluate a computer-assisted virtual surgical procedure for preoperative planning that simulates the reduction and plate fixation for acetabular fractures based on real computed tomography (CT) data using computer softwares on personal computers.

METHODS

Virtual preoperative planning for reduction and plate fixation for seven acetabular fractures was performed. Three-dimensional (3D) models of acetabular fractures based on real CT data in Dicom format were built to perform reduction first. Then fixation was undertaken after plate contouring. Virtual planning was compared with real surgery with respect to operative approach, plate length and screw count. Furthermore, the time required for virtual surgery was recorded.

RESULTS

Virtual surgery was successfully achieved and identical to the real operation in all cases. The mean time required was 79 min.

CONCLUSION

The virtual surgical procedure for acetabular fractures is feasible and useful clinically for surgeons to determine surgical planning. It may be a valuable tool for surgeons in learning about the nature of the fracture and in formulating an appropriate surgical plan.

Effect of a virtual reality interface on the learning curve and on the accuracy of a surgical planner for total hip replacement

The aim of this study is to evaluate the performance of a non-conventional input and output device (virtual reality) in a total hip replacement surgical planner. A test was performed asking five users to position a cup in a defined position. Every user performed the task using three different hardware configurations: (I) conventional mouse and monitor, (II) mouse and auto-stereoscopic monitor, and (III) 12-DOF tracker (haptic device) and auto-stereoscopic monitor. The results were evaluated in terms of root mean square error of the obtained position with respect to the target one and in terms of learning curve. The results showed that the examined VR technology does not show a sufficient positioning accuracy to be considered for clinical assessment.

Mastoid cavity dimensions and shape: method of measurement and virtual fitting of implantable devices

Temporal bone implants can be used to electrically stimulate the auditory nerve, to amplify sound, to deliver drugs to the inner ear and potentially for other future applications. The implants require storage space and access to the middle or inner ears. The most acceptable space is the cavity created by a canal wall up mastoidectomy. Detailed knowledge of the available space for implantation and pathways to access the middle and inner ears is necessary for the design of implants and successful implantation. Based on temporal bone CT scans a method for three-dimensional reconstruction of a virtual canal wall up mastoidectomy space is described. Using Amira software the area to be removed during such surgery is marked on axial CT slices, and a three-dimensional model of that space is created. The average volume of 31 reconstructed models is 12.6 cm(3) with standard deviation of 3.69 cm(3), ranging from 7.97 to 23.25 cm(3). Critical distances were measured directly from the model and their averages were calculated: height 3.69 cm, depth 2.43 cm, length above the external auditory canal (EAC) 4.45 cm and length posterior to EAC 3.16 cm. These linear measurements did not correlate well with volume measurements. The shape of the models was variable to a significant extent making the prediction of successful implantation for a given design based on linear and volumetric measurement unreliable. Hence, to assure successful implantation, preoperative assessment should include a virtual fitting of an implant into the intended storage space. The above-mentioned three-dimensional models were exported from Amira to a Solidworks application where virtual fitting was performed. Our results are compared to other temporal bone implant virtual fitting studies. Virtual fitting has been suggested for other human applications.

Anatomical study of the human middle ear for the design of implantable hearing aids

OBJECTIVE

To generate anatomical data on the human middle ear and adjacent structures to serve as a base for the development and optimization of new implantable hearing aid transducers. Implantable middle ear hearing aid transducers, i.e. the equivalent to the loudspeaker in conventional hearing aids, should ideally fit into the majority of adult middle ears and should utilize the limited space optimally to achieve sufficiently high maximal output levels. For several designs, more anatomical data are needed.

METHODS

Twenty temporal bones of 10 formalin-fixed adult human heads were scanned by a computed tomography system (CT) using a slide thickness of 0.63 mm. Twelve landmarks were defined and 24 different distances were calculated for each temporal bone.

RESULTS

A statistical description of 24 distances in the adult human middle ear which may limit or influence the design of middle ear transducers is presented. Significant inter-individual differences but no significant differences for gender, side, age or degree of pneumatization of the mastoid were found. Distances, which were not analyzed for the first time in this study, were found to be in good agreement with the results of earlier studies.

CONCLUSION

A data set describing the adult human middle ear anatomy quantitatively from the point of view of designers of new implantable hearing aid transducers has been generated. In principle, the method employed in this study using standard CT scans could also be used preoperatively to rule out exclusion criteria.

Today's state of the art in surgical robotics*

OBJECTIVE

This paper describes the current level of development of robots for surgery.

MATERIAL AND METHODS

This paper is based on a literature search in Pubmed, IEEExplore, CiteSeer and the abstract volumes of the MICCAI 2002, 2003 and 2004, CARS 2003 and 2004, CAOS 2003 and 2004, CURAC 2003 and 2004 and MRNV 2004 meetings.

RESULTS

Divided into different disciplines (imaging, abdominal and thoracic surgery, ENT, OMS, neurosurgery, orthopaedic surgery, radiosurgery, trauma surgery, urology), 159 robot systems are introduced. Their functionality, deployment, origin and mechanical set-up are described. Additional contacts and internet links are listed.

CONCLUSIONS

The systems perform diverse tasks such as milling cavities in bone, harvesting skin, screwing pedicles or irradiating tumors. From a technical perspective the strong specialization of the systems stands out. Most of the systems are being developed in Germany, the United States, Japan or France.

Comparison of the implantability of electronic hearing devices in a virtual reality planning environment and in human temporal bones

OBJECTIVE

To develop a procedure using a virtual reality (VR) environment that permitted us to simulate the preoperative fitting of an electronic implantable hearing device (IHD) and assess its implantability.

MATERIAL AND METHODS

This was an experimental, prospective study based on VR simulations involving the pre- and postoperative comparison of the implantability of an IHD. The preoperative possibility of implanting an IHD in a VR environment was compared with the postoperative implantability of the device in the temporal bones of human cadavers and patients. Study groups were analyzed according to the criteria "VR implantation" and "real surgery" using contingency tables.

RESULTS

A computer simulation method based on CT images was developed for the preoperative planning of the implantation. The VR simulation proved feasible in all cases (15 temporal bones and 24 patients). There was no significant difference between the process of implanting the IHD in patients or in the VR environment. These results indicate that VR-based test fittings of an IHD allow prediction of the implantability of an IHD prior to actual surgery.

CONCLUSION

We have described the development of a novel VR procedure for predicting the implantability of hearing devices in otoneurosurgical applications. The VR procedure can be applied universally and may also be used for other parts of the body.

Cochlear implant assessment: imaging issues

Cochlear implants are electronic auditory prostheses used to rehabilitate deafened persons who have lost their hair cells. They are partly worn externally and partly implanted in the ear. They provide a direct stimulation of the spiral ganglion cells of the cochlear nerve by bypassing the destroyed hair cells. The objectives of this article are to summarise what head and neck surgeons need to know before cochlear implantation and to describe the imaging study protocol used and anomalies to look for. A few explanations are resumed about placement of a brainstem implant.