A computed tomographic data-based vibrant bonebridge visualization tool I Todt 1, H Lamecker2, H Ramm 2, A Ernst1 1

Department of Otolaryngology, Head and Neck Surgery at UKB, Hospital of the University of Berlin, Charité Medical School, Berlin, Germany, 2Zuse Institute Berlin (ZIB), 1000 shapes GmbH, Berlin, Germany Aim: Information about the temporal bone size and variations of anatomical structures are crucial for a safe positioning of the Vibrant Bonebridge B-FMT. A radiological based preoperative planning of the surgical procedure decreases the surgical time and minimizes the risk of complications. Materials and methods: We developed a software tool, which allows a catch up of foreign DICOM data based CT temporal bone scans. The individual CT scan is transmitted into a 3D reconstructed pattern of the temporal bone. In this 3D reconstruction the individually favored position of the B- FMT should be found. Results: The software allows a determination of a safe B-FMT position by identifying the individual relation of middle fossa, jugular bulb and external auditory canal. Skull thickness and screw length are contained parameters for the surgical planning. Conclusion: An easy to handle software tool allows a radiologically data based safe and fast surgical positioning of the B-FMT. Keywords: Computed tomographic visualization, Bone conduction implant, Vibrant Bonebridge

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Introduction

Materials and methods

Vibrant Bonebridge (MedEl, Innsbruck, Austria) is the first bone conduction system with an actuator positioned under the skin. A new aspect of this system is the definition of the site of the actuator. Information about temporal bone size and variations of anatomical structures are crucial for a correct positioning of the Vibrant Bonebridge B-FMT. Although different sites are used to place the B-FMT, such as suboccipital or temporal, the sinodural angle is the preferred site. One reason for this is the well-known anatomy of the mastoid where surgery is routinely performed. Although variations of the dura, external auditory canal, and sigmoid sinus height are part of the daily surgical work, evaluation in the context of the 9–16mm-sized B-FMT is new. Surgeries performed to date have demonstrated the need to push the B-FMT against the middle fossa dura or sigmoid sinus to some degree in certain cases. Although no complications have been described, surgeons prefer to avoid such situations if anatomically possible. Radiological data-based preoperative visualization of the B-FMT in the temporal bone might offer valuable preoperative information about potentially conflicting localization of the B-FMT and help determine an optimal point for the attachment of the actuator in the sino-dural angle.

Before developing an independent visualization tool, we defined the requirements of this software solution:

© W. S. Maney & Son Ltd 2014 DOI 10.1179/1467010014Z.000000000155

• It should be independent of fixed or mobile navigation systems. Navigation systems are effective tools for different applications, but they are both costly and time-consuming. • A visualization tool should individually capture important anatomic structures (e.g. sinus, dura, and ear canal) from a computed tomographic (CT) dataset. • It must be applicable in most of the commonly used radiological software solutions. Therefore, it must be able to read DICOM data and build a three-dimensional model based on the individual dataset. • Segmentation and processing time must not be too high because the surgical time allocated for the procedure is between 20 minutes and 1 hour. • Low hardware requirements are essential because it should be applicable in many different settings, including hospitals and outpatient units. • The software must be easy to handle and intuitive, and the users should not be limited to a specific group of professionals (e.g. surgeons). • Because CT data are medical data, privacy and data protection must be ensured. • Therefore, a downloadable or stand-alone solution is preferred over a server-based solution, which might have inherent safety issues.

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Figure 1 B-FMT.

Three-dimensional temporal bone model with the

• Additionally, mandatory.

save-and-print

options

are

Based on these requirements, a solution based on ZIBAmira (amira.zib.de) was developed and 30 temporal bone CT images were used to define an independent three-dimensional model as a basis for individual segmentation.

Results Segmentation time, which includes the transfer of the DICOM dataset to an individual three-dimensional model of the temporal bone, was decreased to approximately 1.5 minutes. This was found to be appropriate

Figure 3

Computed tomographic data-based Vibrant Bonebridge visualization tool

Figure 2

Danger windows that signal potential conflicts.

in relation to the surgical time allocated for the procedure. The first visualization of the three-dimensional model presented the temporal bone at a 90° angle with the temporal bone tip, which is similar to the regular surgical position of the temporal bone. Colour differentiation of the surface of the temporal bone model indicated the specific cortical thickness of the bone. This was helpful for the initial determination of the general thickness of the skull in this area. The software contains different movement modes. In the first mode, the B-FMT model can be moved in the temporal bone in any direction (Fig. 1). The second mode allows the surgeon to move and turn the entire temporal bone and the B-FMT within the

Control of three-dimensional model of the B-FMT position in CT planes.

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Computed tomographic data-based Vibrant Bonebridge visualization tool

temporal bone. Turning the entire temporal bone allows the surgeon to directly evaluate the relationship between the B-FMT and adjacent structures. Indirect evaluation is possible through signalling windows, which open on top of the B-FMT if a close relation or penetration is found. A close relation (