Clinical determination of target registration error of an image-guided otologic surgical system using patients with bone-anchored hearing aids

Abstract

Image guidance in otologic surgery has been thwarted by the need for a non-invasive fiducial system with target registration error (TRE) at the inner ear below 1.5mm. We previously presented a fiducial frame for this purpose that attaches to the upper dentition via patient-specific bite blocks and demonstrated a TRE of 0.73mm (±0.23mm) on cadaveric skulls. In that study, TRE measurement depended upon placement of bone-implanted, intracranial target fiducials-clearly impossible to repeat clinically. Using cadaveric specimens, we recently presented a validation method based on an auditory implant system (BAHA System®; Cochlear Corp., Denver, CO). That system requires a skullimplanted titanium screw behind the ear upon which a bone-anchored hearing aid (BAHA) is mounted. In our validation, we replace the BAHA with a fiducial marker to permit measurement of TRE. That TRE is then used to estimate TRE at an internal point. While the method can be used to determine accuracy at any point within the head, we focus in this study on the inner ear, in particular the cochlea, and we apply the method to patients (N=5). Physical localizations were performed after varying elapsed times since bite-block fabrication, and TRE at the cochlea was estimated. We found TRE to be 0.97mm at the cochlea within one month and 2.5mm after seven months. Thus, while accuracy deteriorates considerably with delays of seven months or more, if this frame is used within one month of the fabrication of the biteblock, it achieves the goal and in fact exhibits submillimetric accuracy.

Accuracy of Image-Guided Surgical Systems at the Lateral Skull Base as Clinically Assessed Using Bone-Anchored Hearing Aid Posts as Surgical Targets

“…These targets, bone-anchored hearing aids (BAHAs), are implanted for aural rehabilitation. The novel concept of utilizing BAHAs as surgical targets for IGS validation was initially tested on skulls [13] and used on patients to determine the accuracy of the EarMark system [14]. The difficulty involved in the validation of an IGS system is identifying anatomical landmarks precisely and repeatably.…”

“…The concept of using BAHA posts as targets for IGS testing was first introduced to validate the fiducial frame system [13], [14]. The current study was undertaken as described below following Institutional Review Board (IRB) approval to find the accuracy of different IGS systems for clinical use.…”

Quantitative error analysis for computer assisted navigation: A feasibility study

“…(3) TRE 2 (r) is governed by the geometric configuration of fiducials-the sum term; the variance of the localization error FLE 2 , and the position of the target, r, in the principal axes coordinate system of the fiducials, d k is the distance of the target from principal axis k, and f k is the RMS distance of the fiducials from principal axis k. 25 In the following TRE 2 is used for TRE 2 (r) for simplicity. Recently, Balachandran 32,33 and Fitzpatrick 10 have introduced the target localization error (TLE), the error associated with the physical localization of a locus on a patient (a marker, a screw, or an anatomical feature). This yields an overall estimate of the application error of clinical navigation in quadrature, the total target error, TTE, 10 of…”

“…Recently Balachandran 32,33 and Fitzpatrick 10 have introduced the Target Localization Error (TLE), the error associated with the physical localization of a locus on a patient (a marker, a screw, or an anatomical feature).This yields an overall estimate of the application error of clinical navigation in quadrature, the Total Target Error, TTE 10 , of (4) Here <TLE 2 >, <FLE 2 >, and <TRE 2 > are assumed to be independent random variables. TRE(r) with anisotropic noise covariance 27 can be predicted as (5) δ ij is the Kronecker delta, ε the smallness parameter of the perturbation-theoretic approach, are the components of the FLE covariance matrix Σ FLE , r i are the coordinates of a point r expressed in the principal axes coordinate system of the fiducials; are the i-th singular values of the fiducial configuration in the principal axes.…”

A Review of Point Feature Based Medical Image Registration

“…These points are commonly used to distinguish soft tissues when there are not enough distinguishable structures to provide reliable references [8][9][10][11][12]. The number of extrinsic points used for registration is small and in most cases, the correspondences between the extrinsic points are usually known before registration.…”