Biomedical subjects

Nam H Kim

Publications and source records attributed to Nam H Kim.

4 recordsLinked to original sources

PubMed2004

Three-dimensional localization of cochlear implant electrodes using epipolar stereophotogrammetry.

Three-dimensional (3-D) localization of individual cochlear implant electrodes within the inner ear is of importance for modeling the electrical field of the cochlea, designing the electrode array, and programming the associated speech processor. A 3-D reconstruction method of cochlear implant electrodes is proposed to localize individual electrodes from two X-ray views in combination with the spiral computed tomography technique. By adapting epipolar geometry to the configuration of an X-ray imaging system, we estimate individual electrode locations in the least square sense without using a patient attachment required by an existing stereophotogrammetry technique. Furthermore, our method does not require any knowledge of the intrinsic and extrinsic parameters of the imaging system. The performance of our method is studied in numerical simulation and with patient data and is found to be sufficiently accurate for clinical use. The maximum root mean-square errors measured are 0.0445 and 0.214 mm for numerical simulation and patient data, respectively.

Cochlea↗

PubMed2003

Alignment of CT images of skull dysmorphology using anatomy-based perpendicular axes.

Rigid body registration of 3D CT scans, based on manual identification of homologous landmarks, is useful for the visual analysis of skull dysmorphology. In this paper, a robust and simple alignment method was proposed to allow for the comparison of skull morphologies, within and between individuals with craniofacial anomalies, based on 3D CT scans, and the minimum number of anatomical landmarks, under rigidity and uniqueness constraints. Three perpendicular axes, extracted from anatomical landmarks, define the absolute coordinate system, through a rigid body transformation, to align multiple CT images for different patients and acquisition times. The accuracy of the alignment method depends on the accuracy of the localized landmarks and target points. The numerical simulation generalizes the accuracy requirements of the alignment method. Experiments using a human dried skull specimen, and ten sets of skull CT images (the pre- and post-operative CT scans of four plagiocephaly, and one fibrous dysplasia patients), demonstrated the feasibility of the technique in clinical practice.

Adolescent↗

PubMed2003

Polygon reduction of 3D objects using Stokes' theorem.

Surface over volume rendering can be useful for many applications. However, the tremendously large number of polygons composing the surface primitives should be reduced to a manageable size so as to utilize the capability of low cost hardware and software rendering engines, a standard Internet protocol and VRML format. In this paper, we propose a novel algorithm that deletes several vertices simultaneously by forming a closed arbitrary shaped boundary. The Stokes' theorem, used in electro-magnetic field analysis, was newly adapted to extract the arbitrary shaped boundary. The simultaneous deletion procedure provides a computational gain and increases the reduction ratio without sacrificing the topological distortion of the original mesh. Numerically synthesized polygonal objects and real CT data were tested to evaluate the performance of the new algorithm and to demonstrate the possibility of a medical rendering application. The new algorithm outperforms the conventional decimation algorithm in both computational and reduction efficiency.

Algorithms↗

PubMed2002

Improvement of multi-channel isolated bio-potential amplifiers using multiplexing.

We propose a simple isolated link circuit for a multi-channel bio-potential amplifier, by adapting the multiplexing/demultiplexing technique that is generally used in digital circuit design. The reduced number of isolation amplifiers, due to the multiplexing technique, results in an increase in the amount of isolation, as well as a reduction in manufacturing cost. The simple incorporation of a dead-zone in multiplexed timing, and a pull-down resistor in the multiplexed signal line, enables a multiple isolated bio-signal transmission over the shared isolation amplifier, with an affordable inter-channel cross talk.

Brain↗