title: An automatic technique for finding and localizing externally attached markers in CT and MR volume images of the head.
abstract: An image processing technique is presented for finding and localizing the centroids of cylindrical markers externally attached to the human head in computed tomography (CT) and magnetic resonance (MR) image volumes. The centroids can be used as control points for image registration. The technique, which is fast, automatic, and knowledge-based, has two major steps. First, it searches the entire image volume to find one voxel inside each marker-like object. We call this voxel a "candidate" voxel, and we call the object a candidate marker. Second, it classifies the voxels in a region surrounding the candidate voxel as marker or nonmarker voxels using knowledge-based rules and calculates an intensity-weighted centroid for each true marker. We call this final centroid the "fiducial" point of the marker. The technique was developed on 42 scans of six patients-one CT and six MR scans per patient. There are four markers attached to each patient for a total of 168 marker images. For the CT images the false marker rate was zero. For MR the false marker rate was 1.4% (Two out of 144 markers). To evaluate the accuracy of the fiducial points, CT-MR registration was performed after correcting the MR images for geometrical distortion. The fiducial registration accuracy averaged 0.4 mm and was better than 0.6 mm for each of the eighteen image pairs.
authors.affiliation: Department of Computer Science, Vanderbilt University, Nashville, TN 37235, USA.
authors.forename: M Y
authors.initials: MY
authors.lastname: Wang
authors.forename: C R
authors.initials: CR
authors.lastname: Maurer
authors.forename: J M
authors.initials: JM
authors.lastname: Fitzpatrick
authors.forename: R J
authors.initials: RJ
authors.lastname: Maciunas
mesh_terms: D000465:Algorithms; D000704:Analysis of Variance; D004867:Equipment Design; D005583:Fourier Analysis; D006257:Head / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019736:Prostheses and Implants; D012680:Sensitivity and Specificity; D012886:Skull / Q000601:surgery*; D012985:Software Design; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed / Q000379:methods*