Summary
Objectives:
To design, implement in Java™, and evaluate a method and means for the automated
localization of artificial landmarks in optical images for tuned-aperture computed
tomography® (TACT®) that allows the replacement of radiographic with optical landmarks.
Methods:
Circular, colored, optical landmarks were designed to provide flexibility with regard
to landmark constellation, imaging equipment, and lighting conditions. The landmark
detection was based on Hough transforms (HT) for ellipses and lines. The HT for ellipses
was extended to enable selective detection of bright ellipses on a dark background
and vice versa, and the number of irrelevant votes in the accumulator arrays was reduced.
An experiment was performed in vitro to test the automated landmark localization scheme, verify registration accuracy,
and measure the required computation time.
Results:
A visual evaluation of the tomographic slices that were produced using the new method
revealed good registration accuracy. A comparison to tomographic slices similarly
produced by means of conventional TACT showed identical results. The algorithm ran
sufficiently fast on standard hardware to allow landmark localization in “real time”
during successive image acquisition in clinical applications.
Conclusions:
The proposed method provides robust automated localization of landmarks in optical
images. Using a hybrid imaging system, TACT can now be clinically applied without
manual interaction of a human operator and without radiopaque landmarks, which might
cover anatomic details of diagnostic interest.
Keywords
Computer-assisted image processing - X-ray computed tomography - three-dimensional
imaging
