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Evaluation of tuned-aperture computed tomography depth discrimination for image series acquired variously with linear
K Yamamoto1, K Nishikawa, N Kobayashi
1Department of Oral and Maxillofacial Radiology, Tokyo Dental College, Chiba, Japan. kazyama@tdc.ac.jp
Objective:
To compare depth discrimination by using tuned-aperture computed tomography (TACT) variously with linear horizontal, linear vertical, combined linear horizontal and linear vertical, and conical beam projection arrays.
Study Design:
The first test object was a metallic mesh angled at 30 degrees to the surface of a computed dental radiography size No. 1 x-ray sensor. The second test object was a dry human mandible. The sensor was mounted on an optical bench constructed to permit free and precise geometrical settings for the horizontal and vertical angulations of the x-ray beam. The extent of blurring of horizontal and vertical wires in each TACT reconstructed image slice was observed for each of the tested beam projection arrays.
Results:
With a linear horizontal beam projection array, it was not possible to determine the depth of structures parallel to the horizontal dimension, such as the mandibular canal. With a linear vertical beam projection, it was not possible to determine the depth of structures parallel to the vertical dimension. A conical array of beam projections was best suited to the task of depth discrimination of objects in all planes. The best second alternative was a combination of linear vertical and linear horizontal projections.
Conclusions:
Beam projection geometry is important for the accurate depth discrimination of TACT reconstructed images. A conical beam projection array is ideal.