Rika Baba MS, Presenter: Nothing to Disclose

Norio Inou PhD, Abstract Co-Author: Nothing to Disclose

Mariko Takahashi DDS, Abstract Co-Author: Nothing to Disclose

Haruhisa Nakano DDS, PhD, Abstract Co-Author: Nothing to Disclose

Koutaro Maki DDS, PhD, Abstract Co-Author: Nothing to Disclose

Dental CT uses cone-beam X-rays and a flat-panel detector. Two-dimensional and three-dimensional images can be measured quickly when subjects are sitting or standing. However, dental CT images have non-uniformity caused by the effects of X-ray scattering and beam hardening. Both effects decrease the accuracy of the CT number and increase artifacts in reconstructed images. Our aim was to acquire high-quality dental CT images of head and neck by correcting these effects.

We developed a new correction method. First, we acquired transmittance images by using a cone-beam CT apparatus with water phantoms of various sizes and a narrow collimator gap (like that of a multi-slice CT apparatus). The mean pixel value of a projected image at the center of each phantom was calculated. Two approximate functions were acquired as the best fit to the size versus mean value plot; that is, when the data was limited to small phantom sizes, one was linear; and when all data was used, the other was polynomial. We formulated the beam-hardening correction function as the best fit to the plot of the values given by the polynomial function and that of the values given by the linear function. Next, we measured transmittance images for various-sized water phantoms and various collimator gaps. After the beam-hardening component was corrected, the scatter component was determined to be the difference between the measured transmittance for a wide collimator gap and that for a very narrow gap. We formulated the approximate scatter component as a function of the mean value and the scatter parameter, which was defined as the ratio of scatter generation and attenuation coefficient.

When the correction method was applied to an inhomogeneous head phantom, the absolute error from the true CT number for the mandible was reduced from 549 to 30 HU. The artifacts in the corrected reconstructed images were also reduced. As a result, volume-rendering images with few artifacts were acquired for head and neck using the reconstructed images with a highly accurate CT number.

The proposed correction method is effective for acquiring the high-quality dental CT images with a highly accurate CT number and few artifacts.

High-quality dental CT images can be acquired for head and neck. The images are effective for diagnostic support and pre-surgical simulation in applications such as orthodontics and orthopedics.

Baba, R, Inou, N, Takahashi, M, Nakano, H, Maki, K, High Quality Head and Neck Imaging Using Dental CT with High Accuracy of CT Number.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9011288.html