Imaging Sci Dent.  2017 Sep;47(3):199-207. 10.5624/isd.2017.47.3.199.

Optimizing the reconstruction filter in cone-beam CT to improve periodontal ligament space visualization: An in vitro study

• Houno Y
• Hishikawa
• Gotoh KI
• Naitoh M
• Mitani A
• Noguchi T
• Ariji E
• Kodera Y

• KMID: 2390085
• DOI: http://doi.org/10.5624/isd.2017.47.3.199

Abstract

PURPOSE
Evaluation of alveolar bone is important in the diagnosis of dental diseases. The periodontal ligament space is difficult to clearly depict in cone-beam computed tomography images because the reconstruction filter conditions during image processing cause image blurring, resulting in decreased spatial resolution. We examined different reconstruction filters to assess their ability to improve spatial resolution and allow for a clearer visualization of the periodontal ligament space.
MATERIALS AND METHODS
Cone-beam computed tomography projections of 2 skull phantoms were reconstructed using 6 reconstruction conditions and then compared using the Thurstone paired comparison method. Physical evaluations, including the modulation transfer function and the Wiener spectrum, as well as an assessment of space visibility, were undertaken using experimental phantoms.
RESULTS
Image reconstruction using a modified Shepp-Logan filter resulted in better sensory, physical, and quantitative evaluations. The reconstruction conditions substantially improved the spatial resolution and visualization of the periodontal ligament space. The difference in sensitivity was obtained by altering the reconstruction filter.
CONCLUSION
Modifying the characteristics of a reconstruction filter can generate significant improvement in assessments of the periodontal ligament space. A high-frequency enhancement filter improves the visualization of thin structures and will be useful when accurate assessment of the periodontal ligament space is necessary.

Keyword

Cone-Beam Computed Tomography; Image Processing, Computer-Assisted; Phantoms, Imaging; Periodontal Ligament

MeSH Terms

Cone-Beam Computed Tomography*
Diagnosis
Evaluation Studies as Topic
Image Processing, Computer-Assisted
In Vitro Techniques*
Matched-Pair Analysis
Methods
Periodontal Ligament*
Phantoms, Imaging
Skull
Stomatognathic Diseases

Figure

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  Fig. 1 Reconstruction filters prepared for observation of the periodontal ligament space. Modified Shepp-Logan (MSL) 1 shows the most highly enhanced high-frequency component, MSL 2 shows medium enhancement, and MSL 3 shows the least-enhanced high-frequency component.

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  Fig. 2 Diagram of the periodontal ligament phantom.

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  Fig. 3 Typical default images from the Alphard apparatus, and images reconstructed by each filter. A: Default, B: Ram-Lak, C: Shepp-Logan, D: modified Shepp-Logan (MSL) 1, E: MSL 2, F: MSL 3.

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  Fig. 4 The scale value calculated by the Thurstone paired-comparison method. A disparity in the scale value larger than 28 was considered a significant difference.

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  Fig. 5 The modulation transfer function (MTF) and Wiener spectrum (WS) of a modified Shepp-Logan (MSL) 2 image and the default image obtained using the Alphard apparatus.

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  Fig. 6 Gray-value profiles of the simulated periodontal ligament space obtained by polar transformation.

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