Imaging Sci Dent.  2019 Jun;49(2):139-151. 10.5624/isd.2019.49.2.139.

Optimization of exposure parameters and relationship between subjective and technical image quality in cone-beam computed tomography

• Park HN
• Min CK
• Kim KA
• Koh KJ

• KMID: 2450180
• DOI: http://doi.org/10.5624/isd.2019.49.2.139

Abstract

PURPOSE
This study was performed to investigate the effect of exposure parameters on image quality obtained using a cone-beam computed tomography (CBCT) scanner and the relationship between physical factors and clinical image quality depending on the diagnostic task.
MATERIALS AND METHODS
CBCT images of a SedentexCT IQ phantom and a real skull phantom were obtained under different combinations of tube voltage and tube current (Alphard 3030 CBCT scanner, 78-90 kVp and 2-8 mA). The images obtained using a SedentexCT IQ phantom were analyzed technically, and the physical factors of image noise, contrast resolution, spatial resolution, and metal artifacts were measured. The images obtained using a real skull phantom were evaluated for each diagnostic task by 6 oral and maxillofacial radiologists, and each setting was classified as acceptable or unacceptable based on those evaluations. A statistical analysis of the relationships of exposure parameters and physical factors with observer scores was conducted.
RESULTS
For periapical diagnosis and implant planning, the tube current of the acceptable images was significantly higher than that of the unacceptable images. Image noise, the contrast-to-noise ratio (CNR), the line pair chart on the Z axis, and modulation transfer function (MTF) values showed statistically significant differences between the acceptable and unacceptable image groups. The cut-off values obtained using receiver operating characteristic curves for CNR and MTF 10 were useful for determining acceptability.
CONCLUSION
Tube current had a major influence on clinical image quality. CNR and MTF 10 were useful physical factors that showed significantly associations with clinical image quality.

Keyword

Optimization; Image Quality; Cone-Beam Computed Tomography

MeSH Terms

Artifacts
Cone-Beam Computed Tomography*
Diagnosis
Noise
ROC Curve
Skull

Figure

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  Fig. 1 A head-sized cylindrical polymethyl methacrylate phantom.

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  Fig. 2 Cone-beam computed tomographic axial images obtained using a SedentexCT IQ phantom show the regions of interest calculated by the Radia software. A. Image noise section. B. Contrast resolution section. C. Spatial resolution section. D. Artifact section.

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  Fig. 3 A real skull phantom with a soft-tissue replica.

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  Fig. 4 Cone-beam computed tomographic images show examples of acceptable (A) and the unacceptable (B) image quality.

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  Fig. 5 Differences between acceptable and unacceptable images in tube voltage (A) and current (B). A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 6 Differences between acceptable and unacceptable images in image noise values according to the measurement positions. A: Acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 7 Differences between acceptable and unacceptable images in the contrast-to-noise ratio (CNR) according to the rod type. LDPE: low-density polyethylene, PTFE: polytetrafluoroethylene, A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 8 Differences between acceptable and unacceptable images in the number of detected rods according to the rod type. LDPE: low-density polyethylene, PTFE: polytetrafluoroethylene, A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 9 Differences between acceptable and unacceptable images in the results of line pair charts according to the axes. A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 10 Differences between acceptable and unacceptable images in the modulation transfer function (MTF) values. A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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  Fig. 11 Differences between acceptable and unacceptable images in the results of metal artifact tests according to the measurement positions. A: acceptable group, Un: unacceptable group, PD: periapical diagnosis, IP: implant planning, Mx: maxilla, Mn: mandible.

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