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Dose and Image Quality Evaluation of a Dedicated Cone-Beam CT System for High-Contrast Neurologic Applications

¹ Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
² Department of Otorhinolaryngology, Mayo Clinic, Rochester, MN.

OBJECTIVE. The purpose of our study was to evaluate the dose and image quality performance of a dedicated cone-beam CT (CBCT) scanner in comparison with an MDCT scanner.

MATERIALS AND METHODS. The conventional dose metric, CT dose index (CTDI), is no longer applicable to CBCT scanners. We propose to use two dose metrics, the volume average dose and the mid plane average dose, to quantify the dose performance in a circular cone-beam scan. Under the condition of equal mid plane average dose, we evaluated the image quality of a CBCT scanner and an MDCT scanner, including high-contrast spatial resolution, low-contrast spatial resolution, noise level, CT number uniformity, and CT number accuracy.

RESULTS. For the sinus scanning protocol, the CBCT system had comparable high-contrast resolution and inferior low-contrast resolution to those obtained with the MDCT scanner when the doses were matched (mid plane average dose 9.2 mGy). The CT number uniformity and accuracy were worse on the CBCT scanner. The image artifacts caused by beam hardening and scattering were also much more severe on the CBCT system.

CONCLUSION. With a matched radiation dose, the CBCT system for sinus study has comparable high-contrast resolution and inferior low-contrast resolution relative to the MDCT scanner. Because of the more severe image artifacts on the CBCT system due to the small field of view and the lack of accurate scatter and beam-hardening correction, the utility of the CBCT system for diagnostic tasks related to soft tissue should be carefully assessed.

Keywords: cone-beam CT (CBCT) • CT dosimetry • image quality

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