Author: Wendy Siman, Wei Zhou 👨🔬
Affiliation: University of Colorado Anschutz Medical Campus, School of Medicine 🌍
Purpose:
To compare the image quality and radiation dose of 3D cone-beam CT modes of a mobile C-arm and an O-arm unit for intraoperative imaging.
Methods:
A 50-µm tungsten wire was imaged at isocenter using the 3D-mode of a mobile C-arm (CIARTIC, Siemens) and an O-arm (Medtronic) to measure the modulation transfer function (MTF). Radiation dose was assessed with a 10-cm ion chamber positioned at five locations (center, 3, 6, 9, and 12 o’clock) in a 16-cm CTDI phantom. Metal artifacts were evaluated by imaging three different screws inserted into the CTDI phantom. An anthropomorphic knee phantom was also imaged at isocenter. C-arm protocols included 110 kV, 0.087 images/mGy, 100 images, and a 160 mm FOV. O-arm acquisitions used 110 kV, 40 mAs, and a 200×150 mm FOV.
Results:
The 50% MTF cut-off frequency was lower for the C-arm (0.21 mm⁻¹) than the O-arm (0.25 mm⁻¹), while the 10% cut-off was higher for the C-arm (0.67 mm⁻¹ vs. 0.57 mm⁻¹). A sharp kernel on the C-arm improved resolution (10% cut-off: 0.99 mm⁻¹). Radiation dose was lower on the C-arm (center: 70.95 mR; periphery: 36.01–136.8 mR) compared to the O-arm (center: 439.3 mR; periphery: 495.4–656.3 mR). Metal artifacts were significantly reduced with the C-arm’s metal artifact reduction reconstruction. Image noise on the knee phantom was higher for the C-arm (106.1 HU, 0.31 mm slice) than the O-arm (28.0 HU, 0.83 mm slice).
Conclusion:
The C-arm’s default protocol delivered over five times lower radiation dose but produced noisier images than the O-arm, which may be acceptable depending on the clinical applications. Advanced reconstruction on the C-arm enhanced spatial resolution and reduced metal artifacts compared to the O-arm.