![]() ![]() Previous studies reported the performance of the mobile CT scanner within the context of its primary indication in image‐guided spine surgery. As such systems are introduced, rigorous technical assessment can help guide clinical implementation and development of future applications in image‐guided interventions. Potentially advantageous features include improved image quality compared to cone‐beam CT (CBCT) and reduced cost / increased flexibility compared to a conventional diagnostic multidetector CT (MDCT) scanner in a dedicated simulation room. One such system is the Brainlab Airo (Brainlab Airo®, Munich, Germany), a mobile CT scanner based on a 32‐row detector with a large bore size (107‐cm inner diameter), small footprint, and slim gantry design. Mobile systems for intraoperative 3D imaging have become prevalent over the last decade. Overall, image quality appeared suitable to relevant clinical tasks in intracavitary and interstitial (e.g., gynecological) brachytherapy, including visualization of soft‐tissue structures in proximity to the applicators. The MAR algorithm provided modest improvement to image quality. Contrast‐to‐noise ratio was suitable to soft‐tissue visualization (e.g., fat and muscle), but windmill artifacts were observed in helical mode in relation to high‐frequency bone and metal. Helical and axial modes demonstrated comparable spatial resolution of ~5 lp/cm, with the MTF reduced to 10% at ~0.38 mm −1. Image nonuniformity (e.g., cupping artifact) in the transverse ( x, y) plane was less than 5 HU, but stitching artifacts (~5 HU) in the longitudinal ( z) direction were observed in axial scan mode. A high degree of HU accuracy and linearity was observed for both axial and helical scan modes. Nominal dose for helical and axial modes, respectively, was 56.4 and 78.9 mGy for the head protocol and 17.8 and 24.9 mGy for the body protocol. Performance in application to brachytherapy was assessed with a set of anthropomorphic brachytherapy phantoms - for example, a vaginal cylinder and interstitial ring and tandem. The manufacturer’s metal artifact reduction (MAR) algorithm was assessed in an anthropomorphic body phantom containing surgical instrumentation. Images were also obtained on a diagnostic CT scanner (Big Bore CT simulator, Philips, Amsterdam, Netherlands) for qualitative and quantitative comparison. Spatial resolution (modulation transfer function, MTF) was assessed with an edge‐spread phantom and visually assessed with respect to line‐pair patterns in the ACR phantom and in structures of interest in anthropomorphic phantoms. Hounsfield unit (HU) accuracy and linearity were assessed using materials of specified electron density (Gammex RMI, Madison, WI), and image uniformity, noise, and noise‐power spectrum (NPS) were evaluated in a 20‐cm‐diameter water phantom as well as an American College of Radiology (ACR) CT accreditation phantom (Model 464, Sun Nuclear, Melbourne, FL). Dose measurements were performed using a 100‐mm‐length pencil chamber at the center and periphery of 16‐ and 32‐cm‐diameter CTDI phantoms. ![]()
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