Purpose: To characterize the dose and 3D imaging performance of a recently FDA-approved mobile isocentric C-arm equipped with a flat-panel detector (FPD) for intraoperative cone-beam CT (CBCT) (Cios Spin 3D, Siemens Healthineers) and identify potential improvements to imaging protocols for pertinent imaging tasks.
Methods: The C-arm features a 30 x 30 cmÂ² FPD and isocentric gantry (116.4 cm source-detector distance) with computer-controlled motion of rotation (0-195Â°), angulation (Â±220Â°), and height (0-45 cm). Standard and custom scan protocols were evaluated in quantitative phantom studies, including variation of number of projections (100-400) and exposure (3-22 mAs). Image reconstruction was based on 3D filtered backprojection with smooth, standard, and sharp reconstruction filters. A new QA phantom designed specifically for CBCT physics testing was used to evaluate uniformity, linearity, contrast, noise (noise-power spectrum, NPS), and spatial resolution (modulation transfer function, MTF), and noise-equivalent quanta (NEQ). Radiation dose was measured for each protocol in terms of the weighted central and peripheral absorbed dose (air kerma, Dw).
Results: The dose (Dw) varied with imaging protocol from ~1-5 mGy (~0.17 mGy/mAs) for head scan protocols to ~6-37 mGy (~0.05 mGy/mAs) for body scan protocols. The axial MTF was consistent with sub-mm resolution, with fâ‚?â‚€ (frequency at 10% modulation) of 0.64 mmâ?»Â¹, 1.0 mmâ?»Â¹, and 1.5 mmâ?»Â¹ for smooth, standard, and sharp filters, respectively. The NPS and NEQ exhibited expected 3D spatial-frequency dependence and provided a guide to selection of technique protocols according to pertinent clinical imaging tasks (e.g., visualization of bone architecture, find instrumentation, or soft-tissue boundaries).
Conclusion: The studies provided objective assessment of the dose and 3D imaging performance of this newly released C-arm, offering an important basis for technique selection, and a benchmark for QA.
Funding Support, Disclosures, and Conflict of Interest: The research was supported by academic industry partnership with Siemens Healthineers (Erlangen, Germany). Gerhard Kleinszig and Sebastian Vogt are employees of Siemens Healthineers.