Purpose: An actuated slot-beam collimator was implemented on an intraoperative cone-beam CT system (Medtronic O-arm™), hypothesizing benefits to dose and soft-tissue contrast resolution for the slot-beam geometry. This study investigates the dose, scatter-to-primary, and contrast-to-noise characteristics for slot- and cone-beam configurations for scenarios that may benefit from improved soft-tissue image quality.
Methods: The collimator features three narrow slots that can be automatically moved into position during scanning, each exposing a detector area of 40 cm width x 2.5 cm longitudinal. Slot- and cone-beam configurations were evaluated with and without a focused linear anti-scatter grid (12:1 GR). Dose, scatter, and soft-tissue contrast resolution were evaluated in phantom studies for head and body protocols (~745 projections over 360°, 0.388 x 0.776 mm² pixels, 80-120 kV, 75-940 mAs) with reconstruction performed via 3D filtered backprojection. Quantitative evaluation included scatter-to-primary ratio (SPR), contrast-to-noise ratio (CNR), modulation transfer function (MTF), and absorbed dose.
Results: The slot-beam configuration reduced SPR by ~6x compared to a cone-beam, and the grid reduced SPR by ~3x compared to no-grid. As anticipated, the slot-beam with a grid yielded the lowest SPR (<0.1 and <0.3 for the head and body, respectively) and increased soft-tissue CNR by 2-2.5x compared to cone-beam at equivalent dose. MTF was unaffected among all configurations. The dose for the slot-beam configuration was ~1/5 that for the cone-beam due to reduction of scatter dose, ranging 0.013-0.037 mGy/mAs for the head and 0.006-0.017 mGy/mAs for the body.
Conclusion: Implementation of an actuated slot-beam collimator demonstrated strong improvements in image quality and dose that may benefit certain interventional imaging scenarios – e.g., high-quality soft-tissue visualization within a region of interest to assess the quality of surgical product or as a check against hemorrhage. It also provides a potential step toward intraoperative helical scanning on such systems.
Funding Support, Disclosures, and Conflict of Interest: The research was supported by academic-industry partnership with Medtronic Inc.
Not Applicable / None Entered.