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Session: New Technologies and Image Reconstruction in CT and CBCT [Return to Session]

Intraoperative Cone-Beam CT Image Quality and Dose with a Slot Collimator On the O-Arm

X Zhang1*, P Wu1, Y Huang1, A Uneri1, C Jones1,2, P Helm3, S Lo4, W Zbijewski1, J Siewerdsen1,4, (1) Johns Hopkins University, Department of Biomedical Engineering, Baltimore, MD, (2) Johns Hopkins University, Department of Computer Science, Baltimore, MD, (3) Medtronic Inc., Littleton, MA, (4) Johns Hopkins University, Department of Neurosurgery, Baltimore, MD


TU-F-TRACK 3-3 (Tuesday, 7/27/2021) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]

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.


    IM- Cone Beam CT: Development (New Technology and Techniques)

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