Intraoperative cone-beam and slot-beam CT: 3D image quality and dose with a slot collimator on the O-arm imaging system

Xiaoxuan Zhang, Wojciech Zbijewski, Yixuan Huang, Ali Uneri, Craig K. Jones, Sheng-fu Lo, Timothy F. Witham, Mark Luciano, William Stanley Anderson, Patrick A. Helm, Jeffrey H. Siewerdsen

Research output: Contribution to journalArticlepeer-review


Purpose: To characterize the 3D imaging performance and radiation dose for a prototype slot-beam configuration on an intraoperative O-arm™ Surgical Imaging System (Medtronic Inc., Littleton, MA) and identify potential improvements in soft-tissue image quality for surgical interventions. Methods: A slot collimator was integrated with the O-arm system for slot-beam axial CT. The collimator can be automatically actuated to provide 1.2° slot-beam longitudinal collimation. Cone-beam and slot-beam configurations were investigated with and without an antiscatter grid (12:1 grid ratio, 60 lines/cm). Dose, scatter, image noise, and soft-tissue contrast resolution were evaluated in quantitative phantoms for head and body configurations over a range of exposure levels (beam energy and mAs), with reconstruction performed via filtered-backprojection. Qualitative imaging performance across various anatomical sites and imaging tasks was assessed with anthropomorphic head, abdomen, and pelvis phantoms. Results: The dose for a slot-beam scan varied from 0.02–0.06 mGy/mAs for head protocols to 0.01–0.03 mGy/mAs for body protocols, yielding dose reduction by ∼1/5 to 1/3 compared to cone-beam, owing to beam collimation and reduced x-ray scatter. The slot-beam provided an ∼6–7× reduction in scatter-to-primary ratio (SPR) compared to the cone-beam, yielding SPR ∼20–80% for head and body without the grid and ∼7–30% with the grid. Compared to cone-beam scans at equivalent dose, slot-beam images exhibited an ∼2.5× increase in soft-tissue contrast-to-noise ratio (CNR) for both grid and gridless configurations. For slot-beam scans, a further ∼10–30% improvement in CNR was achieved when the grid was removed. Slot-beam imaging could benefit certain interventional scenarios in which improved visualization of soft tissues is required within a fairly narrow longitudinal region of interest ((Formula presented.) 7 mm in (Formula presented.))––for example, checking the completeness of tumor resection, preservation of adjacent anatomy, or detection of complications (e.g., hemorrhage). While preserving existing capabilities for fluoroscopy and cone-beam CT, slot-beam scanning could enhance the utility of intraoperative imaging and provide a useful mode for safety and validation checks in image-guided surgery. Conclusions: The 3D imaging performance and dose of a prototype slot-beam CT configuration on the O-arm system was investigated. Substantial improvements in soft-tissue image quality and reduction in radiation dose are evident with the slot-beam configuration due to reduced x-ray scatter.

Original languageEnglish (US)
Pages (from-to)6800-6809
Number of pages10
JournalMedical physics
Issue number11
StatePublished - Nov 2021


  • cone-beam CT
  • fan-beam CT
  • image quality
  • image-guided surgery
  • intraoperative imaging
  • radiation dose
  • x-ray scatter

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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