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O-arm Scatter Cloud

C-13. O-arm Scatter Cloud. Introduction. The O-arm operates as a mobile cone beam CT. It has unique features: Uses a gantry that can be open or close which is very useful in surgery cases. 2D fluoroscopic  images can be reconstructed into 3D images.

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O-arm Scatter Cloud

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  1. C-13 O-arm Scatter Cloud

  2. Introduction • The O-arm operates as a mobile cone beam CT. • It has unique features: • Uses a gantry that can be open or close which is very useful in surgery cases. • 2D fluoroscopic  images can be reconstructed into 3D images. • 3D scans mode can help enhance imaging information (in kyphoplasty procedures, screw position, and orthopedic procedures). • Patient dose and scatter radiation increases.

  3. O-arm Image Acquisition • A single rotation (360 degrees) takes 13 seconds. • The beam is pulsed and the total x-ray on time is 3.91 seconds. • 192 images are reconstructed with slice thickness of 0.83mm. • 3D scan acquisition mode has 4 types of pre-programmed protocols: head, upper torso, lower torso, and leg.   • It has various selections of patient thickness: small, medium, large, and extra large.   With each increase of patient selection, there’s a fixed kVp at 120 and increase in mAs.

  4. Objective and Hypothesis Objective To investigate the scatter cloud produced by an O-arm. Hypothesis A uniform scatter cloud is present during O-arm operation.

  5. Materials: O-arm • The O-arm system • An intraoperative 2D/3D imaging system. • Designed to meet the workflow demands of the surgical environment. • It can be used in variety of procedures including spine, cranial, and orthopedics.

  6. Materials: RaySafe Real-Time Dosimeter • RaySafe visualizes X-ray exposure in real-time. • Includes a set of personal radiation dosimeters coupled with a display and software to provide an immediate visual of radiation exposure. • Measurements are simultaneously stored for post-procedure analysis.

  7. Materials: Acrylic CT Phantom • The acrylic CT phantom is used for dosimetry measurements. • Two adult abdominal phantoms were utilized. • The two phantoms were placed end to end to more accurately simulate a patient with a higher BMI.

  8. Materials: IV Pole • The personal monitoring devices were secured onto an IV pole at different heights. • This was done to measure the dose at different levels of the body. • It was positioned around the O-arm to measure the scatter cloud.

  9. Methods • The dosimeters were placed on the IV pole at levels of 2, 3, 4, and 5 feet above the ground. • The IV pole was placed in 6 different locations at two different distances. • Three feet and six feet from the isocenter of the phantom. • Location 7 was only recorded at one distance (six feet) due to the body of the O-arm obstructing IV pole placement. * * * Symmetry was assumed along the axis of the O-arm

  10. Methods • Two miscellaneous locations were added. • One behind a lead wall in the corner of the OR (7’8” from isocenter). • Another outside the OR door.

  11. Methods • The O-arm was set to the XL technique. • O-arm typically used on high BMI patients. • This setting was used to obtain more accurate readings. • 120 kVp at 400 mAs was utilized.

  12. Findings • The results show between two and four “hot spots” at which the accumulated dose was most intense. • These “hot spots” occurred with greater intensity on the left side of the O-arm. • The most intense readings occurred at the four and five foot levels, and at a distance of three feet from the O-arm. • The lowest values for accumulated dose occurred where the body of the machine shielded the RaySafe dosimeters from the scatter cloud. • The two miscellaneous locations were not included with the graph as they recorded little to no data.

  13. Discussion • The observed “hot spots” and variation in intensity based on the height of the RaySafe dosimeters support the hypothesis that the O-arm produces a non-uniform scatter cloud at all levels measured. • The variation in intensity between the three and six foot distances from the O-arm can likely be explained by the inverse-square law. • This was an expected outcome.

  14. Discussion • The mirroring of the “hot spots” may be attributed to the radiation source rotating around a single axis as well as some inherent shielding present in the O-arm. • This may also explain the intensity being greater at higher levels. • The O-arm produces a greater amount of scatter than other conventional fluoroscopic techniques, and there is significant variation in the scatter cloud produced. • This information can be valuable for medical workers in determining where to position themselves around the room.

  15. References LANDAUER Real-time Dosimetry Service. (n.d.). Retrieved from https://www.landauer.com/real-time-radiation-monitoring Medtronic. (n.d.). Arm - Surgical Imaging Systems. Retrieved from https://www.medtronic.com/us-en/healthcare-professionals/products/neurological/surgical-imaging-systems/o-arm.html Weir, V., Zhang, J., Fajardo, L., Hsiung, H., & Ritenour, E. (2008). WE-E-332-02: Dosimetric Characterization of a Cone Beam O-Arm Imaging System. Medical Physics,35(6Part25), 2957-2957. doi:10.1118/1.2962794 Software Used: AutoCAD 2019 (Version P.46.0.0) [Computer software]. (n.d.). Retrieved March 22, 2019, from https://www.autodesk.com/products/autocad/overview EZGIF Animated GIF editor and GIF maker. (n.d.). Retrieved March 22, 2019, from https://ezgif.com/ Plot.ly. (n.d.). Retrieved March 22, 2019, from https://plot.ly/ Online Graphing Application

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