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UBC Theses and Dissertations

Panorama ultrasound for navigation and guidance of epidural anesthesia Rafii-Tari, Hedyeh


Epidural anesthesia is a common but challenging procedure in obstetrics and surgery, especially for the obese patient, and can result in complications such as dural puncture and nerve injury. Ultrasound has the potential to significantly improve epidural needle guidance, by being able to depict the spinal anatomy and the epidural space. An ultrasound guidance system is therefore proposed, using a transducer-mounted camera to create 3D panorama images of the spine relative to markings on the skin. Guidance will include depiction of the spinal anatomy, identification of individual vertebrae, and selection of a suitable puncture site, trajectory and depth of needle insertion. The camera tracks the transducer movement using a specialized strip of markers attached to the skin surface. This enables 6-DOF absolute position estimation of the transducer with respect to the patient over the full range of the spine. The 3D panorama image can then be resliced in various parasagittal planes to show either the target epidural spaces or the laminae. The overall accuracy of the panorama reconstruction is validated by measuring inter-feature distances of a phantom of steel beads against measurements obtained from an optical tracking system (Optotrak), resulting in an average error of 0.64 mm between camera and Optotrak. The algorithm is then tested in vivo by creating panorama images from human subjects (n=20), obtaining measurements for depth of insertion to the epidural space, intervertebral spacings, and registration of interspinous gaps to the skin, and validating these against independent measurements by an experienced sonographer. The results showed an average error of 1.69 mm (4.23%) for the depth measurements, average error of 4.44 mm (15.2%) for the interspinous distance measurements, and an average error of 6.65 mm for registering the interspinous gaps to the skin (corresponding to 18.5% of the interspinous distances). Tracking of ultrasound images with respect to the marker is implemented in real time and visualized using the 3D Slicer software package.

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