4A-6 Ultrasound Guided Placement of Pedicle Screws in Spinal Fusion Surgery

Transpedicular spinal fusion involves the placement of large screws into the vertebrae, and entails substantial risk to numerous neural and vascular structures. To address the deficiencies of the freehand and currently available guidance techniques we propose the development of an ultrasound based device for pedicle screw guidance. Ultrasonic transmission measurements of seven vertebral cancellous bone specimens were performed along the craniocaudal axis with planar 1 MHz and 3.5 MHz broadband transducers. The center frequency attenuation, normalized Broadband Ultrasound Attenuation (nBUA), and phase speed were measured. Pulse echo methods were used to demonstrate A-mode imaging through cancellous bone as well as boundary detection. Our in vitro results provide good evidence that A-mode imaging for pedicle screw guidance is possible at frequencies as high as 3.5 MHz and that boundaries can be accurately identified.