Imaging Capability at Close Range of High Frequency Ultrasound Transducer on the Perforation of Bony Walls Simulating Pedicle Screw Placement

Background: Ultrasound has been proved to be a promising alternative spine navigation method. High frequency ultrasound transducer has the advantage of high resolution on surface structure, but imaging at close range is difficult, especially in narrow space of the pilot-hole in pedicle.Methods: Twenty cortical bone chips were made and different size of hole with diameter of 1mm, 2mm, 3mm or 5mm was randomly carved in each bone chip. A tailored 30MHz high frequency transducer scanned bone samples at the distance of 4mm, 3mm, 2mm and 1mm. Successive transmission ringingeffect elimination, Hilbert transform and Gray-scale mapping method were utilized to process and optimize attained original images.Results: At the distance of 4mm, 3mm, 2mm and 1mm, the holes with diameter of 5mm, 3mm and 2mm could be discerned. At the distance of 1mm, only the holes with 5mm and 3mm could be clearly distinguished and the 2mm hole appeared obscure. The holes with diameter of 1mm could not be detected at any distance. The holes with diameter of 2mm were able to be detected at the distance of 1mm.Conclusions: This study indicated that the high frequency transducer had limited imaging capability at close range on the bony surface. These results lay a foundation for further developing a novel ultrasound-based spinal pedicle interior imaging and navigation system.