A High-Frequency Ultrasound Endoscope for Minimally Invasive Spine Surgery

The transition to minimally invasive spinal surgery over traditional open procedures requires the development of imaging techniques that meet the size constraints. Due to size restrictions associated with minimally invasive spine surgery (MISS), current imaging techniques are largely limited to microscopy, which is only capable of line-of-sight imaging of the tissue surface. A miniature, high-resolution ultrasound imaging endoscope has been developed as a potential alternative imaging method that would enable intraoperative guidance. We have designed and developed a 30-MHz miniature, 64-element high-resolution imaging endoscope using PIN-PMT-PT single crystal as the piezoelectric substrate. The packaged probe had cross-sectional dimensions of $3.8\times 4.2$ mm and a length of 14 cm. Two editions of the endoscope were created with a forward facing and 40° angle to enable visualization of structures during a medial and lateral approach, respectively. The probe was combined with a custom imaging system that produced real-time images with a field of view ranging between ±32° and an image depth of 15 mm. The two-way axial resolution was measured to be $38~\mu $ m based on the -6-dB width of the pulse envelope. The -6-dB lateral resolution was measured to be 113, 131, and $158~\mu $ m at steering angles of 0°, 12°, and 25°, respectively, which were close to the simulated values of 106, 118, and $144~\mu $ m. Preliminary clinical imaging studies successfully demonstrated the visualization of pertinent spinal anatomy during minimally invasive surgeries. The imaging probe was also able to demonstrate compression and decompression of nerve roots, supporting its potential use as a clinical tool.