Combined Ultrasound and Photoacoustic Image Guidance of Spinal Pedicle Cannulation Demonstrated With Intact ex vivo Specimens

• Published in: IEEE transactions on biomedical engineering Vol. 68; no. 8; pp. 2479 - 2489
• Main Authors: Gonzalez, Eduardo A., Jain, Amit, Bell, Muyinatu A. Lediju
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.08.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplitudes; Array signal processing; Back surgery; Beamforming; Bone segmentation; Bone surgery; Bones; Cancellous bone; Cannulation; Coherence; coherence imaging; Computed tomography; Corridors; Cortical bone; Fasteners; Human performance; Image acquisition; Imaging; Kernel; landmark registration; Optical fibers; Pedicle screws; photoacoustic imaging; Registration; Response time; spinal fusion; Surgery; Ultrasonic imaging; Ultrasound; Vertebrae; Visualization
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/TBME.2020.3046370

Objective: Spinal fusion surgeries require accurate placement of pedicle screws in anatomic corridors without breaching bone boundaries. We are developing a combined ultrasound and photoacoustic image guidance system to avoid pedicle screw misplacement and accidental bone breaches, which can lead to nerve damage. Methods: Pedicle cannulation was performed on a human cadaver, with co-registered photoacoustic and ultrasound images acquired at various time points during the procedure. Bony landmarks obtained from coherence-based ultrasound images of lumbar vertebrae were registered to post-operative CT images. Registration methods were additionally tested on an ex vivo caprine vertebra. Results: Locally weighted short-lag spatial coherence (LW-SLSC) ultrasound imaging enhanced the visualization of bony structures with generalized contrast-to-noise ratios (gCNRs) of 0.99 and 0.98−1.00 in the caprine and human vertebrae, respectively. Short-lag spatial coherence (SLSC) and amplitude-based delay-and-sum (DAS) ultrasound imaging generally produced lower gCNRs of 0.98 and 0.84, respectively, in the caprine vertebra and 0.84−0.93 and 0.34−0.99, respectively, in the human vertebrae. The mean <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> standard deviation of the area of −6 dB contours created from DAS photoacoustic images acquired with an optical fiber inserted in prepared pedicle holes (i.e., fiber surrounded by cancellous bone) and holes created after intentional breaches (i.e., fiber exposed to cortical bone) was 10.06<inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula>5.22 mm<inline-formula><tex-math notation="LaTeX">^2</tex-math></inline-formula> and 2.47<inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula>0.96 mm<inline-formula><tex-math notation="LaTeX">^2</tex-math></inline-formula>, respectively (p <inline-formula><tex-math notation="LaTeX">< </tex-math></inline-formula> 0.01). Conclusions: Coherence-based LW-SLSC and SLSC beamforming improved visualization of bony anatomical landmarks for ultrasound-to-CT registration, while amplitude-based DAS beamforming successfully distinguished photoacoustic signals within the pedicle from less desirable signals characteristic of impending bone breaches. Significance: These results are promising to improve visual registration of ultrasound and photoacoustic images with CT images, as well as to assist surgeons with identifying and avoiding impending bone breaches during pedicle cannulation in spinal fusion surgeries.