A Spine-Specific Phased Array for Transvertebral Ultrasound Therapy: Design and Simulation.

OBJECTIVE

To design and simulate the performance of two spine-specific phased arrays in sonicating targets spanning the thoracic spine, with the objective of efficiently producing controlled foci in the spinal canal.

METHODS

Two arrays (256 elements each, 500 kHz) were designed using multi-layered ray acoustics simulation: a four-component array with dedicated components for sonicating via the paravertebral and transvertebral paths, and a two-component array with spine-specific adaptive focusing. Mean array efficiency (canal focus pressure/water focus pressure) was evaluated using forward simulation in neutral and flexed spines to investigate methods that reduce spine-induced insertion loss. Target-specific four-component array reconfiguration and lower frequency sonication (250 kHz) were tested to determine their effects on array efficiency and focal dimensions.

RESULTS

When neutral, two- and four-component efficiencies were [Formula: see text]% and [Formula: see text]%, respectively, spine flexion significantly increased four-component efficiency ([Formula: see text]%), but not two-component efficiency ([Formula: see text]%). Target-specific four-component re-configuration significantly improved efficiency ([Formula: see text]%). Both arrays produced controlled foci centered within the canal with similar 50% pressure contour dimensions: 10.8-11.9 mm (axial), 4.2-5.6 mm (lateral), and 5.9-6.2 mm (vertical). Simulation at 250 kHz also improved two- and four-component efficiency ([Formula: see text]% and [Formula: see text]%, respectively), but doubled the lateral focal dimensions.

CONCLUSION

Simulation shows that the spine-specific arrays are capable of producing controlled foci in the thoracic spinal canal.

SIGNIFICANCE

The complex geometry of the human spine presents geometrical and acoustical challenges for transspine ultrasound focusing, and the design of these spine-specific ultrasound arrays is crucial to the clinical translation of focused ultrasound for the treatment of spinal cord disease.