Fletcher SMP, Ogrodnik N, O'Reilly MA. Enhanced Detection of Bubble Emissions Through the Intact Spine for Monitoring Ultrasound-Mediated Blood-Spinal Cord Barrier Opening.
IEEE Trans Biomed Eng 2019;
67:1387-1396. [PMID:
31442968 DOI:
10.1109/tbme.2019.2936972]
[Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
OBJECTIVE
We previously developed short burst, phase keying (SBPK) focused ultrasound (FUS) to mitigate standing waves in the human vertebral canal. Here, we show microbubble emissions from these pulses can be detected through the human vertebral arch and that these pulses are effective for blood-spinal cord barrier (BSCB) opening.
METHODS
At f0 = 514 kHz, circulating microbubbles were sonicated through ex vivo human vertebrae (60 kPa-1 MPa) using a dual-aperture approach and SBPK exposures engineered to incorporate pulse inversion (PI). Signals from a 250 kHz receiver were analyzed using PI, short-time Fourier analysis and the maximum projection over the pulse train. In rats (n = 14), SBPK FUS+microbubbles was applied to 3 locations/spinal cord at fixed pressures (∼0.20-0.47 MPa). MRI and histology were used to assess opening and tissue damage.
RESULTS
In human vertebrae between 0.2-0.4 MPa, PI amplified the microbubble/baseline ratio at f0/2 and 2f0 by 202 ± 40% (132-291%). This was maximal at 0.4 MPa, coinciding with the onset of broadband emissions. In vivo, opening was achieved at 40/42 locations, with mean MRI enhancement of 46 ± 32%(16%-178%). Using PI, f0/2 was detected at 14/40 opening locations. At the highest pressures (f0/2 present) histology showed widespread bleeding throughout the focal region. At the lowest pressures, opening was achieved without bleeding.
CONCLUSION
This study confirmed that PI can increase sensitivity to transvertebral detection of microbubble signals. Preliminary in vivo investigations show that SBPK FUS can increase BSCB permeability without tissue damage.
SIGNIFICANCE
SBPK is a clinically relevant pulse scheme and, in combination with PI, provides a means of mediating and monitoring BSCB opening noninvasively.
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