Contrast-enhanced ultrasound to visualize hemodynamic changes after rodent spinal cord injury

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OBJECTIVE

Traumatic spinal cord injury (tSCI) causes an almost complete loss of blood flow at the site of injury (primary injury) as well as significant hypoperfusion in the penumbra of the injury. Hypoperfusion in the penumbra progresses after injury to the spinal cord and is likely to be a major contributor to progressive cell death of spinal cord tissue that was initially viable (secondary injury). Neuroprotective treatment strategies seek to limit secondary injury. Clinical monitoring of the temporal and spatial patterns of blood flow within the contused spinal cord is currently not feasible. The purpose of the current study was to determine whether ultrafast contrast-enhanced ultrasound (CEUS) Doppler allows for detection of local hemodynamic changes within an injured rodent spinal cord in real time.

METHODS

A novel ultrafast CEUS Doppler technique was developed utilizing a research ultrasound platform combined with a 15-MHz linear array transducer. Ultrafast plane-wave acquisitions enabled the separation of higher-velocity blood flow in macrocirculation from low-velocity flow within the microcirculation (tissue perfusion). An FDA-approved contrast agent (microbubbles) was used for visualization of local blood flow in real time. CEUS Doppler acquisition protocols were developed to characterize tissue perfusion both during contrast inflow and during the steady-state plateau. A compression injury of the thoracic spinal cord of adult rats was induced using iris forceps.

RESULTS

High-frequency ultrasound enabled visualization of spinal cord vessels such as anterior spinal arteries as well as central arteries (mean diameter [± SEM] 145.8 ± 10.0 µm; 76.2 ± 4.5 µm, respectively). In the intact spinal cord, ultrafast CEUS Doppler confirmed higher perfusion of the gray matter compared to white matter. Immediately after compression injury of the thoracic rodent spinal cord, spinal cord vessels were disrupted in an area of 1.93 ± 1.14 mm2. Ultrafast CEUS Doppler revealed a topographical map of local tissue hypoperfusion with remarkable spatial resolution. Critical loss of perfusion, defined as less than 40% perfusion compared to the surrounding spared tissue, was seen within an area of 2.21 ± 0.6 mm2.

CONCLUSIONS

In our current report, we introduce ultrafast CEUS Doppler for monitoring of spinal vascular structure and function in real time. Development and clinical implementation of this type of imaging could have a significant impact on the care of patients with tSCI.

ABBREVIATIONS CEUS = contrast-enhanced ultrasound; SCI = spinal cord injury; SEM = standard error of the mean; tSCI = traumatic SCI.

Article Information

Correspondence Christoph Hofstetter: The University of Washington, Seattle, WA. chh9045@uw.edu.

INCLUDE WHEN CITING Published online June 15, 2018; DOI: 10.3171/2018.1.SPINE171202.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Illustration of ultrafast CEUS Doppler’s ability to distinguish between stationary (a, c, and e) and flowing (b, d, and g) microbubbles, as well as estimate the velocity of higher-velocity microbubbles (f). a: Stationary microbubbles are detected using ultrafast CEUS Doppler. b: Detection of flowing microbubbles. c and e: Doppler filtering removing the nonlinear Doppler signals from stationary microbubbles. d: Doppler filtering preserving nonlinear Doppler signals from moving microbubbles. f: Velocity estimates showing a parabola-like flow profile having a peak central velocity of 3 cm/sec. Figure is available in color online only.

  • View in gallery

    Ultrafast CEUS Doppler imaging of spinal vasculature and blood flow in macro- and microcirculations before (a–c) and after (d–f) injury in a rodent spinal cord. Panels a and d show higher-velocity microbubble flow in the larger vasculature before and after tSCI, respectively. Panels b and e show estimates of microbubble velocity in the larger vasculature before and after injury, respectively. Panels c and f show the lower-velocity microbubbles in the microcirculation (i.e., perfusion) before and after injury, respectively. dB = decibel—ratio of Doppler power signals represented in log scale to the lowest signal displayed in black.

  • View in gallery

    Left: Sagittal CEUS image of an injured spinal cord with colors demarcating the injury center with a loss of perfusion (red), an area of hypoperfusion (blue), and an intact area (green). Right: Contrast inflow curves of the areas demarcated in the CEUS image.

  • View in gallery

    Upper: Sagittal contour map delineating the injured spinal cord tissue with critically low tissue perfusion. The outlined area (yellow and white) demarcates the area of the injury with less than 40% tissue perfusion compared to surrounding healthy tissue. Lower: H & E–stained sagittal section of the same spinal cord showing the acute SCI. Note the close resemblance of the necrotic core to the area outlined in the sagittal contour map.

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