Integrated optical coherence tomography and multielement ultrasound transducer probe for shear wave elasticity imaging of moving tissues

Abstract

Accurate measurements of microelastic properties of soft tissues in-vivo using optical coherence elastography can be affected by motion artifacts caused by cardiac and respiratory cycles. This problem can be overcome using a multielement ultrasound transducer probe where each ultrasound transducer is capable of generating acoustic radiation force (ARF) and, therefore, creating shear waves in tissue. These shear waves, produced during the phase of cardiac and respiratory cycles when tissues are effectively stationary, are detected at the same observation point using phase-sensitive optical coherence tomography (psOCT). Given the known distance between the ultrasound transducers, the speed of shear wave propagation can be calculated by measuring the difference between arrival times of shear waves. The combined multitransducer ARF/psOCT probe has been designed and tested in phantoms and ex-vivo studies using fresh rabbit heart. The measured values of shear moduli are in good agreement with those reported in literature. Our results suggest that the developed multitransducer ARF/psOCT probe can be useful for many in-vivo applications, including quantifying the microelasticity of cardiac muscle.

Keywords: acoustic radiation force; cardiac muscle; multielement ultrasound transducer probe; optical coherence tomography and elastography; shear wave elasticity imaging.

Fig. 1

(a) Diagram and microphotograph of the miniature ultrasound transducer. The scale bar is 2 mm. (b) Alignment of the ultrasound transducer and an OCT intravascular catheter. Thick red and thin blue arrows indicate the ultrasound and OCT beams, respectively. The scale bar is 2 mm.

Fig. 2

(a) Microphotograph of the multitransducer ultrasound array with transducer size of $1.5\mathrm{mm}\times 1.5\mathrm{mm}$ square. The scale bar is 2 mm. (b) A diagram of the assembled multitransducer ARF/psOCT probe. (c) A diagram of phantom experiments. (d) Photograph of the ARF/psOCT probe positioned above the rabbit heart. Scale bar is 2 mm.

Fig. 3

(a) Typical M-mode psOCT image of a phantom. The vertical and horizontal scale bars are $100\mu \mathrm{m}$ and 2 ms, respectively. (b) Shear wave detected in phantom. The magnitude of the displacement is smaller than the pixel size of $2.9\mu \mathrm{m}$.

Fig. 4

Shear waves induced in 10 wt. % gelatin phantom by ultrasound transducers closer (solid blue-colored lines) and further (dashed green-colored lines) from the OCT observation spot.

Fig. 5

Representative shear waves produced in rabbit heart muscle by different ultrasound transducers of the ARF/psOCT probe located closer to its tip (solid blue line) and further from the tip (dashed green line).