Changes in tissue biomechanical properties often signify the onset and progression of diseases, such as in determining the vulnerability of atherosclerotic plaques. Acoustic radiation force optical coherence elastography (ARF-OCE) has been used in the detection of tissue elasticity to obtain high-resolution elasticity maps. We have developed a probe-based ARF-OCE technology that utilizes a miniature 10 MHz ring ultrasonic transducer for excitation and Doppler optical coherence tomography (OCT) for detection. The transducer has a small hole in the center for the OCT light to propagate through. This allows for a confocal stress field and light detection within a small region for high sensitivity and localized excitation. This device is a front-facing probe that is only 3.5 mm in diameter and it is the smallest ARF-OCE catheter to the best of our knowledge. We have tested the feasibility of the probe by measuring the point displacement of an agarose tissue-mimicking phantom using different ARF excitation voltages. Small displacement values ranging from 30 nm to 90 nm have been detected and are shown to be directly proportional to the excitation voltage as expected. We are currently working on obtaining 2D images using a scanning mechanism. We will be testing to capture 2D elastograms of phantoms to further verify feasibility, and eventually characterize the mechanical properties of cardiovascular tissue. With its high portability and sensitivity, this novel technology can be applied to the diagnosis and characterization of vulnerable atherosclerotic plaques.
In this study, we have developed an acoustic radiation force orthogonal excitation optical coherence elastography
(ARFOE-OCE) method for the visualization of the shear wave and the calculation of the shear modulus based on the OCT
Doppler variance method. The vibration perpendicular to the OCT detection direction is induced by the remote acoustic
radiation force (ARF) and the shear wave propagating along the OCT beam is visualized by the OCT M-scan. The
homogeneous agar phantom and two-layer agar phantom are measured using the ARFOE-OCE system. The results show
that the ARFOE-OCE system has the ability to measure the shear modulus beyond the OCT imaging depth. The OCT
Doppler variance method, instead of the OCT Doppler phase method, is used for vibration detection without the need of
high phase stability and phase wrapping correction. An M-scan instead of the B-scan for the visualization of the shear
wave also simplifies the data processing.
High-resolution elasticity mapping of tissue biomechanical properties is crucial in early detection of many diseases. We report a method of acoustic radiation force optical coherence elastography (ARF-OCE) based on the methods of vibroacoustography, which uses a dual-ring ultrasonic transducer in order to excite a highly localized 3-D field. The single element transducer introduced previously in our ARF imaging has low depth resolution because the ARF is difficult to discriminate along the entire ultrasound propagation path. The novel dual-ring approach takes advantage of two overlapping acoustic fields and a few-hundred-Hertz difference in the signal frequencies of the two unmodulated confocal ring transducers in order to confine the acoustic stress field within a smaller volume. This frequency difference is the resulting “beating” frequency of the system. The frequency modulation of the transducers has been validated by comparing the dual ring ARF-OCE measurement to that of the single ring using a homogeneous silicone phantom. We have compared and analyzed the phantom resonance frequency to show the feasibility of our approach. We also show phantom images of the ARF-OCE based vibro-acoustography method and map out its acoustic stress region. We concluded that the dual-ring transducer is able to better localize the excitation to a smaller region to induce a focused force, which allows for highly selective excitation of small regions. The beat-frequency elastography method has great potential to achieve high-resolution elastography for ophthalmology and cardiovascular applications.
Light-emitting diode (LED) based endoscopic illumination devices have been shown to have several benefits over arclamp
systems. LEDs are energy-efficient, small, durable, and inexpensive, however their use in endoscopy has been
limited by the difficulty in efficiently coupling enough light into the endoscopic light cable. We have demonstrated a
highly homogenised lightpipe LED light source that combines the light from four Luminus LEDs emitting in the red,
green, blue and violet using innovative dichroics that maximise light throughput. The light source spectrally combines
light from highly divergent incoherent sources that have a Lambertian intensity profile to provide illumination matched
to the acceptance numerical aperture of a liquid light guide or fibre bundle. The LED light source was coupled to a
standard laparoscope and performance parameters (power, luminance, colour temperature) compared to a xenon lamp.
Although the total illuminance from the endoscope was lower, adjustment of the LEDs' relative intensities enabled
contrast enhancement in biological tissue imaging. The LED light engine was also evaluated in a minimally invasive
surgery (MIS) box trainer and in vivo during a porcine MIS procedure where it was used to generate 'narrowband'
images. Future work using the violet LED could enable photodynamic diagnosis of bladder cancer.
In this paper we present a method to visualize the pressure field of an ultrasound beam in a single shot of the CCD and
to image the shear wave propagation based on acousto-optic laser speckle contrast analysis. The contrast images show
features in the near field, far field and central region of the ultrasound beam and the pressure profile fits with that
measured with a hydrophone. The shear wave propagation was acquired by changing the imaging delay time after the
ultrasound burst. This method can be used to study the shear wave properties of common tissue phantoms to guide
experiments on tissue.
KEYWORDS: Modulation, Ultrasonography, Particles, Ultrasound-modulated optical tomography, Monte Carlo methods, Tissue optics, Phase shift keying, Acoustics, Scattering, Signal to noise ratio
Ultrasound modulated optical tomography (UOT) is a hybrid technique which combines optical contrast with ultrasound
resolution and has shown some potential for early cancer detection, functional and molecular imaging. However, one
current problem with this technique is the weak optical modulation signal strength and consequently low Signal-to-Noise
Ratio (SNR). In this study, the effect of increasing the amplitude of the ultrasound induced particle displacement on the
UOT signal is investigated using a Monte Carlo simulation tool. The simulation software was validated against those
reported in the literature and good agreement was achieved. The simulated amplitude of particle displacement was varied
from 0.1 to 500nm . The results showed a significant increase in UOT signal with particle displacement for low
displacements, followed by saturation when displacement increased beyond a certain level. Further simulations were
performed to investigate the saturation by changing the optical wavelength from 400nm to 600nm . The results show
that the UOT signal saturates at lower particle displacements for smaller wavelengths. This suggests that the phase
variations along a photon path can be large enough to cause cancellation as particle displacement increases. This study is
part of ongoing efforts to improve the SNR of UOT through using the large particle displacements created by high
amplitude ultrasound and radiation forces.
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