Abstract
: Optical coherence elastography employs optical coherence tomography (OCT) to measure the displacement of tissues under load and, thus, maps the resulting strain into an image, known as an elastogram. We present a new improved method to measure vibration amplitude in dynamic optical coherence elastography. The tissue vibration amplitude caused by sinusoidal loading is measured from the spread of the Doppler spectrum, which is extracted using joint spectral and time domain signal processing. At low OCT signal-to-noise ratio (SNR), the method provides more accurate vibration amplitude measurements than the currently used phase-sensitive method. For measurements performed on a mirror at OCT SNR = 5 dB, our method introduces <3% error, compared to >20% using the phase-sensitive method. We present elastograms of a tissue-mimicking phantom and excised porcine tissue that demonstrate improvements, including a 50% increase in the depth range of reliable vibration amplitude measurement.
Highlights
Optical coherence elastography (OCE) is a technique for imaging the microscopic mechanical properties of tissue [1], with the potential to provide at least an order of magnitude improvement in spatial resolution over elastography based on ultrasound [2] or MRI [3]
We propose a new method for improved vibration amplitude measurement in dynamic OCE, which is based on an analysis of the frequency tones of the Doppler spectrum obtained from a sample subjected to sinusoidal loading
For high optical coherence tomography (OCT) signal-to-noise ratio (SNR), the phase probability density functions (PDFs) tends towards a delta function, whilst the amplitude PDF is approximated by a Gaussian distribution, with variance determined by the shot noise of the system
Summary
Optical coherence elastography (OCE) is a technique for imaging the microscopic mechanical properties of tissue [1], with the potential to provide at least an order of magnitude improvement in spatial resolution over elastography based on ultrasound [2] or MRI [3]. In OCE, a sample is subjected to mechanical loading (stress) and the resulting local displacement is measured using optical coherence tomography (OCT) [4]. Quasi-static loading was employed and the displacement between consecutive B-scans was measured using cross correlation-based speckle-tracking algorithms [1,6,7]. Quasi-static, phase-sensitive OCE was proposed, in part, to overcome this limitation by improving the lower limit on displacement [11]. This method is based on the linear relationship between the phase of the OCT signal and sample motion [12,13]. A needle-based extension to quasi-static, phase-sensitive OCE has been reported [14]
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