gying Guan

Quantitative elastography provided by surface acoustic waves measured by phase-sensitive optical coherence tomography

We report on a quantitative elastography technique achieved by combining phase-sensitive optical coherence tomography (PhS-OCT) with the surface acoustic wave (SAW) method. Different from traditional optical coherence elastography, the elastography is achieved by impulse-stimulated SAW, rather than by shear waves. PhS-OCT serves not only as a detector to measure SAW signals but also as a means to provide a cross-sectional image of the sample. The experimental results indicate that the combination of PhS-OCT with SAW is feasible to provide quantitative elastography of heterogeneous tissue samples.

Determining elastic properties of skin by measuring surface waves from an impulse mechanical stimulus using phase-sensitive optical coherence tomography

The mechanical properties of skin are important tissue parameters that are useful for understanding skin patho-physiology, which can aid disease diagnosis and treatment. This paper presents an innovative method that employs phase-sensitive spectral-domain optical coherence tomography (PhS-OCT) to characterize the biomechanical properties of skin by measuring surface waves induced by short impulses from a home-made shaker. Experiments are carried out on single and double-layer agar–agar phantoms, of different concentrations and thickness, and on in vivo human skin, at the forearm and the palm. For each experiment, the surface wave phase-velocity dispersion curves were calculated, from which the elasticity of each layer of the sample was determined. It is demonstrated that the experimental results agree well with previous work. This study provides a novel combination of PhS-OCT technology with a simple and an inexpensive mechanical impulse surface wave stimulation that can be used to non-invasively evaluate the mechanical properties of skin in vivo, and may offer potential use in clinical situations.

Noncontact all-optical measurement of corneal elasticity.

We report on a noninvasive and noncontact all-optical method to measure the elasticity of the cornea. We use a pulsed laser to excite surface acoustic waves (SAW) that propagate on the corneal surface, then use a phase-sensitive optical coherence tomography system to remotely record the SAWs from which the corneal elasticity is estimated. In addition, the system is able to provide real-time tomographic images of the cornea being examined, an important consideration for clinical studies. While precisely maintaining a range of intraocular pressures (IOP), a series of measurements is performed on ex vivo intact primate eyes. The measurement results not only demonstrate the feasibility of the proposed system to remotely measure the corneal elasticity, but also suggest a strong correlation between the corneal stiffness and the true IOP.

Detection and characterisation of biopsy tissue using quantitative optical coherence elastography (OCE) in men with suspected prostate cancer

We present first quantitative three-dimensional (3D) data sets recorded using optical coherence elastography (OCE) for the diagnosis and detection of prostate cancer (PCa). 120 transrectal ultrasound guided prostate biopsy specimens from 10 men suspected with prostate cancer were imaged using OCE. 3D quantitative mechanical assessment of biopsy specimens obtained in kilopascals (kPa) at an interval of 40 µm was compared with histopathology. Sensitivity, specificity, and positive and negative predictive values were calculated for OCE in comparison to histopathology. The results show OCE imaging could reliably differentiate between benign prostate tissue, acinar atypical hyperplasia, prostatic intraepithelial neoplasia and malignant PCa. The sensitivity and specificity of OCE for the detection of prostate cancer was 0.98 and 0.91 with AUC > 0.99. Quantitative 3D OCE based on the assessment of mechanical properties of tissues can reliably differentiate prostate tissue specimen in an ex-vivo setting. This is a promising imaging modality for characterising different grades of cancers.

Quantitative evaluation of degenerated tendon model using combined optical coherence elastography and acoustic radiation force method

Abstract. Damage of collagen fibers in tendons is often directly related to changes in a tendon’s mechanical properties. Direct quantitative elasticity measurement of tendons will provide important information in tendon dysfunction diagnosis and treatment assessment. A feasibility study of quantifying the mechanical properties of a degenerated tendon model by a nondestructive imaging modality, which combines optical coherence elastography and acoustic radiation force (ARF) method, is presented. The degenerated tendon model was produced by the partial degradation of chicken tendons through incubation with collagenase at different concentrations and incubation times. A 30-kHz longitudinal ultrasound transducer was used to provide an ARF signal, which was detected by an ultra-high sensitive phase sensitive optical coherence tomography (PhS-OCT) system. The experimental results demonstrate that the combination of ARF method and PhS-OCT can measure the elasticity of tendon quantitatively. The corresponding changes in tendon elasticity due to the application of collagenase have been revealed by this new imaging modality. This method can potentially be used in the assessment of tissue engineering products and in the diagnosis and treatment progression of tendon diseases.

Quantitative elasticity measurement of urinary bladder wall using laser-induced surface acoustic waves

The maintenance of urinary bladder elasticity is essential to its functions, including the storage and voiding phases of the micturition cycle. The bladder stiffness can be changed by various pathophysiological conditions. Quantitative measurement of bladder elasticity is an essential step toward understanding various urinary bladder disease processes and improving patient care. As a nondestructive, and noncontact method, laser-induced surface acoustic waves (SAWs) can accurately characterize the elastic properties of different layers of organs such as the urinary bladder. This initial investigation evaluates the feasibility of a noncontact, all-optical method of generating and measuring the elasticity of the urinary bladder. Quantitative elasticity measurements of ex vivo porcine urinary bladder were made using the laser-induced SAW technique. A pulsed laser was used to excite SAWs that propagated on the bladder wall surface. A dedicated phase-sensitive optical coherence tomography (PhS-OCT) system remotely recorded the SAWs, from which the elasticity properties of different layers of the bladder were estimated. During the experiments, series of measurements were performed under five precisely controlled bladder volumes using water to estimate changes in the elasticity in relation to various urinary bladder contents. The results, validated by optical coherence elastography, show that the laser-induced SAW technique combined with PhS-OCT can be a feasible method of quantitative estimation of biomechanical properties.

Depth profiling of photothermal compound concentrations using phase sensitive optical coherence tomography

A model that describes the concentration of photothermal (light-to-heat converters) compounds as a function of depth in a turbid medium is developed. The system consists of a pump laser (808 nm modulated at 400 Hz), which heats a photothermal compound, and a phase sensitive spectral domain optical coherence tomography system, which detects the changes in the optical path length of the sample induced by the temperature increase. The model is theoretically derived and the coefficients are empirically determined using solid homogeneous gel phantoms. The model is validated by reconstructing the concentration of a photothermal compound in thick single and double layer solid phantoms.

Laser induced surface acoustic wave combined with phase sensitive optical coherence tomography for superficial tissue characterization: a solution for practical application

Mechanical properties are important parameters that can be used to assess the physiologic conditions of biologic tissue. Measurements and mapping of tissue mechanical properties can aid in the diagnosis, characterisation and treatment of diseases. As a non-invasive, non-destructive and non-contact method, laser induced surface acoustic waves (SAWs) have potential to accurately characterise tissue elastic properties. However, challenge still exists when the laser is directly applied to the tissue because of potential heat generation due to laser energy deposition. This paper focuses on the thermal effect of the laser induced SAW on the tissue target and provides an alternate solution to facilitate its application in clinic environment. The solution proposed is to apply a thin agar membrane as surface shield to protect the tissue. Transient thermal analysis is developed and verified by experiments to study the effects of the high energy Nd:YAG laser pulse on the surface shield. The approach is then verified by measuring the mechanical property of skin in a Thiel mouse model. The results demonstrate a useful step toward the practical application of laser induced SAW method for measuring real elasticity of normal and diseased tissues in dermatology and other surface epithelia.

Evaluating elastic properties of heterogeneous soft tissue by surface acoustic waves detected by phase-sensitive optical coherence tomography

The combined use of surface acoustic wave (SAW) and phase-sensitive optical coherence tomography (PhS-OCT) is useful to evaluate the elasticity of layered biological tissues, such as normal skin. However, the pathological tissue is often originated locally, leading to the alternation of mechanical properties along both axial and lateral directions. We present a feasibility study on whether the SAW technique is sensitive to detect the alternation of mechanical property along the lateral direction within tissue, which is important for clinical utility of this technique to localize diseased tissue. Experiments are carried out on purposely designed tissue phantoms and ex vivo chicken breast samples, simulating the localized change of elasticity. A PhS-OCT system is employed not only to provide the ultra-high sensitive measurement of the generated surface waves on the tissue surface, but also to provide the real time imaging of the tissue to assist the elasticity evaluation of the heterogeneous tissue. The experimental results demonstrate that with PhS-OCT used as a pressure sensor, the SAW is highly sensitive to the elasticity change of the specimen in both vertical and lateral directions with a sensing depth of ∼5 mm with our current system setup, thus promising its useful clinical applications where the quantitative elasticity of localized skin diseases is needed to aid in diagnosis and treatment.

Multifunctional nanoprobe to enhance the utility of optical based imaging techniques

Several imaging modalities such as optical coherence tomography, photothermal, photoacoustic and magnetic resonance imaging, are sensitive to different physical properties (i.e. scattering, absorption and magnetic) that can provide contrast within biological tissues. Usually exogenous agents are designed with specific properties to provide contrast for these imaging methods. In nano-biotechnology there is a need to combine several of these properties into a single contrast agent. This multifunctional contrast agent can then be used by various imaging techniques simultaneously or can be used to develop new imaging modalities. We reported and characterized a multifunctional nanoparticle, made from gold nanoshells, which exhibits scattering, photothermal, photoacoustic, and magnetic properties.