Longitudinal shear wave imaging for elasticity mapping using optical coherence elastography

Acoustic radiation force-induced longitudinal shear wave for ultrasound-based viscoelastic evaluation

Acoustic radiation force (ARF) is widely used to induce shear waves for evaluating the mechanical properties of biological tissues. Two shear waves can be generated when exciting with ARF: a transverse shear wave, also simply called shear wave (SW), and a longitudinal shear wave (LSW). Shear waves (SWs) have been broadly used to assess the mechanical properties. Some articles have reported that the LSW can be used to evaluate mechanical properties locally. However, existing LSW studies are mainly focused on the group velocity evaluation using optical coherence tomography (OCT). Here, we report that a LSW generated with ARF can be used to probe viscoelastic properties, including shear modulus and viscosity, using ultrasound. We took advantage of the surface boundary effect to reflect the LSW, named RLSW, to address the energy deficiency of LSW induced by ARF. We systematically evaluated the experiments with tissue-mimicking viscoelastic phantoms and validated by numerical simulations. Phase velocity and dispersion comparison between the results induced by a RLSW and a SW exhibit good agreement in both the numerical simulations and experimental results. The Kelvin-Voigt (KV) model was used to determine the shear modulus and viscosity. RLSW shows great potential to evaluate localized viscoelastic properties, which could benefit various biomedical applications such as evaluating the viscoelasticity of heterogeneous materials or microscopic lesions of tissues.

Supershear Rayleigh wave imaging for quantitative assessment of biomechanical properties of brain using air-coupled optical coherence elastography

Recently, supershear Rayleigh waves (SRWs) have been proposed to characterize the biomechanical properties of soft tissues. The SRWs propagate along the surface of the medium, unlike surface Rayleigh waves, SRWs propagate faster than bulk shear waves. However, their behavior and application in biological tissues is still elusive. In brain tissue elastography, shear waves combined with magnetic resonance elastography or ultrasound elastography are generally used to quantify the shear modulus, but high spatial resolution elasticity assessment in 10 μm scale is still improving. Here, we develop an air-coupled ultrasonic transducer for noncontact excitation of SRWs and Rayleigh waves in brain tissue, use optical coherent elastography (OCE) to detect, and reconstruct the SRW propagation process; in combing with a derived theoretical model of SRWs on a free boundary surface, we quantify the shear modulus of brain tissue with high spatial resolution. We first complete validation experiments using a homogeneous isotropic agar phantom, and the experimental results clearly show the SRW is 1.9649 times faster than the bulk shear waves. Furthermore, the propagation velocity of SRWs in both the frontal and parietal lobe regions of the brain is all 1.87 times faster than the bulk shear wave velocity. Finally, we evaluated the anisotropy in different brain regions, and the medulla oblongata region had the highest anisotropy index. Our study shows that the OCE system using the SRW model is a new potential approach for high-resolution assessment of the biomechanical properties of brain tissue.

Optical coherence elastography and its applications for the biomechanical characterization of tissues

The biomechanical characterization of the tissues provides significant evidence for determining the pathological status and assessing the disease treatment. Incorporating elastography with optical coherence tomography (OCT), optical coherence elastography (OCE) can map the spatial elasticity distribution of biological tissue with high resolution. After the excitation with the external or inherent force, the tissue response of the deformation or vibration is detected by OCT imaging. The elastogram is assessed by stress-strain analysis, vibration amplitude measurements, and quantification of elastic wave velocities. OCE has been used for elasticity measurements in ophthalmology, endoscopy, and oncology, improving the precision of diagnosis and treatment of disease. In this article, we review the OCE methods for biomechanical characterization and summarize current OCE applications in biomedicine. The limitations and future development of OCE are also discussed during its translation to the clinic.

Nanobomb optical coherence elastography in multilayered phantoms

Many tissues are composed of layered structures, and a better understanding of the changes in the layered tissue biomechanics can enable advanced guidance and monitoring of therapy. The advent of elastography using longitudinally propagating shear waves (LSWs) has created the prospect of a high-resolution assessment of depth-dependent tissue elasticity. Laser activation of liquid-to-gas phase transition of dye-loaded perfluorocarbon (PFC) nanodroplets (a.k.a., nanobombs) can produce highly localized LSWs. This study aims to leverage the potential of photoactivation of nanobombs to incudce LSWs with very high-frequency content in wave-based optical coherence elastography (OCE) to estimate the elasticity gradient with high resolution. In this work, we used multilayered tissue-mimicking phantoms to demonstrate that highly localized nanobomb (NB)-induced LSWs can discriminate depth-wise tissue elasticity gradients. The results show that the NB-induced LSWs rapidly change speed when transitioning between layers with different mechanical properties, resulting in an elasticity resolution of ∼65 µm. These results show promise for characterizing the elasticity of multilayer tissue with a fine resolution.

Noncontact longitudinal shear wave imaging for the evaluation of heterogeneous porcine brain biomechanical properties using optical coherence elastography

High-resolution quantification of heterogeneous brain biomechanical properties has long been an important topic. Longitudinal shear waves (LSWs) can be used to assess the longitudinal Young's modulus, but contact excitation methods have been used in most previous studies. We propose an air-coupled ultrasound transducer-based optical coherence elastography (AcUT-OCE) technique for noncontact excitation and detection of LSWs in samples and assessment of the nonuniformity of the brain's biomechanical properties. The air-coupled ultrasonic transducer (AcUT) for noncontact excitation of LSWs in the sample has a center frequency of 250 kHz. Phase-resolved Doppler optical coherence tomography (OCT) was used to image and reconstruct the propagation behavior of LSWs and surface ultrasound waves at high resolution. An agar phantom model was used to verify the feasibility of the experimental protocol, and experiments with ex vivo porcine brain samples were used to assess the nonuniformity of the brain biomechanical properties. LSWs with velocities of 0.83 ± 0.11 m/s were successfully excited in the agar phantom model. The perivascular elastography results in the prefrontal cortex (PFC) of the ex vivo porcine brains showed that the Young's modulus was significantly higher in the longitudinal and transverse directions on the left side of the cerebral vessels than on the right side and that the Young's modulus of the PFC decreased with increasing depth. The AcUT-OCE technique, as a new scheme for LSW applications in in vivo elastography, can be used for noncontact excitation of LSWs in brain tissue and high-resolution detection of heterogeneous brain biomechanical properties.

Hyaluronan Modulates the Biomechanical Properties of the Cornea

Purpose

Hyaluronan (HA) is a major constituent of the extracellular matrix (ECM) that has high viscosity and is essential for maintaining tissue hydration. In the cornea, HA is enriched in the limbal region and is a key component of the limbal epithelial stem cell niche. HA is upregulated after injury participating in the formation of the provisional matrix, and has a key role in regulating the wound healing process. This study investigated whether changes in the distribution of HA before and after injury affects the biomechanical properties of the cornea in vivo.

Methods

Corneas of wild-type (wt) mice and mice lacking enzymes involved in the biosynthesis of HA were analyzed before, immediately after, and 7 and 14 days after a corneal alkali burn (AB). The corneas were evaluated using both a ring light and fluorescein stain by in vivo confocal microscopy, optical coherence elastography (OCE), and immunostaining of corneal whole mounts.

Results

Our results show that wt mice and mice lacking HA synthase (Has)1 and 3 present an increase in corneal stiffness 7 and 14 days after AB without a significant increase in HA expression and absence of scarring at 14 days after AB. In contrast, mice lacking Has2 present a significant decrease in corneal stiffness, with a significant increase in HA expression and scarring at 14 days after AB.

Conclusions

Our findings show that the mechanical properties of the cornea are significantly modulated by changes in HA distribution following alkali burn.

Application of Shear Wave Elastography and Contrast-Enhanced Ultrasound in Transrectal Prostate Biopsy

OBJECTIVE

To explore the clinical value of ultrasound shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS) in transrectal prostate biopsy.

METHODS

A total of 54 patients (average age: 67.79±12.01 years) in the experimental group underwent transrectal prostate biopsy under the guidance of SWE, while 46 patients (average age: 69.22±11.54 years) in the control group underwent transrectal prostate biopsy guided by CEUS.

RESULTS

There were a total of 451 needles, with an average of 8.35±1.67 needles per patient in the experimental group, and a total of 462 needles, with an average of 10.04±1.33 needles per patient in the control group. The difference in puncture times between the two groups was statistically significant (P<0.05). There was no significant difference in the positive detection rate, sensitivity or specificity between the two groups (P>0.05), but there was a significant difference in the diagnostic accuracy between the two groups (P<0.05). The E_mean and E_max of prostate cancer were significantly higher in the experimental group than in benign prostatic hyperplasia (P<0.05). The receiver operating characteristic curve (ROC) analysis showed that the area under the ROC curve (AUC) of E_mean was 0.752 (S.E. =0.072, 95% CI=0.611-0.894, P=0.007), and the best cutoff value was 47.005 kPa.

CONCLUSION

In summary, both SWE- and CEUS-guided transrectal prostate biopsy can help find the focus and guide the puncture, and improve the positive detection rate.

Introduction to optical coherence elastography: tutorial

Optical coherence elastography (OCE) has seen rapid growth since its introduction in 1998. The past few decades have seen tremendous advancements in the development of OCE technology and a wide range of applications, including the first clinical applications. This tutorial introduces the basics of solid mechanics, which form the foundation of all elastography methods. We then describe how OCE measurements of tissue motion can be used to quantify tissue biomechanical parameters. We also detail various types of excitation methods, imaging systems, acquisition schemes, and data processing algorithms and how various parameters associated with each step of OCE imaging can affect the final quantitation of biomechanical properties. Finally, we discuss the future of OCE, its potential, and the next steps required for OCE to become an established medical imaging technology.

Wave-based optical coherence elastography: The 10-year perspective

After 10 years of progress and innovation, optical coherence elastography (OCE) based on the propagation of mechanical waves has become one of the major and the most studied OCE branches, producing a fundamental impact in the quantitative and nondestructive biomechanical characterization of tissues. Preceding previous progress made in ultrasound and magnetic resonance elastography; wave-based OCE has pushed to the limit the advance of three major pillars: (1) implementation of novel wave excitation methods in tissues, (2) understanding new types of mechanical waves in complex boundary conditions by proposing advance analytical and numerical models, and (3) the development of novel estimators capable of retrieving quantitative 2D/3D biomechanical information of tissues. This remarkable progress promoted a major advance in answering basic science questions and the improvement of medical disease diagnosis and treatment monitoring in several types of tissues leading, ultimately, to the first attempts of clinical trials and translational research aiming to have wave-based OCE working in clinical environments. This paper summarizes the fundamental up-to-date principles and categories of wave-based OCE, revises the timeline and the state-of-the-art techniques and applications lying in those categories, and concludes with a discussion on the current challenges and future directions, including clinical translation research.

Repetitive optical coherence elastography measurements with blinking nanobombs

Excitation of dye-loaded perfluorocarbon nanoparticles (nanobombs) can generate highly localized axially propagating longitudinal shear waves (LSW) that can be used to quantify tissue mechanical properties without transversal scanning of the imaging beam. In this study, we used repetitive excitations of dodecafluoropentane (C5) and tetradecafluorohexane (C6) nanobombs by a nanosecond-pulsed laser to produce multiple LSWs from a single spot in a phantom. A 1.5 MHz Fourier-domain mode-locked laser in combination with a phase correction algorithm was used to perform elastography. Multiple nanobomb activations were also monitored by detecting photoacoustic signals. Our results demonstrate that C6 nanobombs can be used for repetitive generation of LSW from a single spot for the purpose of material elasticity assessment. This study opens new avenues for continuous quantification of tissue mechanical properties using single delivery of the nanoparticles.

Advances in Doppler optical coherence tomography and angiography

Since the first demonstration of Doppler optical coherence tomography (OCT) in 1997, several functional extensions of Doppler OCT have been developed, including velocimetry, angiogram, and optical coherence elastography. These functional techniques have been widely used in research and clinical applications, particularly in ophthalmology. Here, we review the principles, representative methods, and applications of different Doppler OCT techniques, followed by discussion on the innovations, limitations, and future directions of each of these techniques.

Characterization of oviduct ciliary beat frequency using real time phase resolved Doppler spectrally encoded interferometric microscopy

Ciliary activity, characterized by the coordinated beating of ciliary cells, generates the primary driving force for oviduct tubal transport, which is an essential physiological process for successful pregnancies. Malfunction of the cilium in the fallopian tube, or oviduct, may increase the risk of infertility and tubal pregnancy that can result in maternal death. While many ex-vivo studies have been carried out using bright field microscopy, this technique is not feasible for the in-vivo investigation of oviduct ciliary beating frequency (CBF). Optical coherence tomography (OCT) has been able to provide in-vivo CBF imaging in a mouse model, but its resolution may be insufficient to resolve the spatial and temporal features of the cilium. Our group has recently developed the phase resolved Doppler (PRD) OCT method to visualize ciliary strokes at ultra-high displacement sensitivity. However, the cross-sectional field of view (FOV) may not be ideal for visualizing the surface dynamics of ciliated tissue. In this study, we report on the development of phase resolved Doppler spectrally encoded interferometric microscopy (PRD-SEIM) to visualize the oviduct ciliary activity within an en face FOV. This novel real time imaging system offers micrometer spatial resolution, sub-nanometer displacement sensitivity, and the potential for in-vivo endoscopic adaptation. The feasibility of the approach has been validated through ex-vivo experiments where the porcine oviduct CBF has been measured across different temperature conditions and the application of a drug. CBF ranging from 8 to 12 Hz have been observed at different temperatures, while administration of lidocaine decreased the CBF and deactivated the motile cilia. This study will serve as a stepping stone to in-vivo oviduct ciliary endoscopy and future clinical translations.

Engineering approaches for characterizing soft tissue mechanical properties: A review

From cancer diagnosis to detailed characterization of arterial wall biomechanics, the elastic property of tissues is widely studied as an early sign of disease onset. The fibrous structural features of tissues are a direct measure of its health and functionality. Alterations in the structural features of tissues are often manifested as local stiffening and are early signs for diagnosing a disease. These elastic properties are measured ex vivo in conventional mechanical testing regimes, however, the heterogeneous microstructure of tissues can be accurately resolved over relatively smaller length scales with enhanced spatial resolution using techniques such as micro-indentation, microelectromechanical (MEMS) based cantilever sensors and optical catheters which also facilitate in vivo assessment of mechanical properties. In this review, we describe several probing strategies (qualitative and quantitative) based on the spatial scale of mechanical assessment and also discuss the potential use of machine learning techniques to compute the mechanical properties of soft tissues. This work details state of the art advancement in probing strategies, associated challenges toward quantitative characterization of tissue biomechanics both from an engineering and clinical standpoint.

Simultaneously imaging and quantifying in vivo mechanical properties of crystalline lens and cornea using optical coherence elastography with acoustic radiation force excitation

The crystalline lens and cornea comprise the eye's optical system for focusing light in human vision. The changes in biomechanical properties of the lens and cornea are closely associated with common diseases, including presbyopia and cataract. Currently, most in vivo elasticity studies of the anterior eye focus on the measurement of the cornea, while lens measurement remains challenging. To better understand the anterior segment of the eye, we developed an optical coherence elastography system utilizing acoustic radiation force excitation to simultaneously assess the elasticities of the crystalline lens and the cornea in vivo. A swept light source was integrated into the system to provide an enhanced imaging range that covers both the lens and the cornea. Additionally, the oblique imaging approach combined with orthogonal excitation also improved the image quality. The system was tested through first ex vivo and then in vivo experiments using a rabbit model. The elasticities of corneal and lens tissue in an excised normal whole-globe and a cold cataract model were measured to reveal that cataractous lenses have a higher Young's modulus. Simultaneous in vivo elasticity measurements of the lens and cornea were performed in a rabbit model to demonstrate the correlations between elasticity and intraocular pressure and between elasticity and age. To the best of our knowledge, we demonstrated the first in vivo elasticity of imaging of both the lens and cornea using acoustic radiation force-optical coherence elastography, thereby providing a potential powerful clinical tool to advance ophthalmic research in disorders affecting the lens and the cornea.

Super-shear evanescent waves for non-contact elastography of soft tissues

We describe surface wave propagation in soft elastic media at speeds exceeding the bulk shear wave speed. By linking these waves to the elastodynamic Green's function, we derive a simple relationship to quantify the elasticity of a soft medium from the speed of this supershear evanescent wave (SEW). We experimentally probe SEW propagation in tissue-mimicking phantoms, human cornea ex vivo, and skin in vivo using a high-speed optical coherence elastography system. Measurements confirm the predicted relationship between SEW and bulk shear wave speeds, agreeing well with both theoretical and numerical models. These results suggest that SEW measurements may be a robust method to quantify elasticity in soft media, particularly in complex, bounded materials where dispersive Rayleigh-Lamb modes complicate measurements.

Longitudinal shear waves for elastic characterization of tissues in optical coherence elastography

In dynamic optical coherence elastography (OCE), surface acoustic waves are the predominant perturbations. They constrain the quantification of elastic modulus to the direction of wave propagation only along the surface of tissues, and disregard elasticity gradients along depth. Longitudinal shear waves (LSW), on the other hand, can be generated at the surface of the tissue and propagate through depth with desirable properties for OCE: (1) LSW travel at the shear wave speed and can discriminate elasticity gradients along depth, and (2) the displacement of LSW is longitudinally polarized along the direction of propagation; therefore, it can be measured by a phase-sensitive optical coherence tomography system. In this study, we explore the capabilities of LSW generated by a circular glass plate in contact with a sample using numerical simulations and tissue-mimicking phantom experiments. Results demonstrate the potential of LSW in detecting an elasticity gradient along axial and lateral directions simultaneously. Finally, LSW are used for the elastography of ex vivo mouse brain and demonstrate important implications in in vivo and in situ measurements of local elasticity changes in brain and how they might correlate with the onset and progression of degenerative brain diseases.

Does group velocity always reflect elastic modulus in shear wave elastography?

Dynamic elastography is an attractive method to evaluate tissue biomechanical properties. Recently, it was extended from US- and MR-based modalities to optical ones, such as optical coherence tomography for three-dimensional (3-D) imaging of propagating mechanical waves in subsurface regions of soft tissues, such as the eye. The measured group velocity is often used to convert wave speed maps into 3-D images of the elastic modulus distribution based on the assumption of bulk shear waves. However, the specific geometry of OCE measurements in bounded materials such as the cornea and skin calls into question elasticity reconstruction assuming a simple relationship between group velocity and shear modulus. We show that in layered media the bulk shear wave assumption results in highly underestimated shear modulus reconstructions and significant structural artifacts in modulus images. We urge the OCE community to be careful in using the group velocity to evaluate tissue elasticity and to focus on developing robust reconstruction methods to accurately reconstruct images of the shear elastic modulus in bounded media.

Longitudinal elastic wave imaging using nanobomb optical coherence elastography

Wave-based optical coherence elastography (OCE) is a rapidly emerging technique for elasticity assessment of tissues having high displacement sensitivity and simple implementation. However, most current noncontact wave excitation techniques are unable to target a specific tissue site in 3D and rely on transversal scanning of the imaging beam. Here, we demonstrate that dye-loaded perfluorocarbon nanoparticles (nanobombs) excited by a pulsed laser can produce localized axially propagating longitudinal shear waves while adhering to the laser safety limit. A phase-correction method was developed and implemented to perform sensitive nanobomb elastography using a ∼1.5  MHz Fourier domain mode-locking laser. The nanobomb activation was also monitored by detecting photoacoustic signals. The highly localized elastic waves detected by the nanobomb OCE suggest the possibility of high-resolution 3D elastographic imaging.

Confocal Shear Wave Acoustic Radiation Force Optical Coherence Elastography for Imaging and Quantification of the In Vivo Posterior Eye

Retinal diseases, such as age-related macular degeneration (AMD), are the leading cause of blindness in the elderly population. Since no known cures are currently present, it is crucial to diagnose the condition in its early stages so that disease progression is monitored. Recent advances show that the mechanical elasticity of the posterior eye changes with the onset of AMD. In this work, we present a quantitative method of mapping the mechanical elasticity of the posterior eye using confocal shear wave acoustic radiation force optical coherence elastography (SW-ARF-OCE). This technique has been developed and validated with both an ex-vivo porcine tissue model and a customized in-vivo rabbit model, which both showed the quantified elasticity variations between different layers. This study verifies the feasibility of using this technology for the quantification and diagnosis of retinal diseases from the in-vivo posterior eye.

Viscosity monitoring during hemodiluted blood coagulation using optical coherence elastography

Rapid and accurate clot diagnostic systems are needed for the assessment of hemodiluted blood coagulation. We develop a real-time optical coherence elastography (OCE) system, which measures the attenuation coefficient of a compressional wave induced by a piezoelectric transducer (PZT) in a drop of blood using optical coherence tomography (OCT), for the determination of viscous properties during the dynamic whole blood coagulation process. Changes in the viscous properties increase the attenuation coefficient of the sample. Consequently, dynamic blood coagulation status can be monitored by relating changes of the attenuation coefficient to clinically relevant coagulation metrics, including the initial coagulation time and the clot formation rate. This system was used to characterize the influence of activator kaolin and the influence of hemodilution with either NaCl 0.9% or hydroxyethyl starch (HES) 6% on blood coagulation. The results show that PZT-OCE is sensitive to coagulation abnormalities and is able to characterize blood coagulation status based on viscosity-related attenuation coefficient measurements. PZT-OCE can be used for point-of-care testing for diagnosis of coagulation disorders and monitoring of therapies.

Acoustic radiation force optical coherence elastography for elasticity assessment of soft tissues

Biomechanical properties of soft tissues are important indicators of tissue functions which can be used for clinical diagnosis and disease monitoring. Elastography, incorporating the principles of elasticity measurements into imaging modalities, provides quantitative assessment of elastic properties of biological tissues. Benefiting from high-resolution, noninvasive and three-dimensional optical coherence tomography (OCT), optical coherence elastography (OCE) is an emerging optical imaging modality to characterize and map biomechanical properties of soft tissues. Recently, acoustic radiation force (ARF) OCE has been developed for elasticity measurements of ocular tissues, detection of vascular lesions and monitoring of blood coagulation based on remote and noninvasive ARF excitation to both internal and superficial tissues. Here, we describe the advantages of the ARF-OCE technique, the measurement methods in ARF-OCE, the applications in biomedical detection, current challenges and advances. ARF-OCE technology has the potential to become a powerful tool for in vivo elasticity assessment of biological samples in a non-contact, non-invasive and high-resolution nature.

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

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.

Coaxial excitation longitudinal shear wave measurement for quantitative elasticity assessment using phase-resolved optical coherence elastography

Optical coherence elastography (OCE) is an emerging imaging modality for the assessment of mechanical properties in soft tissues. Transverse shear wave measurements using OCE can quantify the elastic moduli perpendicular to the force direction, however, missing the elastic information along the force direction. In this study, we developed coaxial excitation longitudinal shear wave measurements for quantification of elastic moduli along the force direction using M-scans. Incorporating Rayleigh wave measurements using non-coaxial lateral scans into longitudinal shear wave measurements, directionally dependent elastic properties can be quantified along the force direction and perpendicular to the force direction. Therefore, the reported system has the capability to image elasticity of anisotropic biological tissues.

Miniature probe for mapping mechanical properties of vascular lesions using acoustic radiation force optical coherence elastography

Cardiovascular diseases are the leading cause of fatalities in the United States. Atherosclerotic plaques are one of the primary complications that can lead to strokes and heart attacks if left untreated. It is essential to diagnose the disease early and distinguish vulnerable plaques from harmless ones. Many methods focus on the structural or molecular properties of plaques. Mechanical properties have been shown to change drastically when abnormalities develop in arterial tissue. We report the development of an acoustic radiation force optical coherence elastography (ARF-OCE) system that uses an integrated miniature ultrasound and optical coherence tomography (OCT) probe to map the relative elasticity of vascular tissues. We demonstrate the capability of the miniature probe to map the biomechanical properties in phantom and human cadaver carotid arteries.