Dynamic Elastography Research Articles

The combined importance of finite dimensions, anisotropy, and pre-stress in acoustoelastography.

Dynamic elastography, whether based on magnetic resonance, ultrasound, or optical modalities, attempts to reconstruct quantitative maps of the viscoelastic properties of biological tissue, properties that are altered by disease and injury, by noninvasively measuring mechanical wave motion in the tissue. Most reconstruction strategies that have been developed neglect boundary conditions, including quasistatic tensile or compressive loading resulting in a nonzero prestress. Significant prestress is inherent to the functional role of some biological tissues currently being studied using elastography, such as skeletal and cardiac muscle, arterial walls, and the cornea. In the present article, we review how prestress alters both bulk mechanical wave motion and wave motion in one- and two-dimensional waveguides. Key findings are linked to studies on skeletal muscle and the human cornea, as one- and two-dimensional waveguide examples. This study highlights the underappreciated combined acoustoelastic and waveguide challenge to elastography. Can elastography truly determine viscoelastic properties of a material when what it is measuring is affected by both these material properties and unknown prestress and other boundary conditions?

Optical coherence elastography for assessing the influence of intraocular pressure on elastic wave dispersion in the cornea

The cornea is a highly specialized organ that relies on its mechanical stiffness to maintain its aspheric geometry and refractive power, and corneal diseases such as keratoconus have been linked to abnormal tissue stiffness and biomechanics. Dynamic optical coherence elastography (OCE) is a clinically promising non-contact and non-destructive imaging technique that can provide measurements of corneal tissue stiffness directly in vivo. The method relies on the concepts of elastography where shear waves are generated and imaged within a tissue to obtain mechanical properties such as tissue stiffness. The accuracy of OCE-based measurements is ultimately dependent on the mathematical theories used to model wave behavior in the tissue of interest. In the cornea, elastic waves propagate as guided wave modes which are highly dispersive and can be mathematically complex to model. While recent groups have developed detailed theories for estimating corneal tissue properties from guided wave behavior, the effects of intraocular pressure (IOP)-induced prestress have not yet been considered. It is known that prestress alone can strongly influence wave behavior, in addition to the associated non-linear changes in tissue properties. This present study shows that failure to account for the effects of prestress may result in overestimations of the corneal shear moduli, particularly at high IOPs. We first examined the potential effects of IOP and IOP-induced prestress using a combination of approximate mathematical theories describing wave behavior in thin plates with observations made from data published in the OCE literature. Through wave dispersion analysis, we deduce that IOP introduces a tensile hoop stress and may also influence an elastic foundational effect that were observable in the low-frequency components of the dispersion curves. These effects were incorporated into recently developed models of wave behavior in nearly incompressible, transversely isotropic (NITI) materials. Fitting of the modified NITI model with ex vivo porcine corneal data demonstrated that incorporation of the effects of IOP resulted in reduced estimates of corneal shear moduli. We believe this demonstrates that overestimation of corneal stiffness occurs if IOP is not taken into consideration. Our work may be helpful in separating inherent corneal stiffness properties that are independent of IOP; changes in these properties and in IOP are distinct, clinically relevant issues that affect the cornea health.

Physical Principles of Elastography: A Primer for Radiologists

AbstractElastography is the noninvasive method of qualitative and quantitative evaluation of strain and elastic modulus distribution in soft tissues. In simpler terms, elastography is the science of measuring tissue stiffness, the deviation of which correlates with pathology of the tissue/organs being evaluated. Whereas, elasticity, refers to the property of solid matter to return to their original shape and size after removal of the deforming forces. In all forms of elastography, irrespective of the types of deforming forces or moduli, the deformation of tissue occurs in the form of shear deformation. The velocity of shear waves in the deformed tissue depends on its density and on the shear modulus. The direction of propagation of shear wave is perpendicular to the inciting mechanical or acoustic wave. The shear wave is then subsequently tracked using multiple tracking pulses, which measures tissue displacement in response to the passing shear wave. The calculated speed of the shear wave is then converted to conventional Young's modulus for the purpose of computing the tissue stiffness.The currently used elastography techniques are static or quasi-static elastography and dynamic elastography. Strain elastography (a form of static or quasi-static elastography) is based on the principle of acquisition of radio-frequency (RF) signals before and after the application of a deforming force in the form of slight compression of tissue by a transducer. RF signals are compared between the pre-compression image data set and the post-compression image data set and correlated between the two data sets.Dynamic elastography may be either ultrasound (US) based or magnetic resonance (MR) based. The types of dynamic US elastography are: acoustic radiation force impulse imaging (ARFI), transient elastography (TE), point shear wave elastography (pSWE), and shear wave elastography (SWE). ARFI uses a standard transducer to produce and propagate rapid bursts of long focused ultrasound pulses, also called as “push pulses” which cause tissue deformity, the propagation of which is tracked using radio-frequency echo tracking. In TE, a probe mounted on a vibrator is used to produce a small thump by piston like motion of transducer. The shear wave which arises from the edges of the transducer is tracked using high pulse repetition frequency tissue Doppler and computed using M-mode for display of quantitative parameters. Point shear wave, also known as quantitative ARFI, uses shear waves generated using transient tissue displacement caused by ARFI and are subsequently subjected to tracking by Doppler. Shear wave elastography is based on the principles of imaging shear wave speed. An acoustic radiation force impulse is transmitted along the acoustic axis to produce tissue displacement and deformation at points of acoustic axis. The generated shear wave is imaged using RF echo tracking over a grid of points, which is translated into a real time image. MR elastography is a dynamic technique and the basic principles of MR elastography are the same as other forms of dynamic elastography. MR elastography has limited utility in iron-overload states and in addition, due to the large amount of time required for acquisition, the technique is not suitable for unstable patients.This review presents a simplified summary of the principles of elastography along with definition of the terms and the types of elastography which are currently available to radiologists for clinical application and concludes with a brief on the newer developments for the future.

Dynamic X-ray elastography using a pulsed photocathode source

X-ray absorption of breast cancers and surrounding healthy tissue can be very similar, a situation that sometimes leads to missed cancers or false-positive diagnoses. To increase the accuracy of mammography and breast tomosynthesis, we describe dynamic X-ray elastography using a novel pulsed X-ray source. This new imaging modality provides both absorption and mechanical properties of the imaged material. We use a small acoustic speaker to vibrate the sample while a synchronously pulsed cold cathode X-ray source images the mechanical deformation. Using these stroboscopic images, we derive two-dimensional stiffness maps of the sample in addition to the conventional X-ray image. In a breast phantom composed of ZrO2 powder embedded in gel, dynamic elastography derived stiffness maps were able to discriminate a hard inclusion from surrounding material with a contrast-to-noise ratio (CNR) of 4.5. The CNR on the corresponding absorption image was 1.1. This demonstrates the feasibility of dynamic X-ray elastography with a synchronously pulsed X-ray source.

Muscle elastography: Stress versus stiffness

Dynamic elastography imaging, whether based on magnetic resonance, ultrasound or optical modalities, attempts to reconstruct quantitative maps of the viscoelastic properties of biological tissue, properties that are altered by disease and injury, as well as response to therapy. Reconstruction often assumes isotropy and homogeneity and neglects the effects of nonhomogeneous boundary conditions. Skeletal muscle violates all these assumptions, posing challenges and opportunities for developing better imaging biomarkers. Muscle activation and varying tensile loads can influence measurement interpretation. For bulk shear waves in an isotropic viscoelastic material not influenced by boundary conditions the measured wavelength correlates with the square root of the tissue’s shear elastic modulus and viscosity, important rheological parameters. But, under significant tensile loading the measured transverse wavelength will also be affected by the induced quasistatic stress field, making identification of the muscle’s inherent rheological properties seem impossible. Acoustoelastic theory, previous studies addressing this issue specifically for muscle, as well as new studies by our group are reviewed, identifying remaining challenges, potential strategies and opportunities for a more comprehensive understanding of both muscle structure and function based on noninvasive measurements. [Support acknowledged: NSF #1852691, NIH #AR071162.]

Changes in use of slow and fast twitch muscle fibers in diabetics with and without neuropathy during gait

In part I of this study, we investigated the elastic Cherenkov effect (ECE) in an incompressible transversely isotropic (TI) soft solid using a combined theoretical and computational approach, based on which an inverse method has been proposed to measure both the anisotropic and hyperelastic parameters of TI soft tissues. In this part, experiments were carried out to validate the inverse method and demonstrate its usefulness in practical measurements. We first performed ex vivo experiments on bovine skeletal muscles. Not only the shear moduli along and perpendicular to the direction of muscle fibers but also the elastic modulus EL and hyperelastic parameter c2 were determined. We next carried out tensile tests to determine EL, which was compared with the value obtained using the shear wave elastography method. Furthermore, we conducted in vivo experiments on the biceps brachii and gastrocnemius muscles of ten healthy volunteers. To the best of our knowledge, this study represents the first attempt to determine EL of human muscles using the dynamic elastography method and inverse analysis. The significance of our method and its potential for clinical use are discussed.

In-situ monitoring and ex-situ elasticity mapping of laser induced metal melting pool using ultrasound: Numerical and experimental approaches

This study presents novel in-situ monitoring of the melting pool behavior and ex-situ inspection of the heat-affected softening in gallium metal using an ultrasonic technique. In the laser welding and laser melting additive manufacturing process, understanding the melting pool's behavior is necessary but challenging. Optical, thermal, and radiational imaging methods provide valuable information but are limited due to the lack of depth and material properties information. An ultrasonic time of flight measurement monitoring technique is numerically and experimentally used to study the behavior of laser-induced melting pools, including phase transition, pool initialization and growth, and solidification in real-time. Besides, a dynamic bulk modulus elastography scan was demonstrated to visualize the laser-heating induced mechanical property reduction as an ex-situ inspection process which can be an in-situ process in the future. The laser softened area had a drop in the elasticity resembling a melt pool's shape. With the continuous development, the unique technique would be suitable and helpful to be used as a diagnostic tool to monitor laser welding, laser melting-based additive manufacturing, and other melt-solidify processing systems.

Elasticity Changes in the Crystalline Lens during Oxidative Damage and the Antioxidant Effect of Alpha-Lipoic Acid Measured by Optical Coherence Elastography

Age-related cataracts are one of the most prevalent causes of visual impairment around the world. Understanding the mechanisms of cataract development and progression is essential to enable early clinical diagnosis and treatment to preserve visual acuity. Reductive chemicals are potential medicines effective on cataract treatment. In this work, we investigated the cataract-induced oxidative damage in the crystalline lens and a kind of reductant, α-lipoic acid (ALA), ability to reduce the damage. We created oxidative environment to investigate the relationship between the progression of oxidative cataract and lenticular biomechanical properties measured by dynamic optical coherence elastography in porcine crystalline lenses ex vivo. The efficacy of ALA to minimize the stiffening of the lens was also quantified. The results showed a significant increase in Young’s modulus of the lens due to the formation of the oxidative cataract. We found a statistically significant difference between Young’s modulus of the lenses stored in phosphate-buffered saline and ALA solution after incubation in H2O2 solution for 3 h (43.0 ± 9.0 kPa versus 20.7 ± 3.5 kPa, respectively). These results show that the lens stiffness increases during oxidative cataract formation, and ALA has the potential to reverse stiffening of the lens caused by oxidative damage.

Minimal portosystemic encephalopathy: A new nosological entity in patients with hereditary haemorrhagic telangiectasia

Background. Portosystemic shunts in Hereditary Haemorrhagic Telangiectasia (HHT) are often overlooked by conventional imaging although they could reduce hepatic clearance of gut-derived toxins.Aims. To evaluate, the presence of subclinical neurological alterations (SNAs), that we named “minimal portosystemic encephalopathy” (mPSE) in HHT patients without advanced liver disease (ALD).Methods. In this cross sectional study, consecutive HHT outpatients were firstly screened by critical flicker frequency (CFF) test (abnormal ≤39Hz), and the simplified animal naming test (S-ANT1) (abnormal <15) was used to confirm the diagnosis of mPSE. Furthermore, we evaluated the effect of lactulose administration on mPSE. Multi-slice CT, cerebral dynamic magnetic resonance, laboratory analyses and transient elastography were also used.Results. None of the 37 enrolled patients showed portosystemic shunts at imaging techniques. However, 33 patients had normal CFF values (CFF-) and 4 displayed CFF alterations (37.0±0.7Hz, CFF+). The S-ANT1 confirmed an impaired neurological performance (10.2±2.8) in CFF+ patients thus confirming the presence of mPSE. Noteworthy, lactulose administration determined a CFF increase (39.1±0.4Hz) and S-ANT1 normalization in these patients. Neither mPSE- nor mPSE+ patients had ALD and showed similar demographic, clinical and laboratory parameters. Finally, no mPSE+ patient showed radiologically-detectable brain vascular malformations or other brain abnormalities at imaging.Conclusions. HHT patients represent a human model of mPSE secondary to portosystemic shunts escaping radiological detection. mPSE evaluation should be incorporated in HHT surveillance protocols since it can affect both health-related/social aspects and pharmacokinetics of orally administered drugs with a narrow therapeutic index and high hepatic first-pass uptake.

Two-dimensional (2D) dynamic vibration optical coherence elastography (DV-OCE) for evaluating mechanical properties: a potential application in tissue engineering.

Mechanical properties in tissues are an important indicator because they are associated with disease states. One of the well-known excitation sources in optical coherence elastography (OCE) to determine mechanical properties is acoustic radiation force (ARF); however, a complicated focusing alignment cannot be avoided. Another excitation source is a piezoelectric (PZT) stack to obtain strain images via compression, which can affect the intrinsic mechanical properties of tissues in tissue engineering. In this study, we report a new technique called two-dimensional (2D) dynamic vibration OCE (DV-OCE) to evaluate 2D wave velocities without tedious focusing alignment procedures and is a non-contact method with respect to the samples. The three-dimensional (3D) Fourier transform was utilized to transfer the traveling waves (x, y, t) into 3D k-space (kx, ky, f). A spatial 2D wavenumber filter and multi-angle directional filter were employed to decompose the waves with omni-directional components into four individual traveling directions. The 2D local wave velocity algorithm was used to calculate a 2D wave velocity map. Six materials, two homogeneous phantoms with 10 mm thickness, two homogeneous phantoms with 2 mm thickness, one heterogeneous phantom with 2 mm diameter inclusion and an ex vivo porcine kidney, were examined in this study. In addition, the ARF-OCE was used to evaluate wave velocities for comparison. Numerical simulations were performed to validate the proposed 2D dynamic vibration OCE technique. We demonstrate that the experimental results were in a good agreement with the results from ARF-OCE (transient OCE) and numerical simulations. Our proposed 2D dynamic vibration OCE could potentially pave the way for mechanical evaluation in tissue engineering and for laboratory translation with easy-to-setup and contactless advantages.

Dynamic X-ray elastography: A new tool for characterizing soft materials

Dynamic X-ray elastography using propagating shear waves is a novel technique to visualize the spatial distribution of elasticity in soft materials. We demonstrate that it can be applied to a gel sample with a fine structure. We prepared a viscoelastic gel sample with a two-dimensional lattice structure filled with ZrO2 particles, and applied the technique to map storage and loss moduli. The obtained storage modulus map successfully distinguished the harder lattice structure from the soft gel matrix with a spatial resolution much higher than those of other conventional elastography techniques using magnetic resonance and ultrasound.

In Vivo Human Corneal Shear-wave Optical Coherence Elastography.

SIGNIFICANCEA novel imaging technology, dynamic optical coherence elastography (OCE), was adapted for clinical noninvasive measurements of corneal biomechanics.PURPOSEDetermining corneal biomechanical properties is a long-standing challenge. Elasticity imaging methods have recently been developed and applied for clinical evaluation of soft tissues in cancer detection, atherosclerotic plaque evaluation, surgical guidance, and more. Here, we describe the use of dynamic OCE to characterize mechanical wave propagation in the human cornea in vivo, thus providing a method for clinical determination of corneal biomechanical properties.METHODSHigh-resolution phase-sensitive optical coherence tomography imaging was combined with microliter air-pulse tissue stimulation to perform dynamic elasticity measurements in 18 eyes of nine participants. Low-pressure (0.1 mmHg), spatiotemporally discreet (150 μm, 800 μs) tissue stimulation produced submicron-scale tissue deformations that were measured at multiple positions over a 1-mm2 area. Surface wave velocity was measured and used to determine tissue stiffness. Elastic wave propagation velocity was measured and evaluated as a function of IOP and central corneal thickness.RESULTSSubmicron corneal surface displacement amplitude (range, 0.005 to 0.5 μm) responses were measured with high sensitivity (0.24 nm). Corneal elastic wave velocity ranged from 2.4 to 4.2 m/s (mean, 3.5; 95% confidence interval, 3.2 to 3.8 m/s) and was correlated with central corneal thickness (r = 0.64, P < .001) and IOP (r = 0.52, P = .02).CONCLUSIONSPhase-sensitive optical coherence tomography imaging combined with microliter air-pulse mechanical tissue stimulation has sufficient detection sensitivity to observe submicron elastic wave propagation in corneal tissue. These measurements enable in vivo corneal stiffness determinations that will be further studied for use with disease detection and for monitoring clinical interventions.

Quantitative Estimation of Passive Elastic Properties of Individual Skeletal Muscle in Vivo Using Normalized Elastic Modulus-Length Curve.

Precise characterization of the passive elastic properties of human skeletal muscle could provide valuable information for functional assessment and medical diagnosis. Using normalized elastic modulus-length curve based on a piecewise exponential model, a non-invasive ultrasonography (US) method was developed for estimating three physiologically meaningful parameters, termed as passive-elastic coefficient k, slack length l0 and slack elastic modulus G0, to quantify the passive elastic properties of human gastrocnemius (GM) muscle, and correlate different findings with healthy and atrophic subjects. Dynamic B-mode US and shear wave elastography (SWE) videos of right GM muscles were performed in 32 healthy subjects and 18 atrophic patients with their ankle angles from 40° plantarflexion to 30° dorsiflexion by an isokinetic dynamometer. During muscle passive stretching induced by ankle rotation, consecutive muscle lengths were measured by automatically tracking the distal muscle-tendon junction positions in B-mode imaging frames using Hough transform and an active contour method. The corresponding elastic moduli were obtained using SWE imaging frames. The Gauss-Newton algorithm was used to estimate the parameters k, l0 and G0 from normalized elastic modulus-length curve. In-vivo experimental results showed that the measured muscle elastic modulus-length data fitted well to the proposed model with three estimated parameters for all subjects (0.942 < R2 < 0.997). The passive-elastic coefficient k was significantly higher for atrophic subjects compared with normal subjects (105.5 ± 45.3 versus 48.4 ± 16.0, p < 0.001). The proposed parameters allow further characterization of muscle essential mechanical properties and have a potential to become effective indexes for muscular disease diagnosis.

Nearly-incompressible transverse isotropy (NITI) of cornea elasticity: model\xa0and experiments with acoustic micro-tapping OCE

The cornea provides the largest refractive power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically. Dynamic optical coherence elastography (OCE), which launches and tracks shear waves to estimate stiffness, provides an attractive non-contact probe of corneal elasticity. To date, however, OCE studies report corneal moduli around tens of kPa, orders-of-magnitude less than those (few MPa) obtained by tensile/inflation testing. This large discrepancy impedes OCE’s clinical adoption. Based on corneal microstructure, we introduce and fully characterize a nearly-incompressible transversely isotropic (NITI) model depicting corneal biomechanics. We show that the cornea must be described by at least two shear moduli, contrary to current single-modulus models, decoupling tensile and shear responses. We measure both as a function of IOP in ex vivo porcine cornea, obtaining values consistent with both tensile and shear tests. At pressures above 30 mmHg, the model begins to fail, consistent with non-linear changes in cornea at high IOP.

Characterization of natural frequencies from nanoscale tissue oscillations using dynamic optical coherence elastography.

We demonstrate the use of OCT-based elastography for soft-tissue characterization using natural frequency oscillations. Sub-micrometer to sub-nanometer oscillations were induced in tissue phantoms and human cornea in vivo by perpendicular air-pulse stimulation and observed by common-path OCT imaging (sensitivity: 0.24 nm). Natural frequency and damping ratio were acquired in temporal and frequency domains using a single degree of freedom method. The dominant natural frequency was constant for different stimulation pressures (4-32 Pa) and measured distances (0.3-5.3 mm), and decreased as the sample thickness increased. The dominant natural frequencies of 0.75-2% agar phantoms were 127-774 Hz (mean coefficient of variation [CV]: 0.9%), and correlated with the square root of Young's moduli (16.5-117.8 kPa, mean CV: 5.8%). These preliminary studies show repeatable in vivo corneal natural frequency measurements (259 Hz, CV: 1.9%). This novel OCE approach can distinguish tissues and materials with different mechanical properties using the small-amplitude tissue oscillation features, and is suitable for characterizing delicate tissues in vivo such as the eye.

X-ray elastography by visualizing propagating shear waves

Elastography, an imaging modality for mapping elastic modulus in soft viscoelastic materials, has been developed using magnetic resonance imaging and ultrasound imaging, but few studies were reported on using X-ray imaging. We report on dynamic X-ray elastography, which relies on shear-wave propagation. We pneumatically vibrated polyacrylamide gel phantoms and obtained two-dimensional maps of storage and loss moduli, which were determined from temporal variation in displacement vectors of the vibrating particles in the phantoms. Our experiment provided storage moduli with a precision of 30% and a spatial resolution was one order of magnitude higher than other imaging modalities.

Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy.

Assessing the biomechanical properties of the crystalline lens can provide crucial information for diagnosing disease and guiding precision therapeutic interventions. Existing noninvasive methods have been limited to global measurements. Here, we demonstrate the quantitative assessment of the elasticity of crystalline lens with a multimodal optical elastography technique, which combines dynamic wave-based optical coherence elastography (OCE) and Brillouin microscopy to overcome the drawbacks of individual modalities. OCE can provide direct measurements of tissue elasticity rapidly and quantitatively, but it is a challenge to image transparent samples such as the lens because this technique relies on backscattered light. On the other hand, Brillouin microscopy can map the longitudinal modulus with micro-scale resolution in transparent samples. However, the relationship between Brillouin-deduced modulus and Young's modulus is not straightforward and sample dependent. By combining these two techniques, we can calibrate Brillouin measurements with OCE, based on the same sample, allowing us to completely map the Young's modulus of the crystalline lens. The combined system was first validated with tissue-mimicking gelatin phantoms of varying elasticities (N = 9). The OCE data was used to calibrate the Brillouin shift measurements and subsequently map the Young's modulus of the phantoms. After validation, OCE and Brillouin measurements were performed on ex-vivo porcine lenses (N = 6), and the Young's modulus of the lenses was spatially mapped. The results show a strong correlation between Young's moduli measured by OCE and longitudinal moduli measured by Brillouin microscopy. The correlation coefficient R was 0.98 for the phantoms and 0.94 for the lenses, respectively. The mean Young's modulus of the anterior and posterior lens was 1.98 ± 0.74 kPa and 2.93 ± 1.13 kPa, respectively, and the Young's modulus of the lens nucleus was 11.90 ± 2.94 kPa. The results presented in this manuscript open a new way for truly quantitative biomechanical mapping of optically transparent (or low scattering) tissues in 3D.

Feasibility of shear wave sonoelastography to detect endoleak and evaluate thrombus organization after endovascular repair of abdominal aortic aneurysm

To investigate the feasibility of shear wave sonoelastography (SWS) for endoleak detection and thrombus characterization of abdominal aortic aneurysm (AAA) after endovascular repair (EVAR). Participants who underwent EVAR were prospectively recruited between November 2014 and March 2016 and followed until March 2019. Elasticity maps of AAA were computed using SWS and compared to computed tomography angiography (CTA) and color Doppler ultrasound (CDUS). Two readers, blinded to the CTA and CDUS results, reviewed elasticity maps and B-mode images to detect endoleaks. Three or more CTAs per participant were analyzed: pre-EVAR, baseline post-EVAR, and follow-ups. The primary endpoint was endoleak detection. Secondary endpoints included correlation between total thrombus elasticity, proportion of fresh thrombus, and aneurysm growth between baseline and reference CTAs. A 3-year follow-up was made to detect missed endoleaks, EVAR complication, and mortality. Data analyses included Cohen's kappa; sensitivity, specificity, and positive predictive value (PPV); Pearson coefficient; and Student's t tests. Seven endoleaks in 28 participants were detected by the two SWS readers (k = 0.858). Sensitivity of endoleak detection with SWS was 100%; specificity and PPV averaged 67% and 50%, respectively. CDUS sensitivity was estimated at 43%. Aneurysm growth was significantly greater in the endoleak group compared to sealed AAAs. No correlation between growth and thrombus elasticity or proportion of fresh thrombus in AAAs was found. No new endoleaks were observed in participants with SWS negative studies. SWS has the potential to detect endoleaks in AAA after EVAR with comparable sensitivity to CTA and superior sensitivity to CDUS. • Dynamic elastography with shear wave sonoelastography (SWS) detected 100% of endoleaks in abdominal aortic aneurysm (AAA) follow-up that were identified by a combination of CT angiography (CTA) and color Doppler ultrasound (CDUS). • Based on elasticity maps, SWS differentiated endoleaks from thrombi within the aneurysm sac (p < 0.001). • After 3-year follow-up, no new endoleaks were observed in SWS negative examinations.

Reverberant 3D optical coherence elastography maps the elasticity of individual corneal layers

The elasticity mapping of individual layers in the cornea using non-destructive elastography techniques advances diagnosis and monitoring of ocular diseases and treatments in ophthalmology. However, transient Lamb waves, currently used in most dynamic optical coherence and ultrasound elastography techniques, diminish the translation of wave speed into shear/Young’s modulus. Here, we present reverberant 3D optical coherence elastography (Rev3D-OCE), a novel approach leveraging the physical properties of diffuse fields in detecting elasticity gradients not only in the lateral direction, but also along the depth axis of the cornea. A Monte Carlo analysis, finite element simulations, and experiments in layered phantoms are conducted to validate the technique and to characterize the axial elastography resolution. Experiments in ex vivo porcine cornea at different intraocular pressures reveal that Rev3D-OCE enables the elastic characterization of single layers that matches the anatomical description of corneal layers with unprecedented contrast in the dynamic OCE field.

Quantitative methods in sonography

B‑mode and color Doppler ultrasound are standard radiological methods to quantify tissue echo texture and tissue perfusion. Microstructure and composition of tissue influence echo texture parameters and acoustic parameters, such as speed of sound, attenuation and backscatter and quantitative color Doppler image parameters are influenced by the hemodynamics in depictable vessels. Dynamic contrast-enhanced ultrasound enables quantification of tissue perfusion and ultrasound elastography assists in assessing tissue stiffness. B‑mode texture analysis, analysis of high-frequency echo signals and quantitative color Doppler image analysis are able to contribute to the assessment of tissue microstructure but have so far not been implemented clinically due to their complexity. Dynamic contrast-enhanced ultrasound and ultrasound elastography have proven to be robust under clinical conditions.