Elastography System Research Articles

Detecting murine Inflammatory Bowel Disease using Optical Coherence Elastography.

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) that causes regions of ulceration within the interior of the colon. UC is estimated to afflict hundreds of thousands of people in the United States alone. Ultrasonic techniques can detect colitis, but have limited spatial resolution, which frequently results in underdiagnoses. Nevertheless, clinical diagnosis of colitis is still generally performed via colonoscopy. Optical techniques such as confocal microscopy and optical coherence tomography (OCT) have been proposed as higher resolution alternative imaging modalities to detect colitis. Additionally, IBD can potentially alter tissue biomechanical properties, which cannot be quantified from structural imaging alone. Elastography is a potential method to assess colon biomechanical properties to provide additional contrast for distinguishing healthy and diseased colon tissue. In this work, we induced elastic waves in ex vivo mouse colon tissue using a focused air-pulse. The elastic waves were detected using a phase-stabilized swept source optical coherence elastography system, and the wave velocity was translated into stiffness. Measurements were taken at six random positions for each sample in order to assess regional sample elasticity. The results show distinct differences ($p \lt 0.05$) in the stiffness between healthy and IBD-diseased samples, with a Young's Modulus of $10.2 \pm 3.7$ kPa and $4.9 \pm 0.3$ kPa, respectively. Dispersion analysis presents another parameter to distinguish tissue health. The high frequency components of the phase velocity dispersion curve indicate a variation between healthy and IBD colonic tissue. Our results show that OCE may be useful for detecting IBD noninvasively.

Viscoelasticity Measurement in Rat Livers Using Shear-Wave US Elastography

To investigate the usefulness of shear-wave speed and dispersion slope measurements obtained, using an ultrasound elastography system in rat livers with various degrees of necroinflammation and fibrosis. A total of 25 male Sprague Dawley rats were randomly divided into 5 groups of 5 rats each: G0 (control), G1 (CCl4 injected twice a week for 1 wk), G2 (CCl4 injected four times a wk for 1 wk), G3 (CCl4 injected twice a wk for 6 wk) and G4 (CCl4 injected twice a wk for 10 wk). The shear-wave speed (m/s) and the dispersion slope ([m/s]/kHz) were measured. Histologic features (inflammation, necrosis and fibrosis) were used as reference standards. In multivariable analysis with histologic features as independent variables, the fibrosis grade was significantly related to shear-wave speed (p < 0.05) and the necrosis grade was significantly related to dispersion slope (p < 0.05). Dispersion slope is more useful than shear-wave speed for predicting the degree of necroinflammation.

Shear wave velocity dispersion analysis in placenta using 2-D transient elastography

Preeclampsia and intrauterine growth restriction are related to placental insufficiency and constitute a major public health challenge. Significant changes in placental microarchitecture have already been described in these situations, including, for example, increases or decreases in the number of villi ramifications and the presence of fibrin deposits in terms of villi. These changes affect the entire placenta and might lead to variations in elasticity compared to normal placentas. In this context, we proposed to develop a 2-D transient elastography system, dedicated to the placenta and adapted for in vivo measurements, based on the coupling of a shear wave generated by an external vibration and ultrasound images acquired at an ultrafast rate. To be particularly sensitive to the structure of this organ, a frequency analysis of the complex shear modulus has been realized by applying a fractional rheological model. This model provides a parameter n which could be sensitive to a shape factor, for example, the variations in the number of villi ramifications in the case of placental insufficiency. An ex vivo feasibility of the method on 20 normal placentas is presented in this work.

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.

Ultrahigh-resolution optical coherence elastography through a micro-endoscope: towards in vivo imaging of cellular-scale mechanics.

In this paper, we describe a technique capable of visualizing mechanical properties at the cellular scale deep in living tissue, by incorporating a gradient-index (GRIN)-lens micro-endoscope into an ultrahigh-resolution optical coherence elastography system. The optical system, after the endoscope, has a lateral resolution of 1.6 µm and an axial resolution of 2.2 µm. Bessel beam illumination and Gaussian mode detection are used to provide an extended depth-of-field of 80 µm, which is a 4-fold improvement over a fully Gaussian beam case with the same lateral resolution. Using this system, we demonstrate quantitative elasticity imaging of a soft silicone phantom containing a stiff inclusion and a freshly excised malignant murine pancreatic tumor. We also demonstrate qualitative strain imaging below the tissue surface on in situ murine muscle. The approach we introduce here can provide high-quality extended-focus images through a micro-endoscope with potential to measure cellular-scale mechanics deep in tissue. We believe this tool is promising for studying biological processes and disease progression in vivo.

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.

To Study Analysis of NAFLD Fibrosis Score Among Type 2 Diabetic Patients in Tertiarycare Hospital

Background and Aim: NAFLD is the commonest liver problem among 10–45% of population around the world. 72% of NAFLD patients has Type 2 DM. 10–75% of Type 2 DM patient has NAFLD. Asians has low prevalence. In India 10–24% of diabetics has NAFLD. It has spectrum with steatosis, steatohepatitis and advanced fibrosis. NAFLD fibrosis score, BARD, APRI, FIB-4 more widely used noninvasive tool to predict fibrosis. The study aimed to apply NAFLD fibrosis Score in separating NAFLD patients with or without fibrosis by using clinical and biochemical variables. To correlate NAFLD fibrosis score with liver stiffness measured by TE. Methods: Type 2 DM patients attending OPD in Stanley Medical College between April 2016 and March 2017 evaluated with clinical, biochemical, ultrasound NAFLD diagnosed subjected to formula using online calculator (www.nafldscore.com) given by Angulo et al. 1.65 + 0.037 × age (years) + 0.094 × BMI (kg/m2) + 1.13 × IFG/diabetes (yes = 1, no = 0) + 0.99 × AST/ALT ratio − 0.013 × platelets (×109/L) 0.66 albumin (g/dl). Inclusion criteria were all patients with Type 2 DM for at least one year on OHA/insulin between 2 = 5–65 years. Exclusion criteria was an alcohol ingestion of >30 g/day in males >20 g/day in females. History suggesting chronic liver disease of any other etiology. Study design is a prospective study during which history, anthropometry, physical examination conducted in Type 2 DM patients fulfilling inclusion criteria, approved by ethical committee. Patients underwent CBC, blood sugar, LFT, HbSAg, anti-HCV, fasting lipid profile. NAFLD is diagnosed by an experienced single sonologist. Transient elastography done in hepatology RGGGH. Results: In this study 500/567 patients satisfied inclusion criteria were analyzed 184 had grade II and grade III fatty liver high NAFLD score subjected to fibroscan. 84 patients fibroscan was not done. 319/500 (68.3%) had fatty liver 181/500 (36.2%) no fatty liver. 38.1%, 51% and 10.3% had GrI, GrII and GrIII fatty liver as diagnosed by ultrasound scan. In this study majority are in 56–65 years age group. Conclusion: The prevalence of non-alcoholic liver disease among the diabetics was 63.85% higher compared to other series. Majority are females 83.1% in contrast to other series. Common age group is 56–65 years. The mean BMI 28.04 ± 4.12 kg/m2 metabolic syndrome was present in 73%. The combination of transient elastography and NAFLD fibrosis scoring system may provide better performance than each of them used alone. The authors have none to declare.

An ultrasound transient elastography system with coded excitation

BackgroundUltrasound transient elastography technology has found its place in elastography because it is safe and easy to operate. However, it’s application in deep tissue is limited. The aim of this study is to design an ultrasound transient elastography system with coded excitation to obtain greater detection depth.MethodsThe ultrasound transient elastography system requires tissue vibration to be strictly synchronous with ultrasound detection. Therefore, an ultrasound transient elastography system with coded excitation was designed. A central component of this transient elastography system was an arbitrary waveform generator with multi-channel signals output function. This arbitrary waveform generator was used to produce the tissue vibration signal, the ultrasound detection signal and the synchronous triggering signal of the radio frequency data acquisition system. The arbitrary waveform generator can produce different forms of vibration waveform to induce different shear wave propagation in the tissue. Moreover, it can achieve either traditional pulse-echo detection or a phase-modulated or a frequency-modulated coded excitation. A 7-chip Barker code and traditional pulse-echo detection were programmed on the designed ultrasound transient elastography system to detect the shear wave in the phantom excited by the mechanical vibrator. Then an elasticity QA phantom and sixteen in vitro rat livers were used for performance evaluation of the two detection pulses.ResultsThe elasticity QA phantom’s results show that our system is effective, and the rat liver results show the detection depth can be increased more than 1 cm. In addition, the SNR (signal-to-noise ratio) is increased by 15 dB using the 7–chip Barker coded excitation.ConclusionsApplying 7-chip Barker coded excitation technique to the ultrasound transient elastography can increase the detection depth and SNR. Using coded excitation technology to assess the human liver, especially in obese patients, may be a good choice.

High-resolution analysis of the mechanical behavior of tissue

The mechanical behavior and properties of biomaterials, such as tissue, have been directly and indirectly connected to numerous malignant physiological states. For example, an increase in the Young's Modulus of tissue can be indicative of cancer. Due to the heterogeneity of biomaterials, it is extremely important to perform these measurements using whole or unprocessed tissue because the tissue matrix contains important information about the intercellular interactions and the structure. Thus, developing high-resolution approaches that can accurately measure the elasticity of unprocessed tissue samples is of great interest. Unfortunately, conventional elastography methods such as atomic force microscopy, compression testing, and ultrasound elastography either require sample processing or have poor resolution. In the present work, we demonstrate the characterization of unprocessed salmon muscle using an optical polarimetric elastography system. We compare the results of compression testing within different ...

Comparison analysis of four processing methods employed in dynamic elastography to estimate viscoelastic parameters of a medium: tests using computational simulation and experiment

Dynamic ultrasound elastography is a method commonly used to quantify the mechanical parameters, such as shear elasticity modulus, and shear viscosity modulus, of biological tissues. Basically, the method employs four processing techniques, in order to estimate the mentioned parameters, denominated: phase velocity dispersion, PVD, attenuation-velocity, AV, complex shear elasticity modulus, CSM, and shear wave velocity, SV. The accuracy and precision of estimated values for and depend on the processing technique and the purpose of this paper is to compare the results obtained with PVD, AV, CSM and SV processing techniques by means of two cases: computer simulation and experiments. In the first case, the processing techniques were evaluated, via simulation, at different conditions for the signal-to-noise-ratio of the ultrasound RF echo signal used to probe the medium with vibrations due to the propagation of shear wave, the vibration amplitude and the viscoelastic properties of the medium itself. The corresponding results are expressed as the magnitudes of the mean and standard deviation of the relative error. In the second case, experiments were conducted based on a dynamic elastographic system with a cylindrical shear wave induced by a repetitive acoustic radiation force, with pulse repetition frequency of 50 Hz. A 4.98 MHz pulse-echo ultrasound system was used to probe the medium, a 3% gelatin phantom, traversed by the shear wave and the received RF echo signals were processed using the four techniques to yield the phantom values of and The results from computer simulation indicate that, in general, the CSM and AV techniques presented highest accuracy and precision. The experimental results obtained in this study are consistent with the values reported in the literature and the values of the shear elasticity modulus estimated by the four processing techniques did not differ significantly.

Building an open-source simulation platform of acoustic radiation force-based breast elastography

Ultrasound-based elastography including strain elastography, acoustic radiation force impulse (ARFI) imaging, point shear wave elastography and supersonic shear imaging (SSI) have been used to differentiate breast tumors among other clinical applications. The objective of this study is to extend a previously published virtual simulation platform built for ultrasound quasi-static breast elastography toward acoustic radiation force-based breast elastography. Consequently, the extended virtual breast elastography simulation platform can be used to validate image pixels with known underlying soft tissue properties (i.e. ‘ground truth’) in complex, heterogeneous media, enhancing confidence in elastographic image interpretations.The proposed virtual breast elastography system inherited four key components from the previously published virtual simulation platform: an ultrasound simulator (Field II), a mesh generator (Tetgen), a finite element solver (FEBio) and a visualization and data processing package (VTK). Using a simple message passing mechanism, functionalities have now been extended to acoustic radiation force-based elastography simulations.Examples involving three different numerical breast models with increasing complexity—one uniform model, one simple inclusion model and one virtual complex breast model derived from magnetic resonance imaging data, were used to demonstrate capabilities of this extended virtual platform. Overall, simulation results were compared with the published results. In the uniform model, the estimated shear wave speed (SWS) values were within 4% compared to the predetermined SWS values. In the simple inclusion and the complex breast models, SWS values of all hard inclusions in soft backgrounds were slightly underestimated, similar to what has been reported. The elastic contrast values and visual observation show that ARFI images have higher spatial resolution, while SSI images can provide higher inclusion-to-background contrast.In summary, our initial results were consistent with our expectations and what have been reported in the literature. The proposed (open-source) simulation platform can serve as a single gateway to perform many elastographic simulations in a transparent manner, thereby promoting collaborative developments.

Strain Elastography System with Quality Control - Auto Strain Ratio System

Strain elastography (SE) and shear wave speed imaging provide us with tissue stiffness information that reflects the pathological information, important for breast diagnosis and treatment. And Strain Ratio is a popular diagnosis method of strain elastography evaluation. However, it can be associated with operator bias in image formation, scanning technique, the selection of the appropriate elastography frame, and ROI setting for strain ratio measurement. To overcome these problems, we have developed an “Auto Strain Ratio System (ASRS)”, which requires no manual compression whilst scanning, with full auto frame selection on freeze and fully automatic ROI target setting. And a preliminary prospective clinical study was performed in 2015. 232 breast masses assessed as BI-RADS Category 3 or above by B-mode images, were scanned using SE. The ASRS values was compared to conventional manual strain ratio measurement (MSR) values by experienced doctors and the diagnostic performance and quality evaluated. There was a significant correlation between the MSR and ASRS with R=0.79 (p<0.001). The MSR (cut-off=3.8) had a sensitivity of 89%, a specificity of 75%, an accuracy of 78%, a positive predictive value (PPV) of 52%, and a negative predictive value (NPV) of 96%. The ASRS (cut-off=3.9) had a sensitivity of 82%, specificity of 89 %, an accuracy of 87%, a PPV of 69%, and a NPV of 94%. The AUCs were 0.88 on MSR and 0.89 on ASRS. We have demonstrated that it is possible to quantify SE and control its accuracy. The ASRS is expected to contribute to the standardization of breast elastography.

超音波Shear Wave Dispersion Imagingによる肝の弾性と粘性の測定

To investigate the value of shear wave (SW) speed (m/s) and dispersion slope ([m/s]/kHz), which is related to viscosity obtained by a prototype ultrasound elastography system in rat livers with various degrees of inflammation and fibrosis. SW speed was significantly higher in the fibrosis model rats (G3) than in the inflammation model rats (G1). Dispersion slope was significantly higher in the inflammation model rats (G2) than in the fibrosis model rats (G4). These results indicate that SW speed is more effective than dispersion slope in assessing the degree of fibrosis and also suggest that dispersion slope is more effective than SW speed in assessing the degree of inflammation. Dispersion slope measurements may provide additional pathophysiological insights into liver tissue.

High-Resolution Elastography for Thin-Layer Mechanical Characterization: Toward Skin Investigation

Interest in elasticity estimation for thin layers is increasing because of the various potential applications, including dermatology and cosmetology. In this context, we propose a dedicated elastographic system using 1-D high-frequency transient elastography (HF-TE) to estimate the 1-D Young's modulus through the dermis and hypodermis, which are the two human skin layers of interest in this study. An experimental validation of the HF-TE method was first carried out on two homogeneous tissue-mimicking hard and soft phantoms. The Young's modulus values obtained in these phantoms were compared with those obtained by two complementary shear wave propagation techniques: shear wave-induced resonance elastography (SWIRE) and supersonic shear imaging (SSI). A third two-layer thin phantom, with mechanical properties similar to those of skin, was used to validate the ability of HF-TE to distinguish layers and measure elasticity. Finally, preliminary in vivo experiments conducted on forearm and cheek skin revealed the promising performance of HF-TE in measuring elasticity in the dermis and hypodermis.

Usefulness of semiquantitative elastography in predicting malignancy in thyroid nodules

ObjectiveTo retrospectively review the diagnostic capacity of semiquantitative elastography in differentiating between benign and malignant thyroid nodules. Patients and methodsWe analyzed 314 thyroid nodules in 295 consecutive patients referred to the endocrinology department for cytological study, studying all by conventional ultrasonography, elastography, and fine-needle aspiration cytology (FNAC). Using a semiquantitative elastography system that portrays tissue stiffness through a color map, we designed our own classification system for thyroid nodules based on their characteristics on elastography. We classified nodules into three groups: predominantly soft, predominantly stiff, and mosaic patterned. We used logistic regression analysis to investigate the relation between elastography and thyroid cancer. ResultsWe obtained a definite diagnosis of malignancy after surgery in 19 nodules, of which on elastography 8 had the mosaic pattern, 6 were predominantly stiff, and 5 were predominantly soft. We found no significant association between the pattern on elastography and the probability of malignancy in any of the models. ConclusionAccording to our study, a probability of malignancy in a thyroid nodule is not related to the findings at elastography. Therefore, semiquantitative elastography as used in this study cannot obviate FNAC.

Investigating Elastic Anisotropy of the Porcine Cornea as a Function of Intraocular Pressure With Optical Coherence Elastography

To evaluate the elastic anisotropy of porcine corneas at different intraocular pressures (IOPs) using a noncontact optical coherence elastography (OCE) technique. A focused air-pulse induced low amplitude (≤ 10 µm) elastic waves in fresh porcine corneas (n = 7) in situ in the whole eye globe configuration. A home-built phase-stabilized swept source optical coherence elastography (PhS-SSOCE) system imaged the elastic wave propagation at different stepped radial directions. A closed-loop feedback system was used to artificially control the IOP and the OCE measurements were repeated as the IOP was incrementally increased from 15 to 30 mm Hg in 5-mm Hg increments. The OCE measurements demonstrated that the stiffness of the cornea increased as a function of IOP and elastic anisotropy of the cornea became more pronounced at higher IOPs. The standard deviation of the modified planar anisotropy coefficient increased from 0.72 ± 0.42 at an IOP of 15 mm Hg to 1.58 ± 0.40 at 30 mm Hg. The presented noncontact OCE method was capable of detecting and assessing the corneal elastic anisotropy as a function of IOP. Due to the noninvasive nature and small amplitude of the elastic wave, this method may be able to provide further information about corneal health and integrity in vivo. [J Refract Surg. 2016;32(8):562-567.].

Utilidad de la elastografía semicuantitativa para predecir la malignidad de los nódulos tiroideos

ObjectiveTo retrospectively review the diagnostic capacity of semiquantitative elastography in differentiating between benign and malignant thyroid nodules. Patients and methodsWe analyzed 314 thyroid nodules in 295 consecutive patients referred to the endocrinology department for cytological study, studying all by conventional ultrasonography, elastography, and fine-needle aspiration cytology (FNAC). Using a semiquantitative elastography system that portrays tissue stiffness through a color map, we designed our own classification system for thyroid nodules based on their characteristics on elastography. We classified nodules into three groups: predominantly soft, predominantly stiff, and mosaic patterned. We used logistic regression analysis to investigate the relation between elastography and thyroid cancer. ResultsWe obtained a definite diagnosis of malignancy after surgery in 19 nodules, of which on elastography 8 had the mosaic pattern, 6 were predominantly stiff, and 5 were predominantly soft. We found no significant association between the pattern on elastography and the probability of malignancy in any of the models. ConclusionAccording to our study, la probability of malignancy in a thyroid nodule is not related to the findings at elastography. Therefore, semiquantitative elastography as used in this study cannot obviate FNAC.

Overhauser-enhanced magnetic resonance elastography.

Magnetic resonance elastography (MRE) is a powerful technique to assess the mechanical properties of living tissue. However, it suffers from reduced sensitivity in regions with short T2 and T2 * such as in tissue with high concentrations of paramagnetic iron, or in regions surrounding implanted devices. In this work, we exploit the longer T2 * attainable at ultra-low magnetic fields in combination with Overhauser dynamic nuclear polarization (DNP) to enable rapid MRE at 0.0065 T. A 3D balanced steady-state free precession based MRE sequence with undersampling and fractional encoding was implemented on a 0.0065 T MRI scanner. A custom-built RF coil for DNP and a programmable vibration system for elastography were developed. Displacement fields and stiffness maps were reconstructed from data recorded in a polyvinyl alcohol gel phantom loaded with stable nitroxide radicals. A DNP enhancement of 25 was achieved during the MRE sequence, allowing the acquisition of 3D Overhauser-enhanced MRE (OMRE) images with (1.5 × 2.7 × 9) mm(3) resolution over eight temporal steps and 11 slices in 6 minutes. In conclusion, OMRE at ultra-low magnetic field can be used to detect mechanical waves over short acquisition times. This new modality shows promise to broaden the scope of conventional MRE applications, and may extend the utility of low-cost, portable MRI systems to detect elasticity changes in patients with implanted devices or iron overload.

Effects of fixation and preservation on tissue elastic properties measured by quantitative optical coherence elastography (OCE)

Fixed and preserved tissues have been massively used in the development of biomedical equipment and instrumentation. Not only the tissue morphology, but also its mechanical properties need to be considered in the fixation and preservation procedures since mechanical properties have significant influence on the design and performance of such instruments. Understanding the effects of storage and preservation conditions on the mechanical properties of soft tissue has both clinical and experimental significance. To this end, we aimed to study the effects of tissue preservation (by 10% formalin and Thiel fluids) on the elastic properties of five different kinds of fresh tissues from pig and chicken; specifically fat, liver, muscle, tendon and cartilage. The tissue elasticity was measured intensively and strictly within a controlled timeline of 6 months by quantitative optical coherence elastography (OCE) system. Our findings suggest that the elasticity change of tissues in the formalin solution has an ascending trend, but that of Thiel remains almost constant, providing a more real texture and properties.

Acoustic Radiation Force Optical Coherence Elastography of Corneal Tissue.

We report on a real-time acoustic radiation force optical coherence elastography (ARF-OCE) system to map the relative elasticity of corneal tissue. A modulated ARF is used as excitation to vibrate the cornea while OCE serves as detection of tissue response. To show feasibility of detecting mechanical contrast using this method, we performed tissue-equivalent agarose phantom studies with inclusions of a different stiffness. We obtained 3-D elastograms of a healthy cornea and a highly cross-linked cornea. Finally we induced a stiffness change on a small portion of a cornea and observed the differences in displacement.