Soft Tissue Elasticity Research Articles

Hoarseness: biomechanisms and quantitative laryngoscopy

Every phonosurgical procedure alters endolaryngeal anatomy; be it by removing tissue, or injection or implantation of autologous or foreign material. However, the effect that an altered airflow cross section and changed soft tissue elasticity will have on the voice cannot be predicted. With the aim of promoting rational indications for phonosurgery, the current article explains the biomechanisms of the normal and the disordered voice, including the complex interdependence of tissue viscoelasticity, glottal airstream and sound production. According to European Laryngological Society (ELS) recommendations, five - not entirely mutually independent - evaluation criteria form the basis of indication assessments: self-rating (by the patient), proxy rating (by the physician), technical signal analysis (computerized), aerodynamics (spirometry) and vibration analysis (stroboscopy). The ELS evaluation standards agreed upon in 2001 enable indications and - by virtue of pre- and postoperative comparisons - therapeutic successes to be assessed. The 10-year-old ELS protocol has been updated by a real-time method for visualizing vocal fold vibrations: the phonovibrogram (PVG) has replaced stroboscopy. Independently of the morphological anatomic details of the larynx, PVG visualizes the symmetry and regularity of vocal fold motion, thus allowing preoperative estimation of tissue elasticity.

Characterization of nonlinearity of shear elasticity using local velocity mapping

The emerging technology of ultrasonic imaging of the soft tissue strain and elasticity, which aims at providing information about the mechanical properties of the tissues, has become a peer research issue since the 1990s. An elasticity imaging method using continuous shear wave excitation (CSWE) is expected to be a safe and quantitative technique. We have already proposed a local velocity mapping method for shear elasticity by reconstructing the small phase modulation components of the harmonic distortion in CSWE. In this paper, we propose a simple model of static hysteresis as the nonlinearity of shear elasticity. This model is based on the presence of harmonic phase modulation components in shear wave propagation. By using this model, we attempt to characterize the static hysteresis of shear elasticity. The relationship between the texture patterns of the local velocity map and the nonlinearity of the medium, which is measured by a rheometer, shows that the proposed model can be adopted for the imaging of the nonlinearity of shear elasticity.

A numerical study of a heart phantom model

In this paper, we develop a computational heart phantom model based on magnetic resonance imaging (MRI) of a dynamic multi-modality heart phantom. The phantom is made of a hydrogel material which mimics the elasticity of human soft tissue, and is composed of anatomically correct left and right ventricle structures. The numerical analysis is carried out using the neo-Hookean constitutive model, and the C++ based object-oriented finite element library libMesh is used to solve the fully nonlinear governing equations. We derive the partial differential equations into a set of Lagrangian mesh, and use the weighted residual Galerkin method and Newton iteration solver in the numerical scheme. To validate the numerical model, the displacements and strains of some representative points are compared with experimental measurements and MRI-based strain estimations. Good agreement is obtained, and limitations of the model are discussed.

1E41 矩形孔の押込による軟組織弾性率異方性計測法の確立とアフリカツメガエル原腸胚への応用(OS2-4:細胞・分子のバイオメカニクス(4))

1E41 矩形孔の押込による軟組織弾性率異方性計測法の確立とアフリカツメガエル原腸胚への応用(OS2-4:細胞・分子のバイオメカニクス(4))

Ultrasound elastography using empirical mode decomposition analysis

Ultrasound elastography is a non-invasive method which images the elasticity of soft-tissues. To make an image, pre and after a small compression, ultrasound radio frequency (RF) signals are acquired and the time delays between them are estimated. The first differentiation of displacement estimations is called elastogram. In this study, we are going to make an elastogram using the processing method named empirical mode decomposition (EMD). EMD is an analytic technique which decomposes a complicated signal to a collection of simple signals called intrinsic mode functions (IMFs). The idea of paper is using these IMFs instead of primary RF signals. To implement the algorithms two different datasets selected. The first one was data from a sandwich structure of normal and cooked tissue. The second dataset consisted of around 180 frames acquired from a malignant breast tumor. For displacement estimating, two different methods, cross-correlation and wavelet transform, were used too and for evaluating the quality, two conventional parameters, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) calculated for each image. Results show that in both methods after using EMD the quality improves. In first dataset and cross correlation technique CNR and SNR improve about 16 dB and 9 dB respectively. In same dataset by using wavelet technique, the parameters show 14 dB and 10 dB improvement respectively. In second dataset (breast tumor data) CNR and SNR in cross correlation method improve 18 dB and 7 dB and in wavelet technique improve 17 dB and 6 dB respectively.

Global approach for transient shear wave inversion based on the adjoint method: a comprehensive 2D simulation study

Shear wave imaging (SWI) maps soft tissue elasticity by measuring shear wave propagation with ultrafast ultrasound acquisitions (10 000 frames s−1). This spatiotemporal data can be used as an input for an inverse problem that determines a shear modulus map. Common inversion methods are local: the shear modulus at each point is calculated based on the values of its neighbour (e.g. time-of-flight, wave equation inversion). However, these approaches are sensitive to the information loss such as noise or the lack of the backscattered signal. In this paper, we evaluate the benefits of a global approach for elasticity inversion using a least-squares formulation, which is derived from full waveform inversion in geophysics known as the adjoint method. We simulate an acoustic waveform in a medium with a soft and a hard lesion. For this initial application, full elastic propagation and viscosity are ignored. We demonstrate that the reconstruction of the shear modulus map is robust with a non-uniform background or in the presence of noise with regularization. Compared to regular local inversions, the global approach leads to an increase of contrast (∼+3 dB) and a decrease of the quantification error (∼+2%). We demonstrate that the inversion is reliable in the case when there is no signal measured within the inclusions like hypoechoic lesions which could have an impact on medical diagnosis.

Non-identifiability of the Rayleigh damping material model in Magnetic Resonance Elastography

Magnetic Resonance Elastography (MRE) is an emerging imaging modality for quantifying soft tissue elasticity deduced from displacement measurements within the tissue obtained by phase sensitive Magnetic Resonance Imaging (MRI) techniques. MRE has potential to detect a range of pathologies, diseases and cancer formations, especially tumors. The mechanical model commonly used in MRE is linear viscoelasticity (VE). An alternative Rayleigh damping (RD) model for soft tissue attenuation is used with a subspace-based nonlinear inversion (SNLI) algorithm to reconstruct viscoelastic properties, energy attenuation mechanisms and concomitant damping behavior of the tissue-simulating phantoms. This research performs a thorough evaluation of the RD model in MRE focusing on unique identification of RD parameters, μI and ρI.Results show the non-identifiability of the RD model at a single input frequency based on a structural analysis with a series of supporting experimental phantom results. The estimated real shear modulus values (μR) were substantially correct in characterising various material types and correlated well with the expected stiffness contrast of the physical phantoms. However, estimated RD parameters displayed consistent poor reconstruction accuracy leading to unpredictable trends in parameter behaviour. To overcome this issue, two alternative approaches were developed: (1) simultaneous multi-frequency inversion; and (2) parametric-based reconstruction. Overall, the RD model estimates the real shear shear modulus (μR) well, but identifying damping parameters (μI and ρI) is not possible without an alternative approach.

Correlation of B-mode sonography and compression elastography for diagnosis of tendon degeneration: a pictorial review

A pictorial review of 76 examinations of the extensor carpi ulnaris tendon using compression sonoelastography in conjunction with B-mode ultrasound imaging is presented here. A comparison of these two technologies is presented and the corresponding images were evaluated to determine whether there is correlation between the two technologies. Furthermore, the possibility that tendon degeneration and softening can be diagnosed earlier than has previously been possible using both of these technologies rather than B-mode imaging alone was explored and the results presented. Patients with unilateral or bilateral extensor carpi ulnaris tenosynovitis were scanned as part of a larger rheumatoid arthritis research study, which included extensor carpi ulnaris evaluation as part of its protocol. B-mode images were acquired with corresponding compression sonoelastography colour map, the region of interest being that portion of the tendon between the ulnar styloid and the insertion at the fifth metacarpal base. Seven paired images from different patients, which represent the varying appearances of extensor carpi ulnaris tenosynovitis seen in the study cohort are shown. Healthy tendons have a uniform hyperechoic fibrillar pattern longitudinally on B-mode imaging with predominantly mid-blue overlay on elastography. Tenosynovitis is shown on grey scale to have the usual appearances of loss of fibrillar echotexture and hypoechoic mucoid degeneration with the elastographic colour map showing predominantly red, yellow and green areas of tendon softening. There appears to be good correlation between the B-mode images and the elastographic overlay. The additional tissue characteristics yielded by sonoelastography in relation to tendon and peritendinous soft tissue elasticity may provide clinicians with information that could alter patient management. This technique shows promise in the earlier detection of tendon degeneration.

Patient-specific modelling of the calf muscle under elastic compression using magnetic resonance imaging and ultrasound elastography

Compression therapy is traditionally employed to achieve a variety of therapeutic goals related to venous insufficiency but its mechanisms are neither clearly understood nor conclusively demonstrated. (Avril et al., 2010) have pointed out that the capacity of the treatment to achieve the desired medical goal is closely related to the question of transmission of pressure through the soft tissues, as a result of which biomechanical models have been developed (Dubuis et al., 2012). In these models, the prediction of pressure was made based on the rather strong assumption that the behaviour of soft tissues (muscles and adipose tissues) can be approximated as homogeneous materials. Recent developments in ultrasound imaging can be helpful to improve both our understanding of the effect of medical compression stockings (MCS) on the blood return and on the quality of our predictions. (Bercoff et al., 2004) introduced a new ultrasound based technology called Supersonic Shear Imaging (SSI), for real-time soft tissue elasticity mapping. This transient elastography technique remotely produces a low frequency shear wave inside soft tissue through a radiation force by focusing ultrasonic beams at a supersonic speed. The shear wave motion is captured at a frame rate of 5 MHz. The velocity field of the medium can be mapped an dassuming the medium to be elastic, Young's modulus can be estimated quantitatively. This non-invasive technique allows identifying the material property heterogeneities inside the different compartments of the human leg. Using this experimental technique combined with FE modeling, the present study aims at shedding a light on the influence of those heterogeneities of material properties on the pressure inside the leg under elastic compression.

Microstructural characterization of vocal folds toward a strain-energy model of collagen remodeling

Collagen fibrils are believed to control the immediate deformation of soft tissues under mechanical load. Most extracellular matrix proteins remain intact during frozen sectioning, which allows them to be scanned using atomic force microscopy (AFM). Collagen fibrils are distinguishable because of their periodic roughness wavelength. In the present study, the shape and organization of collagen fibrils in dissected porcine vocal folds were quantified using nonlinear laser scanning microscopy data at the micrometer scale and AFM data at the nanometer scale. Rope-shaped collagen fibrils were observed. The geometric characteristics for the fibrils were fed into a hyperelastic model to predict the biomechanical response of the tissue. The model simulates the micrometer-scale unlocking behavior of collagen bundles when extended from their unloaded configuration. Force spectroscopy using AFM was used to estimate the stiffness of collagen fibrils (1±0.5MPa). The presence of rope-shaped fibrils is postulated to change the slope of the force–deflection response near the onset of nonlinearity. The proposed model could ultimately be used to evaluate changes in elasticity of soft tissues that result from the collagen remodeling.

MREJ: MRE elasticity reconstruction on ImageJ

Magnetic resonance elastography (MRE) is a promising method for health evaluation and disease diagnosis. It makes use of elastic waves as a virtual probe to quantify soft tissue elasticity. The wave actuator, imaging modality and elasticity interpreter are all essential components for an MRE system. Efforts have been made to develop more effective actuating mechanisms, imaging protocols and reconstructing algorithms. However, translating MRE wave images into soft tissue elasticity is a nontrivial issue for health professionals. This study contributes an open-source platform – MREJ – for MRE image processing and elasticity reconstruction. It is established on the widespread image-processing program ImageJ. Two algorithms for elasticity reconstruction were implemented with spatiotemporal directional filtering. The usability of the method is shown through virtual palpation on different phantoms and patients. Based on the results, we conclude that MREJ offers the MRE community a convenient and well-functioning program for image processing and elasticity interpretation.

Comb-Push Ultrasound Shear Elastography (CUSE) With Various Ultrasound Push Beams

Comb-push ultrasound shear elastography (CUSE) has recently been shown to be a fast and accurate 2-D elasticity imaging technique that can provide a full field-of-view (FOV) shear wave speed map with only one rapid data acquisition. The initial version of CUSE was termed U-CUSE because unfocused ultrasound push beams were used. In this paper, we present two new versions of CUSE-focused CUSE (F-CUSE) and marching CUSE (M-CUSE), which use focused ultrasound push beams to improve acoustic radiation force penetration and produce stronger shear waves in deep tissues (e.g., kidney and liver). F-CUSE divides transducer elements into several subgroups which transmit multiple focused ultrasound beams simultaneously. M-CUSE uses more elements for each focused push beam and laterally marches the push beams. Both F-CUSE and M-CUSE can generate comb-shaped shear wave fields that have shear wave motion at each imaging pixel location so that a full FOV 2-D shear wave speed map can be reconstructed with only one data acquisition. Homogeneous phantom experiments showed that U-CUSE, F-CUSE, and M-CUSE can all produce smooth shear wave speed maps with accurate shear wave speed estimates. An inclusion phantom experiment showed that all CUSE methods could provide good contrast between the inclusion and background with sharp boundaries while F-CUSE and M-CUSE require shorter push durations to achieve shear wave speed maps with comparable SNR to U-CUSE. A more challenging inclusion phantom experiment with a very stiff and deep inclusion shows that better shear wave penetration could be gained by using F-CUSE and M-CUSE. Finally, a shallow inclusion experiment showed that good preservations of inclusion shapes could be achieved by both U-CUSE and F-CUSE in the near field. Safety measurements showed that all safety parameters are below FDA regulatory limits for all CUSE methods. These promising results suggest that, using various push beams, CUSE is capable of reconstructing a 2-D full FOV shear elasticity map using only one push-detection data acquisition in a wide range of depths for soft tissue elasticity imaging.

A Mathematical Model for Analyzing the Elasticity, Viscosity, and Failure of Soft Tissue: Comparison of Native and Decellularized Porcine Cardiac Extracellular Matrix for Tissue Engineering

The clinical success of tissue-engineered constructs commonly requires mechanical properties that closely mimic those of the human tissue. Determining the viscoelastic properties of such biomaterials and the factors governing their failure profiles, however, has proven challenging, although collecting extensive data regarding their tensile behavior is straightforward. The easily calculated Young's modulus remains the most reported mechanical measure, regardless of its limitations, even though single-relaxation-time (SRT) models can provide much more information, which remain scarce due to a lack of manageable tools for implementing these models. We developed an easy-to-use algorithm for applying the Zener SRT model and determining the elastic moduli, viscosity, and failure profiles of materials under different mechanical tests in a user-independent manner. The algorithm was validated on the data resulting from tensile tests on native and decellularized porcine cardiac tissue, previously suggested as a promising scaffold material for cardiac tissue engineering. This analysis yields new and more accurate measurements such as the elastic moduli and viscosity, the model's relaxation time, and information on the factors governing the materials' failure profiles. These measurements indicate that the viscoelasticity and strength of the decellularized acellular extracellular matrix (ECM) are similar to those of native tissue, although its elasticity and apparent viscosity are higher. Nonetheless, reseeding and culturing the ECM with mesenchymal stem cells was shown to partially restore the mechanical properties lost after decellularization. We propose this algorithm as a platform for soft-tissue analysis that can provide comparable and unbiased measures for characterizing viscoelastic biomaterials commonly used in tissue engineering.

Combining ultrasound-based elasticity estimation and FE models to predict 3D target displacement

During minimally invasive surgical procedures (e.g., needle insertion during interventional radiological procedures), needle–tissue interactions and physiological processes cause tissue deformation. Target displacement is caused by soft-tissue deformation, which results in misplacement of the surgical tool (needle). This study presents a technique to predict target displacement in three-dimensions (3D) by combining soft-tissue elasticity estimation using an ultrasound-based acoustic radiation force impulse (ARFI) technique and finite element (FE) models. Three different phantoms with targets are manufactured, and subjected to varying loading and boundary conditions. Ultrasound images are acquired using a 3D probe during loading and unloading of each phantom, and subsequently target displacement is calculated. 3D FE models of the phantoms are developed, and they are used to predict target displacement. The maximum absolute error in target displacement between the experiments and FE analyses is found to be 1.39mm. This error is less than the smallest tumor diameter (2.0–3.0mm) which can be detected in breast tissue. This study shows that the combination of soft-tissue elasticity estimation using the ARFI technique and 3D FE models can accurately predict target displacement, and could be used to develop patient-specific plans for surgical interventions.

The Staged Face Lift

Although early secondary face lift is a highly scrutinized procedure, it is beneficial for a select group of patients. Justification for performing the early secondary face lift or staged face lift is more apparent when considering the biomechanical limitations of the primary face lift. All patients undergoing primary face-lift procedures performed by the senior author (T.A.M.) between 1998 and 2008 were followed for 2 years to determine which patients would benefit from an early secondary rhytidectomy. Early secondary face lifts were performed in the same sub-superficial musculoaponeurotic system plane as the primary procedure and entailed full undermining. Forty-seven of 742 patients (6.3 percent) undergoing a primary face-lift procedure underwent an early secondary rhytidectomy. Identified limiting factors of the primary face lift included suture-tearing force, viscoelastic properties (tissue creep and stress relaxation), blood supply, and an attempt to avoid an overly pulled appearance. Indications for early secondary rhytidectomy included early symptoms of recurrence or residual age-related changes in patients with severe preoperative laxity or poor soft-tissue elasticity and mainly involved the perioral region. There were no significant complications and there was high patient satisfaction in all cases. With thorough understanding of the viscoelastic properties of facial tissues and proper consultation with patients, the early secondary face lift can be used as a safe and effective option with which to address the limitations of a primary face lift. Therapeutic, IV.

Soft tissue stability after segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up

Soft tissue changes were analysed retrospectively in 17 patients following distraction osteogenesis (DO) of the mandibular anterior alveolar process. Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated at T1 (17.0 days), after DO at T2 (mean 6.5 days), at T3 (mean 24.4 days), at T4 (mean 2.0 years), and at T5 (mean 5.5 years). Statistical analysis was carried out using Kolmogorov–Smirnov test, paired t-test, Pearson's correlation coefficient, and linear backward regression analysis. 5.5 years postoperatively, the net effect for the soft tissue at point B′ was 88% of the advancement at point B while the lower lip (labrale inferior) followed the advancement of incision inferior to 24%. Increased preoperative age was correlated (p<0.05) with more horizontal backward movement (T5–T3) for labrale inferior and pogonion′. Higher NL/ML′ angles were significantly correlated (p<0.05) to smaller horizontal soft tissue change at labrale inferior (T5–T3). The amount of advancement at point B was significantly correlated with an upward movement (T5–T3) of labrale inferior (p<0.01) and stomion inferior (p<0.05). It can be concluded that further change in soft tissues occurred between 2.0 and 5.5 years postoperatively. The physiological process of ageing and loss of soft tissue elasticity should be considered as possible reasons.

Real-time 1-D/2-D transient elastography on a standard ultrasound scanner using mechanically induced vibration

Transient elastography has been well established in the literature as a means of assessing the elasticity of soft tissue. In this technique, tissue elasticity is estimated from the study of the propagation of the transient shear waves induced by an external or internal source of vibration. Previous studies have focused mainly on custom single-element transducers and ultrafast scanners which are not available in a typical clinical setup. In this work, we report the design and implementation of a transient elastography system on a standard ultrasound scanner that enables quantitative assessment of tissue elasticity in real-time. Two new custom imaging modes are introduced that enable the system to image the axial component of the transient shear wave, in response to an externally induced vibration, in both 1-D and 2-D. Elasticity reconstruction algorithms that estimate the tissue elasticity from these transient waves are also presented. Simulation results are provided to show the advantages and limitations of the proposed system. The performance of the system is also validated experimentally using a commercial elasticity phantom.

Combining MR elastography and diffusion tensor imaging for the assessment of anisotropic mechanical properties: A phantom study

To investigate the anisotropic elasticity of soft tissues using MR elastography (MRE) combined with diffusion tensor imaging (DTI). The storage moduli parallel (μ(‖)) and perpendicular (μ(⊥)) to the local fiber orientation were calculated assuming a transversely isotropic model. The local fiber orientation was provided by DTI. The proposed technique was validated against rheometry using anisotropic viscoelastic phantoms with various fiber volume fractions (V(f) = 0%, 15%, and 35%) and bovine skeletal muscle samples. The anisotropic ratio (μ(‖)/μ(⊥)) as measured by MRE correlated well with rheometry for all samples (R(2) = 0.809). The combined MRE/DTI technique was also able to differentiate different levels of mechanical anisotropy with the mechanical anisotropy (μ(‖)/μ(⊥)) of the V(f) = 35% phantoms being significantly higher than the V(f) = 15% and the isotropic (V(f) = 0%) phantoms. The bovine muscle samples showed significantly higher mechanical anisotropy than all phantoms. This study has demonstrated the feasibility of the proposed imaging technique for characterizing mechanical anisotropy of anisotropic materials and biological tissues, and validated the mechanical anisotropy results.

Calculation of strain images of a breast‐mimicking phantom from 3D CT image data

Elastography is a medical imaging modality to visualize the elasticity of soft tissues. Ultrasound and MRI have been exclusively used for elastography of soft tissues since they can sensitize the tissues' minute displacements of an order of μm. It is known that ultrasound and MRI elastography show cancerous tissues with much higher contrast than conventional ultrasound and MRI. To evaluate possibility of combining elastography with x-ray imaging, we have calculated strain images of a breast-mimicking phantom from its 3D CT image data. We first simulated the x-ray elastography using a FEM model which incorporated both the elasticity and x-ray attenuation behaviors of breast tissues. After validating the x-ray elastography scheme by simulation, we made a breast-mimicking phantom that contained a hard inclusion against soft background. With a micro-CT, we took 3D images of the phantom twice, changing the compressing force to the phantom. From the two 3D phantom images taken with two different compression ratios, we calculated the displacement vector maps that represented the compression-induced pixel displacements. In calculating the displacement vectors, we tracked the movements of image feature patterns from the less-compressed-phantom images to the more-compressed-phantom images using the 3D image correlation technique. We obtained strain images of the phantom by differentiating the displacement vector maps. The FEM simulation has shown that x-ray strain imaging is possible by tracking image feature patterns in the 3D CT images of the breast-mimicking phantom. The experimental displacement and strain images of a breast-mimicking phantom, obtained from the 3D micro-CT images taken with 0%-3% compression ratios, show behaviors similar to the FEM simulation results. The contrast and noise performance of the strain images improves as the phantom compression ratio increases. We have experimentally shown that we can improve x-ray strain image quality by applying 3D image correlation to the two sets of 3D CT images taken with different compression ratios. But, we need further investigations to evaluate the strain imaging performance considering the noise and decorrelation effects as well as the extra dose caused by two scans.

On the importance of modelling organ geometry and boundary conditions for predicting three-dimensional prostate deformation

The use of an ultrasound probe or a needle guide during biopsy deforms both the rectal wall and the prostate, resulting in lesion motion. An accurate patient-specific finite element (FE)-based biomechanical model can be used to predict prostate deformations. In this study, an FE model of a prostate phantom is developed using magnetic resonance images, while soft-tissue elasticity is estimated in vivo using an ultrasound-based acoustic radiation force impulse imaging technique. This study confirms that three-dimensional FE-predicted prostate deformation is predominantly dependent on accurate modelling of prostate geometry and boundary conditions. Upon application of various compressive displacements, our results show that a linear elastic FE model can accurately predict prostate deformations. The maximum global error between FE-predicted simulations and experimental results is 0.76 mm. Moreover, the effect of including the urethra, puboprostatic ligament and urinary bladder on prostate deformations is investigated by a sensitivity study.