The purpose of this study was to establish interobserver reproducibility of Young's modulus (YM) derived from ultrasound shear wave elastography (US-SWE) in the normal prostate and correlate it with multiparametric magnetic resonance imaging (mpMRI) tissue characteristics. Twenty men being screened for prostate cancer underwent same-day US-SWE (10 done by two blinded, newly-trained observers) and mpMRI followed by 12-core biopsy. Bland–Altman plots established limits of agreement for YM. Quantitative data from the peripheral zone (PZ) and the transitional zone (TZ) for YM, apparent diffusion coefficient (ADC, mm2/s from diffusion-weighted MRI), and Ktrans (volume transfer coefficient, min−1), Ve (extravascular-extracellular space, %), Kep (rate constant, /min), and initial area under the gadolinium concentration curve (IAUGC60, mmol/L/s) from dynamic contrast–enhanced MRI were obtained for slice-matched prostate sextants. Interobserver intraclass correlation coefficients were fair to good for individual regions (PZ = 0.57, TZ = 0.65) and for whole gland 0.67, (increasing to 0.81 when corrected for systematic observer bias). In the PZ, there were weak negative correlations between YM and ADC (p = 0.008), and Ve (p = 0.01) and a weak positive correlation with Kep (p = 0.003). No significant intermodality correlations were seen in the TZ. Transrectal prostate US-SWE done without controlling manually applied probe pressure has fair/good interobserver reproducibility in inexperienced observers with potential to improve this to excellent by standardization of probe contact pressure. Within the PZ, increase in tissue stiffness is associated with reduced extracellular water (decreased ADC) and space (reduced Ve).
Diagnosis and prognosis of coronary artery atherosclerosis evolution currently rely on plaque morphology and vessel stenosis degree. Such information can accurately be accessed with IntraVascular UltraSound (IVUS) imaging. A severe complication of coronary artery atherosclerosis is thrombosis, a consequence to plaque rupture or fissure, which might lead to myocardial infarction, and sudden ischemic death. Plaque rupture is a complicated mechanical process, correlated with plaque morphology, composition, mechanical properties and with the blood pressure and its long term repetitive cycle. Extracting information on the plaque local mechanical properties and on the surrounding tissues may thus reveal relevant features about plaque vulnerability. According to that, EndoVascular Elastography (EVE) was introduced as a complementary tool to IVUS in the process of coronary artery disease investigations. In this paper, in vivo elastographic data are reported for three patients who were diagnosed with severe coronary artery stenoses. The radio-frequency (RF) data were acquired, in the minutes preceding angioplasty, using a CVIS (ClearView, CardioVascular Imaging System Inc.) ultrasound scanner working with a 30 MHz mechanical rotating single-element transducer. Due to the blood flow pulsation, the vascular tissue was naturally compressed/dilated. The elastograms, or radial strain distributions inside the vessel wall, were computed offline using the Lagrangian Speckle Model Estimator (LSME). This model-based approach considers the speckle as a material property that is, on average, conserved with tissue motion. According to that, tissue mechanical parameters (namely the strain tensor) were inferred from the speckle kinetics. The results showed the potential of the LSME to characterize and to distinguish coronary atherosclerotic plaques from the normal vascular tissue. Namely, a hard atherosclerotic plaque was detected for one patient (PAT1), whereas high strain values in the plaque region suggested the potential presence of a lipid core for PAT2. In conclusion, these results confirm that EVE might be a very relevant clinical tool to support IVUS echograms in the characterization of coronary artery. Nevertheless, further investigations are required to fully state on the potential of the method to predict the vulnerability of coronary artery atherosclerotic plaques.
Noninvasive micro-vascular ultrasound elastography (MicroNIVE) was recently proposed for insitu phenotyping in rat models of hypertension through the assessment of mechanical properties of carotid arteries. This paper reports comparisons between MicroNIVE and M-Mode strain measurements. Brown Norway male rats (n = 5) were investigated over 24 weeks. The common carotid arteries were imaged with an ultrasound biomicroscope equipped with a 40-MHz central frequency probe and an external workstation to collect radio-frequency (RF) data. Time-sequences of RF and M-mode signals were recorded over several consecutive cardiac cycles. MicroNIVE strain cartographies were computed for each pair of successive RF images with the Lagrangian Speckle Model Estimator. Diastolic strain (s D ) and systolic strain (s s ) parameters were estimated. M- mode strain estimations were computed as s M (t) = (w(t)-w max )/w max , with w(t) and w max being the wall thicknesses at time "t" and at end-diastole, respectively. MicroNIVE diastolic and systolic strains were consistent with a Pearson correlation coefficient (r) of 0.75 (p < 10 -11 ). M-mode and MicroNIVE strain measurements were correlated with r = 0.74 (p < 10 -5 ) between s M and s D and r = 0.67 (p < 10 -4 ) between s M and s s . Corroborated by Bland-Altman plots, M-mode and MicroNIVE were found in very good concordance.
The objective of elastography is to complement mammography and ultrasound to better differentiate between benign and malignant breast lesions. In this aim, strain-related criteria have been introduced, based on axial strain imaging but also shear strain imaging. In this study, size and shape of fibroadenomas and cancers between B-mode and axial strain images are compared. To quantify the size differences observed, the area of the lesions in elastograms and sonograms were determinedand the strain/B-mode area ratios computed.
Ultrasound elastography allows the estimation of tissue elasticity and can be used to characterise atherosclerotic plaques. In order to quantify the difference in elasticity of the various plaque materials, our aim is to calibrate the intravascular elastography images. For that, we make comparison between the modeling and experiments on vessel mimicking phantoms. Use of phantoms permits one to control many parameters. The range of Young's modulus in arteries goes from 1 kPa for lipids to 1000 kPa for the axial Young's modulus of the adventicia. Experiments were done to characterise a vessel mimicking materials, polyvinyl alcohol cryogel, and were compared with arterial values. The process consists of creating a pattern on a lateral side of the homogenous sample, to apply a uniform controlled pressure loading, then a CCD camera takes a photograph of the patterned side before and after compression. Image correlation software estimates axial and lateral strain and permits one to calculate the elastic modulus. These values are then included in finite element modeling. Then we combine a finite element analysis with a simulation of ultrasound response of the phantom to generate echograms for different compression levels of the vessel. The compression is radial and uniform inside the vessel. An estimated elastogram is obtained from two images using an adaptive stretching algorithm. This study shows that cryogel is a good material to make vessel mimicking phantoms due to the similarity of its elastic modulus to that which we can find in an artery, and therefore its relative breaking resistance.
This work presents a new approach to lateral strain estimation in the field of tissue elasticity imaging with ultrasound. A particular beamforming is used to produce a point spread function (PSF) with lateral oscillations. Lateral RF signals can then be considered as the juxtaposition of RF samples coming from the same depth. This enables to estimate the lateral strain with a scaling factor estimator applied to the lateral signals. The approach is validated in simulation on a medium stretched only in the lateral direction. The estimation is unbiased for lateral strain values from 0.5 to 7 % with standard deviation less than 0.5 %.
The presence of a mobile fluid in a porous tissue modifies aspects of the tissue's mechanical behaviour such as the time variation of strain induced by a sustained compression. Elastography can be used to follow such responses and to estimate poroelastic parameters. This preliminary study examined axial strain variation in a poroelastic cylinder embedded in a quasi-elastic (or weakly permeable) background. Finite element analysis and experiment were compared. Unlike the case of purely elastic materials a region with high strain decaying with time was observed at the interface between the cylinder and the background. The time variation of strain in different regions of the phantom showed known poroelastic behaviour in that, as fluid was expelled, some regions contracted axially while others expanded axially. The strain relaxation time varied in a systematic manner in the different materials.
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