A Finite Element Study of Ultrasound Elastography Using Shear Wave Interference Patterns Generated by Miniature Surface Sources (original) (raw)
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Ultrasound in Medicine & Biology
It has been postulated that in the liver, applying increased probe pressure during ultrasound-based shear wave elastography (SWE) might lead to a false increase in the SWE result. We aimed to determine the influence of increased intercostal probe pressure when performing SWE of the liver. We also investigated the number of measurements required to achieve technically successful and reliable SWE examinations. This prospective, clinical study included 112 patients and 2240 SWE measurements of the liver. We applied probe pressure intercostally, to reduce the skin-to-liver capsule distance (SCD), which could stabilize the SWE signal and thus increase the number of technically successful measurements. We performed 10 measurements with maximum probe pressure and 10 with normal pressure in each patient. Thus, two analysis groups were compared for differences. Compared with normal pressure, maximum probe pressure significantly reduced the SCD (p < 0.001) and significantly increased the number of technically successful measurements from 981 to 1098, respectively (p < 0.001). The SWE results with normal and maximum probe pressure were 5.96 kPa (interquartile range: 2.41) and 5.45 kPa (interquartile range: 1.96), respectively (p < 0.001). In obese patients, a large SCD poses a diagnostic challenge for ultrasound SWE. We found that maximum intercostal probe pressure could reduce the SCD and increase the number of technically successful measurements, without falsely increasing the SWE result. Only three measurements were required to achieve technically successful and reliable SWE examinations.
Ultrasound in medicine & biology, 2018
We evaluated variation in fibrosis staging caused by depth, pre-load force and measurement off-axis distance on different ultrasound shear wave elastography (SWE) systems prospectively in 20 patients with diffuse liver disease. Shear wave speed (SWS) was measured with transient elastography, acoustic radiation force impulse (ARFI) and 2-D shear wave elastography (SWE). ARFI and 2-D-SWE measurements were obtained at different depths (3, 5 and 7 cm), with different pre-load forces (4, 7 and 10N and variable) and at 0, 2 and 4cm off the central axis of the transducer. A single, blinded pathologist staged fibrosis using the METAVIR system (F0-F4). Area under the receiver operating characteristic curve was charted to differentiate significant fibrosis (F ≥ 2). Depth was the only factor found to influence ARFI-derived values; no acquisition factors were found to affect 2-D-SWE SWS values. ARFI and 2-D-SWE for diagnosis of significant fibrosis at a depth of 7cm along the central axis had g...
Medical ultrasonography, 2018
Non-invasive methods to assess the severity of chronic liver diseases have become more and more popular. The aim of our study was to evaluate the correlation of four Shear Waves Elastographic methods in a cohort of patients with chronic liver diseases of mixed etiologies and to compare their performances for liver fibrosis evaluation. A prospective study was conducted on 127 consecutive patients with chronic liver diseases of mixed etiologies. LS measurements were performed in all subjects, in one session, during the same day, by means of 4 elastographic methods: Transient Elastography (TE), Virtual Touch Quantification (VTQ), ElastPQ and 2D-SWE.SSI. The diagnosis accuracies of VTQ, ElastPQ, 2D-SWE.SSI were then compared using TE as reference method. Valid LS measurements by all four shear waves ultrasound elastographic methods were obtained in 116/127 subjects with VTQ, in 108/127 subjects with 2D-SWE.SSI, in 111/127 with TE and in 109/127 with ElastPQ, so the final analysis inclu...
Physics in Medicine and Biology, 2020
Two-dimensional (2-D) ultrasound shear wave elastography (SWE) has been widely used for soft tissue properties assessment. Given that shear waves propagate in three dimensions (3-D), extending SWE from 2-D to 3-D is important for comprehensive and accurate stiffness measurement. However, implementation of 3-D SWE on a conventional ultrasound scanner is challenging due to the low volume rate (tens of Hertz) associated with limited parallel receive capability of the scanner's hardware beamformer. Therefore, we developed an external mechanical vibration-based 3-D SWE technique allowing robust 3-D shear wave tracking and speed reconstruction for conventional scanners. The aliased shear wave signal detected with a sub-Nyquist sampling frequency was corrected by leveraging the cyclic nature of the sinusoidal shear wave generated by the external vibrator. Shear wave signals from different sub-volumes were aligned in temporal direction to correct time delays from sequential pulse-echo events, followed by 3-D speed reconstruction using a 3-D local frequency estimation algorithm. The technique was validated on liver fibrosis phantoms with different stiffness, showing good correlation (r = 0.99, p < 0.001) with values measured from a state-of-the-art SWE system (GE LOGIQ E9). The phantoms with different stiffnesses can be well-differentiated regardless of the external vibrator position, indicating the feasibility of the 3-D SWE with regard to different shear wave propagation scenarios. Finally, shear wave speed calculated by the 3-D method correlated well with magnetic resonance elastography performed on human liver (r = 0.93, p = 0.02), demonstrating the in vivo feasibility. The proposed technique relies on low volume rate imaging and can be implemented on
Medical Ultrasonography
Aim: To evaluate the feasibility of two elastographic methods, point Shear Wave Elastography (pSWE) and two dimensional Shear Wave Elastography (2D-SWE), integrated in the same ultrasound machine, for liver fibrosis (LF) assessment, using Transient Elastography (TE) as the reference method.Material and methods: We included in the study 115 subjects in which LF was evaluated in the same session by TE (FibroScan, EchoSens), pSWE and 2D-SWE (Samsung-Medison RS85). Reliable liver stiffness (LS) measurements were defined: for TE the median value of 10 measurements with interquartile range (IQR/M)≤30%,while for pSWE and 2D-SWE the median value of 10 measurements, with a reliability measurement index (RMI)≥0.5 and IQR/M≤30%. For classification of LF severity we used TE as the reference method with the following cut-offs: F2≥7kPa, F3≥9.5kPa and F4≥12kPa.Results: Reliable measurements by TE were obtained in 98.2% of cases (113/115), by pSWE in 93.9% of cases (108/115) and by 2D-SWE in 92.1% ...
Physics in Medicine and Biology, 2016
Ultrasound and magnetic resonance elastography techniques are used to assess mechanical properties of soft tissues. Tissue stiffness is related to various pathologies such as fibrosis, loss of compliance, and cancer. One way to perform elastography is measuring shear wave velocity of propagating waves in tissue induced by intrinsic motion or an external source of vibration, and relating the shear wave velocity to tissue elasticity. All tissues are inherently viscoelastic and ignoring viscosity biases the velocity-based estimates of elasticity and ignores a potentially important parameter of tissue health. We present Attenuation Measuring Ultrasound Shearwave Elastography (AMUSE), a technique that independently measures both shear wave velocity and attenuation in tissue and therefore allows characterization of viscoelasticity without using a rheological model. The theoretical basis for AMUSE is first derived and validated in finite element simulations. AMUSE is validated against the traditional methods for assessing shear wave velocity (phase gradient) and attenuation (amplitude decay) in tissue mimicking phantoms and excised tissue. The results agreed within one standard deviation. AMUSE was used to measure shear wave velocity and attenuation in 15 transplanted livers in patients with potential acute rejection, and the results were compared with the biopsy findings in a preliminary study. The comparison showed excellent agreement and suggests that AMUSE can be used to separate transplanted livers with acute rejection from livers with no rejection.
2018
The development of haptic technology in laparoscopic simulations indicates a demand of constant upgrade of tactile feedback, which is currently considered to be unsatisfactory. Presumably, one of its causes may be insufficiently examined and described mechanical parameters of soft tissues in vivo, including liver tissue. The aim of the following work was the attempt at assessing the applicability of data from shear wave elastography in organ modelling by correlating the mechanical parameters of the liver obtained by this noninvasive method, with the mechanical parameters obtained by indentation. Methods: Each one out of 12 porcine livers, was subjected to elastography and subsequently to the indentation test. The mean Young's modulus for each liver lobe was obtained using elastography, while in indentation Young's moduli in three different strain ranges and maximum load were calculated. Results: Differences between mechanical parameters of lobes were not found but the parameters were calculated for different methods and strain ranges. Conclusions: The limitations of both methods prevent the unambiguous assessment of the applicability of elastography in liver modelling for laparoscopic simulations, at the presented stage of research. Nevertheless, the presented study provides a valuable introduction to the development of a methodology for testing the mechanical parameters of liver tissue.