This article reports the methodology used to develop a high-precision ultrasound transit time flow meter dedicated to liquid hydrocarbons. This kind of flow meter is designed for custody transfer ...applications requiring accuracy better than 0.15% of reading. We focus here on certain specific points to achieve this accuracy. The transit time method needs to estimate accurately the time delay between signals received by a pair of transducers. In this study, we review different ways of estimating this time delay. We also propose a specific configuration of the flow meter paths. In particular, this configuration compensates for the swirl phenomenon, which has a significant impact on the accuracy of the flow meter. We also propose a theoretical parametric profile to reconstruct the fluid velocity profile in order to perform in situ diagnosis of the flow. The parameters of the model are estimated from the measurements of the flow meter. Simulations and experimental results showed that this method provides characterization of the flow in disturbed and undisturbed flow conditions.
Recent improvements in computational tools opened the possibility of patient-specific modeling to aid clinicians during diagnosis, treatment, and monitoring. One example is the modeling of blood flow ...for surgical planning, where modeling can help predict the prognosis. Computational analysis is used to extract hemodynamic information about the case; however, these methods are sensitive to assumptions on blood properties, boundary conditions, and appropriate geometry accuracy. When available, experimental measurements can be used to validate the results and, among the modalities, ultrasound-based methods are suitable due to their relative low cost and non-invasiveness. This work proposes a procedure to create accurate patient-specific silicone replicas of blood vessels and a power Doppler compatible experimental setup able to simulate and measure realistic flow conditions. The assessment of silicone model geometry shows small discrepancies between these and the target geometries (median of surface error lies within 57 µm and 82 μm). Power Doppler measurements were compared against computational fluid dynamics results, showing discrepancies within 10% near the wall. The experimental approach offers a setup to quantify flow in in vitro systems and provide more accurate results where other techniques (e.g., particle image velocimetry and particle tracking velocimetry) have shown limitations due to the interference of the interface.
Nonalcoholic fatty liver disease (NAFLD) is characterized by accumulation of fat within the Liver. The main objective of this work is (1) to evaluate the feasibility of measuring in vivo in the liver ...the shear wave phase velocity dispersion cs(ω) between 20Hz and 90Hz using vibration-controlled transient elastography (VCTE); (2) to estimate through the rheological Kelvin-Voigt model the shear elastic μ and shear viscosity η modulus; (3) to correlate the evolution of these viscoelastic parameters on two patients at Tours Hospital with the hepatic fat percentage measured with T1-weighted gradient-echo in-and out-phase MRI sequence. For the first volunteer who has 2% of fat in the liver, we obtained μ = 1233 ± 133Pa and η = 0.5 ± 0.4Pa.s. For the patient with 22% of fat, we measure μ = 964 ± 91Pa and η = 1.77 ± 0.3Pa.s. In conclusion, this novel method showed to be sensitive in characterizing the visco-elastic properties of fatty liver.
The GreenLight laser is one of the main alternative treatments for benign prostatic hyperplasia (BPH). Ultrasonography with contrast (ECUS) is one of the main innovations in radiology that has led to ...the examination of tissue vascularity. The objective of the study was to measure the impact of photovaporization of the prostate (PVP) on the prostate gland with ECUS.
We conducted a pilot study to assess the impact of PVP on the prostate by using ECUS intraoperatively (ethical committee approval No. 2012-001451-39). Twelve patients undergoing PVP for symptomatic BPH were enrolled in this study after providing their informed consent. ECUS was performed just before and after PVP in the operating room and at 1 month postoperatively.
Comparative analysis showed that after PVP, a nonvascularized area with an average thickness of 11.1 mm was observed beyond the operative cavity. The nonvascularized area was thinner at 1 month postoperatively and disappeared at 6 months for the six patients evaluated. This is the first study using contrast-enhanced ultrasonography to measure the impact of PVP on the prostate. Our study has the limitations of a pilot study with a small population and a short follow-up. Based on these results, we would advise beginners to take into account the necrosis thickness and to limit the depth of vaporization.
Through the use of ECUS, our study demonstrated that a large area of necrosis is induced around the surgical cavity from the action of the GreenLight laser. Being aware of this phenomenon will certainly reduce the risk of complications induced by surgery.
Several studies have been carried out in the last twenty years on the characterization and detection of cerebral artery emboli. From the detection point of view the existing methods are largely based ...on the classical Fourier analysis of which the well known limitations provide poor accuracy. This paper first recalls existing methods based on Fourier, Wigner-Ville and wavelet approaches. It then presents new emboli detection methods based on parametric signal processing approaches. The basic idea of these parametric methods is to compare the Doppler embolic signal to its autoregressive model. The detection principle consists in constructing a decision information which contains the signature of the micro-embolus being sought. The detection is finally evaluated using receiver operating characteristic (ROC) curves. Comparison between the new methods and classical approaches is performed using a realistic embolic signal simulation. Furthermore, to validate the authors' theoretical study, they tested their new algorithms using in vivo signals. This comparison shows the significant inaccuracy of existing methods to detect micro-emboli.
An analytical model is presented to achieve simultaneous prediction of the elementary electroacoustic response and directivity pattern of a one-dimensional (1D) piezocomposite array. The theoretical ...approach was based on guided wave theory in a multilayered structure in which the 1-3 piezocomposite material is considered as a homogeneous piezoelectric plate. A matrix method was applied to simulate the displacement fields generated at the surface of the array when one element was excited with an electrical pulse. A test device was manufactured, then characterized through measurements of displacement performed with an interferometric laser probe when the array vibrated in air and in water. The experimental results are presented and compared with theory
In the field of biological tissue characterization, fundamental acoustic attenuation properties have been demonstrated to have diagnostic importance. Attenuation caused by scattering and absorption ...shifts the instantaneous spectrum to the lower frequencies. Due to the time-dependence of the spectrum, the attenuation phenomenon is a time-variant process. This downward shift may be evaluated either by the maximum energy frequency of the spectrum or by the center frequency. In order to improve, in strongly attenuating media, the results given by the short-time Fourier analysis and the short-time parametric analysis, we propose two approaches adapted to this time-variant process: an adaptive method and a time-varying method. Signals backscattered by an homogeneous medium of scatterers are modeled by a computer algorithm with attenuation values ranging from 1 to 5 dB/cm MHz and a 45 MHz transducer center frequency. Under these conditions, the preliminary results obtained with the proposed time-variant methods, compared with the classical short-time Fourier analysis and the short-time auto-regressive (AR) analysis, are superior in terms of standard deviation (SD) of the attenuation coefficient estimate. This study, based on nonstationary AR spectral estimation, promises encouraging perspectives for in vitro and in vivo applications both in weakly and highly attenuating media.
Investigation of cross-coupling in 1-3 piezocomposite arrays Certon, D.; Felix, N.; Lacaze, E. ...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control,
2001-Jan., 2001, 2001-Jan, 2001-01-00, 20010101, Volume:
48, Issue:
1
Journal Article
Peer reviewed
Plate waves inside the piezoelectric layer are much involved in the element cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite ...materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using a network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S/sub 0/ mode is responsible for the inter-element coupling, whereas the S/sub 3/ mode widens the effective width of the excited element.
High-frequency transient elastography (HF-TE) is a noninvasive technique for assessing shear-wave speed and finally elasticity in thin tissue such as the skin. It has never been validated for ...monitoring fibrotic skin diseases. The purpose was to evaluate the potential of HF-TE to assess skin fibrosis in patients with chronic venous disorders (CVD).
This clinical study enrolled 48 patients at various stages of CVD and 48 paired healthy volunteers. Subjects underwent a clinical examination with an evaluation of Rodnan's fibrosis skin score. We studied the dermis thickness measured using ultrasound (US) and elasticity measurements using cutometer and HF-TE studied according to 3 cutaneous zones positioned on the leg. The area under the receiver operating characteristic curve (AUC) was calculated to evaluate the diagnosis performance for a combined parameter (PRL) based on a logistic regression model using both elasticity and dermal thickness.
Patients with CVD had significantly higher values of skin elasticity than healthy subjects, 134.5 kPa and 132.1 kPa vs. 91.3 kPa, respectively. The dermis thickness also increased with escalation in CVD stage for all studied zones. The PRL parameter had an AUC value of 0.79 for all zones and stages of CVD clustered. The discriminating power of PRL increased with escalation of the CVD stage; with an AUC value of up to 0.89 for evolved stages, and a sensitivity and specificity of 0.79 and 0.89, respectively.
HF-TE, coupled with a US measurement of dermis thickness, made it possible to propose a new biomarker, which proved to be a good diagnostic tool for skin fibrosis.
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