M. Gindre

Echography using correlation techniques: choice of coding signal

Theoretical studies made in the early 1980s suggest that ultrasonic imaging using correlation technique can overcome some of the drawbacks of classical pulse echography. Indeed by transmitting a continuous coded signal and then compressing it into a short, high resolution pulse at the receiver the total signal to noise ratio (SNR) is improved. The target location is determined by cross correlation of the emitted and the received signal. The band compression allows, by increasing SNR, the retrieval of echo signals buried in the receiver noise. Thus in medical-type echography, where the signal attenuation at fixed depth is proportional to the frequency, the SNR improvement allows the use of higher frequency signals and leads to improved resolution. We report here the results of comparative experimental studies of simple echo B type images as obtained by the classical pulse echo and correlation techniques. Because the optimisation of the coded signal plays a crucial role in the performance of the correlation technique we will also present a comparative study of the performances of the most common codes (m-sequences and complementary series). In particular we shall emphasise the following points: the relative importance of the central lobe as compared to the side lobes of the correlation function, which is directly related to the dynamic of the imaging system, the width of the correlation peak which is directly related to the axial resolution of the system, the facility of the realisation. The merit of B-mode images obtained with the coded signals will be discussed showing that as far as signal modulation is used the best results are obtained with periodic m-sequences.<<ETX>>

An alternative quantitative acoustical and electrical method for detection of cell adhesion process in real-time

Sauerbrey [(1956), Z Phys 55:206–222] showed that the shift in resonance frequency of thickness shear mode (TSM) of a quartz crystal sensor is proportional to the mass, which is deposited on it. However, new powerful electrical circuits were developed that are capable of operating TSM quartz crystal sensors in fluids which enabled this method to be introduced into electrochemical and biological applications. These applications include the detection of virus capsids, bacteria, mammalian cells, the interaction of DNA and RNA with complementary strands, specific recognition of protein ligands by immobilized receptors, and last but not least the study of complete immunosensors. Piezoelectric quartz transducers allow a label‐free identification of molecules; they are more than mass sensors since the biosensor response is also influenced by the surface charge of adsorbed proteins, interfacial phenomena, surface roughness and viscoelastic properties of the adhered biomaterial. These new characteristics have recently been used to investigate cell, liposome, and protein adhesion onto surfaces, thus permitting the rapid determination of morphological cell changes as a response to pharmacological substances, and changes in the water content of biopolymers avoiding of time‐consuming methods. We validated an alternative quantitative acoustical engineering for cell adhesion process monitored by the TSM. Shear acoustical results (motional resistance) are further correlated to cell counting procedures and are sensitive of adhesion processes in real‐time. Biotechnol. Bioeng. 2011; 108:947–962.

Compressibility of nano inclusions in complex fluids by ultrasound velocity measurements

We present a high precision ultrasonic velocimeter for a small volume sample (1 cm/sup 3/) for a path length of 1 cm achieved. The method used is based on the time of flight measurement with an original signal processing technique: the barycenter method. With our system, we have measured the sound velocity with an accuracy of 10/sup -5/. The detection of a difference in velocity between two liquids of about 2 cm/s is achieved. The compressibility of the reference liquid can then be deduced with an accuracy better than 0.2%. Using this custom-made system, we have studied and characterized complex fluids, systems biomimetic of biological membranes, as well as proteins included in nanometric water droplets. Under these experimental conditions, we have reached the value of protein compressibilities with an accuracy better than 10%.

Mechanical displacement induced in a piezoelectric structure: Experimental measurement by laser interferometry and simulation by a finite element method

From the knowledge of piezoelectric material tensorial components one can, by the finite element method, calculate the electrical impedance versus frequency and simulate the mechanical deformation of piezoelectric bars. Here, the simulation results obtained with lead zirconate‐titanate and lead titanate ceramics are reported. In order to check the validity of the simulation, interferometric measurements of the mechanical deformation amplitude were performed. It is shown that these measurements are able to reveal the inhomogeneity of the materials under study and that a small error in the tensorial parameter absolute values leads to an inconsistent picture of simulated mechanical deformation.

Model and measurements of the electrical input impedance of a plate-liquid-plate acoustic resonator

A plate-liquid-plate acoustic resonator is used to measure the acoustic velocity of liquids. An analytical model of the electrical input impedance of the resonator is proposed. Theoretical results are compared with experimental measurements using reference liquids. Accuracy of the sound velocity calculation is found to be better than 1%. Finally, factors limiting the achievable accuracy are discussed.

Short time correlation analysis in porous medium

The study of the mechanical and physico-chemical properties of porous media containing water is of great interest in particular during the phase change. Some thermodynamic models may provide relatively good understanding of this problem but these models are complex because of space averaging differential equations. To check the results obtained with the models, we have developed an acoustic system which monitors the phase change interface over time. The medium used to model the porous medium is a stacking of glass spheres whose diameters are fixed and large compared with the ultrasonic wavelength and whose spaces are filled with water (or ice). Because of spheres induced speckle, the water-ice interface cannot be seen a priori. In order to evidence this interface we have used a method based on correlation similar to the short time Fourier analysis. The result thus obtained shows that the water-ice interface can then be seen clearly. The speed measurements of the ultrasonic wave in porous medium obtained with this method agree with Blots theory. The preliminary experimental results show a good agreement with the semi-analytical solution.

Gelation monitoring by quartz microbalance in pulse mode

Classical viscoelastic measurement setup with a quartz crystal microbalance uses a steady state input signal in order to measure the complex equivalent electrical parameters. Using a network analyzer, this method enables the measurement of the equivalent impedance around the first resonance peak of the quartz within a tiny frequency range (typically 10 kHz around a 6 MHz resonance frequency). However, due to the network analyzer acquisition time, such a setup cannot make two successive acquisitions in less than 15 s for one resonance peak. We excite the quartz by a short pulse and record its time impulse response. This kind of excitation allows us to record higher resonance peaks (up to the 11th order) and to reduce drastically the acquisition time, enabling up to 100 acquisitions per second.

Gel formation monitoring by acoustic spectroscopy

An acoustic technique in the audible range has been developed to characterize the sol–gel process. Resonances appear at the sol to gel transition of a sol–gel matrix when submitted to an acoustic wave. The range of the associated resonance frequencies leads to a very low propagation speed of sound (about 20 m/s). The resonance frequencies versus time curves, corresponding to the harmonic propagation modes, converge to a unique intersection point with the time axis corresponding to the gelation time tg. The temporal evolution of the resonance frequencies features the formation of the network. Actually, the evolution of the matrix is independent of the initial conditions (precursor concentration, hydrolysis rate). Depicting the ‘‘reduced frequency’’ fi/fi(∞) [fi(∞) is the long‐term resonance frequency for the harmonic mode i] versus the ‘‘reduced time’’ t/tg for various Si concentrations and hydrolysis rates results in a unique curve, revealing the insensitivity of the matrix formation process to the input ...

Effects of materials conductivity on the viscosity measurement using a QCM

Quartz crystal microbalance (QCM) is commonly used to characterize the viscosity of soft materials. For biomedical applications the modified BVD model of QCM is unsuitable due to the conductivity of the biomaterial. In order to take into account the electrical effects, a new model including a static lossy capacitor is proposed. A theoretical study of the shear wave propagation in the quartz shows that these effects modify the static and the motional branches of the BVD circuit. The conductivity effects of the material at the surface of the QCM can be modeled by same parallel elements added in both branches. In the motional branch the electromechanical coupling factor is applied to these elements. To validate the new lumped element model measurements for KCl mixtures are achieved. The results show that an accurate extraction of viscosity (<5%) can be obtained for a middle of conductivity less than 0.3 S/m. In addition for water/glycerol mixtures the resonant frequency shift and damping follow an accurate l...

Adhesion of human osteoprogenitor cells on peptide immobilization onto titanium monitored a quartz crystal resonator technique

The thickness shear mode (TSM) quartz crystal resonator has been extensively used as sensitive sensor in various electrochemical and biological applications. This technique is based on the transverse propagation of an acoustic shear wave generated by a sinusoidal electric field through a piezoelectric quartz resonator. Its provides a non destructive and powerful mean for probing changes at solid-solid or solid-liquid interfaces, and for characterizing specific cell-substrate interactions. In the present work, we show the results obtained by using the thickness shear mode sensor based technique to characterize activation of human osteoprogenitor (HOP) cells on different peptide immobilization on titanium. We have measured the time evolution of a quartz electric characteristic: the motional resistance in the vicinity of the mechanical sensor resonant frequency. The quartz crystal resonator was coated with different biomaterials to test the cell adhesion: hydroxyapatite, the Arg-Gly-Asp (RGD) adhesion sequence, type I collagen and untreated titanium as a reference. The effects of a progressive induced activation for HOP adhesion on peptide immobilization on titanium were analyzed and finally discussed in the frame of a possible application in the biomaterial field such as bone prostheses