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Lead Zirconate Titanate (PZT) transducers are commonly used to generate guided acoustic waves for health monitoring of structures made of isotropic and anisotropic materials. Therefore, characterization of PZT transducers is very important not only for reliability but also for the accuracy of data. In this research, Scanning Acoustic Microscopy (in reflection mode) at 30 MHz excitation frequency is conducted for determining the quality of disc type guided wave transducers. Multiple samples are scanned but only four transducers are selected for further investigation. Guided waves are dispersive in nature and multiple guided wave modes can coexist at single frequency. It has been already reported in the literature that good bonding condition between transducer and testing material is very important to restrict other factors that can affect the strength of recorded signals. Chirp signal is excited in the specimen in a single sided excitation/detection setup to investigate the effects of transducer quality on monitoring plate like structures. Sideband peak count technique is used for comparative study of transducers.

Ultrasound (US) is a widely used modality for medical imaging, since it is non-invasive and relatively inexpensive. The ability of US imaging to detect internal structures, like tissue interfaces or lesion sites makes it a promising candidate for dental imaging. So far, the inherent technical difficulties of US imaging in tissues and organs with very heterogeneous (acoustic) properties and limited access have prevented its widespread use. In this study, we characterized the acoustic properties of sectioned teeth by scanning acoustic microscopy in reflection and transmission modes. The spatial distribution of sound velocity was measured in sections of extracted human teeth by use of a scanning acoustic microscope (SAM). Freshly extracted teeth were fixed in 4% formaldehyde solution and embedded in a polymer block (PMMA). Sections of approximately 1 mm thickness were cut along the coronal-apical axis. Radio frequency (RF) data of teeth were collected in a scan region of 15 × 15 mm 2 by a SAM operating at 30 MHz with a lateral step size of 50 µm and a sampling rate of 500 MSa/s. Sound velocity was determined from the time resolved reflection and transmission signals. Values for sound velocity from transmission mode were about 20% lower than that from the reflection mode, if thickness information from reflection mode was used. If thickness was determined from the transmission mode, sound velocities from transmission were very close to those obtained from the reflection mode. Transmission mode is less sensitive to artifacts caused by the inclination of the specimen.

Among the methods for the determination of mechanical properties of living cells acoustic microscopy provides some extraordinary advantages. It is relatively fast, of excellent spatial resolution and of minimal invasiveness. Sound velocity is a measure of the stiffness of the cell. Attenuation of cytoplasm is a measure of supramolecular interactions. These parameters are of crucial interest for studies of cell motility, volume regulations and to establish the functional role of the various elements of the cytoskeleton. Using a phase and amplitude sensitive scanning acoustic microscope, longitudinal wave speed, attenuation and thickness profile of a biological cell have been measured earlier by Kundu, Bereiter-Hahn and Karl (2000) from the voltage versus frequency or V(f) curves in the frequency range 980-1100 MHz. Two limitations of that study are overcome in this paper. In that study it was assumed that the cell properties did not change through the cell thickness and could vary only in the lateral direction. Secondly, the acoustic microscope generated ultrasonic signal was modeled in that study as a plane wave striking the cell and the substrate at normal incidence. Such assumption ignores the contribution of the surface skimming Rayleigh waves. Improved and more generalized analysis that is presented here avoids such restrictive assumptions. For the first time, in this paper the cell is modeled as a multi-layered material with different properties for nucleus and surrounding cell material. The inverse problem is solved to study the effect of drugs on living cells.

In the middle of the 90s, the image processing and analysing method subtraction scanning acoustic microscopy (SubSAM) was developed to display and quantify cell surface motility. Since then, the approach of this method supported already existing models and provided new insights into the regulation of cell surface motility. The investigations with SubSAM revealed that cell surface motility is modulated by tension and is regulated by known F-actin reorganising signal transduction pathways via the small GTP-binding protein Rac and protein kinase C. Beyond that, the in vitro cell surface motility as revealed by SubSAM corelates with cell transformation respectively the invasive or metastatic potential. The enhancement of cell surface motility is always accompanied by characteristic actin reorganisation: loss of stress fibers and the formation of cortical F-actin knots or larger aggregates. From these observations a model has been developed for the regulation of cell surface motility and an addtitional mechanism for cell surface deformation based on myosin-dependent F-actin aggregation is proposed.

The physical properties of cytoplasm are primarily determined by the state of cytoskeletal element, i.e. their polymerisation, crosslinking and supramolecular interactions with other molecules. These interactions are involved in signal transduction processes as well as in morphogenesis. Scanning acoustic microscopy proved to be a powerful tool to determine the mechanical properties of living cells. The interpretation of the sound propagation parameters, however, has to be based on investigation of in vitro models. Therefore polymerisation of actin and tubulin have been followed using a novel oscillating rod rheometer which allows for synchronous determination of sound velocity, sound attenuation and viscosity. Sound velocity measures the elastic propterties of cytogels, attenuation the supramolecular associations. All these parameters are evaluated with minimal strain, in the range of 1- 100 nm actin with glycolytic enzymes not only modulated polymerisation in a specific, and substrate dependent manner, but also the stiffness of the fibrils was altered, e.g. by hexokinase in the presence of high ATP, this enzyme exhibited actin severing properties and reduced stiffness. Differences in polymerisation kinetics were observed comparing pyrene-labeled actin fluorimetry and oscillating rod viscosimetry. This comparison led to the detection of pseudocrystalline structures produced by g-actin and aldolase (in the absence of fructose-bisphophate, the substrate of aldolase). Elastic stiffness of actin filaments can be modulated by ATP/ADP and by actin binding proteins (e.g. the glycolytic enzyme hexokinase) as well. The in vitro observations support the interpretation of SAM data calculated for living cells.