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Abstract: It is now accepted that an effective way to investigate the elastic properties of soft tissues is to generate a localized transient acoustic radiation force and to follow the associated displacements in the time/space domain. Shear waves induced by this stress field are particularly interesting in this kind of medium because they are governed by the shear elastic modulus μ, which is directly linked to the Young modulus, and spatial distribution and temporal evolution of the transient motion induced must therefore be obtained in detail. We report here a model based on the elastodynamic Green’s function formalism to describe these displacements. 3D simulation of radiation force in homogenous elastic media was performed and the displacement curves computed at different radial distances for different temporal force profiles. Amplitude and duration of displacement were found to be reliable parameters to characterize the elastic properties of the medium. Experimental measurements were performed in a homogeneous agar-gelatin tissue-mimicking phantom, and two transducers were used to generate the radiation force and follow the induced displacements. Displacements obtained from different lateral locations around the applied force axis were then used to reconstruct the shear-wave propagation in a scan plane as a function of time. The experimental displacements/curves agreed with the theoretical profiles obtained by the elastodynamic Green’s function formalism. [Copyright &y& Elsevier]

Abstract: Recently, the in vivo feasibility of tissue harmonic imaging (THI) with a mechanically-rotated intravascular ultrasound (IVUS) catheter was experimentally demonstrated. To isolate the second harmonic signal content, both pulse inversion (PI) and analog filtering were used. In the present paper, we report the development of a simulation tool to investigate nonlinear IVUS beams and the influence of rotation on the efficiency of PI signal processing. Nonlinear 20MHz beams were simulated in a homogeneous tissue-mimicking medium, resulting in second harmonic pressure fields at 40MHz. The acoustic response from tissue was simulated by summing radio-frequency (RF) pulse–echo responses from many point-scatterers. When the transducer was rotated with respect to the point-scatterers, the fundamental frequency suppression using PI degraded rapidly with increasing inter-pulse angles. The results of this study will aid in the optimization of harmonic IVUS imaging systems. [Copyright &y& Elsevier]

Abstract: A method to increase the image resolution and dynamic range is to use the acquired data from several emissions (lines) and to beamform the collected RF signals treating the focal point in transmit as a virtual source of a spherical wave. The transducer is swept mechanically over the region of interest to scan a full volume. The same beamformation procedure is applied both in the azimuth and the elevation planes. This paper presents a study of the influence of the position of the transmit focus on the image resolution, the signal-to-noise ratio and penetration depth. The investigation is based on simulations and measurements. The system used in this work is a research scanner developed at the department. The transducer is a 7.5MHz linear array with a pitch of 208μm and a fixed focus in the elevation direction at 25mm. The field is simulated for points placed at every 5mm between 10 and 150mm depths. Different positions (100) of the transmit focus are investigated. For every transmit focus the image is beamformed and evaluated. Finally the gain in signal-to-noise ratio and penetration depth are investigated experimentally for the setup, with which the best resolution is achieved. Simulations indicate that the size of the point spread function at a depth of 60mm is decreased from 3mm to 0.66mm and from 4mm to 2.5mm in the azimuth and elevation planes, respectively. The gain in signal-to-noise ratio measured in a tissue mimicking phantom is 10dB. The penetration depth increases from 70 to 100mm. The method can be applied in applications, where the image quality is of prime importance, such as in the classification of atherosclerotic lesions in the carotid artery. [Copyright &y& Elsevier]

The article presents an abstract of the paper titled "MAP-Kinase and PI-3-Kinase As Transducers of Antiapoptotic BDNF Signaling in CNS Neurons." It investigates the role of neurotrophins MAP-Kinase and PI-3-Kinase in promoting the survival and suppressing apoptosis in the central nervous system neurons.

Reports on a study on the use of portable transducer catheter in the diagnosis of sleep apnea in the United States, as presented in the August 1995 issue of the `American Journal of Respiratory and Critical Care Medicine.' Features and capabilities of the device; Advantages of using the device.

The article offers information on the input transducers as part of an effort to guide biologists in the selection of instrumentation. It states that the input transducer converts the variable which is to be measured into some form of energy signal which can be amplified or transmitted to the site of recording. It mentions that the main requirement for input transducers is that the measurement information energy must be acquired without altering the state or process under investigation by more than the permissible amount, which is to be judged by the investigator. It states that the two types of input transducers include active devices such as the thermocouple, and passive devices such as the thermistor. It also offers information on some reference books available on the transducers.