This paper describes a technique of forming images of the average size and scattering strength of scatterers in a random medium using ultrasound. Quantitative ultrasound images provide a more direct interpretation of the underlying structure of the medium, e.g. size, shape, number and elastic properties of scatterers, and increased detectability for regions of varying structure. A signal-to-noise analysis was used to show quantitatively how properties of the imaging system influence low-contrast detectability in quantitative ultrasound images. In one experiment, signal-to-noise measurements using phantoms were compared with B-mode imaging for several transducer bandwidths to observe variations in image contrast and speckle noise. The findings are being used to optimise the design of quantitative imaging systems for specific diagnostic tasks.i Originally presented at VI11 European workshop on ultrasonic tissue characterisation and echographic imaging (Nijmegen, The Netherlands), 15-18 October 1989.
The author and coengineers have developed, put to practical use, mass-produced, and commercialized various surface acoustic wave (SAW) devices. Their success depended largely on the development of SAW substrate materials, SAW device structures, and the processes of producing with the cooperation of many engineers. The author reports the development and practical applications of several SAW devices: (1) ZnO/glass structure SAW filters for video intermediate frequency (VIF) for televisions (TVs) or video cassette recorders (VCRs), (2) small resonators and filters using Bleustein-Gulyaev-Shimizu (BGS) wave's edge reflection on ceramic substrates, (3) small filters using shear horizontal leaky SAWs on heavy-density-metal electrode/quartz structures, (4) ZnO/quartz structure SAW filters, and (5) SAW duplexers with excellent temperature characteristics for personal communication services (PCSs) in the US.
Three variants of the Schiff equation are investigated to model the spectra produced by megavoltage linear accelerators. These models are tested against well-validated Monte Carlo (MC) generated spectra on the central axis of large-area fields, and show excellent agreement. Numerical reconstructions of 6 and 10 MV spectra using the same models are then presented, using experimental attenuation data derived from an electronic portal imager. The process of deriving spectra from experimental attenuation data is shown to be inherently badly constrained mathematically, with the derived spectrum being highly sensitive to noise in the source data, and non-unique. By placing a priori constraints on the Schiff model from both physical knowledge of the construction of the accelerator and MC data, physically useful results are gained and presented for both the energy dependence and off-axis behaviour of photon spectra.
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