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.
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.
Using a flattened SiO2/Cu electrode/36–48° LiTaO3 structure, a small (5×5 mm2) surface acoustic wave (SAW) duplexer with a good temperature coefficient of frequency (TCF) for US personal communication services (PCS) was realized by the authors. However, a smaller duplexer is strongly required. Using the flip-chip bonding process of SAW chips and a Rayleigh SAW propagating on a flattened SiO2/Cu electrode/126–128° YX-LiNbO3 structure, which has a larger coupling factor than the above-mentioned substrate, a smaller (3×2.5 mm2) SAW duplexer with a good TCF was realized.
The transition bandwidth of 20 MHz between the transmission (Tx: 1850–1910 MHz) and the receiving (Rx: 1930–1990 MHz) bands of personal communication service (PCS) handy phones in the United States (US) is very narrow compared with those of other systems. We have already realized surface acoustic wave (SAW) duplexers with sizes of 5.0×5.0×1.7 and 3.0×2.5×1.2 mm3 for PCS handy phones in the US with an excellent temperature coefficient of frequency (TCF) by using a shear horizontal (SH) wave on a flattened SiO2/Cu electrode/36–48° YX-LiTaO3 structure and a Rayleigh wave on a SiO2/Cu electrode/120–128° YX-LiNbO3 structure. Although the surface of the above-mentioned structures is flattened SiO2, we have also studied the shape of the SiO2 surface. As a result, in addition to increasing the stop-band width, which corresponds to the reflection coefficient, the TCF and power durability have been improved by forming convex portions on the surface of the SiO2 over the interdigital transducer (IDT) gaps.
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