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The factors limiting the resolution achievable with array-based imaging methods are considered. The limitations on beamwidth and field of view for beam scanning systems are first examined using plane wave diffraction theory, treating focusing and any array curvature as separable to the plane wave analysis. It is found that in all cases the number of(More)
The strength of agreement between two noninvasive methods of assessing lower limb arterial disease and their relationship to patient symptoms following exercise have been investigated. Color-duplex ultrasound (CDU) and ankle/brachial pressure index (ABPI) (before and afer exercise) measurements were obtained from 200 consecutive patients referred to a(More)
Surveys published up to 1991 have highlighted a steady increase in the acoustic outputs from diagnostic ultrasound equipment. Since 1991 we have made measurements of the maximum peak negative pressure (p-) and spatial peak temporal average intensity (ISPTA) produced by 223 probes from 82 scanning systems in current clinical use in the Northern Region in the(More)
Temperature rises due to diagnostic ultrasound exposures have been calculated for a simple third-trimester pregnancy tissue model. This consisted of a layer of soft tissue representing the abdominal/uterine wall, a layer of liquid and a layer of fetal bone. The ultrasound field parameter used in the calculations was the temporal average of the square of the(More)
The reconstruction of the speed-of-sound distribution within a target can be achieved by CT techniques from measurements on transmitted ultrasonic pulses. The mathematical relationship between speed-of-sound imaging and the conventional CT situation is explained. An experimental system, which has been developed to investigate speed-of-imaging and other(More)
In the first part of the review, recent developments in medical imaging technology are described. Developments in transducer materials and matching, leading to improvements in band-width and sensitivity are discussed. Improvements in dynamic range due to increased transducer sensitivity, lower electronic noise levels and more efficient filtering are then(More)
1. We have tested the hypothesis that the fall in hepatic mass with age influences the age related increase in sensitivity to warfarin. In 39 otherwise healthy outpatients, aged 50-87 years, stabilised on warfarin for prophylaxis of thromboembolism, age, mean International Normalised Ratio (INR), and mean warfarin dosage were recorded. Liver volume was(More)