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The future of the ultrasound camera depends on improving its resolution: present camera tubes offer only a coarse picture (45 lines). This is nevertheless fine enough to display the 2000 bits of information which is the most the ultrasonic converter end-plate in present tubes can supply. Mechanical strength is the limiting factor. The plate is cut to be half a wavelength thick so as to resonate in sympathy with the incident ultrasound. Under these circumstances the point resolution on the plate face is about half a wavelength: greater resolution calls for higher frequencies and thinner plates but plates soon become too thin to be self-supporting. Other developments are linked to optical scanning, to the use of phase-sensitive detection for examining thickness changes and the flow in fluids and to pulsed ultrasound for displaying thick objects at chosen depths. This paper is based on the author's contribution to the symposium “Acoustic imaging and pulsed light” organized by the Mine Advisory Committee of the National Academy of Sciences at Berkeley, California, in December 1964

The effect of repeated periods of Summary intermittent suction on limbs has been examined in patients who had a long history of peripheral vascular disease but who were not amenable to surgical treatment. Measurements demonstrated that calf blood-flow can be increased by this technique, and 24 (60%) of 40 patients claimed subjective benefit.

The following review was presented as an introductory talk to the Medical and Biophysical Ultrasonics session at the ULTRASONICS FOR INDUSTRY 1969 Conference on 7 October 1969. Techniques which have become established are described. Most of the recent effort in medical ultrasonics has been devoted to overcoming difficulties on the road to improved techniques of visualization.

Some u.h.f. measurement techniques based on the use of coaxial line resonators are described.The methods cover the measurement of permittivity and power factor of disc and tubular samples, and in the latter case it is a simple matter to measure the effect of temperature.In both cases a fixed oscillator is employed, resonance being obtained by movement of the inner conductor of the line with a micrometer drive.For disc samples, machining or grinding is necessary in order that they may be a close but sliding fit in the line and, though not essential, time in computation is reduced if a standard thickness is employed, The experimental procedure involves so placing the disc in the line that the line length of resonance is a minimum and then measuring the resonant length and current. These quantities together with the disc dimensions and frequency are sufficient to determine the permitivity and power factor.In the case of thin discs the formulae used are very simple, but with thick discs, which are often necessary to obtain reasonable accuracy in power-factor measurements, more complicated formulae are involved.The accuracy obtainable is about 1% for permittivity and 5% for power factor.Temperature dependence of the dielectric constants cannot be measured with this apparatus as differential thermal expansion between he metal and the dielectric disc prevents free movement of the disc.In the case of tubular samples the only machining necessary is j utting the material to a given length. This is a great advantage when ceramic materials or glass are involved. To carry out the measurement the tube is cut to the required length and placed symmetrically in the measuring line over the inner conductor, the inner and outer liametcrs of the tube being immaterial so long as this can be done. The change of length of the inner conductor to re-establish resonance hen allows the permittivity to be calculated, and the reduction in esonant current enables the power factor to be found. As no close ncchanical clearances are involved this method enables measurements o be carried out at other than room temperature without difficulty. fhe accuracy obtained depends upon the uniformity of the dielectric tube: with a reasonable uniformity the error is in the range ±10%.

The ultra-sound image camera enables a visible image to be reproduced of the ultra-sound intensity distribution on the camera face. Coupled with acoustic lenses, and immersed in a suitable medium, the internal structure of substances or objects transparent to ultrasonic waves can be studied with the instrument. In its uses it is complementary to X-ray and to ultrasonic pulse-echo inspection methods. It has applications to the non-destructive testing of materials and engineering components, and also to medical diagnosis.An ultra-sound camera tube and complete viewing equipment have been built. The sensitivity for unity signal/noise ratio is 10−7 W/cm2 at the camera face, and the resolution is 0.5 mm at 4 Mc/s. It is one of several possible types of ultra-sound camera. The design is discussed, and directions into which further research and development might be taken are also considered.