A. J. Cousin

New phase-lock tracking instrument for foetal breathing monitoring

An instrument has been developed that allows foetal breathing movements to be recorded with a laboratory resolution of about 0·06 mm. The new tracking scheme is described in addition to the complete instrument incorporating a number of these tracking units for multichannel movement monitoring. The multiple tracking scheme is implemented by adapting a commercial real-time array and building a custom or special instrument to process the signals. The instrument is capable of simultaneously tracking up to six separate echo complexes selected on an electronically-switched real-time B-scan image of the foetus. It therefore can provide any permutation of three channels of differential movement at the same time. Early clinical results obtained using the new instrument are presented.

On processing of Doppler returns from the foetal heart: An electronic processing method for extraction of valvular timing information

An electronic processing scheme intended for use in conjunction with a multicrystal ultrasonic array to measure cardiac intervals in the human foetus is described. This new processing method possesses sufficient signal extraction capability to allow the time of opening of the aortic valve to be determined and tracked. Application of this method to a pulsed Doppler and continuous wave Doppler system is discussed. Features include amplitude independent detection, rapid response time and excellent frequency selectivity. Laboratory and clinical test results are presented that demonstrate the viability of an instrument based on this principle.

Sequential transient filtering: an automated method of frequency derivative detection

Of several techniques currently available for recognition of swept-frequency transient signals, most are limited fundamentally in their ability to detect signals with high normalized sweep rates (e.g. 100 sec-1 and up‡), and immersed in a noisy environment. Furthermore, common techniques incorporating Phase Lock Loops (PLL) and Voltage Tunable Filters (VTF) are not inherently noise immune and are easily unlocked by noise of various types. A scheme is presented which has the capability of detecting fast, swept-frequency transient signals in the presence of many varieties of disturbances within the frequency range of the sweep. The disturbances tolerated being not completely without restriction, can be characterized by the relationship of their power spectra to factors including filter bandwidths and resonant frequencies, signal sweep rate, and signal to noise ratio. With a Blight modification incorporated in the circuit realization, the detection scheme is able to cope with swept signals of continuously va...

A Calibrated Ultrasonic Field Measuring System for General Use

An instrumentation scheme is presented which provides a calibrated field intensity equivalent plot using common laboratory equipment. The parameter that is measured gives a direct indication of the merit of an ultrasonic transducer for a given application in terms of its beam shape. The composite output of the system yields a three-dimensional representation of the intensity equivalent parameter as a function of a two-dimensional spatial field. Several applications of the resulting instrumentation are given including the effects of crystal window flatness and acoustic lensing.

A Generalized Biquadratic Filter with Parameter Display

An instrument that couples a new type of biquadratic filter with a picture display capability of s-plane pole and zero locations is described. The filter design allows easily movable, continuous, and orthogonal pole-zero adjustment by the user of all possible stable combinations of biquadratic functions. The resulting instrument represents a uniquely useful educational tool for graphically portraying the effects of network pole-zero positioning on time and frequency domain response.