Abstract: A broadband ultrasonic transducer has a layer of piezoelectric material sandwiched between respective layers of backing and matching material. The piezoelectric element is coupled to a pair of electrical terminals, across which a varying voltage is produced. The piezoelectric layer has a structure such that in response to the varying voltage, a forward-propagating wave emanating from its back surface does not destructively interfere with a forward-propagating wave emanating from its front surface when the frequency of the waves is an even multiple of the half-wave frequency of the particular piezoelectric layer. This effect can be attained by roughening the back surface of the piezoelectric layer or by spatially varying the piezoelectric coupling in the thickness direction in a portion of the piezoelectric layer which is proximate to the back surface.

Abstract: A method and an apparatus for imaging the nonlinear components of an ultrasound signal returned from ultrasound scatterers in tissue or contrast agents in blood. The method employs a code-modulated wavelet for transmission combined with correlation filtering on reception. Coding methods are used to simultaneously manipulate the linear and nonlinear terms. The manipulations affect the magnitude and temporal arrangement of the resulting decoded waveforms. Among the simultaneous manipulations of linear and harmonic decoded signals are: orthogonal linear terms, finite linear terms, minimum sidelobe with optimal peak harmonic terms and optimally compressed harmonic terms.

Abstract: A method and an apparatus for imaging a nonlinear signal component isolated from the echo signal derived from transmission of a base waveform having fundamental frequency f.sub.0 and relatively high peak power. The nonlinear signal component is isolated by subtracting the linear signal component from the echo signal. This is accomplished using a second transmit firing derived from the same base waveform, but having different transmit characteristics, i.e., the base waveform is convolved with a code sequence to form a coded waveform. The coded waveform is transmitted at relatively low peak power. The beamsummed signal produced from the low-peak-power coded transmit is pulse compressed and then subtracted from the beamsummed signal produced from the high-peak-power uncoded transmit. The signals are scaled as necessary to achieve cancellation of the linear signal components when one beamsummed signal is subtracted from the other, leaving the nonlinear signal component for imaging.

Abstract: A method and an apparatus for imaging the nonlinear components of an ultrasound signal returned from ultrasound scatterers in tissue or contrast agents in blood. The method employs a code-modulated wavelet for transmission combined with correlation filtering on reception. Transmit codes are used to modulate the phases of wavelets for successive transmit firings focused at the same transmit focal position. For example, for a first transmit firing a first transmit code is used to modulate a base wavelet to form a first coded wavelet and for a second transmit firing a second transmit code is used to modulate the same base wavelet to form a second coded wavelet. On reception, the receive signals resulting from the first and second transmit firings are decoded by correlating the receive signals with first and second receive codes respectively.

Abstract: A PASS ultrasonic system includes a separate receive channel for each respective element in an ultrasonic transducer array which imparts a delay to the echo signal produced by each respective element. The delayed echo signals are summed to form a steered, dynamically focused and dynamically windowed receive beam which can be readily interpreted even when the transmit beam does not emanate from the center of the array.

Abstract: A PASS ultrasonic system includes a receive channel for each element in an ultrasonic transducer array which imparts a delay to the echo signal produced by each element. The delayed echo signals are summed to form a steered and dynamically focused receive beam. Each receive channel is formed as an integrated circuit. The integrated circuit calculates the required time delay for dynamic focussing in the receive channel as a function both of elapsed time in unit increments related to unit phase rotation increments of the carrier frequency and of previously calculated time delay values, in order to control a phase rotator and delay FIFO in the receive channel to implement echo signal delay control.

Abstract: Optimal measurement of ultrasonic random backscatter from the myocardium is obtained by band limiting and whitening the received signal, squaring, summing and scaling same. The whitening is carried out for all spectrally altering factors to which the ultrasonic signal has been subjected. This includes whitening for the power law frequency response characterstics of the myocardium itself. Scaling includes a factor accounting for the energy of the effective transmitted ultrasonic signal and a factor providing appropriate units of measurement. The optimal measurement may be time averaged over one or more heartbeats for use in the diagnosis of ischemia or other cardiac conditions. It may be subjected to discrete Fourier transform analysis, to obtain its amplitude modulation and phase characteristics for similar purposes.