A method of correcting for phasefront aberrations in ultrasound imaging uses highly spaced apart point scatterers artificially placed in the tissue being imaged. The point scatterers reflect the transmitted sound and are individually differentiated to provide singular reference points for correction of signals reflected from the surrounding tissue. The differentiation is performed by comparison of the third or fourth harmonic frequencies of the reflected signals. To ensure the necessary high dispersal of the point scatterers, high amplitude pulses of the transmitted signal destroy point scatterers in selected image regions. In an alternate embodiment, correction is performed by stochastic analysis of signals reflected from the highly dispersed point scatterers. A reference signal is compared to the second harmonic of the reflected signal to reduce noise.

A method and related apparatus for non-destructive evaluation of composite materials by determination of the quantity known as Integrated Polar Backscatter, which avoids errors caused by surface texture left by cloth impressions by identifying frequency ranges associated with peaks in a power spectrum for the backscattered signal, and removing such frequency ranges from the calculation of Integrated Polar Backscatter for all scan sites on the composite material.

A method for the scanning of non-linearly dispersive objects whereby changes of the energy spectrum of echographic signals can be quantitatively related to parameters of the objects examined, that is to say the ultrasonic attenuation factor .beta. and the exponent r which characterizes the relationship between the non-linear variation of the attenuation and the frequency. To this end, the signals received are split into a number of (n) substantially equally wide, consecutive frequency bands which together cover approximately all frequencies of the signals received. The envelope of the signals in each frequency band is determined and each of the envelopes is multiplied by a correction signal in order to compensate for the diffraction effect. The logarithm of the envelopes thus corrected is determined, after which the following operations are performed by means of the n signals thus obtained: (a) the slope .beta.f.sub.i.sup.r of each of these n signals is determined; (b) this signal .beta.f.sub.i.sup.r is converted into logarithmic form; (c) in a table or a curve the relationship is laid down between the logarithmic value of the frequency for each channel log f.sub.i and the logarithmic value log .beta.f.sub.i.sup.r is generated; and (d) the slope of the curve thus obtained and the value of log .beta.f.sup.r for log f=0 are determined.

This invention relates to a reflection type ultrasonic living body tissue characterization method obtaining highly accurate measuring result. The reflected ultrasonic wave power from the tissue to be measured is measured for respective frequency ranges. Then, it is normalized by the result of measuring the reflected ultrasonic wave power using a standard reflector placed in the equivalent region in non-attenuative medium to measure the tissue transfer function. Thereby, the characteristic of the measuring system can be eliminated. Moreover, unknown values not dependent on frequency are eliminated by normalizing the values measured at other frequencies with the value measured at a particular frequency. In addition, the corresponding transfer function of the tissue model is described with a product of an exponential function. Dividing the measured tissue transfer function with the non-exponential function and taking the logarithm makes the regression calculation of the measured function to the model function easier. Thereafter, various parameters indicating the tissue characteristic are obtained by regression calculations.

The present invention relates to a signal processing apparatus for quantitatively measuring ultrasonic characteristics of a medium, such as a human body and realizes the high speed quantitative measurement by processing all signals in the time domain. In the processing for eliminating an error, produced by a degree of convergence of the ultrasonic beam, a correcting function that is a function of the depth and frequency is employed. The correcting function is measured in a no-attenuation medium and converted into a form suited to the time domain processing. The function is stored and such frequency characteristics of the function are sequentially read during an actual medium measurement to control the characteristic of a variable characteristic filter to correct the received signal.