Cyclostationarity: half a century of research

Ultrasonic testing of materials: Josef and Herbert Krautkramer Springer-Verlag Publishing Company, Berlin, Heidelberg, New York (1975) 669 pp, $63.00

https://www.dtc.umn.edu/s/resources/bib05eurasip.pdf

Bibliography on cyclostationarity

The quasiperiodicity of regularly spaced scatterers results in characteristic patterns in the spectra of backscattered ultrasonic signals from which the mean scatterer spacing can be estimated. The mean spacing has been considered for classifying certain biological tissue. This paper addresses the problem of estimating the mean scatterer spacing from backscattered ultrasound signals using the frequency-smoothed spectral autocorrelation (SAC) function. The SAC function exploits characteristic differences between the phase spectrum of the resolvable quasiperiodic scatterers and the unresolvable uniformly distributed (diffuse) scatterers to improve estimator performance over other estimators that operate directly on the magnitude spectrum. Mean scatterer spacing estimates are compared for the frequency-smoothed SAC function and a cepstral technique using an AR model. Simulation results indicate that SAC-based estimates converge more reliably over smaller amounts of data than cepstrum-based estimates. An example of computing an estimate from liver tissue scans is also presented for the SAC function and the AR cepstrum. >

Estimating mean scatterer spacing with the frequency-smoothed spectral autocorrelation function

An ultrasonic backscattered signal from material comprised of quasiperiodic scatterers exhibit redundancy over both its phase and magnitude spectra. This paper addresses the problem of estimating mean‐scatterer spacing from the backscattered ultrasound signal using spectral redundancy characterized by the spectral autocorrelation (SAC) function. Mean‐scatterer spacing estimates are compared for techniques that use the cepstrum and the SAC function. A‐scan models consist of a collection of regular scatterers with Gamma distributed spacings embedded in diffuse scatterers with uniform distributed spacings. The model accounts for attenuation by convolving the frequency dependent scattering centers with a time‐varying system response. Simulation results indicate that SAC‐based estimates converge more reliably over smaller amounts of data than cepstrum‐based estimates. A major reason for the performance advantage is the use of phase information by the SAC function, while the cepstrum uses a phaseless power spec...

/pdf/mean-scatterer-spacing-estimates-with-spectral-correlation-23y4992fxo.pdf

Mean‐scatterer spacing estimates with spectral correlation

The effects of using spectral correlation in a maximum-likelihood estimator (MLE) for backscattered energy corresponding to coherent reflectors embedded in media of microstructure scatterers is considered. The spectral autocorrelation (SAC) function is analyzed for various scatterer configurations based on the regularity of the interspacing distance between scatterers. It is shown that increased regularity gives rise to significant spectral correlation, whereas uniform distribution of scatters throughout a resolution cell results in no significant correlation between spectral components. This implies that when a true uniform distribution for the effective scatterers exists, the power spectral density (PSD) is sufficient to characterize their echoes. However, as the microstructure scatterer distribution becomes more regular, SAC terms become more significant. MLE results for 15 A-scans from stainless steel specimens with three different grain sizes indicate an average 6-dB signal-to-noise ratio (SNR) improvement in the coherent scatterer (flat-bottom hole) echo intensities for estimators using the SAC characterization as opposed to the PSD characterization. >

/pdf/spectral-correlation-in-ultrasonic-pulse-echo-signal-4q0d5ty8gi.pdf

Spectral correlation in ultrasonic pulse echo signal processing

A nonlinear digital filtering technique (median filtering) is suggested for processing the projections to reduce error without the distortion introduced by linear filtering. The rationale for the application of these filters is discussed. To compare the effectiveness of linear filtering and median filtering, computer simulations and further experiments are suggested. It is expected that median filters have potential to improve image quality beyond that of linear filtering, particularly for edge reproduction. >

J.M. Bressler

Papers

Spectral correlation in ultrasonic pulse echo signal processing

Projection processing for improved resolution and noise suppression of reconstructed images of computer tomography