Acoustical Imaging Using the Phase of Echo Waveforms

Pulse–echo imaging via zero manipulation

“…The socalled B-scan images are derived from a family of such envelope detected rfA-lines. For this reason, we follow Ferrari et al (1982) in referring to this technique as "AM" imaging. The procedure discards the phase information content of the rf A-line.…”

“…Indeed, it is only recently that the explicit use of signal phase or instantaneous frequency (time derivative of signal phase) in ultrasound signal processing has become an active research area (Klepper et al, 1984;Nassi et al, 1984). Ferrari et al (1982) were the first to propose and implement a medical ultrasound imaging technique based on the extraction of signal phase, rather than envelope, information. In their system, envelope demodulation is replaced by frequency demodulation, resulting in a mapping of signal instantaneous frequency, termed an "FM" image.…”

Digital Image Processing For Instantaneous Frequency Mapping

“…Given a band -limited RF A -line, f(t) the associated Analytic signal, i(t), is f(t) = f(t) + jfH(t) (1) where j = /11 and fH(t) is the Hilbert Transform of f(t). Signal envelope e(t), and instantaneous frequency 0(t), are given by, e(t) = lf(t)1 ; 0(t) = d /dt CArctan(fH(t) /f(t))] (2) All frequency-derived images presented in this paper were generated by linearly mapping the magnitude of instantaneous frequency deviations from the mean, to form a grey -scale image.…”

Significance of envelope detection in underwater acoustic imaging systems

“…Some methods for overcoming these effects in imaging applications, have been proposed [4,5,6], however, to the best of our knowledge, such effects have not yet been deeply analysed and their importance has not yet been evaluated.…”

“…The detailed results of the analyses are covered in [5]. In summary, detection ranges of 685 to 1143 meters were obtained except in one case where the strong negative gradient of the SSP limited the detection range to 228 meters.…”