Phase-derivative imaging. I: Methods and stabilization analysis

The potential of using the phase derivative (PD) for echographic imaging was investigated. The PD data were calculated by four methods: zero crossing (ZCS) with squelch addition, analytic signal either with squelch addition (ASS) or with employment of a Wiener kernel (ASW), and unwrapped phase (UWP). The large peaks which occur in an unprocessed PD signal were "stabilized" by some kind of smoothing algorithm. The effects of the amplitude of the squelch signal and of the degree of smoothing were systematically investigated for experimental and simulated 1-D and 2-D rf echograms. The optimal pictures obtained for all four PD estimation methods were compared to the amplitude modulated (AM) image obtained from the same rf data. It is concluded that three different PD images can be derived: AM dominated (ZCS, ASS), mixed AM-PD (ASW) and pure PD (UWP) images. Some preliminary conclusions regarding the potential of PD imaging for medical diagnostics were drawn. These conclusions were based on quantitative 1st order statistics and on a qualitative assessment of 2nd order statistics of the PD image texture.