Abstract
Lag-one coherence (LOC) estimates local levels of acoustic noise by measuring the spatial coherence between backscattered echo signals received by neighboring pairs of transducer elements. LOC can be directly related to signal to noise ratio (SNR) and contrast to noise ratio (CNR). We have acquired B-mode images and matched pixelwise LOC estimates in the livers of 10 healthy volunteers using a C5-2v probe on a Verasonics Vantage system and in Fullwave simulations with six abdominal walls over uniform speckle. We present evidence of temporally stable regions of suppressed LOC beneath the abdominal wall which recover to a stable asymptotic value at depth. Fullwave simulation results suggest that reverberation determines the initial amount of coherence suppression and aberration determines the asymptotic LOC value. The in vivo LOC values beneath the abdominal wall range from roughly 0.4 to 0.85, corresponding to SNRs of −3.5 dB to 15 dB, and the length of coherence suppression ranges from 0.5cm to 2.5 cm. These regions are occult; they present as temporally stable uniform liver on B-mode images. This is significant because clinicians will not be aware that lesions may be much more difficult to detect in this region, potentially leading to missed diagnoses.
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