Implications of Lag-One Coherence on Real- Time Adaptive Frequency Selection
Hepatic image quality has been shown to be degraded by the clutter-generating effects of the abdominal wall, and while beamforming and signal processing methods exist to minimize clutter, there is currently no automated method by which parameters such as imaging frequency are selected. Adaptive imaging seeks to optimize these parameters using lag-one coherence (LOC), a direct estimate of clutter levels in vivo, as a real-time feedback metric. The aim of this study is to determine the viability of using LOC to adaptively select imaging frequencies in the presence of clutter. Across in silico, ex vivo, and in vivo setups, a monotonic decrease in LOC was observed as imaging frequency was increased, indicating increased clutter, but the lesion conspicuity metric (LCM), which includes the expected increase in resolution with frequency, is optimized. The cases in which no abdominal wall is present, and therefore without a near-field source of clutter, had the highest measured LOC values and allowed for the highest optimized frequencies. The results suggests that an optimal frequency can be automatically selected for lesion detection. The findings of this study also match the clinical experience, in which lower frequencies are used for difficult-to-image patients.
