Short-lag spatial coherence of backscattered echoes: imaging characteristics

Abstract

Conventional ultrasound images are formed by delay-and-sum beamforming of the backscattered echoes received by individual elements of the transducer aperture. Although the delay-and-sum beamformer is well suited for ultrasound image formation, it is corrupted by speckle noise and challenged by acoustic clutter and phase aberration. We propose an alternative method of imaging utilizing the short-lag spatial coherence of the backscattered echoes. Compared to matched B-mode images, short-lag spatial coherence (SLSC) images demonstrate superior SNR and CNR in simulated and experimental speckle-generating phantom targets, but are shown to be challenged by limited point target conspicuity. Matched B-mode and SLSC images of a human thyroid are presented. The challenges and opportunities of real-time implementation of SLSC imaging are discussed.

Short-lag spatial coherence beamforming of photoacoustic images for enhanced visualization of prostate brachytherapy seeds

“…9, where higher values of M offer better lateral resolution at the expense of poorer CNR and SNR. Similar trade offs were observed when the SLSC beamformer was applied to ultrasound data [14,15,17]. These trade-offs are associated with changes in spatial frequency content, off-axis spatial coherence information, and background noise sensitivity as the value of M is modulated.…”

“…The incident laser beam required for photoacoustic imaging is comparable to ultrasound imaging with a broad, unfocused transmit beam. In this scenario, the spatial coherence of the received signals is mainly determined by the geometry of the target, unlike SLSC applied to pulse-echo ultrasound data acquired with focused transmit beams wherein the spatial coherence of received signals is dually determined by the transmit beam and the target geometry [14,27]. The SLSC PA image sensitivity to target geometry, and hence sensitivity to seed orientation, is particularly evident when comparing the transverse and longitudinal scans in Fig.…”

“…This beamformer calculates the spatial coherence of signals received by closely-spaced transducer elements and displays the information as an image [14]. SLSC imaging improved lesion detectability in the presence of acoustic noise artifacts, when compared to conventional B-mode ultrasound imaging [15].…”

“…SLSC imaging improved lesion detectability in the presence of acoustic noise artifacts, when compared to conventional B-mode ultrasound imaging [15]. In addition, this beamformer was applied to in vivo ultrasound data to reduce clutter noise artifacts in cardiac [16][17][18], liver [19], thyroid [14], and vascular [15] images. Similar clutter reduction benefits were achieved when the SLSC beamformer was applied to photoacoustic data [20].…”

Equivalence of time and aperture domain additive noise in ultrasound coherence

“…3,4 Short-lag spatial coherence (SLSC) imaging is a technique to create an image solely from the measured coherence, but the results show sensitivity to effects such as channel noise and phase aberration in ways not seen in conventional imaging. 5 Such effects have been previously exploited to evaluate and improve B-mode image quality. Mallart and Fink described the use of a "coherence factor" to evaluate aberration correction schemes, showing a loss of coherence corresponding to the severity of phase corruption, 6 while Liu and Waag proposed a "wavefront similarity factor" for their studies.…”