Acoustic-Field Beamforming-Based Generalized Coherence Factor for Handheld Ultrasound

Handheld ultrasound devices have been widely used for diagnostic applications. The use of the acoustic-field beamforming (AFB) method has been proposed for handheld ultrasound to reduce electricity consumption and avoid battery and unwanted heat issues. However, the image quality, such as the contrast ratio and contrast-to-noise-ratio, are poorer with this technique than with the conventional delay-and-sum method. To address the problems associated with the worse image quality in AFB imaging, in this paper we propose the use of an AFB-based generalized coherence factor (GCF) technique, in which the GCF weighting developed for adaptive beamforming is extended to AFB. Simulation data, experimental results, and in vivo testing verified the efficacy of our proposed AFB-based GCF technique.

Comparative investigation of coherence factor weighting methods for an annular array photoacoustic microscope

To achieve fine visualization of the peripheral microvascular networks, we have developed a photoacoustic (PA) microscope equipped with a four-channel annular array transducer. The quality of PA images processed with Delay-and-Sum (DAS) method is degraded by off-axis signals. Thus, to achieve higher image quality for the PA microscope, this study evaluated the efficacy of the five coherence factor weighting methods: coherence factor, sign coherence factor, phase coherence factor, circular coherence factor, and vector coherence factor. Using PA signals acquired from a 100 µm microtube and the skin microvessels, we generated PA images with DAS and one of the weighting methods, and quantitatively evaluated the image quality by calculating the sharpness, contrast ratio, and contrast-to-noise ratio. The results showed the phase coherence factor and the vector coherence factor methods were more effective to clearly visualize the microvascular structure, in terms of vessel sharpening and noise suppression performances, than the other methods.

Applying Coherence Factor to Double-Stage Delay Multiply and Sum Beamforming in Medical Ultrasound Imaging

The Filtered Delay Multiply and Sum (F-DMAS) beamforming algorithm has recently been proposed to improve the resolution and contrast in ultrasound imaging. Based on F-DMAS, some researchers have introduced an alternative named Double-Stage Delay Multiply and Sum (DS-DMAS), which can be considered as an enhanced version of F-DMAS. The DS-DMAS expands the DMAS algorithm to synthesize some new signals, which are then beamformed using a DMAS beamformer. However, the way to generate new signals in DS-DMAS can be thought of as a Delay and Sum (DAS) operation. There are some shortages in the DAS algorithm, so we proposed a new approach named Coherence Factor based Double-Stage Delay Multiply and Sum (DS-DMAS-CF) to address these issues. The key idea of our method is to optimize the DAS operation in DS-DMAS. Therefore, a modified coherence factor (CF) is applied to weight each item in DS-DMAS. The simulation, experimental and in vivo data are used to compare the performance between DAS, F-DMAS, DS-DMAS and DS-DMAS-CF The results show that the DS-DMAS-CF gets better resolution and contrast in comparison with the other three algorithms.