Abstract
Transducers with a larger aperture size are desirable in ultrasound imaging to improve resolution and image quality. A coherent multi-transducer ultrasound imaging system (CoMTUS) enables an extended effective aperture through the coherent combination of multiple transducers. In this study, the discontinuous extended aperture created by CoMTUS and its performance for deep imaging and through layered media are investigated by both simulations and experiments. Typical image quality metrics—resolution, contrast and contrast-to-noise ratio—are evaluated and compared with a standard single probe imaging system. Results suggest that the image performance of CoMTUS depends on the relative spatial location of the arrays. The resulting effective aperture significantly improves resolution, while the separation between the arrays may degrade contrast. For a limited gap in the effective aperture (less than a few centimetres), CoMTUS provides benefits to image quality compared to the standard single probe imaging system. Overall, CoMTUS shows higher sensitivity and reduced loss of resolution with imaging depth. In general, CoMTUS imaging performance was unaffected when imaging through a layered medium with different speed of sound values and resolution improved up to 80% at large imaging depths.
Highlights
Limited resolution and a restricted field of view (FOV) are two of the main challenges in ultrasound (US) imaging that, in principle, are fundamentally limited by the extent of the transmitting and receiving apertures
Coherent plane waves (PWs) imaging with a conventional aperture provides the reference for image quality with and without the paraffin wax layer
These findings show that, if the separation between the transducers is limited, the extended effective aperture created by coherent multi-transducer ultrasound imaging system (CoMTUS) confers benefits in resolution and contrast that improve image quality, at large imaging depths, compared with a single probe standard system, and even in the presence of acoustic clutter imposed by tissue layers of different speed of sound (SOS) (Figures 10 and 13)
Summary
Limited resolution and a restricted field of view (FOV) are two of the main challenges in ultrasound (US) imaging that, in principle, are fundamentally limited by the extent of the transmitting and receiving apertures. The image lateral resolution of ultrasonography is diffraction limited and mostly depends on the wavelength of the transmission wave, the imaging depth and the aperture size (measured by the F-number) [1]. Since high frequency acoustic waves are absorbed and attenuated by tissues, the use of low frequencies is the only choice when the imaging region is located in deep areas in the body. It is not clear that a large aperture will overcome the expected resolution loss through depth in the presence of acoustically heterogeneous tissues [2]. Inhomogeneities and tissue layers with different acoustic properties cause phase errors restricting the improvements provided by large arrays [3]. Transabdominal US imaging is difficult in obese patients because of the increased imaging depth with longer attenuation paths and the presence of clutter associated with
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