  Transducers with 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 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 few centimetres), CoMTUS
provides benefits to image quality compared to 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.
