Abstract
Ultrasound images are severely degraded by the presence of obstacles such as bones and air gaps along the beam path. This paper describes a method for imaging structures that are distal to obstacles that are otherwise impenetrable to ultrasound. The method uses an optically-inspired holographic algorithm to beam-shape the emitted ultrasound field in order to bypass the obstacle and place the beam focus beyond the obstruction. The resulting performance depends on the transducer aperture, the size and position of the obstacle, and the position of the target. Improvement compared to standard ultrasound imaging is significant for obstacles for which the width is larger than one fourth of the transducer aperture and the depth is within a few centimeters of the transducer. For such cases, the improvement in focal intensity at the location of the target reaches 30-fold, and the improvement in peak-to-side-lobe ratio reaches 3-fold. The method can be implemented in conventional ultrasound systems, and the entire process can be performed in real time. This method has applications in the fields of cancer detection, abdominal imaging, imaging of vertebral structure and ultrasound tomography. Here, its effectiveness is demonstrated using wire targets, tissue mimicking phantoms and an ex vivo biological sample.
Highlights
Non-invasive, real-time ultrasound imaging is a powerful diagnostic tool with advantages including cost effectiveness, deep penetration, widespread availability and safety
Various techniques have been used to overcome the difficulties associated with ultrasound imaging and therapy in the presence of obstacles
Ultrasound beam shaping is often used in hyperthermia treatments[13,14], ultrasonic neuro-modulation[15], and in the generation of acoustic holograms[16]
Summary
Non-invasive, real-time ultrasound imaging is a powerful diagnostic tool with advantages including cost effectiveness, deep penetration, widespread availability and safety. Other methods combine the geometrical approach with improved focusing[7,8] and beam shaping[9] Because these techniques have been applied for therapeutic purposes, they have relied on continuous wave insonation, rather than on single-cycle transmission (as is required for imaging purposes). If the problem involves a thick obstacle farther from the transducer, the redundancy method cannot be used Another method uses the geometrical approach combined with optimization based on the pseudo-inverse (PI) method[11] to adapt focusing in imaging applications[12]. We propose applying beam-shaping technology to manipulate the acoustic wavefront in order to look behind solid objects that would otherwise be impenetrable to ultrasound
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