Abstract
Medical ultrasound is an imaging technique that utilizes ultrasonic signals as information carriers, and has wide applications such as seeing internal body structures, finding a source of a disease, and examining pregnant women. The most commonly used ultrasonic transducer today is based on piezoelectricity. The piezoelectric transducer, however, may have a limited bandwidth and insufficient sensitivity for reduced element size. Laser-generated ultrasound (LGUS) technique is an effective way to resolve these issues. The LGUS approach based on photoacoustic effect is able to greatly enhance the bandwidth of ultrasound signals and has the potential for high-resolution imaging. High-amplitude LGUS could also be used for therapy to accomplish high precision surgery without an incision. Furthermore, LGUS in conjunction with optical detection of ultrasound allows all-optical ultrasound imaging (i.e., ultrasound is generated and received optically). The all-optical platform offers unique advantages in providing high-resolution information and in facilitating the construction of miniature probes for endoscopic ultrasound. In this article, a detailed review of the recent development of various LGUS transmitters is presented. In addition, a recent research interest in all-optical ultrasound imaging, as well as its applications, is also discussed.
Highlights
Ultrasound, defined as sound with frequencies from 20 kHz to several GHz, has demonstrated broad applications in medical imaging [1], material science, physics, chemistry, and nanotechnology.In classical medical ultrasound, an ultrasound pulse is transmitted into the body and the pulse is reflected due to the interfaces between tissues with different acoustic impedances as image contrast
Besides all-optical ultrasound imaging (AOUSI), the Laser-generated ultrasound (LGUS) approach offers a valuable tool for nondestructive testing and biomedical applications. (i) Characterization of the resonant frequencies of a cured PDMS thin film is Besides AOUSI, the LGUS approach offers a valuable tool for nondestructive testing and presented using a fiber-optic LGUS transmitter and an FP ODUS detector [78]
In this the recent advances that have been made for LGUS transmitters are presented
Summary
Ultrasound, defined as sound with frequencies from 20 kHz to several GHz, has demonstrated broad applications in medical imaging [1], material science, physics, chemistry, and nanotechnology. LGUS transmitters usually consist of optical absorbers for efficient conversion of light energy into heat, and surrounding media with high coefficients of thermal expansion for generating high-intensity ultrasound. LGUS transmitters are favorable for high-frequency arrays for high-resolution ultrasound imaging compared with traditional piezoelectric ultrasound transducers [28,29]. Efficient and broadband laser-generated focused ultrasound enables broad HIFU applications such as high-precision therapy [30] and micro-droplet ejection [31]. The LGUS transmitters can be realized with a similar size, for example, using a point-like laser source or light-absorbing material for ultrasound excitation Such features can be utilized to construct a miniature AOUST probe without sacrificing its sensitivity, which facilitates a range of applications such as endoscopic ultrasound imaging and minimally invasive clinical procedures. A summary and an outlook about LGUS transmitters and AOUSI are provided
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