A major challenge to in vivo optical imaging techniques is the highly scattering nature of light in biological tissue. As a result, its spatial resolution significantly decreases with increasing imaging depth (typically in the region over 1 mm). Photoacoustic imaging is an emerging hybrid bio-photonic imaging technique that detects absorbed photons using ultrasound and locally through the photoacoustic effect. The marriage of ultrasound and light in this technique overcomes the resolution drawback of pure optical imaging due to overwhelming light scattering in biological tissues, and possesses the merit and most compelling features of both optics and ultrasound—namely, high optical absorption contrast and sub-millimeter ultrasound resolution—up to an imaging depth of centimeters.

Photo-acoustic imaging has been applied to vasculature structural imaging, breast tumor detection, oxygenation monitoring in single blood vessels (important in tumor growth), and molecular imaging of targeting nanoparticles (personalized medicine) etc. Photoacoustic signals are induced as a result of transient thermo-elastic expansion when biological tissues absorb the pulsed laser energy. These signals are then detected by acoustic transducers and reconstructed to form images representative of optical absorption distribution. Based on differences in optical molar extinction spectra of absorbers, multiple-wavelength/spectroscopic photo-acoustic imaging techniques offer separation of different absorber contributions, which enables functional imaging with endogenous hemoglobin contrast and molecular imaging with exogenous molecular contrast. Photoacoustic imaging technology may provide a new paradigm for functional imaging, molecular imaging, and gene expression imaging based on optical absorption contrast.

In BUIL, we are now working on developing all kinds of photoacoustic imaging systems ranging from small-scale (cell-level), mid-scale (small-animal level)  to large-scale (human-level) imaging, and exploring the related applications.

Ultrasound is sound with frequencies high than the audible range, i.e., > 20 KHz. Typically, frequencies ranging from 0.1 MHz to 50 MHz are used in biomedical applications. For diagnostic purpose, ultrasound is transmitted to human bodies or testing objects, interrogating with tissues, and then received by ultrasound transducers. The received signals are then decoded into images regarding anatomic structures and functional information. Advantages of diagnostic ultrasound are non-invasive, real time, portable, and offering Doppler flow imaging. Wide-spectrum applications of ultrasound imaging are available (see wikipedia). In BUIL, we are looking for breakthrough in ultra-high frame rate array imaging/beamformation, image guidance of high-intensity focused ultrasound (HIFU) thermal ablation, and calcification imaging.

Backward-mode Magnetomotive Ultrasound Imaging System

Recently, magnetomotive ultrasound (MMUS) imaging has been introduced to detect magnetic nanoparticles (MNPs) which are not able to be visualized by conventional B-mode ultrasound. However, to date, only forward-mode MMUS where the imaging object is placed in between an ultrasound probe and an electromagnet is implemented in the literature. Such a MMUS mode is not suitable for clinical use. To facilitate clinical translation of MMUS, we propose a backward-mode ultrafast pulsed MMUS system.

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