Medical ultrasound imaging has firmly established its own territory as a diagnostic tool due to its real-time capability, portability, safety, and functional imaging capability. These features are prominent advantages over other imaging modalities such as magnetic resonance imaging (MRI) and computer tomography (CT), thus making it possible for ultrasound imaging to occupy the position of the second most popular modality in the medical imaging market. Here, our research goal is to push the envelope of medical ultrasound modality by seeking new and hybrid techniques. This will extend preclinical and clinical applications of ultrasound and make ultrasound become a pivotal driving factor in future biomedical engineering. Our primary research goals are to develop the solutions for:

Photoacoustic Imaging

An ultrasound image is constructed after transmitting acoustic waves (i.e., ultrasound) into the body and receiving echoes from tissue boundaries. By contrast, a photoacoustic (PA) image is acquired after delivering light (e.g., laser pulses) into the body and receiving acoustic waves (i.e., photoacoustic signals) generated within light absorbers. Photoacoustic imaging rests on the transient thermoelastic expansion of target molecules; light with a particular wavelength induces the vibrational and rotational oscillation of a specific molecule such as hemoglobin in blood when the molecule absorbs the light energy. In the molecule, the absorbed light energy is subsequently converted into heat. When light pulse width is shorter than thermal transport time of absorbed energy, defined as thermal confinement, the energy brings about transient thermoelastic expansion and thus generates acoustic waves (or photoacoustic signals). Finally, PA images are constructed using the PA signals in an ultrasound imaging system. Therefore, this new imaging modality can be considered as molecular imaging. As a result, PA imaging combines both advantages of high optical contrast and good ultrasound spatial resolution in relatively deep-lying tissues. We are intensively conducting translational research to find ways to use this new technique in clinics. The real-time detection of the microcalcification in breast tissues (center), identification of sentinel lymph node and its metastasis (right side), and development of various PA contrast agents (left side) are some examples of our recent achievements.

Signal & Image Processing and Systems

The realization of new imaging and therapeutic techniques frequently requires the development of new systems and signal/imaging processing algorithms. For high-performance imaging and therapeutic systems, we are researching on the design and implementation of analog and digital circuit boards with on-board FPGA (field programmable gate array) (left side of the above figure). In addition, we are developing new digital signal and imaging processing algorithms to improve ultrasound and photoacoustic image quality.

Therapeutic Ultrasound and light

High-intensity focused ultrasound (HIFU) have come into the spotlight as an effective and noninvasive therapeutic technique. In contrast to ultrasound imaging, delivering HIFU energy into target lesions such as cancer leads to inducing localized heating in the target lesion. By doing so, coagulation necrosis can occur, thus causing cell death in the target lesion. During HIFU treatment, it is pivotal to have complete awareness and control of the treatment process by prescribing the appropriate HIFU dosage and by identifying the exact lesion locations for maximized treatment efficacy. In addition to seeking out new clinical applications of HIFU such as beauty treatment, we are researching on the development of real-time monitoring method during HIFU surgery to provide feedback regarding the tissue response to the HIFU and to track undesirable movements such as patient heart beat and/or respiration. Furthermore, we are seeking out a new way to improve therapeutic efficacy, such as combining optical and HIFU energy.

Ultrasound Sensors

In medical ultrasound imaging and therapeutic systems, ultrasound transducers are a pivotal module that influences image quality and therapeutic efficacy. To use new imaging and therapeutic techniques in clinics, it is frequently necessary to develop new high-performance ultrasound transducers dedicated to a target clinical application. For new ultrasound transducers, the development of new materials used for the transducer, the accurate structural design using FEM (finite element method), the development of fabrication process are crucial. Our facilities enable us to fulfill all these activities. The 15-MHz concave array, 15-MHz linear array, 7.5-MHz large aperture linear array, 60-MHz intravascular ultrasound transducer, and double-focused HIFU transducer are some examples of our recent achievements.