3D Clinical Handheld Photoacoustic/Ultrasound Imaging Scanner and System

Abstract

Photoacoustic (PA) medical imaging is a technology that uses ultrasound (US) signals generated when light is irradiated to biological tissues. In biological tissues, there are several light absorbers such as water, lipid, melanin, oxy-, and deoxy- hemoglobin, each of them has a different degree of light absorption coefficient relying on the wavelength. Therefore, PA imaging can provides selectively represented body components such as water, fat, skin, and blood vessels using different light wavelengths. For this reason, PA imaging is advantageous for use in a variety of clinical applications (e.g., peripheral microvascular, skin, cancer, hemorrhagic, and ischemic diseases). PA imaging is mainly performed in the two-dimensional (2D) space, and 2D PA imaging may provide low reproducibility, which negatively affects diagnosis, making accurate clinical verification difficult. Overcoming the limitation requires a three-dimensional (3D) PA imaging system that provides high reproducibility. 3D PA imaging can be implemented using conventional 2D array US transducers or 1D array US transducers combined with mechanical stages, but this is not suitable for use in various clinical applications due to the difficulty of using handheld behavior. To perform various clinical trials while utilizing the advantages of 3D imaging, it is necessary to develop a 3D handheld PA imaging system. Based on this motivation, this thesis demonstrates 3D clinical handheld PA/US imaging scanners and systems. The specific contents are as follows. (1) Review of 3D handheld PA/US imaging systems and their applications, (2) 3D clinical handheld PA/US scanner, and (3) Panoramic volumetric clinical handheld PA/US imaging. The first part describes 3D handheld PA/US imaging systems and their applications. 3D handheld imaging systems are developed based on various scanning methods, such as direct, mechanical, mirror, and freehand scanning methods. The systems developed according to each scanning method are reviewed in various ways, such as performance, cost, complexity, functions, and limitations. The second part introduces a 3D clinical handheld PA/US imaging scanner and system. The handheld scanner was developed based on the scotch yoke mechanism, which converts rotational movement into linear reciprocating motion. The scanner was controlled by a motion control program and synchronized with the image processing system. Using the developed system, 3D PA/US imaging of various human body parts such as the human neck, arm, thigh, and foot is performed. The acquired image data is post-processed using volume reconstruction to provide images of human skin, muscles, bones, vascular structures, and oxygen saturation in the blood to evaluate the potential for clinical use. The third part, panoramic volumetric clinical handheld PA/US imaging scanner and system are introduced. Here, technical updates of the 3D handheld scanner and image processing system are performed to address the unmet needs of the previous system. The updated handheld scanner offers a lighter weight and smaller size than the previously developed handheld scanner. The updated scanner also provides reduced PA artifacts, deeper PA penetration depth, and improved SNR and resolution compared to previously developed scanners. The image processing system is updated to display PA/US maximum amplitude projection (MAP) images online to provide 3D images in real time. Panoramic 3D PA/US imaging is additionally developed online and offline to overcome the small field of view of the newly updated handheld scanner, and thus wide-field human images of body parts are successfully provided with various structural and functional information. Overall, this thesis demonstrates 3D clinical handheld PA/US imaging scanners and systems based on the mechanical scanning method. With the developed systems, 3D PA/US imaging of various human body parts has been performed, and usability and effectiveness are evaluated successfully. Based on these results, it is believed to apply to various clinical diseases such as peripheral microvascular, skin, cancer, hemorrhage, and ischemic diseases in the future.