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Handheld ultrasound-photoacoustic imaging system for clinics

9 Jan | By Biophotonics.World
Handheld ultrasound-photoacoustic imaging system for clinics
By: M. Pramanik

Researchers at Nanyang Technological University, Singapore have integrated light and sound to develop a handheld dual mode ultrasound + photoacoustic imaging system for clinical use. Various potential clinical applications are possible in the future. Imaging of sentinel lymph node (SLN) and urinary bladder has been demonstrated in small animal model using such imaging system in articles published in the Journal of Biophotonics in 2018.

Photoacoustic imaging (PA) is a rapidly emerging biomedical imaging modality. It is a non-invasive imaging modality which combines the best of optical contrast and ultrasound resolution. This method uses a pulsed laser is as illumination source. The light absorbed by the chromophores causes’ thermal expansion, which leads to the generation of pressure (acoustic) waves. The acoustic waves can be detected with the help of ultrasound transducers. Recently, food and drug administration (FDA) approved a clinical ultrasound system which can perform photoacoustic imaging and is commercially available. 

“We demonstrated the possibility of a clinical dual modal ultrasound-photoacoustic imaging system for different pre-clinical applications” said Kathyayini Sivasubramanian, a researcher working with Dr. Manojit Pramanik, assistant professor at Nanyang Technological University, School of Chemical and Biomedical Engineering, Singapore.


Applications of clinical ultrasound-photoacoustic system

SLN imaging is used for staging of breast cancer. PA imaging can be used for non-invasive imaging of SLN with the help of using FDA approved contrast agents like methylene blue (MB), indocyanine green (ICG), etc. Identification of SLN was combined with non-invasive needle guidance using dual modal ultrasound-photoacoustic imaging on small animals (rat). Human SLN imaging scenario was mimicked using chicken breast tissue. 

SLN imaging, using a Nd:YAG laser pumped by an optical parametric oscillator (OPO) laser of frequency 10 Hz combined with a clinical ultrasound system and a compatible linear array transducer, was shown. In-house holder was 3D printed to hold the fiber bundle and ultrasound transducer. Dr. Pramanik said “external integration of illumination source and transducer is better than integrating the illumination inside the transducer due to the complexity of the ultrasound transducer manufacturing process.”

“Furthermore we have shown PA imaging for the application of urinary bladder imaging up to an imaging depth of 2 cm” said Vijitha Periyasamy, a researcher working in the research group of Dr. Manojit Pramanik.

Urinary bladder PA imaging was shown using black ink and gold nanoparticles. Structural imaging of the urinary bladder is essential for the diagnosis of diseases like vesicoureteral reflux and bladder tumors. The use of PA imaging for vesicoureteral reflux using phantom imaging was also shown. Additionally, the feasibility of PA imaging for functional imaging using the gold nanorods clearance from rats for a period of 2.5 hours was demonstrated.

A high optical contrast from deep tissue is achieved in PA imaging. The depth of imaging is increased using FDA approved dyes such as ICG and MB. Integrating illumination and ultrasound transducer is the need of the hour to translate PA imaging to clinic. Once in clinic, US-PA systems are expected to assist in imaging of SLN, urinary bladder, melanoma, thyroid, malaria diagnosis and others. Currently, the preclinical studies of PA imaging are being explored. With further developments concerning the integration of illumination with ultrasound transducer and FDA approved dyes, PA imaging is expected to be in clinic shortly.


Original articles: 

1. K. Sivasubramanian, V. Periyasamy, R. A. Dienzo, and M. Pramanik, “Hand-held, clinical dual mode ultrasound-photoacoustic imaging of rat urinary bladder and its applications,” Journal of Biophotonics 11(5), e201700317 (2018).


2. K. Sivasubramanian, V. Periyasamy, and M. Pramanik, “Non-invasive sentinel lymph node mapping and needle guidance using clinical handheld photoacoustic imaging system in small animal,” Journal of Biophotonics 11(1), e201700061 (2018).


This article was contributed by M. Pramanik.


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