Insights into photoacoustic speckle and applications in tumor characterization

doi:10.1016/j.pacs.2019.02.002

Photoacoustics

Volume 14, June 2019, Pages 37-48

https://doi.org/10.1016/j.pacs.2019.02.002 Get rights and content

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Abstract

In ultrasound imaging, fully-developed speckle arises from the spatiotemporal superposition of pressure waves backscattered by randomly distributed scatterers. Speckle appearance is affected by the imaging system characteristics (lateral and axial resolution) and the random-like nature of the underlying tissue structure. In this work, we examine speckle formation in acoustic-resolution photoacoustic (PA) imaging using simulations and experiments. Numerical and physical phantoms were constructed to demonstrate that PA speckle carries information related to unresolved absorber structure in a manner similar to ultrasound speckle and unresolved scattering structures. A fractal-based model of the tumor vasculature was used to study PA speckle from unresolved cylindrical vessels. We show that speckle characteristics and the frequency content of PA signals can be used to monitor changes in average vessel size, linked to tumor growth. Experimental validation on murine tumors demonstrates that PA speckle can be utilized to characterize the unresolved vasculature in acoustic-resolution photoacoustic imaging.

Keywords

Photoacoustic speckle

Ultrasound speckle

Spatial resolution

Autocovarience function

Tumor vasculature

In-vivo imaging

Vascular trees

Cited by (0)

Eno Hysi is a PhD candidate in the Department of Physics at Ryerson University and a Vanier Scholar. Eno received his BSc degree in 2010 from Ryerson University (Toronto) in Medical Physics where he was first introduced to photoacoustic imaging. He continued his research at Ryerson’s Department of Physics where, in 2012, he graduated from his MSc in Biomedical Physics with a Gold Medal. His research has resulted in a number of publications and he has co-authored a book chapter. Throughout his studies, Eno has been the recipient of numerous academic awards and scholarships including the Ontario Graduate Scholarship, NSERC’s Alexander Graham Bell Canada Graduate Scholarship and most recently the Vanier Canada Graduate Scholarship. His research interests include ultrasound and photoacoustic tissue characterization for biomedical applications such as cancer treatment monitoring and blood hemodynamics.

Muhannad N. Fadhel completed his B.Sc. Hons in Biology with biophysics minor at Ryerson University in 2011. In 2014, he earned my M.Sc. in Biomedical physics from Ryerson University with a title of "Ultra-high frequency acoustic impedance imaging of cancer cells". The research focused on understanding the source of the scattered ultrasound signals from biological structures to improve the current techniques in analyzing and quantifying ultrasound images. He is currently a PhD student in the department of physics at Ryerson university under the supervision of Dr. Michael Kolios. Muhannad’s doctoral research focuses on the use of quantitative analysis and multispectral imaging to improving the capability of photoacoustics imaging to detect physical and biochemical changes red blood cells undergo in response to cancer therapy.

Michael J. Moore received his B. Math degree in Mathematical Physics from the University of Waterloo, Ontario, Canada, in 2013. He is currently pursuing his Ph.D. degree at Ryerson University, Ontario, Canada, in the CAMPEP Accredited Biomedical Physics program. His research interests include acoustic microscopy, photoacoustic microscopy, and high-frequency quantitative photoacoustics of single biological cells.

Eric M. Strohm received his B.Sc. degree in Physics from McMaster University in 1999. From 2002–2007, he was employed as a member of research staff at the Xerox Research Centre of Canada. He received his M.Sc. degree in 2009 and Ph.D. degree in 2013 in Biomedical Physics from Ryerson University. He is currently a Postdoctoral Fellow in the Cellular Mechanobiology Laboratory at the University of Toronto. His research interests include high frequency ultrasound and photoacoustic imaging for the characterization of biological cells and tissues.

Michael C. Kolios is a Professor in the Department of Physics at Ryerson University and associate Dean of Research and Graduate Studies in the Faculty of Science. His work focuses on the use of ultrasound and optics in the biomedical sciences. He has published 73 peer-reviewed journal publications, 5 book chapters, and 96 papers in conference proceedings. He has been invited to speak at 35 different organizations or conferences, and has been the keynote and plenary speaker for conferences in Canada, India and China. He has received numerous teaching and research awards, including the Canada Research Chair in Biomedical Applications of Ultrasound and the Ontario Premier’s Research Excellence Award. He is on the editorial board of the journals Ultrasound Imaging and Photoacoustics and is member of many national and international committees, including the IEEE International Ultrasonics Symposium Technical Program Committee. He is a member of the National Institutes of Health (NIH) Biomedical Imaging Technology A study section and was previously a member of the Canadian Institutes of Health Research (CIHR) Medical Physics and Imaging (MPI) panel.

¹: These authors made equal contributions.