High-frequency ultrasound detection of cell death: Spectral differentiation of different forms of cell death in vitro
Maurice M. Pasternak1,2, Ali Sadeghi-Naini1,3,4,5, Shawn M. Ranieri3, Anoja Giles3, Michael L. Oelze6, Michael C. Kolios7, Gregory J. Czarnota1,3,4,5
1Department of Radiation Oncology, Sunnybrook Health Sciences Center, Toronto, ON, Canada
2Department of Laboratory Medicine & Pathobiology, University of Toronto, ON, Canada
3Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada
4Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
5Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada
6Department of Electrical and Computer Engineering, University of Illinois, IL, U.S.A.
7Department of Physics, Ryerson University, Toronto, ON, Canada
Gregory J. Czarnota, email: Gregory.Czarnota@sunnybrook.ca
Keywords: quantitative ultrasound, apoptosis, oncosis, imaging, midband fit
Received: June 01, 2016 Accepted: August 12, 2016 Published: September 12, 2016
High frequency quantitative ultrasound techniques were investigated to characterize different forms of cell death in vitro. Suspension-grown acute myeloid leukemia cells were treated to cause apoptosis, oncosis, mitotic arrest, and heat-induced death. Samples were scanned with 20 and 40 MHz ultrasound and assessed histologically in terms of cellular structure. Frequency-domain analysis of 20 MHz ultrasound data demonstrated midband fit changes of 6.0 ± 0.7 dBr, 6.2 ± 1.8 dBr, 4.0 ± 1.0 dBr and -4.6 ± 1.7 dBr after 48-hour cisplatinum-induced apoptosis, 48-hour oncotic decay, 36-hour colchicine-induced mitotic arrest, and heat treatment compared to control, respectively. Trends from 40 MHz ultrasound were similar. Spectral slope changes obtained from 40 MHz ultrasound data were reflective of alterations in cell and nucleus size. Chromatin pyknosis or lysis trends suggested that the density of nuclear material may be responsible for observed changes in ultrasound backscatter. Flow cytometry analysis confirmed the modes of cell death and supported midband fit trends in ultrasound data. Scatterer-size and concentration estimates obtained from a fluid-filled sphere form factor model further corresponded with spectral analysis and histology. Results indicate quantitative ultrasound spectral analysis may be used for probing anti-cancer response and distinguishing various modes of cell death in vitro.