Eric StrohmPost Doctoral Fellow
Supervisor: Dr. Michael Kolios
Characterization of single cells using high frequency ultrasound and photoacoustic methods
Ultrasound and photoacoustic measurements
High frequency ultrasound and photoacoustic methods can be used to probe single cells for the purpose of identifying the cell type by extracting their intrinsic physical properties. This can be used to identify tumor cells in a blood or tissue sample, and differentiate cell types such as red blood cells and white blood cells. When cells are irradiated with ultrasound that has a wavelength similar to the size of the cell (frequencies over 100 MHz), the scattered ultrasound signal is encoded with unique signatures based on the properties of that cell. Through signal processing methods, the size, shape, composition and microstructure of the cell can be extracted from the signal power spectrum. When irradiated with a laser, the cell absorbs the laser energy and emits a photoacoustic pressure wave that can be measured using ultrasound hardware. Like ultrasound, the photoacoustic signal is encoded with unique information based on the properties of that cell. However for photoacoustic signals to be generated, the cell must absorb the laser energy, and that depends on the absorption properties of the cell. By using specific dyes with varying optical absorption profiles, different components of the cell can be targeted (such as the nucleus, cytoplasm and organelles); the resulting photoacoustic signals carry unique information about those structures. We are currently using these methods to detect hematological malignancies and circulating tumor cells in blood samples.
Numerical simulations, finite element models and analytical solutions of equations are used to solve physical problems such as interactions of ultrasound and photoacoustic waves with cells, particularly from asymmetric or heterogeneous particles such as red blood cells. These models help visualize wave propagation and understand their underlying physical mechanisms. Comparing the measured signals to theoretical models allows extraction of specific cellular parameters such as the size, shape and sound speed to aid in specific cell identification.
Book chapters (2)
1. E. Hysi, E.M. Strohm and M. C. Kolios. “Probing different length scales using photoacoustics: from 1-1000 MHz” in Handbook of Photonics for Biomedical Engineering, Aaron H.P. Ho, D. Kim and M.G. Somekh (Eds.). Springer, 2015.
2. E.M. Strohm, G. Czarnota, M.C. Kolios, “Acoustic microscopy of cells” in Quantitative Ultrasound of Soft Tissue, J. Mamou and M. Oelze (Eds.). Springer, 2013.
Publications in refereed journals (7)
1. Y. Sun, Y. Wang, C. Niu, E.M. Strohm, Y. Zheng, H. Ran, R. Huang, D. Zhou, Y. Gong, Z. Wang, D. Wang, M.C. Kolios, “Laser-activated PLGA theranostic agents for cancer therapy in vivo”, Advanced Functional Materials (Accepted Sept. 3, 2014)
2. E.M. Strohm, I. Gorelikov, N. Matsuura, M.C. Kolios, “Modeling photoacoustic spectral features of micron-sized particles”, Physics in Medicine and Biology, 59(19), 2014, pp. 5795-5810.
3. E.M. Strohm, E. Berndl, M.C. Kolios, “High frequency label-free photoacoustic microscopy of single cells”, Photoacoustics, 1(3), 2013, pp. 49-53.
4. E.M. Strohm, E. Berndl, M.C. Kolios, “Probing red blood cell morphology using high frequency photoacoustics,” Biophysical Journal, 105(1), 2013, pp. 59-67.
5. E.M. Strohm, I. Gorelikov, N. Matsuura, M.C. Kolios, “Acoustic and photoacoustic characterization of micron-sized perfluorocarbon emulsions”, Journal of Biomedical Optics, 17(9), 2012, pp. 096016-26.
6. E.M. Strohm, M. Rui, I. Gorelikov, N. Matsuura, M.C. Kolios, “Vaporization of perfluorocarbon droplets using optical irradiation”, Biomedical Optics Express, 2(6), 2011, pp. 1432-1442.
7. E.M. Strohm, G. Czarnota, M.C. Kolios “Quantitative Measurements of Apoptotic Cell Properties Using Acoustic Microscopy”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 57(10), 2010, pp. 2293-2304.