High-Frequency Acoustic Impedance Imaging of Cancer Cells

Variations in the acoustic impedance throughout cells and tissue can be used to gain insight into cellular microstructures and the physiologic state of the cell. Ultrasound imaging can be used to create a map of the acoustic impedance, on which fluctuations can be used to help identify the dominant ultrasound scattering source in cells, providing information for ultrasound tissue characterization. The physiologic state of a cell can be inferred from the average acoustic impedance values, as many cellular physiologic changes are linked to an alteration in their mechanical properties. A recently proposed method, acoustic impedance imaging, has been used to measure the acoustic impedance maps of biological tissues, but the method has not been used to characterize individual cells. Using this method to image cells can result in more precise acoustic impedance maps of cells than obtained previously using time-resolved acoustic microscopy. We employed an acoustic microscope using a transducer with a center frequency of 375 MHz to calculate the acoustic impedance of normal (MCF-10 A) and cancerous (MCF-7) breast cells. The generated acoustic impedance maps and simulations suggest that the position of the nucleus with respect to the polystyrene substrate may have an effect on the measured acoustic impedance value of the cell. Fluorescence microscopy and confocal microscopy were used to correlate acoustic impedance images with the position of the nucleus within the cell. The average acoustic impedance statistically differed between normal and cancerous breast cells (1.636 ± 0.010 MRayl vs. 1.612 ± 0.006 MRayl), indicating that acoustic impedance could be used to differentiate between normal and cancerous cells.