High frequency ultrasound imaging and spectral analysis of sea urchin oocytes

Abstract

High frequency ultrasound measurements were made of sea urchin oocytes at 40 MHz and compared to numerical simulations. The urchin oocytes are non-nucleated cells, and have uniform size and biomechanical properties; thus, the signals measured from each cell are similar, unlike typical nucleated mammalian cells. The power spectra calculated from the measured time domain signals were periodic, with minima located approximately 10 MHz apart. This was a result of the consistent size and biomechanical properties of the cells. Numerical simulations were developed that calculated the superposition of ultrasound scattered from each cell within the transducer field of view using the Faran scattering model. Good agreement to the measured spectral features were observed. Using cepstral analysis, the size of the cells was determined to be 78.7 µm (measured) and 81.4 µm (simulated), which was similar to the size of a single cell. This work shows how ultrasound is discretely scattered from cells within a bulk homogeneous sample, with applications towards understanding the complex scattering behaviour from heterogeneous tissues.