Medical and Biological Physics(DMBP)
Physique médicale et biologique (DPMB)
Michael C. KOLIOS
Ryerson University
High frequency ultrasound imaging and spectroscopy for the imaging of cell damage and death
In high frequency ultrasound imaging, compressional waves (20-60MHz) are used to interrogate tissue structure. While even at these frequencies individual cells cannot be resolved, the speckle pattern produced from cell ensembles can be analyzed and changes due to treatment visualized. We have shown that i) the ultrasound backscatter intensity, ii) the statistics of the backscatter envelope and iii) the power spectra of the backscatter change when cells and tissues are damaged. In this presentation we will present some of our recent data for our effort to explain the nature of these changes. It is shown that cell size is a major determinant of backscatter for cell ensembles both in-vivo and in-vitro. The mid-band fit (a measure of backscatter intensity) from cell pellets of a prostate cancer cell line (diameter ~30 microns) is 12dB greater than the MBF of cell pellets using an acute myeloid leukemia (AML) cell line (diameter ~10-15 microns). The measured spectral slope (with no compensation for attenuation) was 0.43 dB/MHz for the prostate cell line vs. 0.75 dB/MHz for the AML cell line, consistent with the smaller diameter of the AML cell. To determine whether treatment effects can be detected in-vivo, we have grown non-Hodgkin’s lymphoma tumors in mice (14 to date), which were then treated using CHOP chemotherapy. The ultrasound backscatter increased in the treated tumors in a time-dependent fashion, peaking at 24-48h after exposure. The kinetics and etiology of the increase will be discussed.