Tissue Stiffness as a Measure of a Health.

Matthew Urban (Urban.Matthew@mayo.edu) and his colleagues at the Mayo Clinic College of Medicine are designing ways to measure the stiffness of tissues as a non-invasive diagnostic tool. Monitoring a tissue's material properties may not be as obvious a gauge of its health as looking at its biological or chemical properties, but changes to these properties can be a good indicator of disease. Areas of stiffness in a tissue, for instance, are often a good warning sign of cancer---the basic premise behind breast self-examination.

Likewise when cancerous tumors form on the liver or another one of the body's organs, they are often stiffer than the surrounding tissues because there are more blood vessels to support the tumors. The problem is, how can you measure stiffness in tissues deep within the body? There is no such thing as a liver self-exam. At this week's ASA meeting, Urban reports on his latest experiments, in which he and his colleagues used focused ultrasound waves to deliver tiny vibrations to a steel sphere encased in gelatin, a model of a tissue with a stiff lesion.

They were able to measure the frequency response of the sphere to acoustical waves of multiple frequencies, which can then be used to determine the stiffness of the tissue-mimicking material. The method also provides new ways to non-invasively cause vibration for assessment of tissue stiffness without the presence of the steel sphere. Moreover, they were able to deliver the energy to the sphere without heating the surrounding gelatin. This is one of the challenges of using highly focused ultrasound, because acoustical energy can be absorbed by nearby tissues in the form of heat. (Talk 3pBB1, meeting website: http://www.acoustics.org/press/)