Human applications

OptoSonics originally developed its TCT technology as an imaging system to detect breast cancer. Rather than stimulating the thermoacoustic effect using infrared or near-infrared light, as we do in the small animal scanner, we chose to use a different portion of the electromagnetic spectrum — namely radio waves (RF).

Radio waves offer the potential to significantly improve our ability to diagnose cancer because they tell us something about the molecular structure of tissue and organs, as opposed to x-rays and ultrasound (US), which only tell us about the atomic and mechanical properties of tissue.

Two properties of tissue most affect the degree of RF absorption — 1) conductivity and 2) dipolar relaxation (i.e., RF-induced "spinning") of water molecules in the tissue. A small increase in concentration of ionic water in tissue can produce a large increase in RF absorption. This is especially true for RF frequencies between 100 and 1000 MHz.

OptoSonics believes that the ionic water content in cancer is increased due to a more dense concentration of blood and other proteins. Such increases are the result of angiogenesis (blood vessel creation) within rapidly growing tumors. The use of RF in the vicinity of 400-500 MHz should be ideal for measuring these effects in the breast.

The company adapted its TCT technology to image RF absorption in the human breast with a spatial resolution < 2 mm. Figure 1 represents the RF absorption in a normal breast. Tissues with higher ionic water concentrations (e.g., skin and glandular tissue) display greater RF absorption (brightness) than tissues with low ionic water concentration (e.g., fat).

Figure 1. TCT image of normal breast tissue (using RF excitation)

The next image is a 3-D TCT view of normal breast glandular tissue (press the Animate button to continuously rotate the image):

OptoSonics has worked with Kathy Miller, MD, Department of Hematology/Oncology at Indiana University Medical Center to study the use of RF for measuring the response of breast cancer to chemotherapy. Longitudinal changes in breast architecture during primary chemotherapy produce dramatic changes in RF absorption as revealed with TCT. In this case, tumor mass appears to have decreased markedly after seven weeks of chemotherapy treatment, as indicated by the arrows, but little change thereafter. This example underscores the diagnostic monitoring capabilities of TCT during prolonged treatment.

Basline	+7 weeks	+13 weeks