The dielectric properties of rabbit tissue, pure water and various liquids suitable for tissue phantoms at 35 GHz

Feasibility of using thermal response to Ka band millimeter wave heating to assess skin blood flow

OBJECTIVE

Implementation of clinical guidelines for diagnosing peripheral artery disease will demand screening many millions of patients who are considered at-risk. This will require faster, easier screening technologies to identify patients with compromised blood flow to the extremities.

APPROACH

The feasibility of using surface temperature response to K_a band (26.5-40 GHz) near-field irradiation to assess skin blood flow was explored using an animal model. Ears of domestic rabbits were subjected to low-power continuous wave radio frequency heating from an open-ended waveguide (WR-28) at f  =  35 GHz. Three flow conditions were evaluated: (1) a baseline flow condition, (2) occluded flow and (3) reactive hyperemia. Surface temperatures were monitored continuously by means of an infrared thermography camera during each 2 min exposure.

MAIN RESULTS

Ensemble average results showed significant differences (p  <  .05) at exposure times 30, 60, 90 and 120 s between baseline and occluded conditions, and between baseline and reactive hyperemia conditions. The occluded condition (N  =  12) resulted in an average temperature increase of 21.4 °C  ±  3.9 after 2 min, compared with an average increase of 12.1 °C  ±  1.6 for baseline conditions (N  =  9) and 4.7 °C  ±  3.6 for post-occlusion/hyperemic conditions (N  =  8).

SIGNIFICANCE

Results are compared with the results of a simple two parameter mathematical model. These results suggest a method for non-invasive skin blood flow assessment to screen for peripheral artery disease and associated risk of cardiovascular events.

A fractal interpretation of the dielectric response of animal tissues

An improvement to Schwan's model of the dielectric response of biological tissues is proposed which is based on a fractal interpretation of the power law behaviour (epsilon' alpha epsilon" alpha f"-1) often observed. This interpretation allows the response to be more specifically related to the sub-cellular and cellular organization of the tissue through its self-similar hierarchical nature. A number of examples are discussed ranging in tissue type from the mostly cellular liver tissue to nerve tissue (grey matter). Applications of the technique to diseased and damaged tissue are briefly touched upon so as to illustrate its potential for precisely defining their effect upon the cells' electrical behaviour at a specific organizational level.