Feasibility of using thermal response to K_a 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. (paper)