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A comparison using tissue electrical properties and temperature rise to determine relative absorption of microwave power in malignant tissue
Author(s) -
Joines William T.,
Shrivastav Shashi,
Jirtle Randy L.
Publication year - 1989
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596308
Subject(s) - microwave , materials science , absorption (acoustics) , microwave power , biological tissue , nuclear magnetic resonance , biomedical engineering , medicine , physics , composite material , quantum mechanics
This paper compares two methods for determining the radio frequency absorbed power in tissue: from the measured electrical properties of the tissue, and from the induced temperature rise per unit time. In previous research, we measured the radio frequency electrical properties of muscle, mammary gland, and malignant mammary tissue (SMT‐2A mammary adenocarcinoma) in female W/Fu isogeneic rats. From those measurements we calculated for each tissue the power absorption versus frequency, and formed the ratio of malignant‐to‐normal power absorption. This ratio exhibited a peak within the 150 to 400 MHz range, indicating a selective absorption of power in this type of malignant tissue over that of the normal host tissue. In the present study, by an entirely different method, we have directly tested the results of our earlier research. We filled a 20‐cm‐long section of rigid coaxial line (ordinarily air filled) with either normal (beef muscle or fat) or malignant (SMT‐2A) tissue, and measured the temperature increase versus time at the irradiated tissue surface for the same absorbed power in each tissue type. We made the measurements from 50 to 915 MHz, and found that the initial temperature increase per second per watt absorbed ( d T / d t / P a ) was greater in malignant tissue than in muscle or fat at each frequency tested, with the greatest differences occurring below 450 MHz. Power absorption based on the measured values of d T / d t / P a was again greatest for the malignant tissue (SMT‐2A mammary adenocarcinoma) within the 150 to 400 MHz range.