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A study of infrared thermographic assessment of liquid nitrogen cryotherapy
M A Pogrel1, C K Yen, R Taylor
1Department of Oral and Maxillofacial Surgery, University of California, San Francisco, USA.
Objective:
To assess whether infrared thermography can accurately predict the area of soft tissue necrosis that results from liquid nitrogen cryoprobe therapy.
Study Design:
Eight rats received cryosurgery on the shaved abdomen with a liquid nitrogen cryoprobe in a triple-freeze technique. The therapy was monitored with infrared thermography and thermocouple probes. The temperature reached was correlated with the area of tissue necrosis found on histologic examination at sacrifice 1 week after the cryotreatment. A parallel study was carried out on pieces on beefsteak to assess the depth and shape of freeze.
Results:
The -20 degrees C isotherm, which is felt to correspond to the cell lethal zone, occupied the inner 70% of the area of the iceball produced. Histologically, the -20 degrees C isotherm corresponded well to the area of tissue necrosis. In depth, the iceball takes on a semicircular shape.
Conclusions:
Infrared tomography is expensive to use clinically and cannot be readily used in the oral cavity. However, this study does show that one can clinically estimate that the inner 70% of the area of an iceball produced by liquid nitrogen on soft tissues will ultimately undergo necrosis.