Tissue Models: T-CEM43
Thermal Tissue Damage Model
The CEM43 tissue model is used to quantify effects resulting from transient heating and is applied to define exposure thresholds [1]. This metric, first proposed by Sapareto and Dewey [2], quantifies thermal exposure in terms of the number of minutes of heating at 43°C needed to obtain equivalent effects in biological tissues. The approach permits the impact of different transient heat exposure scenarios (e.g., short heating at high temperature vs. prolonged moderate heating), or a specific exposure to be compared to a previously identified damage threshold. Knowing the effect of a specific exposure duration at 43°C, the user can compare it to exposures at other temperatures and durations. CEM43 therefore provides a thermal dose concept based on temperature-weighted reaction kinetics, integrated over time, with the added benefits that it is applicable to a wide range of thermal effects from the tissue to the subcellular level, does not require tissue or reaction-specific constants, and is valid across a wide temperature range.
The biological response of a system is dependent not only on the temperature distribution but also on the sensitivity of the various tissues and the effect of interest. Tissue- and response-specific damage thresholds expressed in CEM43 have been reported in the literature [3] and can be used to assess potential tissue damage based on the simulated CEM43 distributions.
The Arrhenius tissue damage model is a metric that represents the percentage of tissue damaged in an affected region. For a given temperature and exposure duration, the tissue injury is calculated based on experimental cell survivability studies. Whereas CEM43 is often used to determine thresholds for a non-damaging or therapeutic exposure, the probabilistic Arrhenius model is primarily applied to determine ablated volumes in high-temperature exposure scenarios.
Treatment planning for liver radiofrequency ablation (RFA) (specific absorption rate (SAR), CEM43 thermal tissue damage assessment).
References
[1] Gerard C. van Rhoon, et. al., "CEM43°C thermal dose thresholds: a potential guide
for magnetic resonance radiofrequency exposure levels?", Eur Radiol (2013) 23:2215–2227
[2] Sapareto SA, Dewey WC., "Thermal dose determination in cancer therapy." Int J Radiat Oncol Biol Phys. 1984;10:787–800
[3] Yarmolenko PS, et. al., "Thresholds for thermal damage to normal tissues: An update." Int J Hyperthermia, 2011; 26:1–26
