Predicting brain temperature in humans using bioheat models: Progress and outlook

Abstract

Brain temperature, regulated by the balance between blood circulation and metabolic heat generation, is an important parameter related to neural activity, cerebral hemodynamics, and neuroinflammation. A key challenge for integrating brain temperature into clinical practice is the lack of reliable and non-invasive brain thermometry. The recognized importance of brain temperature and thermoregulation in both health and disease, combined with limited availability of experimental methods, has motivated the development of computational thermal models using bioheat equations to predict brain temperature. In this mini-review, we describe progress and the current state-of-the-art in brain thermal modeling in humans and discuss potential avenues for clinical applications.

Keywords: Brain thermal model; bioheat equations; brain temperature; therapeutic hypothermia; thermal ablation.

Figure 1.

(a) Schematic of conductive, advective, and convective heat transfer in vascularized tissue within a control volume. Arterial vessel segments are depicted with red cylinders as they include oxygenated hemoglobin, and venous vessel segments are depicted with blue cylinders to represent deoxygenated blood. Blue, red, and purple arrows represent conductive, advective, and convective heat flow, respectively. (b) Detailed representation of conductive, advective, and convective heat flow in tissue and blood vessels. $K$  = local thermal conductivity; $\rho$  = tissue density; $c_b\hspace{0.17em}$ = specific heat of blood; $U_n\hspace{0.17em}$ = local fluid velocity normal to the surface; $h$  = local heat transfer coefficient; $T_t$  = tissue temperature; $T_b$  = blood temperature; $A_t^{\prime }$  = surface area of tissue control volume; $A_b^{\prime }$  = surface area of blood control volume; $A_{c,t}^{\prime }$  = cross-sectional area between tissue voxels; $A_{c,b}^{\prime }$  = cross-sectional area between vessel segment; $A_w^{\prime }$  = surface area of blood vessel wall.

Figure 2.

Representations of the human brain used in biophysical modeling. (a) Early representations included simple hemispheric models, and (b) more recently have advanced to realistic human brain models with both tissue and vasculature. (c) Model-predicted brain temperatures in degrees Celsius from three healthy human subjects.Figure 2(a) was adapted and reprinted from literature, with permission from Elsevier. Figure 2(b) was adapted from literature and used under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Figure 2(c) was adapted from literature and used under the Creative Commons Attribution 4.0 International (CC BY 4.0) license.