A. Seer. Parameterization of a Spatial Cerebral Temperature Model Using Thermal Image Information. Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT). Masterarbeit. 2020
The ischemic stroke is a major health problem because of its high probability to cause permanent loss of neurological functions or even life-threatening situations for the patient. Today, it is one of the leading causes of death in Western countries. Therapeutic hypothermia (TH) is a promising therapy to reduce the damage to brain tissue resulting from the cerebral hypoperfusion. A new catheter system aims at selective brain hypothermia through intrac- arotid blood cooling and simultaneously allows for a mechanical thrombectomy of the vessel occlusion. For evaluating the effect of blood cooling on the spatio-temporal temperature distribution in the brain tissue, a spatial cerebral temperature model based on Pennes’ bioheat equation was developed, since temperature measurements inside the patient’s brain would increase the risk of injuries. In this work a parameterization of the spatial cerebral temperature model was performed. Therefore, simulation results of the model were compared to real experimental data, which consist of thermal videos tracing the brain surface temperature of a patient suffering from acute ischemic stroke (AIS), who underwent a decompressive craniectomy and received a cold saline bolus injection. The model was adapted to the present situation of the head in the thermal video to enable the comparison. A 3D head geometry was modified to represent the patient’s head after a decompressive craniectomy. Further a vessel occlusion in the left middle cerebral artery (MCA) was included into a pre-existing hemodynamics model, which is based on a 1D transmission line approach. The thermal boundary conditions of the spatial cerebral temperature model were adjusted to represent the modified head geometry. A more realistic blood temperature model was developed, to simulate the cold saline bolus mixing with the venous blood and to consider a more realistic arterial blood temperature in the bioheat equation. Simulations showed an impact of the cold saline bolus on the blood and ischemic brain tissue temperature by a temperature drop of about -0.3 K after 11 seconds, followed by a longer rewarming phase of over 70 seconds. In the thermal video, this behavior was only visible for a selected artery on the brain surface, but the surface temperature on the remaining brain tissue showed no distinct temperature change after the bolus injection. The parameterization of the blood temperature model enabled a realistic simulation of the cold saline bolus impact on the blood temperature and the simulation results coincided with the observed cerebral artery temperature course in the thermal video. However, since the temperature drop induced by the cold saline bolus is small in the ischemic brain tissue, it might have been covered under the signal fluctuations.