gms | German Medical Science

Objective: Time-resolved thermography is a novel method to image temperature gradients and heterogeneities of tissue and blood by detecting the emitted infrared radiation. Therefore, it is a sensitive, noninvasive, label-free and fast application to investigate blood perfusion. The aim of this study is the characterization of the cortical perfusion by intraoperative thermographic imaging and detection of a systemic cold bolus serving as a contrast agent with temporally and spatially limited signal intensities.

Method: Seven patients were investigated and a cortical thermogram was recorded. Five patients had a brain tumor, one suffered a space-occupying stroke due to the occlusion of ICA, and one had an arteriovenous malformation. Thermographic image sequences of the cortex were recorded with an infrared imaging system (VarioCam hr head, InfraTec, Germany) which provides a thermal resolution of 0.03 K at 30°C, a geometrical resolution of 620 x 480 pixel and a temporal resolution of 20 ms. During the recording, a cold bolus was induced by injection 20 ml of cold (2–4°C) normal saline solution into a central venous line. Data analysis was performed with MATLAB Package (Version 8, The MathWorks Inc.).

Results: In the temperature curves, the intravenously applied cold bolus induced a thermographically detectable temperature drop of up to 0.15 K. According to the shape of the temperature drop an inverse Gaussian function with positive skewness was approximated to the thermal profiles in order to extract its features for all pixels. The parameters of the approximation provide information about the arrival time of the maximal temperature difference of the drop. For the considered patient cases following values were observed; arrival time for arteries lies between 12 and 20 s, for veins between 30 and 45 s after application. Graphical representation of the arrival time as images results in coarse flow maps, which match the anatomy of the recorded cerebral regions and displayed individual characteristics depending on the type of lesion.

Conclusions: Thermographic imaging is a sensitive method to detect an intravenously applied cold bolus on the exposed human brain surface. Analysis of thermal temperature curves provided information about the temperature drop passing the cortex and allowed tracking its way. The different types of tissue and blood vessels had varying cold bolus sequences which might offer an additional diagnostic tool to characterize the cortical blood flow.