Article
Intraoperative visualisation of functional brain areas – a comparative study of thermal and optical imaging
Intraoperative Visualisierung funktioneller Hirnareale – eine Vergleichsstudie zur thermischen und optischen Bildgebung
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Published: | June 26, 2020 |
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Objective: Intraoperative imaging techniques should support the surgeon in his decision-making process of effective tumour treatment while preserving functional brain tissue. Previous studies proved that both Intraoperative Optical Imaging (IOI) and Intraoperative Thermal Imaging (ITI) can visualise functional brain areas by monitoring changes in cerebral metabolism in a contactless, non-invasive, and marker-free manner. This work provides a direct comparison of both imaging techniques to investigate their potential.
Methods: Measurements were performed on 10 patients with cortical lesions that underwent craniotomy for tumour resection near the somatosensory cortex. In all cases, median nerve stimulation was performed for 9 minutes with alternating 30 s rest and 30 s stimulation periods. During stimulation, IOI and ITI were acquired simultaneously. By calculation of the spectral power density for stimulation frequency, two-dimensional maps were created visualising areas of neuronal activity following stimulation. The localisation of the somatosensory cortex was validated with electrophysiological measurement (phase reversal).
Results: In 9 out of 10 cases, both IOI and ITI were able to identify and differentiate the postcentral region corresponding to the electrophysiological measurements. In one case, the stimulated area was not trepanned and appropriately IOI and ITI displayed no activity. Three measurements showed only a low ITI activity in accordance with also a low activity in IOI, whereas the electrophysiology still delivered plausible results. Detailed analysis revealed variations in the position and size of the detected activity regions on the somatosensory cortex. Different measuring principles with specific signal properties, imaging and preprocessing methods lead to slightly different regions between IOI and ITI. Furthermore, while it is known that IOI displays blood volume changes, the physiological effects resulting in the observed thermal signal of ITI due to neural activation will require further investigations.
Conclusion: Both intraoperative imaging techniques reveal a high sensitivity to the detection of functional areas within the central region. IOI can easily be integrated into a clinical routine due to its standard hardware setup whereas the application of ITI is illumination independent and also suitable for further perfusion analysis. When selecting an appropriate imaging method respective advantages should be considered individually.