Intraoperative Functional Ultrasound

A wide spectrum of methods is used to image brain activation in vivo. It can be directly detected by neurons electrical activity imaging (cortical simulation mapping, calcium imaging, voltage sensitive dyes) or indirectly by imaging hemodynamic changes induced by the neurovascular coupling in the vessels surrounding the activated neurons (intrinsic optical imaging, photoacoustic imaging, positron emission tomography (PET), functional magnetic resonance imaging (fMRI)).

Ultrasound as the potential to complement these functional imaging techniques at low cost. Ultrasound imaging can do real-time in-depth imaging of brain. However, its use to imaging of major vessels has been limited until now due to its poor sensitivity. To overcome this limitation functional ultrasound (fUS) was developed in Institut Langevin since 2011. This technique enables high spatio-temporal resolution imaging of whole-brain microvasculature dynamics in response to brain activation without the need of contrast agent.

This fUS method relies on a new power Doppler imaging sequence sensitive enough to detect blood flow in most of cerebral vessels (arterioles, big venules and larger vessels). Repeating the acquisition of such ultrasensitive Doppler images over time enables to follow flow dynamics in such vessels modulated by local neuronal activity.

Applied to the rat brain, fUS was proved able to map brain activation at high spatiotemporal resolution and high signal to noise ratio. The aim of this study is now to apply fUS on human brain in intraoperative condition.

The main objective of this study is to find activation maps through intraoperative ultrasensitive Doppler compared to gold standard cortical simulation mapping and functional MRI.

Secondly the investigators want to test sensitivity of this new Doppler mode. fUS method will be used for different types of stimuli and intensity and the investigators will do some control acquisitions. Blood vessel density observed with a conventional Doppler will be compared to the one measured with the ultrasensitive Doppler to prove that this new Doppler mode enhance micro vessel visualization.