Laser Speckle Imaging of blood flow in the microcirculation of the cerebral cortex

Imaging activities in the human brain form one of the major challenges in the
field of neuroscience, and advances in this area will directly affect
approaches in the fields of neurology and neurosurgery. To date, the methods
for visualizing neuronal activity in humans suffer from several limitations.
They either reflect differences in neuronal activity indirectly by measuring
changes in vascular perfusion (fMRI and PET-scan), or they directly reflect
neuronal electrical activity, but do not provide robust neuro-anatomical
specificity (EEG and MEG). These technologies suffer respectively from
relatively limited temporal and spatial resolutions. Usually brain tumors are
initially identified using standard MRI, and once the patient is subjected to
neurosurgery, an attempt is made to obtain a total resection of the tumor with
minimal loss of surrounding vital neuronal tissue, especially that of areas
involved in pivotal functions such as speech and limb movements. The currently
used golden-standard procedure for identifying functional regions surrounding
the tumor is the electrocortical stimulation mapping (ECM) technique.
Unfortunately, ECM has several disadvantages (risk of hemorrhage, seizures and
time-consuming). Here, we provide an alternative by using the non-invasive
Laser Speckle Imaging technique, a technique with a high spatiotemporal
resolution for imaging local blood flow changes, which are known to be coupled
to neuronal activity.

1. Protocol A: Laser Speckle Imaging (LSI) of blood flow changes coupled to
neuronal activity in the human cerebral cortex: To investigate and optimize the
use of LSI to visualize blood flow changes coupled to neuronal activity. The
aim is to identify and discriminate specific functions of vital neuronal tissue
more precise, more efficient and faster as compared to current methods.

2. Protocol B: Effect of systemic medication on microcirculatory flow in the
brain assessed by Laser Speckle Imaging (LSI): Evaluation of the effects of
routinely used systemic medication and surgical devices (standard interventions
during neurosurgical procedures) on the local microcirculation in parts of the
cerebral cortex, with (not routinely used) and without the use of Transcranial
Doppler.

The study design will be observational without invasive measurements. Recording
will be made during taskperforming (in the awake craniotomy) and during the
standard infusion of mannitol and phenylephrine as described in the protocol.

There will be no risks involving taking the measurements, it is a non-invasive
method and the camera will stay approximately 30 centimeter above the cortex of
the brain. The LSI measurements will take at most 15 minutes and are not
painfull or dangerous. The measurements will not have a negative influence on
the patient, the surgery or the surgeon. The surgeon will be monitoring the
medical situation at all times.