Biomedical Engineering Reference
In-Depth Information
areas in relation to a tumor or an epileptic focus to minimize surgical risk. Mass
lesions can frequently distort normal neuroanatomy, which makes the identification
of eloquent cortices inaccurate with normal neuroanatomical landmarks. MEG is
increasingly being used for preoperative functional brain imaging. By mapping rel-
evant somatosensory, auditory, and motor cortices preoperatively, retained areas of
function can be delineated. Preoperative localization of functionally intact brain tis-
sue helps guide neurosurgical planning and limits the region of resection, allowing
for improved long-term patient morbidity and neurological function.
Examples that show howMEG imaging is used to map the motor cortex in presur-
gical patients are given in [
7
]. This study performed localization of
-band desyn-
chronization preceding the index finger flexion for a subject with a frontal tumor,
and showed the location of hand motor cortex relative to a single dipole localization
of hand somatosensory cortex. These results were confirmed with electrical cortical
stimulation. This investigation demonstrated that MEG source images obtained using
beta-band event-related desynchronization reliably localize the hand motor cortex.
β
1.5.2 Functional Connectivity Imaging
Functional connectivity analysis has been shown to have profound clinical signifi-
cance, because disturbances in networks aremanifested as abnormalities in functional
connectivity and such abnormalities can be detected using resting state MEG. Recent
studies have shown this to be the case, and abnormalities in functional connectivity
during resting state are observed in many clinical conditions such as brain tumors
[
8
], strokes [
9
], traumatic brain injury [
10
], schizophrenia [
11
,
12
], and Alzheimer
disease [
13
].
Utilizing MEG imaging, changes in the alpha-band functional connectivity in
patients with traumatic brain injury were measured and compared to healthy con-
trols in [
10
]. In this investigation, mean imaginary coherence (MIC) (described in
In one male patient's case, his initial MEG scan was obtained 9months after his
injury and the results of MIC mapping demonstrated several regions of decreased
resting state functional connectivity compared to the control group. The follow-up
secondMEG scan was obtained 23months after the initial scan and the results of MIC
mapping demonstrated a decrease in the volume of cortex with reduced connectivity,
although some of the cortical regions with the greatest reductions in functional con-
nectivity seen in the initial MEG remained abnormal even in the second MEG scan.
The investigation described next identifies brain regions that exhibited abnor-
mal resting-state connectivity in patients with schizophrenia [
11
,
12
]. Associations
between functional connectivity and clinical symptoms were found in stable outpa-
tient participants. Resting-sateMEGwasmeasured from thirty schizophrenia patients
and fifteen healthy control subjects. The MIC mapping was computed in the alpha
