Signal Processing - May 2016 - 49

diffusion tensor imaging and tractography, Zalesky et al. [50]
compared the anatomic connectivity network of 74 schizophrenia patients with 32 controls matched in age and gender.
They found statistically significant differences in connectivity
involving the medial frontal parieto-occipital lobe and the left
temporal lobe between the patients and controls.

that brain regions are not connected equally, but some play
more central roles than others (Figure 15). For each subject,
they simulated nearly 3 million fiber tracks with a fixed step
size of 1 mm and then derived a connectivity matrix between
998 regions on the cortex surface, each of approximately
1.5 cm2. On the basis of graph theory, they found that brain
regions within the posterior medial parietal cerebral cortex and
several temporal and frontal lobe areas form a highly mutually
connected network and constitute hubs linking other regions.
The functional activities of these regions are also highly coupled when the brain is at rest.
From childhood to adulthood, the brain experiences profound development to reach its peak of intelligence and mental
capacity. Comparing the brains of 439 individuals aged 12-30
years, Dennis et al. [49] found that not all connections are
strengthened during the development, but some are "pruned."
They scanned the subjects with high angular resolution diffusion imaging, reconstructed their fiber networks, and analyzed
the networks with graph theory and linear regression regarding
the subjects' gender and age. It was found that fiber density
relating to the frontal cortex decreases, but that relating to the
temporal cortex increases, as shown in Figure 16.
Many mental disorders are related to abnormal functional integration caused by aberrant brain connectivity. Using

future scope
Advances in dMR imaging have provided a platform for investigating brain connectivity in vivo at unpreceded spatial and
angular resolutions. Current acquisition and analyzing techniques have not reached their full potential. Under active development, they will be more efficient, more accurate, and more
reliable in the established framework.
As these techniques are becoming more accessible, it is
important to explore their clinical applications, such as brain
surgical planning and prognosis of recovery from trauma,
stroke, and so on. A connectivity network reconstructed from
a patient's dMR images may provide valuable information for
surgeons to more precisely locate the spot of intervention or
for doctors to better predict the mental impact of trauma or
hemorrhage. A single imaging modality such as dMR might be
insufficient to explain underlying physiological or pathological changes. To obtain a more comprehensive understanding of

Age 12

Decrea

ses in N

odal De

gree an

d Fiber

Density
Age 30

Age 12

Increas

es in N

odal De

gree an

d Fiber

Density
Age 30

FIGURe 16. Dennis et al. [49] compared the brains of 439 individuals aged 12-30 years by high angular resolution diffusion imaging and found that
not all connections are strengthened during development, but some are pruned. Only the connections with significant correlations with age are shown.
The node size is proportional to the number of connections, and the thickness of the connection edges is proportional to relative fiber density. (Figure
reprinted from [49] with permission.)
IEEE Signal Processing Magazine

May 2016

Table of Contents for the Digital Edition of Signal Processing - May 2016