Biomedical Engineering Reference
In-Depth Information
and reviews of childhood records, only one subject had a history of a clinically
significant delay in acquisition of spoken language suggestive of a developmental
language disorder. This subject spoke well by the time he entered school and, at
the time of study, showed good spoken language, with an average Verbal IQ, and
excellent reading comprehension, much like our other subjects, and thus was not
excluded. Controls (all right-handed males) were free of any history of develop-
mental disorder, attention deficit disorder, special education, and reading decoding
or spelling deficits. All scored well within an average range or above on reading
measures. All but one had additional psychometric testing (one was not tested
because of his familiarity with some of the tests, a factor that would invalidate his
scores). The controls were matched to the dyslexic group with respect to gender,
age, educational level, socioeconomic status, handedness, and estimated IQ, ob-
tained with a short form of the WAIS-R. The dyslexic sample and 13 of the 14
controls reported here participated in a study of planum temporale asymmetry re-
ported in [5, 28]. Fourteen of the 16 dyslexic men and 11 of the 14 controls studied
here also participated in functional brain imaging studies [5, 28, 29] that suggested
functional variations in left and right temporal and inferior parietal cortex in the
dyslexic men.
3.3. Magnetic Resonance Imaging Protocol
All images were acquired with the same 1.5-T Signa MRI scanner (General
Electric, Milwaukee, WI) using a 3D spoiled gradient recall acquisition in the
steady state (time to echo = 5 ms; time to repeat = 24 ms; flip angle = 45; repetition
= 1; field of view = 24 cm
2
). Contiguous axial slices, 1.5 mm in thickness (124
per brain), were acquired. The images were collected in a 192
×
256 acquisition
matrix and were 0-filled in k-space to yield an image of 256
×
256 pixels, resulting
in an effective voxel resolution of approximately 0.9375.0
×
0.9375
×
1.5 mm.
4.
PROPOSED APPROACH
The proposed approach consists mainly of four steps, as shown in Figure 4.
First, a brain extraction algorithm is applied to remove all the non-brain tissues
from the images. Second, brain segmentation is performed to isolate the white
matter. Third, white matter parcellation is performed to parcel the white matter
into inner and outer compartments, and, finally, volumetric measures of the whole
white matter as well as the outer compartment are recorded. Tests of the hypothesis
are then performed to investigate if there exists a significant difference between
the groups or not in terms of volume changes. The following subsections will
provide a detailed description of each of the previously mentioned steps.
