Marc A. Steed, Psychology

The surface area of the cerebral cortex (Cc-sa) was first measured in 1864. Since that time various methods have been applied, always post mortem. This project is the first to estimate Cc-sa from Magnetic Resonance Imaging (MRl) scans ante mortem.

I have faced several challenges in my project. My proposal stated I would be using 40 sets MRl scans (equally divided between gender and high/low intelligence) previously acquired at the University of Texas at Austin to investigate gender differences in Cc-sa. At the time I wrote my proposal I had several computer tapes from UT-Austin which supposedly held the scan data. As the laboratory I work in is not set up to read nine-track computer tapes, I utilized the facilities at the LDS Hospital Department of Radiology to transfer the scan data to an optical disk format usable in the lab. Much to my disappointment, the tapes contained MRl scans of the skull. These “bone window” scans were unsuitable to use for my project, as the brain is not visible at all. I corresponded with people at UTAustin who were surprised by the mix-up, but nonetheless informed me the data I wanted was not available.

However, I obtained a sample MRl scan (courtesy of Dr. Richard A. Robb, Biomedical Imaging Resource, Mayo Foundation, Rochester, MN) suitable for 3- dimensional (3D) rendering that would allow development of an algorithm to measure Cc-sa. Extensive editing of the MRl images was performed using ANALYZE image display/analysis software (Mayo Foundation, 1994) to segment the brain from the skin, skull, and meninges. Another editing step removed the brain stem, cerebellum, and other midbrain structures not considered cortical gray matter.

The images containing only brain were then rendered as a 3D object and a surface area measurement algorithm was applied. This algorithm takes each point that lies on the 3D surface and places them in a stack to find the invisible points. Each point on the stack is checked to see if any neighboring points are surface points (at least one of its neighbors is outside the threshold range). If so, the point is added to the stack. This continues until all points have been examined.

This algorithm yielded satisfactory results. A literature review found post mortem measures of Cc-sa ranging from 1500 cm2 to 3050 cm2, with variation attributed to age, gender, and methodology. My results are listed below. Measurements were taken from different aspects to account for possible anisotropy.

Under advice from Dr. Bigler, I am investigating if Cc-sa measurements in male traumatic brain injury (TBI) patients is significantly different than that of normal controls. However, the scanning protocol used to acquire the TBI images is different from the protocol needed to render a threedimensional image using the ANALYZE software: Rather than having over 100 contiguous slices 1 millimeter (mm) thick, the TBI scans consist of approximately 20 slices that are 5 mm thick, with a single slice acquired every 7 mm.

In order to compensate for this difference in protocols, I removed slices from the 3D MRI series such that the series represented the TBI protocoL My surface area algorithm will not measure area on this series, so I manually traced the gray matter perimeter for each slice and multiplied that number by the slice thickness (l mm) to obtain a general approximation of Ccsa. These two measurements were used to derive a correction factor. This correction factor, when multiplied by the total surface area measured on a TBI series of scans, will give an approximate measure of cortical surface area.

While not as elegant as the study originally proposed, the current study is the first in the literature to examine cortical surface area and TBI, and as such will have significant impact on future research. With the support of Dr. Bigler, I am continuing my study and expanding it into my master’s thesis. The money given to me by the Office of Research and Creative Work has been compensation that has allowed me to complete much of the preliminary work on my thesis. I am extremely grateful to the Office of Research and Creative work for awarding me an Undergraduate Creative Research Scholarship this past year for my research on the importance of cortical surface area. The money made it possible for me to purchase a personal computer, a tool that will be very helpful in the coming year as I complete my masters degree and move on to a Ph.D. program. I will continue to develop and hopefully validate my preliminary findings. Dr. Bigler assures me I am on the right track and that we will be able to publish this research sometime this year.