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Abstract:
While considerable attention has been directed towards
defining criteria for anatomical regions of interest (ROI), the
difference between absolute and. proportional measures has not been
adequately addressed. Given that male brains tend to be larger than
female brains, the use of raw volumes may overestimate the relative
size of male structures. The purpose of this study was to compare
proportional and volumetric measures in determining sex effects.
MRI volume measures were obtained for total brain area (TBA)
Heschl's gyrus (H), planum temporale (PT), posterior ascending
ramus (PAR), and posterior superior temporal gyrus (pSTG)
(left+right hemispheres) for 35 children (20 males, 15 females).
Proportional measures were calculated for each ROI (100 x
volume/total brain volume). TBA was significantly larger in males
than females. A mixed MANOVA yielded a significant Sex by
Measurement-Type interaction. Size differences between males and
females varied dramatically according to whether volume or
proportion scores were used. For H and PAR, males were found to
have larger volumes than females, but the magnitude of the
difference was significantly reduced with proportional measures.
More importantly, the difference shifted direction for the PT and
pSTG. Raw scores favored males in size; proportional scores favored
females. Such differences would result in different conclusions
regarding sex effects on the development of cortical structures.
(Support NIDCD, MOD)
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