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THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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2. Preparation of data for contour identification<br />

In order to prepare metatarsal cross sectional shapes for curve detection<br />

software, the outlines of each metatarsal were selected and filled with color.<br />

Every fifth slice was sampled initially, to evaluate the potential of this sampling<br />

frequency for accurate 30 reconstruction. Object-Image for Macintosh software<br />

facilitated selection. Wrth a standard ADB mouse, I used the point-connect lasso<br />

tool for larger curves, decreasing the spacing between points for lower-radius<br />

cuwes. The continuous lasso tool served for selecting very small curves, such as<br />

those subtending the medullary cavity. Holding down the shift or control keys<br />

during selection allowed additions or subtractions to seleded curves. This<br />

enabled selection of the medullary cavity outline within the larger outer bone<br />

contour, and also allowed for the correction of errors and refinement of selection<br />

shape.<br />

Because contour detection software searches for pixels of uniform color<br />

value, each metatarsal was assigned a different fil1 color. The Graphic<br />

lnterchange Format (GIF) color palette provides only 256 colors. The limited GIF<br />

color space ensured that precise colors were applied to respective metatarsals in<br />

each image. The Object-Image's Fill command applied chosen colors to spaces<br />

bound by selected curves. The second metatarsal was assigned red, the third<br />

metatarsal green, and the fourai metatarsal was filled with blue. The red-green-<br />

blue color values were checked using the eyedropper tool from Adobe

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