Hi, First, the original source of the geometry was MRI, as you have read. However, our interest in the bone data came later and they were not visible enough in the MRI to extract from there. Instead, we acquired standardized rib and spine geometry and fit them to the torso model. With that said, there is considerable variation among patients with regard to heart shape and even location. Some hearts are long and relatively narrow while others sit higher and are larger in a transverse slice. The variation you have spotted between the textbook and the Utah torso is, I believe, well within that normal range of variation. Finally, gating to the R wave does not ensure systole in the images of the heart for a couple reasons. The first reason is that electrical and mechanical systole are not aligned in time. Each cell of the heart experiences a delay between electrical and mechanical excitation, up to 200 ms in fact.. The result is that the R wave occurs during end diastole of the mechanical cycle, i.e., well before mechanical systole. Even more important, using the R wave to gate the image acquisition does not mean that all images have to be captured at the time of the peak of the R wave; rather the peak of the R wave provides a common reference so that acquisitions from different beats can capture the same phase of the heart cycle. The actual acquisition moment can be offset from the time of the R wave using a simple delay, i.e., each acquisition can occur with the same delay from that peak of the R wave. I hope that with this information you can see that the Utah torso geometry can, indeed, be trusted to represent reasonably the geometry of an adult human torso. Just as with the visible human data, this is only one specific case and there are simply not enough data available to begin to create a true atlas that specifies the ranges of normal anatomy of the entire torso. There are atlases like this of the brain but I don't know of any other organ system that has received enough attention to begin to quantify anatomical variation. Best regards, Rob MacLeod On Feb 10, 2006, at 1:31 AM, Hongyu Sun wrote:
---------------------------------------------------------------- Rob MacLeod, Ph.D. University of Utah Dept. of Bioengineering, CVRTI, and SCI (www.sci.utah.edu) 95 South 2000 East Room 207 Salt Lake City, Utah 84112-5000 ____ __o Internet: macleod@cvrti.utah.edu ____ -\<, Phonemail: (801)587-9511 ....0/ 0 Fax: (801)581-3128 URL: www.cvrti.utah.edu/~macleod Nora Eccles Harrison Cardiovascular Research and Training Institute ---------------------------------------------------------------- |
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