Well, I am finally nearing completion of the stability overhaul which has sidetracked me for almost 2 weeks now. The important thing is that I am now getting reproducible and more accurate results.  It turns out that my concepts were significantly more sound than my code.  At any rate, now I will finally be able to get back to finishing up the iliac tracking algorithm.  From there, I will be able to re-enable the bone segmentation algorithms and so I should have all of that completed by the end of the year.
I had never intended to start the vascular segmentation until after the bone segmentation algorithm had already run, but I ran into problems with the bone propagation algorithm.  Then, I was only going to track the aorta and leave the iliac until later, but there ended up being a handful (<3) studies in the set where the iliac became an issue and so now I have ended up performing the entire vascular tracking out of necessity rather than intentionally.  That being said, the current vascular tracking is leaps and bounds ahead of the previous (primarily CPU based) code.
For this code, I had to go with sensitivity rather than specificity because even minor missed points can send the bone segmentation out of whack.  At least now I have an accurate center-line extraction so that once the bone segmentation is completed, it will be straight forward to go back and fine tune the vascular lumen segmentation.