At long last, I finally completed the iliac tracking algorithm about 2 weeks ago and have since moved on to updating the bone segmentation algorithm.  As you might expect, with the vascular segmentation out of the way, the bone segmentation proceeds much more smoothly than before.  In fact, when you couple the bone tracking algorithm with the anatomic data that was obtained in the aorto-iliac tracking, the overall process goes much more smoothly.
One problem that has arisen is that the VT algorithm doesn't include the internal iliacs since they are of no real significance and are variably patent.  Well, part of the problem with loosening the bone tracking criteria is that now in approximately 10% of scans, the internal iliacs are included in the initial bone segmentation.  Whether or not this turns out to be an actual issue or simply a nuisance that can be dealt with later is still to be determined.
At this point, the sub-segmentation of the ribs and spine is complete which leaves just the bony pelvis and femurs to go.  Interestingly, the previous versions of the software sub-segmented only the pelvis and femurs and relied primarily on anatomic models and the anatomic match points extracted from the wire-frame analysis.
I don't think this pre-production version of the software will make any use of anatomic models since I find them difficult to work with and time consuming to properly fit.
Well, the next step is the sacral segmentation and then I will do the femurs and finally the iliacs.  Looks like things are going much more smoothly than in previous versions of the software... mostly because I have learned to avoid some of the simple mistakes that used to consume hours of debugging time.