For DVTs, the clots become part of your vein wall. So to say they never go away is kind of a semantic thing. Some people have what are called chronic clots where there's still evidence of a clot but its adhered to the vein so there's no danger. For some people, the clot is completely resolved.

I think generally speaking, ultrasound and sonogram are basically the same thing which is seeing images of the clot. The doppler part of the ultrasound is used to pick up the sounds of blood moving in the arteries, from what I understand. So they're checking on the status of the clot, and they may use that information to determine the effectiveness of your anticoagulants, duration of the anticoagulant therapy,, etc. Most people aren't given a second doppler ultrasound. Your doc may be doing this because you're on the newer anticoagulant. Not sure. I'd ask him.

Actually, many times the clots do go away completely. Many folks have clots completely disappear over time. The body has to work to dissolve them (the medicine is not doing that) and some bodies are just better at it than others.

Me personally, I've got chronic DVTs in my right leg from 2005 and 2009. BUT, the clots I had in my lungs in 2010 were gone completely in five weeks. Clots are funny things. There was one gal on the PE boards that had her PEs take two years to go away completely.

Assuming that a sonogram is the same as an ultrasound (and I have no idea), they're probably just looking to see how blood flow is, I would guess, and whether the clots are dissolving/stabilizing. You could ask your doc why he ordered the test and what he hopes to learn from it, if you're really curious.

I had a Doppler ultra sound when I was diagnosed and 5 weeks after. One of the cat scans showed I had an enlarged lymph node and they needed to determine what a good time to bridge me off of warafin would be to do a biopsy. I was also in a teaching hospital and the intervention radiology dept were doing studies.