The ultrasound is actually a device. You put conductive gel on the area (I always make sure mine is in a place where it won't get cold) and then you run the device over the area (constantly moving so you don't burn yourself). It's a deeper sort of heat...I don't even really feel like the area gets hot...but it does help. I've found that generally using the ultrasound extends the amount of relief and length of time I get relief after the hot bath with Epsom salts. It especially helpful for me with the spasms.

They used a similar device (bigger...mine is a portable version) when I did outpatient physical therapy and I found that when they did it at the beginning of the sessions that things were easier for me than without it. The routine of ultrasound at the beginning and stim with heat at the end actually did a great job at reducing my pain levels...more than any meds ever did.