On the high end of capture devices we recommend the Epiphan AV.io, This device is fast and has connectors to all ultrasound video outputs. They also accommodate the different video resolutions that come off of different ultrasound machines;
This capture device works with every ultrasound we have encountered. It is fast and very reliable.
There are some lower price capture devices that will also work;
To stream successfully a PC should have a minimum of 8 gigs of RAM and a Intel i5 or AMD A6 or greater processor. Here is a link to a laptop that would work well for streaming;
The minimum speed of the internet connection should be 10 megs down and 2 megs up.