Patents question - territorial limits in the internet

I am curently researching a few patents since our company is considering to make the leap and attract some american companies as customers. We are providing a web analytics solution which works by putting a pixel into the website to be tracked. Said pixel is stored on our servers in Europe. Now I wonder how patents on webanalytics are applicable, when they are filed in the United States. Our company would not operate an office there, we do not even have servers there. The client computers would receive their pixel from europe and an american company would access a frontend in europe or collect data via SOAP.

If we now attract american customers and provide stats for american websites are we then suddenly violating patents, because they are american? I don't understand how the international fences are drawn and before we start setting out to the american market we certainly will ask a lawyer, but my experiences with lawyers were rather bad when it came to such technical and complicated issues they rarely understand. So if anyone of you has some reasonsable speculations to offer or could point me to a source or a case, let me know.