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Spurred by health care trends and technological advances, telemedicine is growing into a mainstream industry.

A fifth of Americans live in places where primary care physicians are scarce, according to government statistics. That need is converging with advances that include lower costs for video-conferencing equipment, more high-speed communications links by satellite, and greater ability to work securely and dependably over the Internet. "The technology has improved to the point where the experience of both the doctor and patient are close to the same as in-person visits, and in some cases better," says Dr. Kaveh Safavi, head of global health care for Cisco Systems, which is supporting trials of its own high-definition video version of telemedicine in California, Colorado and New Mexico. The interactive telemedicine business has been growing by almost 10 percent annually, to more than $500 million in revenue in North America this year, according to Datamonitor, the market research firm. It is part of the $3.9 billion telemedicine category that includes monitoring devices in homes and hundreds of health care applications for smartphones.