To properly detect ruptures in silicone implants, an MRI is recommended. However, that doesn’t mean you need to get an MRI all the time. It’s recommended that you get them every couple of years, and sooner if you suspect there’s a problem. Although silicone tends to be more popular these days, you can still get saline if you wish. Just make your wish known to your surgeon.
The only way you can tell if a silicone gel implant is ruptured is by a MRI x-ray, and health insurance may or may not cover the cost. Currently, the FDA and the implant manufacturers recommend that you check for rupture 3 years after your breast implant surgery and then every two years after that. For more information on this and similar topics, I recommend a plastic surgery Q&A book like "The Scoop On Breasts: A Plastic Surgeon Busts the Myths."