Method and apparatus for detecting static magnetic fields

An apparatus, comprising:

• a first detection circuit adapted to receive a first portion of a signal provided by a sensor positioned in an implantable medical device, wherein the sensor is adapted to sense the presence of a magnetic resonance imaging device;
• a second detection circuit adapted to receive at least a second portion of the signal;
• and
• an interface adapted to receive a first notification from the first detection circuit when a first selected quantity derived from the first portion exceeds a first selected value and a second notification from the second detection circuit when a second selected quantity derived from the second portion substantially exceeds a second selected value, and wherein the interface is adapted notify a processor unit in the implantable medical device when the second selected quantity substantially exceeds the second selected value.

A method, comprising:

• sensing a magnetic field near a system using a sensor;
• comparing the magnitude of the magnetic field to a predetermined threshold magnitude;
• and
• notifying the system when the magnitude of the magnetic field substantially exceeds the predetermined threshold magnitude.

A method, comprising:

• sensing a first, a second, and a third signal proportional to a first, a second, and a third component of a magnetic field near an implantable medical device using a three-axis sensor, the second and the third components of the magnetic field being approximately orthogonal to the first component of the magnetic field and to each other;
• deriving a first quantity from the first signal;
• comparing the first quantity to a first selected value using a first detection circuit;
• comparing a second quantity derived from the first, the second, and the third signal to a second selected value using a second detection circuit, the second detection circuit being enabled following notification that the first quantity substantially exceeds the first selected value;
• and
• notifying a processing unit in the implantable medical device when the second quantity substantially exceeds the second selected value.