Apparatus and method of acquiring physiological gating signals for magnetic resonance imaging of moving objects

In an MRI system having a main magnet with a central bore and a RF coil for generating RF signals which excite nuclei in an image region of a subject positioned in the bore of said main magnet so as to generate MR data for acquisition by said system, a method of providing data indicative of the physiological motion of the subject, said method comprising the steps of:

• exciting said RF coil with an RF source at a first frequency different from a second frequency used to acquire MR data;
• sensing a portion of said first frequency which is reflected by said coil back to said RF source;
• comparing the characteristics of the reflected signals with those of the generated signals to produce a trigger signal indicative of relative changes in the characteristics of the generated and reflected signals such that the magnitude of said trigger signal is approximately linearly related to the extent of physiological motion in the imaging region and the slope of said trigger signal is approximately linearly related to the direction and speed of the physiological motion in the imaging region;
• and
• triggering acquisition of MR data in response to said trigger signal so as to generate an MR image which is not blurred by the physiological motion of said imaging region.

In a MRI system, an apparatus for acquiring data related to the physiological motion of an imaging region of a subject, said apparatus comprising:

• means (1) for generating a signal by exciting an RF coil of said system at a frequency .omega..sub.1 different from a frequency .omega..sub.2 used by said MRI system to excite said RF coil for acquisition of MR imaging data;
• means (2) for sensing a portion of said signal at the frequency .omega..sub.1 reflected by said RF coil as a result of the interaction of the generated signal with the RF coil and the subject;
• means (3) for comparing the generated and reflected signals at the frequency .omega..sub.1 to provide a trigger signal at the frequency .omega..sub.1 whose characteristics are linearly related to the physiological motion of the imaging slice;
• and
• means (4) for receiving the trigger signal and in response thereto signal the acquisition of MR data so that the image of the slice is not blurred by the physiological movement of the slice.