Non-invasive examination apparatus and methods

A patient (B) is disposed in a region of interest of a magnetic resonance apparatus (A). During an imaging sequence, changing magnetic field gradients and radio frequency pulses are applied to the region of interest. The changing magnetic field gradients induce a corresponding electrical response in the patient. Electrodes (40) of a cardiac monitor (C) sense the electrocardiographic signal of the patient as well as the electrical response to the magnetic field gradient changes, and the monitor (C) produces an output signal having a cardiac component and a noise component. The bandwidth of the noise component varies in accordance with the changes of the magnetic field gradients. An adaptive filter (80) filters the output signal to remove the changing magnetic field gradient induced noise. The bandwidth of the filter function with which the output signal is filtered is varied or adjusted in accordance with the magnetic field gradient changes. The magnetic field gradient changes are monitored (84), their rate of change determined (88), and the bandwidth of the filter function is adjusted (92) in accordance with the rate of change. Alternately, the magnetic field gradient changes are determined a priori from a knowledge of the imaging sequence. As the imaging sequence progresses, a look-up table (150) is addressed to retrieve preprogrammed filter function information for various views or stages of the imaging sequence.