Dual slew-rate limiting for reducing gradient field interference in cardiac gated magnetic resonance imaging

A method is presented for minimising gradient field interference on the electrocardiogram (ECG) of a patient undergoing cardiac magnetic resonance imaging. A two lead ECG amplifier uses a single slew-rate limiter in the main signal path, this path providing the ECG signal plus slew-rate limited gradient interference from the scanner. A secondary signal path, also containing a slew-rate limiter, is derived from the main path and provides only slew-rate limited gradient interference. This signal can then be subtracted from the main path to cancel the original interference. This simple arrangement operates in real-time, needs no control signals from the scanner and has been successfully employed in a clinical environment.