Amplitude demodulation of the electrocardiogram signal (ECG) for respiration monitoring and compensation during MR examinations

A method for respiration monitoring during MR-sequences using the electrocardiogram signal (EGG) is presented. The basic principle is known in conventional patient monitoring and is based on the fact that the amplitude of the EGG-signal varies with respiratory motion, A demodulation of this ''cardiorespiratory signal'' yields a respiration curve that can be used for patient monitoring, triggering, or respiration compensation of MRI sequences, Since no drift is introduced by digital demodulation, this method is superior to analog signal processing. The proposed method was applied during MR examinations using an optically coupled ECG sensor that has the advantage of almost negligible interference due to the MR sequences (much less than 10% of the main ECG signal), The respiration signal obtained is strongly correlated (r = 0.79 to 0.98) with the position of the diaphragm in inferior-superior direction measured during breath-holding MRI.