Method for identifying R waves in an ECG signal and an ECG measuring instrument as well as a magnetic resonance device

An ECG measuring instrument, comprising:

• an ECG channel for measuring:
• a reference ECG signal of a patient in an environment without being disturbed by an gradient field of a magnetic resonance device, and
• an ECG signal of the patient in an environment being disturbed by the gradient field of the magnetic resonance device;
• and
• a processing unit adapted to:
• identify an R wave in the reference ECG signal;
• determine a reference quantity from the reference ECG signal in a time interval starting before the R wave and lasting maximum up to an occurrence of the R wave using the processing unit;
• create a first comparison rule from the reference quantity comprising an optimal filter and outputting a similarity value using the processing unit;
• compare the measured ECG signal with the reference quantity based on the first comparison rule;
• create a second comparison rule comprising determining a deviation of the reference quantity from the measured ECG signal multiplied by a factor using the processing unit, wherein the factor is dependent on the similarity value of the first comparison rule;
• compare the measured ECG signal with the reference quantity based on the second comparison rule;
• and
• issuing a trigger signal for the magnetic resonance device if results of the comparison based on the first and the second comparison rules are positive.

A magnetic resonance device, comprising:

• an ECG measuring instrument for measuring:
• a reference ECG signal of a patient in an environment without being disturbed by an gradient field of the magnetic resonance device, and
• an ECG signal of the patient in an environment being disturbed by the gradient field of the magnetic resonance device;
• and
• a processing unit adapted to:
• identify an R wave in the reference ECG signal;
• determine a reference quantity from the reference ECG signal in a time interval starting before the R wave and lasting maximum up to an occurrence of the R wave using the processing unit;
• create a first comparison rule from the reference quantity comprising an optimal filter and outputting a similarity value using the processing unit;
• compare the measured ECG signal with the reference quantity based on the first comparison rule;
• create a second comparison rule comprising determining a deviation of the reference quantity from the measured ECG signal multiplied by a factor using the processing unit, wherein the factor is dependent on the similarity value of the first comparison rule;
• compare the measured ECG signal with the reference quantity based on the second comparison rule;
• and
• issue a trigger signal for the magnetic resonance device if results of the comparison based on the first and the second comparison rules are positive.