Patient Monitoring During Magnetic Resonance Imaging Exams by Means of Ballistocardiography

Karen Meyer zu Hartlage, Enrico Pannicke, Johannes Passand, Georg Rose, Ralf Vick
Otto von Guericke University Magdeburg


Introduction: Magnetic resonance imaging (MRI) has become indispensable in modern medicine. MRI is used for diagnostic purposes as well as for guiding minimally invasive interventions. In many cases, it is necessary to monitor the vital signs of the patient, particularly the heart rate and the heart rhythm, during an MRI exam. These parameters are usually obtained from the patient’s electrocardiogram (ECG) or via pulse oximetry. Both techniques, however, require an additional preparation of the patient and are prone to errors under certain conditions. In order to avoid an additional patient preparation and to circumvent the mentioned errors, this work makes use of the ballistocardiographic (BCG) effect for obtaining a heart rate estimate. Material and Methods: To measure body motions caused by the BCG effect, an inflated air cushion was integrated into the MRI patient table in the position of the upper chest. An external pressure sensor placed outside the MR scanner detected the pressure changes caused by the BCG effect. A synchronously acquired ECG was used as reference for evaluation purposes. Five subjects were included in this preliminary study. The measurements were performed inside a 3T MRI scanner. Results: The measurements showed a high agreement between the heart rates estimated from the ECG and the BCG signals. Signal artifacts lead to false positive or false negative detections in subjects which moved during the measurement procedure. Discussion and Conclusion: This preliminary study showed the feasibility of using BCG signals for patient monitoring during MR exams. Because patients are asked to remain in resting positions, only minor artefacts were observed during the measurements and can be expected during real measurements. In conclusion, this approach enables patient monitoring during MRI exams and eliminates the time-consuming patient preparation.