Analysis and correction of ballistocardiogram contamination of EEG recordings in MR.
OBJECTIVE
To examine the influence of cardiac activity-related head movements and varying blood pulse frequencies on the shape of electroencephalography (EEG) recordings in a high magnetic field, and to implement a post-processing technique to eliminate cardiac activity-related artifacts.


METHODS
Respiratory thoracic movements, changes of blood pulse frequency and passive head movements of 20 healthy subjects were examined outside and inside an MR magnet at rest in a simultaneously recorded 21-channel surface EEG. An electrocardiogram (ECG) was recorded simultaneously. On the basis of the correlation of the left ventricular ejection time (LVET) with the heart-rate, a post-processing heart-rate dependent subtraction of the cardiac activity-related artifacts of the EEG was developed. The quality of the post-processed EEG was tested by detecting alpha-activity in the pre- and post-processed EEGs.


RESULTS
Inside the magnet, passive head motion but not respiratory thoracic movements resulted in EEG artifacts that correlated strongly with cardiac activity-related artifacts of the EEG. The blood pulse frequency influenced the appearance of the cardiac activity-related artifacts of the EEG. The removal of the cardiac activity-related artifacts of the EEG by the implemented post-processing algorithm resulted in an EEG of diagnostic quality with detected alpha-activity.


CONCLUSIONS
When recording an EEG in MR environment, heart rate-dependent subtraction of EEG artifacts caused by ballistocardiogram contamination is essential to obtain EEG recordings of diagnostic quality and reliability.
Jäger
L
L
Institut für Klinische Radiologie, Klinikum Grosshadern, Universität München. jaeger@med.uni-muenchen.de
Hoffmann
A
A
Werhahn
K J
KJ
Reiser
M F
MF
D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001450:Ballistocardiography / Q000379:methods*; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D019416:Head Movements; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009068:Movement; D015203:Reproducibility of Results; D012149:Restraint, Physical / Q000379:methods*; D012680:Sensitivity and Specificity