Optimal filter design for shielded and unshielded ambient noise reduction in fetal magnetocardiography

The greatest impediment to extracting high-quality fetal signals from fetal magnetocardiography (fMCG) is environmental magnetic noise, which may have peak-to-peak intensity comparable to fetal QRS amplitude. Being an unstructured Gaussian signal with large disturbances at specific frequencies, ambi...

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Bibliographic Details
Published in:Physics in medicine & biology 2005-12, Vol.50 (23), p.5509-5521
Main Authors: Comani, S, Mantini, D, Alleva, G, Di Luzio, S, Romani, G L
Format: Article
Language:English
Subjects:
Algorithms
Arrhythmias, Cardiac
Fetal Heart - pathology
Fetal Monitoring - methods
Gestational Age
Heart Rate, Fetal
Humans
Magnetics
Magnetoencephalography - instrumentation
Magnetoencephalography - methods
Models, Statistical
Normal Distribution
Pattern Recognition, Automated
Prenatal Diagnosis
Signal Processing, Computer-Assisted
Software
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Summary:The greatest impediment to extracting high-quality fetal signals from fetal magnetocardiography (fMCG) is environmental magnetic noise, which may have peak-to-peak intensity comparable to fetal QRS amplitude. Being an unstructured Gaussian signal with large disturbances at specific frequencies, ambient field noise can be reduced with hardware-based approaches and/or with software algorithms that digitally filter magnetocardiographic recordings. At present, no systematic evaluation of filters' performances on shielded and unshielded fMCG is available. We designed high-pass and low-pass Chebychev II-type filters with zero-phase and stable impulse response; the most commonly used band-pass filters were implemented combining high-pass and low-pass filters. The achieved ambient noise reduction in shielded and unshielded recordings was quantified, and the corresponding signal-to-noise ratio (SNR) and signal-to-distortion ratio (SDR) of the retrieved fetal signals was evaluated. The study regarded 66 fMCG datasets at different gestational ages (22-37 weeks). Since the spectral structures of shielded and unshielded magnetic noise were very similar, we concluded that the same filter setting might be applied to both conditions. Band-pass filters (1.0-100 Hz) and (2.0-100 Hz) provided the best combinations of fetal signal detection rates, SNR and SDR; however, the former should be preferred in the case of arrhythmic fetuses, which might present spectral components below 2 Hz.
ISSN:0031-9155
1361-6560
DOI:10.1088/0031-9155/50/23/006