Tham khảo tài liệu 'new developments in biomedical engineering 2011 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 432 New Developments in Biomedical Engineering second-order-gradiometer pickup ỡ2Bz ỡz2 with a baseline of 70 mm. The flux transformer was assumed to be electronically balanced to CB 10-3 Vazquez-Flores 2007 . Fig. 5. The prevalence of principal classes of fetal presentation along gestation as observed in 2 276 subjects by Scheer and Nubar 1976 . Another significant factor affecting fMCG waveform morphology and the SNR is fetal presentation. Fetal presentations are categorized into three principal classes cephalic breech and transverse. Scheer and Nubar 1976 made an exhaustive study of 2 276 pregnant women in which they classified their respective babies into one of the principal presentations. The observed prevalence of fetal presentations in the longitudinal study is summarized in Fig. 5. There is limited published information about the SNR variation and changes in fMCG waveform morphology for various fetal presentations Horigome et al. 2006 . Although the incidence of cephalic presentation increases with increasing gestational age the non-cephalic presentation is a common occurrence in early pregnancy when the fetus is highly mobile within a relatively large volume of amniotic fluid. Figure 6 illustrates rather large changes occurring in magnetic field distribution Bz component above a gravid abdomen GA 40 weeks calculated for cephalic presentation and various axial rotations of fetal body Biomagnetic Measurements for Assessment of Fetal Neuromaturation and Well-Being 433 Fig. 6. Magnetic field normal component distribution above a gravid abdomen GA 40 weeks for a cephalic presentation for various fetal body rotations. Biomagnetic modeling data show that up to 30 signal amplitude variation is possible due to fetal body rotation Vazquez-Flores 2007 . 4. Biomagnetic Signal Processing and QRS Detection The beat-to-beat changes in fetal heart rate may be masked by incorrect signal processing and QRS detection procedures. Although a wide diversity of QRS detection .
