Fractional moving blood volume in fetal organs estimated using power Doppler ultrasound

Abstract: Power Doppler ultrasound (PDU) is a sensitive technique to detect slow blood movement. The aim of the present study was to develop a standardized method for quantification of the PDU signals recorded from a specific region of interest (ROI) within fetal organs. The quantification method - fractional moving blood volume (FMBV) - compensating for factors potentially affecting the final results, e.g., depth and attenuation, was compared with the previous method of PDU signal quantification, the mean pixel intensity (MPI). FMBV was estimated in the lungs of 29 healthy fetuses at 35-37 weeks of gestation. The FMBV values were in the range of 27-47% (mean 36.2%) and showed less variation than the MPI values. FMBV in the adrenal glands of 8 fetal lambs exposed to severe asphyxia was compared with blood perfusion measurements with radioactive micrsopheres (RMS) and a high correlation between the two methods was found (r=0.90). The reproducibility of the fetal lung FMBV estimation, performed by two experienced operators in 20 normally grown human fetuses at 32-35 weeks of gestation, was good with an intraclass correlation coefficient of 0.92 and interclass correlation coefficient of 0.70. FMBV was estimated in the lungs of 47 normally grown (NG) and 25 intrauterine growth restricted (IUGR) fetuses after 32 weeks of gestation. The NG fetuses showed a higher lung FMBV values than the IUGR fetuses (p=0.003). Finally, FMBV was estimated in the fetal adrenal gland of lamb fetuses exposed to severe hypoxia. FMBV was maintained for 5 min of severe asphyxia; thereafter a significant reduction in FMBV occurred. After resuscitation, the neonatal adrenal gland FMBV and cortisol levels were significantly higher in the asphyctic than in control lambs. The results of this study indicated that the standardized FMBV is a reliable method for assessment of fetal organ blood circulation.