MRI Measurement Of Fetal Renal Volume And Amniotic Fluid

ObjectiveTo explore the feasibility of measuring fetal kidney volume (FKV)and amniotic fluid volume accurately with MRI.To explore FKV correlation with amniotic fluid volume, gestational weeks (GW) and gender.To compare the amniotic fluid volume measured with MRI and 2D ultrasound and evaluate diagnostic value of amniotic fluid index(AFI) to estimate abnormal amniotic fluid volume.Methods1. Five rabbits were examined by MRI with axial, sagittal and coronal sections(slices thickness of 5mm and interval space of 0.5mm), and the volume of 10 kidneys was measured on the workstation of MRI system. After autopsy,the volume of 10 kidneys was practically measured,and then MRI error rate was calculated. In addition, the best scanning section was chosen.2. Two postmordem female fetuses (aging 29 and 31 weeks respectively) were placed in round polypropylene containers with formalin solution (specimens completely immersed in solution). Then the kidney volume (slices thickness of 5mm and interval space of 0.5mm)and solution volume(slices thickness of 8mm and interval space of 0.5mm) were measured on the axial images. After autopsy, the volume of fetal kidneys and solution was practically measured and then MRI error rate was calculated.3. MRI volumetric measurement of fetal kidney and amnion fluid was performed in 114 fetuses ranging from 30 to 39 weeks gestation without any urinary abnormality,which was confirmed by MRI and follow-up. Before MRI examination 2D ultrasound was performed in all pregnant women and AFI was measuered.4.The reliability study of MRI volumetric measurement of fetal kidney was performed in 5 rabbits and 10 fetuses between interobserver and intraobserver. Statistical analysis was used for all data. Results1. The best scanning section of rabbit kidneys was axial. The correlation coefficient(CC) of MRI renal volume with the practice was 0.991 and the mean MRI error rate was (2.26±0.55)%.2. The mean MRI error rate was (2.41±0.14)% in the kidneys of postmordem fetuses.It was (6.73±0.38)% in the solution of specimen.3. The kidneys of 114 fetuses ranging from 30 to 39 weeks gestation were shown clearly in MRI and FKV could be measured successfully. The mean FKV at 30th GW was (6.42±1.28) cm3 and become as large as (14.14±2.26) cm3 at 39th GW. The correlation coefficient of the renal volume with amniotic fluid volume was r= 0.127 (P>0.05) and with GW r=0.766(P＜0.05). The renal volume of male fetuses was bigger than that of female at the same GW (P＜0.05). The correlation coefficient of the amniotic fluid volume with AFI was r=0.804 (P<0.05). The AFI detection rate was low in oligohydramnios4. The CC of twice measurements between intraobserver was 0.987 and 0.963 in rabbits and fetuses respectively; They were 0.975 and 0.906 between interobserver. Conclusion1. The validity and reliability of MRI volume measurements were high, FKV and amniotic fluid volume of late pregnancy could be measured by MRI successfully and accurately. MRI volumetic measurement was able to provide reliable reference data for clinical obsteric work.2. The FKV was correlate with GW, but not with amniotic fluid volume. The kidney volume of male fetuses was bigger than that of female fetuses.3. The AFI detection rate was low in oligohydramnios.