Abstract: 【Objective】 To investigate the value of intravoxel incoherent motion (IVIM) diffusion weighted imaging (DWI) on quantitative assessment of normal placental perfusion. The secondary aim was to investigate whether placental perfusion changes with increasing gestational age in normal pregnancy during the second and third trimester. 【Methods】 The study population included 54 singleton pregnancies who underwent MR examination for some suspected minor congenital abnormality

uterine artery pulsatility index (PI) was measured by Doppler ultrasound and placental perfusion was measured by IVIM Echo-planar imaging at 1. 5T in whole placental regions for each woman. Fifty-four pregnancies were divided into three groups according to gestational age (GA): groupⅠ: 22-26 weeks (n = 14)

Ⅱ: 27-33 weeks (n = 25)

Ⅲ: 34-40 weeks (n = 15). IVIM-DWI protocol: respiratory- triggered DWI with one set of 11 b-values: 0

10

30

50

70

100

150

200

500

800

1000 s/mm2. Maps of perfusion fraction (f)

pseudodiffusion coefficient (D*) and standard diffusion coefficient (D) were generated automatically by using PRIDE DWI tool with bi-exponential fit

and then measured by two practitioners using image-post-processing software Image J. Reproducibility of parameters measurement were determined by interclass correlation coefficient (ICC). Difference of Parameters (D

D*

f) between three GA groups were compared by one-way ANOVA analysis. Regression analysis was used to examine the significance of the association between placental perfusionfraction(f) and GA and uterine artery PI values. 【Results】 f (ICC = 0.808

P < 0.001) and D (ICC = 0. 881

P < 0. 001) measurements demonstrated good reproducibility

while D* (ICC = 0.754

P < 0. 001) measurement showed poorer reproducibility. One way ANOVA analysis showed that there wassignificant difference in famong three GA groups (33.81± 2.94)

(29.41± 2.70)

(27.71 ± 1.53)%

respectively (P = 0.000). Whiledifference of D(1.28 ± 0.12) × 10-3

(1.32 ± 0.14) × 10-3

(1.27 ± 0.15) × 10-3 mm2/s

respectively (P = 0.591) and D* (80.82 ± 9.86) × 10-3

(81.33 ± 12.55) × 10-3

(81.28 ± 10.30) × 10-3 mm2/s

respectively (P = 0.982) in three GA groups showed no statistical significance. Regression analysis demonstrated that f correlated negatively with GA (r = -0.790

P < 0.05). The median uterine artery PI was 0. 74. There were significant association between uterine artery PI and placental perfusion assessed by IVIM (r = 0.833

P < 0.05). 【Conclusion】 Perfusion fraction (f) can be used as a stable and reliable index to evaluate placenta perfusion

which offering a new choice for the pregnant women who cannot use contrast agent. Placental perfusion measured by IVIM Echo-planar imaging was found to be strongly associated with impedance to flow in the uterine arteries. The value of f showed a trend of decrease while GA is increasing on second and third trimester.