The placenta plays an important role in the growth rate of the fetus and its well-being and its dysfunction is associated with neonatal morbidity, such as intrauterine growth restriction (IUGR), the delivery of small-for-gestational age (SGA) neonates. Recently, quantitative values obtained from MRI has been reported in many articles for identifying indexes of placental dysfunction or fetal well-being ［1-3］. Half-Fourier acquisition single-shot turbo spin-echo (HASTE) imaging is now widely used for placental and fetal imaging due to its rapidity and its low sensitivity to fetal movement［4］.The placental T2 relaxation time is known to be one of the noninvasive biomarkers for IUGR in both human and animal models［2,5-8］. T2 relaxation time has been reported to be associated with placental dysfunction, birth of small neonate, complicated pregnancies such as pre-eclampsia and so on［5,7］. However, the measurements of T2 relaxation time on MRI is time-consuming and not easy for clinical usage. If placental dysfunction is predicted quantitative value obtained from HASTE image, it will be a great advantage to evaluating placental well-being. This study aimed to investigate the index of placental dysfunction by using HASTE imaging.This prospective study included 41 singleton pregnancies who underwent MRI examinations within period from February 2014 to June 2015, carried out in the Department of Gynecology and Obsterics. All examinations were performed using a 1.5-Tesla MR units (Avanto; Siemens Healthcare), with our routine placental MRI protocol, including three direction of HASTE images, and additionally measurements of T2 relaxation times. As quantitative evaluation, the six signal intensity ratio(SIR)s measured using HASTE images were included to comparing the correlation with T2-values of placenta. The six SIRs were as follows: the placental SIR to the amniotic fluid (SIR_{pl/amn. flu.} ＝ placental mean SI_HASTE / mean SI amniotic fluid), to the fetal ocular globes (SIR_{pl/ocular globe}), to the gastric fluid (SIR_{pl/gastric flu.}), to the bladder (SIR_pl/bladder), to the maternal psoas major muscles (SIR_{pl/psoas muscle}) and to the maternal abdominal subcutaneous adipose tissue (SIR_{pl/adipose tissue}). The measurements were performed by one reader. In cases with delivered placenta, we compared T2 relaxation time and SIR_{pl/psoas muscle} between histopathologically abnormal and normal placentas in 3rd trimester.Thirty-nine placentas were calculated T2 relaxation time and signal intensity ratio(SIR)s and the following cases were excluded due to oligohydramnios (n=1), chronic abruption-oligohydramnios sequence(CAOS)(n=1). Among these 39 cases, histopathological examinations were performed on 21cases (normal 12 cases, abnormal 9cases). Since other 15 were regarded as “normal placenta” clinically, pathological diagnoses were not performed. The remaining two cases could not followed and one placenta was remained within the uterus due to placenta accreta. The most significant correlation with placental T2 relaxation time were observed with SIR_{pl/psoas muscle} (r= -0.4145, p= 0.0087; Fig.1), and there is a weak association between placental T2 relaxation and SIR_{pl/ocular globe} (r= -0.3414, P=0.033). In the comparison between histopathologically abnormal (n=11) and normal (n=20) placentas in 3rd trimester, the value for normal placenta was higher in both T2 relaxation times and SIR_{pl/psoas muscle}, though there was no significance (p=0.016, p=0.098, respectively).This study revealed that placental signal intensity ratio(SIR) in HASTE imaging was well associated with placental T2 relaxation time, which has been known to show close correlation with placental dysfunction. Especially, the placental signal intensity ratio to the maternal psoas major muscles (SIR_{pl/psoas muscle}) showed the best correlation to T2 relaxation times of placenta. The signal intensity of maternal psoas major muscles can be obtained without effect of motion artifact of the fetus such as amniotic fluid and bladder. In addition, there was possibility that SIR_{pl/psoas muscle} may have relation with fetal outcomes. Since HASTE image is now essential sequence for fetal imaging, radiologists may indicate the placenta and fetal functional condition using SIR_{pl/psoas muscle} in addition to the morphological information.