title: Placental magnetic resonance imaging T2* measurements in normal pregnancies and in those complicated by fetal growth restriction.
abstract: OBJECTIVE
  The magnetic resonance imaging (MRI) variable transverse relaxation time (T2*) depends on multiple factors, one important one being the presence of deoxyhemoglobin. We aimed to describe placental T2* measurements in normal pregnancies and in those with fetal growth restriction (FGR).
  
  
  METHODS
  We included 24 normal pregnancies at 24-40 weeks' gestation and four FGR cases with an estimated fetal weight below the 1(st) centile. Prior to MRI, an ultrasound examination, including Doppler flow measurements, was performed. The T2* value was calculated using a gradient echo MRI sequence with readout at 16 different echo times. In normal pregnancies, repeat T2* measurements were performed and interobserver reproducibility was assessed in order to estimate the reproducibility of the method. Placental histological examination was performed in the FGR cases.
  
  
  RESULTS
  The method was robust regarding the technical and interobserver reproducibility. However, some slice-to-slice variation existed owing to the heterogeneous nature of the normal placenta. We therefore based T2* estimations on the average of two slices from each placenta. In normal pregnancies, the placental T2* value decreased significantly with increasing gestational age, with mean ± SD values of 120 ± 17 ms at 24 weeks' gestation, 84 ± 16 ms at 32 weeks and 47 ± 17 ms at 40 weeks. Three FGR cases had abnormal Doppler flow, histological signs of maternal hypoperfusion and a reduced T2* value (Z-score < -3.5). In the fourth FGR case, Doppler flow, placental histology and T2* value (Z-score, -0.34) were normal.
  
  
  CONCLUSIONS
  The established reference values for placental T2* may be clinically useful, as T2* values were significantly lower in FGR cases with histological signs of maternal hypoperfusion. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Department of Obstetrics and Gynecology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Sinding
authors.affiliation: Department of Clinical Engineering, Central Denmark Region, Aarhus, Denmark.
authors.forename: D A
authors.initials: DA
authors.lastname: Peters
authors.affiliation: Department of Radiology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: J B
authors.initials: JB
authors.lastname: Frøkjaer
authors.affiliation: Department of Obstetrics and Gynecology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: O B
authors.initials: OB
authors.lastname: Christiansen
authors.affiliation: Department of Pathology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Petersen
authors.affiliation: Department of Obstetrics and Gynecology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Uldbjerg
authors.affiliation: Department of Obstetrics and Gynecology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Sørensen
mesh_terms: D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010920:Placenta / Q000000981:diagnostic imaging*; D011247:Pregnancy; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal / Q000379:methods
keywords: MRI; T2*; fetal growth restriction; placenta; reproducibility; transverse relaxation time