title: PP084. Magnetic resonance imaging measurements of T2 relaxation times within contrasting regions of murine placenta is dependent upon blood flow.
abstract: BACKGROUND
  It has been postulated that reduced placental perfusion as a result of abnormal placental implantation is the initiating event that leads to the maternal symptoms of preeclampsia. To be able to directly measure blood flow and perfusion in the placenta in experimental models of preeclampsia would provide valuable insight into the structural abnormalities of this syndrome. Magnetic resonance imaging (MRI) offers visualization of anatomy and analysis of changes in tissue morphology and function including blood flow and perfusion. The major source of image contrast in MRI comes from the variation in relaxation times between tissues. Previously, human placenta has appeared as fairly homogeneous in studies of T1 and T2 relaxation times, with no internal morphology apparent.
  
  
  OBJECTIVE
  The aim of this study was to investigate, using much higher field strengths (11.7Tesla) and much higher resolution than have been used previously, whether structural inhomogeneities in the placenta can be discerned by T2 mapping and whether T2 mapping is capable of detecting structural abnormalities that may affect blood flow in a preeclamptic placenta.
  
  
  METHODS
  Magnetic resonance images were acquired on an anaesthetised C57BL/6JArc mouse placed in a vertical animal probe using a Bruker Avance 11.7Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e., 1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest within 5 individual placenta. Additional T2 measurements were acquired on the same slices immediately after blood flow was reduced to zero.
  
  
  RESULTS
  Three distinct regions of T2 contrast were discerned in the mouse placenta, likely correlating to the labrynthine, junctional and decidual zones. The contrast between the inner two regions was substantially abrogated when blood flow ceased upon euthanasia of the animal by anaesthetic overdose (p<0.005), whereas the decidual region remained unchanged (p=0.13).
  
  
  CONCLUSIONS
  These results demonstrate that morphologically distinct regions of the mouse placenta can be detected through the mapping of T2 relaxation times. The contrast between regions is lost when blood flow ceases and the placenta becomes homogeneous in appearance, suggesting that differences in T2 relaxation times across regions of the placenta may be used to non-invasively examine structural abnormalities and blood flow in the placenta of experimental animal models of preeclampsia.
authors.affiliation: School of Medicine, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Bobek
authors.affiliation: Nanoscale Organisation and Dynamics, University of Western Sydney, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Stait-Gardner
authors.affiliation: School of Medicine, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Surmon
authors.affiliation: School of Medicine, Australia; The Heart Research Institute, University of Sydney, Sydney, Australia; Liverpool Hospital, Liverpool, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Makris
authors.affiliation: School of Medicine, Australia; Nanoscale Organisation and Dynamics, University of Western Sydney, Australia.
authors.forename: W S
authors.initials: WS
authors.lastname: Price
authors.affiliation: School of Medicine, Australia; Nanoscale Organisation and Dynamics, University of Western Sydney, Australia; The Heart Research Institute, University of Sydney, Sydney, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Hennessy