Quantitative MRI of the Placenta

1
Quantitative MRI of the Placenta

• Penny Gowland
• Sir Peter Mansfield Magnetic Resonance Centre
• University of Nottingham
• Castang Trust, October 2003

2
MR in pregnancy?

• Uterine abnormalities
• Pelvimetry
• Structural scanning for congenital abnormalities.

39 weeks
3

qMRI in pregnancy?

• Assessing fetal growth
• Quantifying utero-placental blood flow and
  placental structure.
• Monitoring fetal organ maturation, in particular
  fetal brain development.

4
Anatomical MRI
5
Organ volume measurement

• Can organ volume measurements predict FGR with
  high specificity?

36 weeks
6
Comparison to ultrasound

• Standard 2D Ultrasound uses growth charts to
  relate 1D measurements (eg crown-rump length) to
  fetal weight
• 3D ultrasound is being introduced
• Ultrasound results are adversely affected by
  bowel gas, amniotic fluid and obesity

Placenta
Fetal Brain
Fetal Liver
Fetal Lung
36 weeks
7
Liver volume measurements in FGR
FGR Normals
US
MRI
8
Liver volume measurements in FGR
Underestimation by 3D ultrasound
Normals
FGR
3-D Ultrasound
Ribs probably lead to underestimation with
ultrasound. Ultrasound data taken from Laudy et
al. Ultrasound Obstet Gynecol 1998
9
Fetal brain volume MRI v US
USS
MRI
18 GA (weeks) 40
10
Functional MRI

• Placental structure

11
Placental transverse relaxation
Single spin-echo EPI
Magn. Res. Imag., 16, 3, 241-246, 1998.
12
Placental longitudinal relaxation
NS/S IR EPI
Magn. Res. Imag., 16, 3, 241-246, 1998.
13
Placental structure

• Infection would classically increase relaxation
  times
• Thrombosis would decrease relaxation times
• Lesions usually bright

• NMR relaxation times give information about
  tissue properties
• macromolecule concentration (MT, T2)
• water binding (T1, T2)
• Tissue oxygenation? (T2)
• viscoelastic properties in future?

14
Functional MRI

• Blood flow through the placenta

15
Blood flow through placenta

• Determined by
• maternal delivery to placenta
• fetal placental flow
• mixing within the placenta
• MRI can measure
• uterine artery blood flow
• spiral artery blood movement
• movement of blood in placenta

16
Uterine vessel blood flow
Fetal brain
Uterine vein
Static
Flowing
17

Placental blood movement

• Inflow (FAIR)
• similar to perfusion, multidirectional
• Gradient sensitization (IVIM)
• a moving blood volume which depends on blood
  velocity and sequence parameters
• Tagging ?
• Transit times ?

18
FAIR Perfusion
gt1000 500-1000 300-500 lt100
Perfusion rate ml/100g/min
19
Perfusion Histograms
Low perfused fraction increased for low IBR
Lancet 19983511397-99
20
Measuring IVIM perfusing fraction

• f measures the volume of randomly flowing blood
  as a fraction of the voxel-volume of water

21
Raw IVIM images

• Regions of interest data fitted to 4 parameters
• S(b) So f e-bD (1-f) e -bD
• D diffusion coefficient, D is the
  pseudodiffusion coefficient, f is the perfusing
  fraction

0545
b 3 s/mm
b 15 s/mm
2
2


Fluid
Lungs
b 80 s/mm
b 47 s/mm

2
2

22
Placental IVIM summary

• Normal placenta generally maternal zone contains
  a significantly greater perfusing fraction
  compared to the fetal zone.
• Compromised pregnancy generally the maternal
  zone has a reduced perfusing fraction however,
  the fetal zone appears normal

IUGR
Normal
Perfusing fraction ()
0
50
100
23
IVIM of basal plate

• 3 pixel width ROI chosen to lie over basal plate
  (only identified in certain orientations)
• Measure the pattern of signal attenuation in this
  region
• Eliminate scans affected by motion

Basal plate ROI
24
Basal plate IVIM
60
Normal Longitudinal
50
Normal Cross sectional
Pre-eclampsic
40
IUGR
f
30
Cross sectional groups f reduced in PE (p lt
0.005)
?
20
10
0
15
25
35
45
Gestation (weeks)

• Depends on
• Blood volume AND blood velocity
• Number of spiral arteries recruited
• Lumen diameter

25
Fetal maturation
20 weeks 053301
26 weeks 056902
Brain
Liver
Lung
20 weeks
26 weeks
26
Fetal fMRI
Results
Hearing
Seeing
27
Conclusion

• MRI has the potential to become an important tool
  in
• managing fetuses with abnormalities
• managing compromised pregnancies
• understanding the aetiology of IUGR and PE
• studying normal and abnormal fetal brain
  development
• Prospective studies, and more detailed studies of
  high risk pregnancies are required.

28
Acknowledgements

• Physicists
• Jon Fulford
• Rachel Moore
• Damien Tyler
• Sir Peter Mansfield
• Biologists
• Billy Dunn
• Terry Mayhew
• Technical
• Paul Clark
• Ron Coxon

• Clinicians
• Ian Johnson
• Phil Baker
• Stephen Ong
• Keith Duncan
• David James
• Bryony Strachen
• Shantilla Vadeyar
• Our Volunteers