Inutero Diffusion Measurements to Asses Fetal Lung Maturation'

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In-utero Diffusion Measurements to Asses Fetal
Lung Maturation.

• R J. Moore, P. Tokarczuk, B. Issa, K Duncan,
• R. Bowtell, B. Worthington,
• P Baker, I Johnson, P. A. Gowland
• Magnetic Resonance Centre, Department of Physics,
  Nottingham University, Department of Obstetrics
  and Gynaecology, City Hospital, England.

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Introduction

• Clinical Aspects
• Development of the fetal lung.
• Technical Aspects
• Echo Planar Imaging in obstretrics.
• Diffusion and the PGSE sequence.
• Experiment
• Methods and results in normal healthy pregnancy.
• Conclusions

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Fetal Lung Development

• 16 Weeks - Vascularization of the terminal
  tubules increasing the surface area
  available for gas exchange.
• 26 Weeks - Production of phospholipid
  surfactant to prevent fetal lung collapse
  at birth.

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Clinical Implications

• 90 of infants delivered before 28 weeks and
• 50 of infants delivered before 32 weeks
• suffer from Respiratory Distress Syndrome.
• The production of surfactant is tested with
  Amniocentesis.
• There is currently no method of assessing
  vascular changes before 26 weeks.

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Echo Planar Imaging (EPI)in Fetal Medicine

• Short imaging time.
• freezes physiological motion.
• minimises patient discomfort or stress.
• Minimal RF power deposition.
• The image is acquired in a single shot.
• Susceptibility of the fetus and the surrounding
  tissue are well matched.

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Imaging Parameters

• 130 ms per image
• 22 images in total
• repetition rate 10s
• 128 x 128 matrix size
• 7 mm slice thickness
• 2.5 x 3.5 mm in plane
• resolution
• Sagittal Reconstruction

0309
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Diffusion imaging
180o
90o
time
r.f.
?
G
br_grad

?
imaging
EPI
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Diffusion Parameters

• b ?2 G2 ?2 ??- ?/3
• Where
• ? 40 ms, ? 13 ms
• Eleven values of b where used
• ranging from 0 to 500 s/mm2
• All diffusion gradients where
• applied on the broadening axis.

b 0 s/mm2
b 3 s/mm2
b 47 s/mm2
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Subjects and Methods

• Gestational ages ranged from 20 to 39 weeks,
  n25.
• A transverse multislice set was initially
  acquired to locate the lungs and measure their
  volume.
• An appropriate slice was selected for further
  diffusion imaging.

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Data Analysis

• Regions Of Interest where chosen over the fetal
  lung.
• Averaged signal was fitted to the expression
• S(b) So e-bD
• to calculate the diffusion coefficient, D.

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Results

• D increases at a rate of 0.08 m2/s per week
• p lt 2 x 10-5
• Before 26 weeks D(AVE) 1.4/-0.3 m2/s (n7)
• After 26 weeks D(AVE) 2.3/-0.5 m2/s (n18)

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The Variation of Diffusion With Gestational Age
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Conclusions

• This Study reports the first in-vivo
• measurements of fetal lung diffusion, and
• demonstrates that D increases during
• gestational age.
• These measurements potentially provide an
• indication of fetal lung maturation from 20
• weeks gestation to term.

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Acknowledgements

• This work was financed by the medical
• research council.
• We would like to thank Dr R Coxon and
• Mr P. Clarke for their technical support.