Assessment of normal pulmonary development using functional MRI techniques.

BACKGROUND: The mainstay of assessment of the fetal lungs in clinical practice is via evaluation of pulmonary size, primarily using 2D ultrasound and more recently with anatomical MRI.  The emergence of advanced MR techniques such as T2* relaxometry in combination with the latest motion correction post-processing tools now facilitates assessment of the metabolic activity/perfusion of fetal pulmonary tissue in vivo.

OBJECTIVE: To characterise normal pulmonary development using T2* relaxometry, accounting for fetal motion, across gestation.

METHODS: Datasets were analysed from women with uncomplicated pregnancies that delivered at term. All subjects had undergone T2-weighted imaging and T2* relaxometry on a Phillips 3T MRI system antenatally. T2* relaxometry of the fetal thorax was performed using a gradient echo single-shot echo planar imaging sequence. Following correction for fetal motion using slice-to-volume reconstruction, T2* maps were generated using in-house pipelines. Lungs were manually segmented and mean T2* values calculated for the right and left lungs individually, and both lungs combined.  Lung volumes were generated from the segmented images and right, left and both lungs combined were also assessed.

RESULTS: Eighty-seven datasets were suitable for analysis. The mean gestation at scan was 29.9 ± 4.3 weeks (range: 20.6-38.3) and mean gestation at delivery was 40± 1.2 weeks (range: 37.1-42.4). Mean T2* values of the lungs increased over gestation for right and left individually and for both lungs assessed together (p=0.003; p= 0.04; p=0.003). Right, left, and total lung volumes were also strongly correlated with increasing gestational age (p < 0.001 in all cases).

CONCLUSIONS:   This is the largest study to date assessing the developing lungs using T2* imaging across a wide gestational age range. Mean T2* values increased with gestational age which may reflect increasing perfusion and metabolic requirements and alterations in tissue composition as gestation advances. In the future, evaluation of findings in fetuses with conditions known to be associated with pulmonary morbidity may lead to enhanced prognostication antenatally consequently improving counselling and perinatal care planning.