Intra-voxel incoherent motion MRI of the living human foetus: technique and test-retest repeatability

Abstract

Background: Our purpose was to test the within-subject (test-retest) reproducibility of the perfusion fraction, diffusion coefficient, and pseudo-diffusion coefficient measurements in various foetus organs and in the placenta based on the intra-voxel incoherent motion (IVIM) principle.

Methods: In utero diffusion-weighted IVIM magnetic resonance imaging (MRI) was performed in 15 pregnant women (pregnancy age 21-36 weeks) on 1.5-T and 3.0-T clinical scanners with b-factors in the range of 0-900 s/mm² in 16 steps. A bi-exponential model was fitted on the volume-averaged diffusion values. Perfusion fraction (f), diffusion coefficient (d), and pseudo-diffusion coefficient (D*) were calculated. Within-subject reproducibility was evaluated as test-retest variability (VAR %) of the IVIM parameters in the foetal frontal cortex, frontal white matter, cerebellum, lungs, kidneys, liver, and in the placenta.

Results: For the foetal lungs, liver and the placenta, test-retest variability was in the range of 14-20% for f, 12-14% for d, and 17-25% for D*. The diffusion coefficients of the investigated brain regions were moderately to highly reproducible (VAR 5-15%). However, f and D* showed inferior reproducibility compared to corresponding measures for the lungs, liver, and placenta. The IVIM parameters of the foetal kidney were revealed to be highly variable across scans.

Conclusions: IVIM MRI potentially provides a novel method for examining microvascular perfusion and diffusion in the developing human foetus. However, reproducibility of perfusion and diffusion parameters depends greatly upon data quality, foetal and maternal movements, and foetal-specific image post-processing.

Keywords: Diffusion-weighted imaging (DWI); Foetus; Intra-voxel incoherent motion (IVIM); Magnetic resonance imaging (MRI); Repeatability (reproducibility); Test–retest variability.

Fig. 1

Post-processing steps to correct fetal in utero IVIM datasets for subject motion

Fig. 2

VOI delineation of various foetal organs and the placenta. VOIs have been manually delineated to test the within-subject repeatability of the parameters that are calculated from IVIM data. Red overlay: manual outlines of the organs. Background image: coronal or axial DW images

Fig. 3

IVIM imaging in utero. a Bi-exponential model fitting on the DWI measurements that have been acquired with increasing b-factor. b IVIM imaging of the placenta. Left: coronal T2-weighted image; middle: DW image (placenta delineated); right: IVIM signal and estimates of the diffusion coefficient d, pseudo-diffusion coefficient D* and the microvascular perfusion fraction f, based on VOI-averaged values. c IVIM image of a sacrococcygeal teratoma

Fig. 4

Foetal brain. a DW axial images showing the foetal brain at the level of the third ventricle. b Perfusion fraction map at the same level. c IVIM model fitting curve of the foetal brain based on a frontal white matter VOI. d DW axial images showing the foetal brain and the central part of the placenta. e Perfusion fraction map at the same level. f IVIM curve of the central placenta. Cross: central part of the placenta, asterisk: basal plate of the placenta

Fig. 5

a–c Congenital diaphragmatic hernia: hypoplastic left lung (arrow); normal right lung. a T2-weighted coronal image. b DWI, b-factor = 0 image. c IVIM perfusion fraction map showing decreased microvascular perfusion fraction in the hypoplastic left lung. d–f Congenital cystic adenomatoid formation of the right lung. d Coronal T2-weighted image showing a hyperintense abnormality at the inferior lobe of the right lung. e DWI, b-factor = 0 image. f IVIM perfusion fraction map showing a demarcated zone of decreased microvascular perfusion fraction in the affected region of the inferior lobe (arrow)

Fig. 6

IVIM imaging of a foetus that has moved considerably during the acquisition. a T2-weighted image. b DW image. c Bi-exponential fitting based on the IVIM measurements. Sudden changes in position and foetal breathing movements cause particularly large displacements of foetal abdominal organs, such as the liver (red outline, middle image), and increase or decrease the measured signal intensity (red arrows)