Results
The examples of 2D vs. 3D lung segmentations for 4 cases are depicted in
Figure 2; motion corruption of the axial-plane stack can clearly be
appreciated in the coronal plane, with the coronal section of the DSVR
shown alongside each case. DSVR was able to produce clear images even
from severely motion-corrupted stacks (Figure 2C) and the resultant
images can be examined in any plane and at a higher resolution than that
of the original input stack (Figure 1, Video 1). The resultant
segmentation of fetal lungs demonstrates a smooth outline, with normal
cases depicting sufficient detail even to appreciate the lingula (Figure
2A) or a systemic feeding vessel in cases of CLL (Figure 2B). Comparison
of the volumes generated from 2D and 3D segmentation is made in Figure
3; results correlated strongly, however a consistently lower measurement
was made with 3D segmentation (Bland-Altman: Bias
-1.44cm3 [95% confidence limits -2.63 to -0.24]).
This was felt to be due to the enhanced ability to exclude structures of
the vascular hilum in 3D reconstructions, as well as an inherent
reduction in interpolation error.
Having defined the fidelity of DSVR-derived 3D TLV, we proceeded to
produce a normal curve based upon 100 healthy cases undergoing fetal MRI
as normal controls for research, presented in Figure 4. The
corresponding fitted TLV normogram has a high correlation with the
previously reported gestational TLV curves produced from conventional 2D
segmentation data by Cannie et al11 and Meyers et
al12. The generated regression line had a similar
R2 (0.72) to those published and was subsequently used
to generate the “Expected” value for the depiction of
Observed:Expected total lung volume in the abnormal cases.
The manually segmented 2D lung volumes and corresponding DSVR lung
volumes are depicted graphically in Figure 5 with reference to the
DSVR-derived normal curve. Table 1 displays data calculated from anomaly
cases. CPAM lesion volumes were calculated from DSVR reconstructions and
are presented as a percentage of the remaining TLV; of note one case had
CDH and a BPS of the lung on the same side as the hernia, this case had
significantly smaller lesion volume related to lung volume.