Strengths and limitations
Imaging of thick tissue (i.e., no need to make thin sections) allowed
imaging of nearly intact 3D morphology of placental villi. This
supported accurate identification of knots, bridges and sprouts, and
allowed assessment of the intact 3D organization of the villous tree and
intact microvascular networks. Classical histopathology is only able to
give a single plane 2D representation of these complex 3D structures
(Figures 1A,1B) and therefore MPM offers a better alternative. Imaging
of even larger fields of view by image stitching (2 X 2,5
mm2) is possible as demonstrated in Video S1, although
it is more time consuming (3 hours).
MPM penetration depth of unprocessed placenta is limited to
approximately 200 μm. Consequently, images of small (and frequently
incomplete) networks cause risk for sampling bias. This could be
addressed by optically clearing the tissue40, a
process that homogenizes the tissue’s refraction index, to allow imaging
down to some millimetres. Combining image stitching and optical clearing
would increase the imaged volume many fold. Larger coverage would reduce
sampling bias and improve image quantification. However, image
acquisition time would increase correspondingly.
Limited sample size only allowed to generate preliminary results, but
our goal was to demonstrate the method and its potential. Future efforts
should focus on investigating regional variation within the same
placenta (sampling bias) and variation between placentas with larger
sample size. Additionally, obtaining a complete overview of clinical
information (including doppler ultrasound findings41is crucial for future research, so that observations can be correlated
accordingly.