*4.2.1. Autopsy imaging of human embryos and fetuses*

Additional imaging modalities can be applied for dead embryos and fetuses. Classically, solid reconstruction and fine drawing were primarily the approaches used; the first 3D morphological imaging technique was the wax plate technique, using serial histological sections of human embryos, which was developed by Born [60]. Recently, the 3D reconstruction of serial sections has been carried out by using computer graphic methods, which has made the 3D reconstruction much easier and quicker than before. The 2D image stacks generated from serial sections have a high resolution, although the issues of section registration and distortion remain unsolved. A solution to this problem is a novel imaging modality for the generation of high-resolution 3D reconstructed images [61], which uses episcopic fluorescence image capture (EFIC). In EFIC imaging, tissue autofluorescence is used to image the block face prior to cutting any section. Although the samples are sliced and some lost during the procedure, the optical resolution of EFIC is reported to reach approximately 5–6 μm [62].

MRI is a useful imaging modality, not only for living prenatal embryos and fetuses, but also for dead embryos and fetuses in autopsy imaging. Despite the longer time taken to capture images, the higher resolution is definitely an advantage; the time required for a high-resolution imaging ranges from several hours to days. MR devices should be selected depending on the sample size; specially, MR microscopy, clinical MRI, and experimental MRI are suitable for small-sized embryos, larger fetuses, and embryos/fetuses with an intermediate size, respectively [39] (**Figure 5**) [2, 63, 64].

X-ray imaging is also used for dead embryos and fetuses. Since there is no need to consider the impact of radiation exposure on the tissue, longer time may be devoted to capture high resolution images. Conventional (absorption-contrast) X-ray CT (cCT) is used for fetal skeletal imaging (**Figure 6A** and **B**). Phase-contrast X-ray CT (pCT) is another method of X-ray imaging [40]. Since X-rays are electromagnetic waves, phase-contrast X-ray imaging is capable of recording the phase-shift of X-rays while passing through the samples and reconstructing 2D/3D images of the samples in combination with CT. An embryo or an early fetus, mostly composed of soft tissue, is suitable for pCT imaging (**Figure 6C** and **D**).

Ultrasonography of living embryos and fetuses is very commonly performed nowadays, and many malformations can be diagnosed during the early prenatal period. In the cases of pregnancy termination, not all the aborted fetuses are dissected and pathologically diagnosed, due to technical difficulties associated with the dissection of small fetuses. However, the imaging modalities presented here can be used for autopsy imaging of embryos and fetuses, regardless of their size. If any clue to the fetal anomaly (that might have led to the abortion) could be identified by using these imaging modalities, supplemented by appropriate genetic tests, then a final accurate diagnosis can be obtained. Based on the final diagnosis, parents would be provided with sufficient detailing of their lost pregnancy, which would enable them to receive a genetic counseling prior to the next pregnancy.

The imaging modalities described in this section are summarized in **Figures 5** and **6**. The appropriate modalities for imaging dead embryos or fetuses should be used depending on the stage of pregnancy.
