A Swiss research group has reported that a 0.31 tesla MRI scanner can deliver results concordant with autopsy and histology findings in postmortem fetal exams, and it can even overcome a challenge presented by autolysis in fetal autopsies.
In an article published on 26 December by the International Journal of Legal Medicine, a team led by joint first authors Dominic Gascho and Dr. Anna Kuntze from the Institute of Forensic Medicine at the University of Zurich, evaluated the efficacy of a low-field MRI scanner in postmortem imaging of fetuses. While high-field MRI is considered the gold standard for imaging in postmortem perinatal pathology, especially in instances where conventional autopsy is not performed due to legal constraints or parental refusal, it is costly, resource-heavy, and not always widely accessible.
Fetus 2, with a left-sided diaphragmatic hernia (a) characterized by displacement of the liver (1), spleen (2), and intestinal loops (3) into the left hemithorax, along with left lung hypoplasia (4) and a rightward shift of the heart (5).All figures courtesy of Dominic Gascho and Dr. Anna Kuntze and International Journal of Legal Medicine
With the limitations presented by conventional x-ray and CT in imaging soft tissue, low-field MRI can present a viable option, as it is more cost-effective and readily available than high-field MRI, the authors wrote.
The team examined three fetuses between two and six days after medical pregnancy termination using a 0.31 tesla MRI scanner originally optimized for visualizing extremities. The three fetuses were at 13, 26, and 21 weeks of gestation and weighed 12 g, 663 g, and 223 g, respectively. Autopsies and histology had been performed on all three of the fetuses.
All images were reviewed by a board-certified radiologist with more than five years of experience in postmortem forensic imaging.
Volume rendering of Fetus 1 with a virtual cut through the brain illustrates a cerebral finding in the left parietal brain (a and b). The cerebral finding is hyperintense (bright) on T2-weighted MRI (c) and a hypointense (dark) on T1-weighted MRI (d).
Gascho and colleagues determined that, through optimizing sequences specifically for the properties of fetal anatomy rather than extremities (as the system was designed for), the resulting sequences were of sufficient quality to demonstrate high agreement with autopsy and histological findings.
Low-field MRI was able to identify key anatomical abnormalities consistent with autopsy and histology: for Fetus 1, findings consistent with hydrops fetalis with generalized edema and hemorrhagic ascites; for Fetus 2, a left-sided diaphragmatic hernia; for Fetus 3, an oligocystic kidney and a defect due to gastroschisis with herniated bowel.
Fetus 3, showing a suspected oligocystic kidney (a, green circle), as well as a defect due to gastroschisis with herniated bowel (b and c, red circle).
Furthermore, MRI demonstrated a cerebral lesion that could not be recognized during autopsy in Fetus 1, the 12-g fetus at an early stage of development. According to the authors, this lesion could not be found on autopsy because of autolysis-related loss of structural integrity and partial liquefaction of the brain after the skullcap was opened.
This finding highlights that MRI can compensate for a significant limitation of fetal autopsy: MRI allows for in-situ visualization of structures and findings that may be lost due to early postmortem autolysis and subsequent loss of structural integrity.
As the authors have noted, the routine implementation of MRI as an adjunct to postmortem fetal autopsy and histology is not without practical and logistical challenges. The use of low-field MRI could overcome obstacles associated with the gold-standard high-field MRI -- namely, its availability, particularly in settings with limited resources. In addition, the study team noted the utility of postmortem imaging as a noninvasive approach in situations involving parental objections to autopsy.
In implementing the use of MRI, they added that the findings of a previous European survey on postmortem MR imaging “underscored the necessity of standardized protocols to ensure diagnostic consistency, a crucial consideration for integrating low-field MRI into routine practice.”
In a news report about the analysis by Gascho, Kuntze, and colleauges, bioengineer.org noted that “the particular magnetic environment of 0.31 tesla might reduce certain imaging artifacts commonly encountered in high-field MRI, such as susceptibility effects near air-tissue interfaces,” also remarking on the team’s optimized protocol for maintaining image quality within the specific parameters for fetal imaging.
Postmortem MRI should be considered as an adjunct to current methods, according to the authors, as it is limited in its ability to diagnose infections and metabolic disorders, even while highly effective at identifying major structural abnormalities -- thus, it cannot replace histological analysis. MR spectroscopy could be used to mitigate this limitation, further increasing the demonstrated utility and efficacy of low-field MRI, they added.
Read the full analysis here.
