Introduction
Superb microvascular Imaging (SMI), a recent blood flow imaging technique produced by Canon Medical Systems (Japan), employs a unique algorithm to minimize motion artifacts by eliminating signals based on the analysis of tissue movement. Compared to the conventional color Doppler imaging methods, SMI can significantly better visualize low-velocity blood flow in small vessels 1, which allows depiction of the pathology and diagnoses of placental abnormalities. Placental pathological examination is retrospectively performed after delivery to evaluate placental abnormalities that could have resulted in complications during pregnancy. However, if it is possible to predict the pathological findings antenatally using ultrasound examination, it would be useful to understand the disease state and predict the prognosis. Therefore, we investigated the evaluation of placental pathologic findings using SMI.
Using SMI, in a normal placenta, villous blood vessels can be visualized from the umbilical cord insertion to the stem villi and terminal villi. Additionally, slow blood flow in the intervillous space from the spiral artery is also visualized as a ”scatter” that matches the heart rate of the mothers. In contrast, we previously demonstrated, in placenta increta, not only the thin myometrium with invasive placental tissue, but also the avascularity of the peripheral villous tree and congested stem vessels using SMI 2.
Furthermore, in a pilot study, we demonstrated various placental pathological findings antenatally using SMI and compared them with placental pathological findings 3. According to our investigations, pathologically confirmed placental infarctions are expressed in echo-free space without both villous trees and background scatters. In cases of avascular villi, only background ’scatter’ was expressed in SMI. Consequently, it was confirmed that the findings of SMI match the pathological findings.
In the present study, in order to demonstrate objectivity and reproducibility, the diagnostic accuracies of various ultrasound findings of the pathologic placenta were evaluated. The aim of the present study was to clarify the accuracy of antenatal ultrasound evaluation using SMI for placental pathological findings.