Fetal abdominal blood vessels and organ microvasculature detected by Slow<i>flow</i> HD

Abstract

With the latest advances in color and power Doppler ultrasound, such as superb microvascular imaging (SMI), it is possible to visualize clearly the small fetal peripheral blood vessels, fetal organ microvasculature and placental microvasculature. We have shown previously that SMI with an 18-MHz probe can be used to depict clearly fetal intra-abdominal blood vessels and organ microvasculature; however, this high-resolution abdominal probe allows only near-field visualization because of its shallow penetration1. SlowflowHD™ (Voluson E10 BT19; GE Healthcare, Zipf, Austria) is a new Doppler modality which can detect the low flow velocities of smaller fetal vessels in branching vascular beds2. This technique has a high-display frame-rate, high-line density (high resolution) and good sensitivity. We present our experience with SlowflowHD to depict fetal intra-abdominal blood vessels and organ microvasculature. Twenty-six normal fetuses of low-risk pregnancies at 18–38 weeks of gestation and one fetus with left multicystic dysplastic kidney at 31 + 4 weeks were studied. Approval from the Ethics Committee of Miyake Clinic was obtained to examine these patients and all participants provided oral informed consent following a detailed explanation of the planned examinations. SlowflowHD examinations were performed by an experienced operator (T.H.), using a transabdominal linear probe (C2-9-D, 3–9 MHz; GE Healthcare). The parallel course of the descending aorta and inferior vena cava, and their branches, were visualized clearly (Figures 1 and S1). The celiac artery giving rise to the splenic and common hepatic arteries, as well as the superior mesenteric artery, renal artery and inferior mesenteric artery, were identified (Figure S2). The inferior vena cava, portal vein, adrenal vein, renal vein and common iliac vein were also depicted clearly (Figures 1, 2, S1, S3 and S4). The hepatic microvasculature had a fishnet-like appearance (Figure 3) while the splenic microvasculature showed a honeycomb-like appearance (Figure 4). Each adrenal artery was clearly noted using SlowflowHD (Figure S5). The renal microvasculature had a camphor tree-like appearance (Figure S6). In the fetus with left multicystic dysplastic kidney, decreased microvasculature in the renal parenchyma was evident in the left kidney, whereas abundant blood vessels were depicted in the normal right kidney (Figure S7). Numerous studies have used conventional color/power Doppler to assess fetal intra-abdominal arteries3 and veins4. However, the image quality of conventional Doppler techniques can be poor and does not allow clear identification of the small intra-abdominal blood vessels and organ microvasculature. We have shown here that this can be achieved using SlowflowHD. Previously, we were able to visualize fetal intra-abdominal organ microvasculature using SMI with Doppler Luminance1. However, the microvasculature patterns differ slightly between SMI with Doppler Luminance and SlowflowHD. When using SMI with Doppler Luminance, the hepatic microvasculature showed a coral-like appearance, compared with the fishnet-like appearance seen with SlowflowHD, the splenic microvasculature had a palisade arrangement of small vascular trees, compared with the honeycomb-like appearance seen in the current study, and the renal microvasculature had a baobab tree-like appearance compared with the camphor tree-like appearance seen with SlowflowHD. The reason for these differences is unclear. One possible explanation is the different ultrasonic frequency of the probes used, which was 18 MHz in SMI with Doppler Luminance and 3–9 MHz in this study. Another possible explanation is the subjective assessment of fetal intra-abdominal organ microvasculature in both studies. SlowflowHD may prove to be a valuable diagnostic tool in clinical practice and research. It can provide novel information for the antenatal diagnosis of fetal intra-abdominal anomalous vascularity, such as intra-abdominal umbilical vein varix, persistent right umbilical vein or agenesis of the ductus venosus5, and abnormal organ microvasculature, such as hepatoblastoma, hepatic hemangioma, polycystic kidney or multicystic dysplastic kidney. In the current study, decreased renal microvasculature was noted in a case with left multicystic dysplastic kidney. The main limitations of SlowflowHD were motion artifacts and noise due to fetal heartbeats, fetal movements and maternal respiratory movements. Maternal obesity also influenced the ability to discern the fetal intra-abdominal vasculature due to poor penetration of the Doppler beam. Future technical advances in SlowflowHD are likely to resolve these limitations. Figure S1 Fetal intra-abdominal blood vessels depicted using SlowflowHD at 19 + 2 weeks. Ao, descending aorta; IVC, inferior vena cava; LCIA, left common iliac artery; LCIV, left common iliac vein; LRA, left renal artery; RCIA, right common iliac artery; RCIV, right common iliac vein; RRA, right renal artery. Figure S2 Fetal intra-abdominal blood vessels depicted using SlowflowHD at 24 + 3 weeks (a,b), 19 + 2 weeks (c) and 38 + 6 weeks of gestation (d). AA, adrenal artery; AG, adrenal gland; Ao, descending aorta; BL, bladder; CA, celiac artery; CHA, common hepatic artery; IMA, inferior mesenteric artery; IVC, inferior vena cava; LK, left kidney; LRA, left renal artery; LRV, left renal vein; RPV, right portal vein; RRV, right renal vein; S, spleen; SA, splenic artery; SMA, superior mesenteric artery; Sp, spine; St, stomach; UV, umbilical vein. Figure S3 Fetal hepatic vessels depicted using SlowflowHD in 31-week fetus. Ao, descending aorta; DV, ductus venosus; IVC, inferior vena cava; PS, portal sinus; RPV, right portal vein; UV, umbilical vein. Figure S4 Fetal adrenal vein (AV) depicted using SlowflowHD at 37 + 6 weeks of gestation. AG, adrenal gland; Ao, descending aorta; IVC, inferior vena cava; L, liver. Figure S5 Fetal adrenal microvasculature depicted using SlowflowHD at 38 + 6 weeks of gestation. AG, adrenal gland; Ao, descending aorta; IAA, inferior adrenal artery; IVC, inferior vena cava; L, liver; MAA, middle adrenal artery; S, spleen; SA, splenic artery; Sp, spine; St, stomach. Figure S6 Fetal renal microvasculature depicted using SlowflowHD at 31 + 4 weeks of gestation. Ao, descending aorta; IVC, inferior vena cava; RK, right kidney; RRA, right renal artery; RRV, right renal vein. Figure S7 Images of right (a) and left (b) kidneys obtained using SlowflowHD in 31 + 4-week fetus with left multicystic dysplastic kidney. Arrow indicates decreased microvasculature in left kidney (LK). Abundant blood vessels are seen in normal right kidney (RK). Ao, descending aorta; IVC, inferior vena cava. 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