Comparison of micro-flow imaging and contrast-enhanced ultrasonography in assessing segmental congestion after right living donor liver transplantation

Abstract

Purpose: This study aimed to determine whether micro-flow imaging (MFI) offers diagnostic performance comparable to that of contrast-enhanced ultrasonography (CEUS) in detecting segmental congestion among patients undergoing living donor liver transplantation (LDLT).

Methods: Data from 63 patients who underwent LDLT between May and December 2022 were retrospectively analyzed. MFI and CEUS data collected on the first postoperative day were quantified. Segmental congestion was assessed based on imaging findings and laboratory data, including liver enzymes and total bilirubin levels. The reference standard was a postoperative contrast-enhanced computed tomography scan performed within 2 weeks of surgery. Additionally, a subgroup analysis examined patients who underwent reconstruction of the middle hepatic vein territory.

Results: The sensitivity and specificity of MFI were 73.9% and 67.5%, respectively. In comparison, CEUS demonstrated a sensitivity of 78.3% and a specificity of 75.0%. These findings suggest comparable diagnostic performance, with no significant differences in sensitivity (P=0.655) or specificity (P=0.257) between the two modalities. Additionally, early postoperative laboratory values did not show significant differences between patients with and without congestion. The subgroup analysis also indicated similar diagnostic performance between MFI and CEUS.

Conclusion: MFI without contrast enhancement yielded results comparable to those of CEUS in detecting segmental congestion after LDLT. Therefore, MFI may be considered a viable alternative to CEUS.

Keywords: Contrast-enhanced ultrasound; Diagnostic accuracy; Hepatic congestion; Living donor liver transplant; Micro-flow imaging.

Fig. 1.. Flow diagram of the study population.

LDLT, living donor liver transplantation; MFI, micro-flow imaging; CEUS, contrastenhanced ultrasonography.

Fig. 2.. icro-flow imaging and vascular area index quantification in a transplanted liver graft.

A representative example of a microflow imaging examination is shown, with P5 positioned as the central anatomical landmark in the intercostal view. To ensure reproducibility, the gain was set to 45% to properly capture vascularity. Inset: For the quantification of the vascular area index using ImageJ, the target area on the anterior segment of the transplanted liver graft was manually outlined (indicated by the yellow dotted line), with the right hepatic vein serving as the boundary. The imaging depth was set at 4 cm from the liver capsule.

Fig. 3.. A 63-year-old man with class A liver cirrhosis (A, B) and a 43-year-old woman with Budd-Chiari syndrome (C, D), both of whom underwent living donor liver transplantation without reconstruction of the middle hepatic vein territory.

A. A vascular area index was 5.3% on a micro-flow image (MFI). No flow signal is evident in V5 (arrow) on the MFI image, indicating the presence of segmental congestion. B. Contrast-enhanced ultrasonography (CEUS) reveals low echogenicity of the affected parenchyma during the portal venous phase, further verifying the presence of segmental congestion. Consequently, this patient was confirmed to have segmental congestion. C. A vascular area index was 1.0% on MFI, with the absence of flow signal within V5 (indicated by the arrow) confirming MFI congestion. D. Subsequently, CEUS was performed. CEUS reveals low echogenicity of the affected liver parenchyma during the portal venous phase, confirming CEUS congestion. The patient was ultimately diagnosed with segmental congestion.

Fig. 4.. A 48-year-old man with class B liver cirrhosis who underwent living donor liver transplantation.

Segmental congestion was not evident on ultrasound or computed tomography images. A. The vascular area index was 22.8% on microflow imaging (MFI), which exceeded the cutoff value; thus, it did not indicate segmental congestion. The arrow on the MFI image indicates flow signals within V5 and its branches. B. Contrast distribution in the portal venous phase was uniform on the contrast-enhanced ultrasonography image.