Superb Microvascular Imaging (SMI) Compared with Color Doppler Ultrasound for the Assessment of Hepatic Artery in Pediatric Liver Transplants: A Feasibility Study

Abstract

(1) Background: Despite progression in surgical techniques and immunological treatments, hepatic artery (HA) thrombosis and stenosis still develop as an early or late liver transplant (LT) complication. We aimed to compare superb microvascular imaging (SMI) with conventional Doppler imaging (CDI) in the assessment of HA in a cohort of pediatric patients undergoing follow-up ultrasound (US) for LT. (2) Methods: This prospective, observational study included 73 pediatric LT recipients (median age, 7 years; IQR, 5.8 years; 35 females) who underwent US during LT follow-up from March to December 2019. For each examination, CDI and SMI were separately assessed in terms of HA visibility and spectral waveform morphology (SWM). The former was scored based on HA discrimination from the blooming signal of the surrounding vessels, as follows: 0, not visible; 1, majority course hardly distinguishable; and 2, majority course clearly distinguishable. The latter was scored on a two-point scale: 0, combined venous and arterial SWM, and 1, pure arterial SWM. The patient’s overall score was finally calculated by adding the two individual scores. (3) Results: Both the absolute scores and frequency of overall scores equal to 3 (maximum global score) were higher using SMI compared with CDI. The median overall score was 3 for SMI and 2 for CDI (p = 0.011; IQR = 1). An overall score equal to 3 was obtained in 74% and 49.3% of the study population using SMI and CDI, respectively (p = 0.002). This was attributable to a better score in HA visibility (p = 0.007). (4) Conclusions: SMI has shown promise for assessing HA in pediatric LT recipients, possibly serving as a complementary non-invasive tool of CDI in everyday practice.

Special Issue on “Advances in Image-Guided Diagnosis and Treatment of Abdominal Diseases”

“…SMI proved to be comparable to contrastenhanced ultrasound with a higher than 90% agreement compared to the standard of reference, computed tomography angiography. Also, Collaku et al [2] investigated the role of SMI in another interesting but very selected vascular application. The authors showed the added value of the technique, coupled with conventional color Doppler, in order to enhance the visibility of the hepatic artery in pediatric patients with liver transplants.…”

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“…During the last decades, different US developments have been introduced, including elastography, contrast-enhanced US (CEUS), and novel doppler techniques[ 6 - 9 ].…”

“…CEUS is useful for lesion detection and characterization in several clinical settings, without the use of ionizing radiations and with higher temporal resolution compared to CT or MRI[ 6 ]. It can be useful in non-oncologic, non-cirrhotic patients[ 6 , 9 ], for the assessment of incidental focal lesions, in cirrhotic patients, allowing characterization of contrast enhancement patterns of hepatocellular carcinoma (HCC) with good sensitivity and specificity[ 6 ], and in oncologic patients, providing higher sensitivity compared to the standard US for liver metastases detection and indeterminate CT or MRI lesions characterization[ 12 ]. CEUS can also be used to guide, in real-time, both focal lesions procedures[ 7 , 8 ] and locoregional ablative therapies, as well as for treatment response assessment[ 13 , 14 ].…”

“…Among novel third-generation doppler developments, US manufacturers have introduced techniques such as superb microvascular imaging (SMI) that has improved the sensitivity and accuracy of Doppler US in the assessment of hepatic vascular anatomy[ 9 ] and the detection of liver tumors vascularity with a safe, inexpensive, and readily available modality[ 6 ]. SMI is based on an adaptive algorithm that separates low flow signals from overlaying tissue motion artifacts; thereby SMI allows visualization of microscopic vessels (either native or within lesions), with no need for contrast agents injection[ 9 ].…”

Hepatic Artery Delineation on Ultrasound Volumes Comparing B-Flow and Color Doppler for Postoperative Monitoring of Pediatric Liver Transplants

“…It is less angle-dependent than Doppler-based flow techniques and has been shown to be especially useful in areas with simultaneous low and high blood flow. Its efficacy in detecting small vessels has been demonstrated across diverse clinical applications, including the hepatic vasculature in native and transplanted livers [ 14 , 15 , 16 , 17 ].…”