Contrast-enhanced ultrasound applications in liver transplant imaging

Contrast-enhanced ultrasound (CEUS) in the follow-up of abdominal solid organ trauma: an international survey prior to the PseAn study

BACKGROUND

The blunt and penetrating abdominal trauma follow-up relies on contrast CT scan to detect solid organ injuries. CEUS is not widely used worldwide, despite its accuracy and feasibility in identifying parenchymal and vascular lesions. This survey aims to define the current use of CEUS in Trauma Centers and the expectations of Emergency Surgeons regarding its role.

METHODS

We sent an online questionnaire composed of 10 questions to trauma physicians worldwide during the period of September 2022 to March 2023.

RESULTS

59 participants from 53 different centers answered the questionnaire. 76.2% of the enrolled participants have CEUS available at their Institution, and 49.2% think that it can replace CT scan. Contrast-CT scan remains the preferred option in the follow-up of blunt liver (69.5%), spleen (72.9%) and kidney (76.3%) injuries, followed by CEUS which is used in 18.6% for liver, 20.3% for spleen and 15.3% for kidney injuries. The results are similar for penetrating abdominal trauma, with contrast CT scan being the first-line imaging technique (91.5% for liver, 91.5% for spleen and 88.1% for kidney injuries), followed by CEUS (5.1% for liver, 5.1% for spleen and 6.8% for kidney injuries).

CONCLUSIONS

Our survey shows that CEUS is still underutilized in the follow-up of abdominal trauma, even though many emergency surgeons consider it as a valid alternative to contrast CT scan.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

European Society of Pediatric Radiology survey of perioperative imaging in pediatric liver transplantation: (3) postoperative imaging

BACKGROUND

Liver transplantation is the state-of-the-art curative treatment for end-stage liver disease. Imaging is a key element in the detection of postoperative complications. So far, limited data is available regarding the best radiologic approach to monitor children after liver transplantation.

OBJECTIVE

To harmonize the imaging of pediatric liver transplantation, the European Society of Pediatric Radiology Abdominal Taskforce initiated a survey addressing the current status of imaging including the pre-, intra-, and postoperative phases. This paper reports the responses related to postoperative imaging.

MATERIALS AND METHODS

An online survey, initiated in 2021, asked European centers performing pediatric liver transplantation 48 questions about their imaging approach. In total, 26 centers were contacted, and 22 institutions from 11 countries returned the survey.

RESULTS

All sites commence ultrasound (US) monitoring within 24 h after liver transplantation. Monitoring frequency varies across sites, ranging from every 8 h to 72 h in early, and from daily to sporadic use in late postoperative phases. Predefined US protocols are used by 73% of sites. This commonly includes gray scale, color Doppler, and quantitative flow assessment. Alternative flow imaging techniques, contrast-enhanced US, and elastography are applied at 31.8%, 18.2%, and 63.6% of sites, respectively. Computed tomography is performed at 86.4% of sites when clarification is needed. Magnetic resonance imaging is used for selected cases at 36.4% of sites, mainly for assessment of biliary abnormalities or when blood tests are abnormal.

CONCLUSION

Diagnostic imaging is extensively used for postoperative surveillance of children after liver transplantation. While US is generally prioritized, substantial differences were noted in US protocol, timing, and monitoring frequency. The study highlights potential areas for future optimization and standardization of imaging, essential for conducting multicenter studies.

Liver Transplant Imaging prior to and during the COVID-19 Pandemic

BACKGROUND

The suspension of the surgical activity, the burden of the infection in immunosuppressed patients, and the comorbidities underlying end-stage organ disease have impacted transplant programs significantly, even life-saving procedures, such as liver transplantation.

METHODS

A review of the literature was conducted to explore the challenges faced by transplant programs and the adopted strategies to overcome them, with a focus on indications for imaging in liver transplant candidates.

RESULTS

Liver transplantation relies on an appropriate imaging method for its success. During the Coronavirus Disease 2019 (COVID-19) pandemic, chest CT showed an additional value to detect early signs of SARS-CoV-2 infection and other screening modalities are less accurate than radiology.

CONCLUSION

There is an emerging recognition of the chest CT value to recommend its use and help COVID-19 detection in patients. This examination appears highly sensitive for liver transplant candidates and recipients, who otherwise would have not undergone it, particularly when asymptomatic.

First-Pass Arrival Interval of Ultrasound Contrast Medium in the Hepatic Artery and Portal Vein as a Marker for Assessment of Liver Transplant Recipients

BACKGROUND

This study measures the first-pass arrival times in the hepatic artery and portal vein of the transplanted liver using contrast-enhanced ultrasound (CEUS) and assess its correlation with graft performance in the early posttransplant period.

METHODS

This study evaluated 35 liver transplant recipients who underwent CEUS examination within 1 month of transplant surgery. CEUS under contrast-specific harmonic imaging mode were recorded for 60 seconds immediately after intravenous administration of microbubble ultrasound contrast medium (Sonazoid, GE Healthcare, Oslo, Norway). The recorded video clips were reviewed by 2 readers to determine the first-pass arrival times in the hepatic artery and portal vein, and the difference between the 2 was defined as the arterial-portal arrival interval (APAI). Laboratory data on the same date of CEUS examination were collected as indicators to correlate with APAI.

RESULTS

The intra- and inter-rater reliability for APAI measurement were excellent, with intraclass correlation coefficients > .95. The mean APAI was 4.5 ± 1.8 seconds (range, 2.0-10.5 seconds). The APAI was positively correlated with the serum total bilirubin level (r = 0.357, P = .035) and negatively correlated with the platelet count (r = -0.354, P = .037). At the 5 second cutoff point, a total serum bilirubin of >8 mg/dL was reported in 5 of 11 patients (45.4%) with APAI of >5 seconds and in only 3 of 24 patients (12.5%) with APAI of <5 seconds (P < .05).

CONCLUSIONS

The APAI is a quantitative marker that links the hemodynamics and the clinical status of the liver graft.

Non-occlusive hepatic artery hypoperfusion syndrome and imaging findings: a systematic review

Non-occlusive hepatic artery hypoperfusion syndrome (NHAHS), in other words, splenic steal, is a rare disorder that can arise following liver transplantation. After liver transplantation, its frequency has been defined as between 0.6 and 10.1%. The diversion of flow from hepatic to splenic arteries results in low perfused hepatic artery which causes elevated liver enzymes, hyperbilirubinemia, and graft dysfunction. This may result from a high resistance in the hepatic arteries, enlarged splenic arteries, a limited hepatic arterial flow due to high portal flow, or a discordance of the graft size and hepatic arterial flow. There may be a need for some prophylactic and/or posttransplant treatment procedures. We aimed to describe pre and post-treatment imaging findings of NHAHS.

Noninvasive markers of liver steatosis and fibrosis after liver transplantation - Where do we stand?

In the last two decades, advances in immunosuppressive regimens have led to fewer complications of acute rejection crisis and consequently improved short-term graft and patient survival. In parallel with this great success, long-term post-transplantation complications have become a focus of interest of doctors engaged in transplant medicine. Metabolic syndrome (MetS) and its individual components, namely, obesity, dyslipidemia, diabetes, and hypertension, often develop in the post-transplant setting and are associated with immuno-suppressive therapy. Nonalcoholic fatty liver disease (NAFLD) is closely related to MetS and its individual components and is the liver manifestation of MetS. Therefore, it is not surprising that MetS and its individual components are associated with recurrent or "de novo" NAFLD after liver transplantation (LT). Fibrosis of the graft is one of the main determinants of overall morbidity and mortality in the post-LT period. In the assessment of post-LT steatosis and fibrosis, we have biochemical markers, imaging methods and liver biopsy. Because of the significant economic burden of post-LT steatosis and fibrosis and its potential consequences, there is an unmet need for noninvasive methods that are efficient and cost-effective. Biochemical scores can overestimate fibrosis and are not a good method for fibrosis evaluation in liver transplant recipients due to frequent post-LT thrombocytopenia. Transient elastography with controlled attenuation parameter is a promising noninvasive method for steatosis and fibrosis. In this review, we will specifically focus on the evaluation of steatosis and fibrosis in the post-LT setting in the context of de novo or recurrent NAFLD.