Abstract
Purpose
Ultrasound plays a central role in liver transplant evaluation. Acute, subacute, and chronic complications can be readily identified using grayscale and color Doppler ultrasound. Contrast-enhanced ultrasound adds a new dimension to liver transplant evaluation, depicting vascular and parenchymal processes with exquisite detail. In addition, emerging evidence suggests that contrast-enhanced ultrasound may allow for localization of biliary leak in select patients. We aimed to assess the use of multiparametric ultrasound—including grayscale, color and spectral Doppler, and contrast-enhanced ultrasound—in the setting of liver transplantation.
Methods
A literature review was performed using the MEDLINE bibliographic database through the National Library of Medicine. The following terms were searched and relevant citations assessed: “abdominal ultrasound,” “contrast-enhanced ultrasound,” “liver transplant,” and “ultrasound.”
Results
Grayscale and color Doppler ultrasound represent the mainstay imaging modalities for postoperative liver transplant evaluation. The addition of contrast enhancement plays a complementary role and can provide valuable information related to the allograft vasculature, parenchyma, and biliary tree. The appropriate implementation of grayscale, color Doppler, and contrast-enhanced ultrasound can optimize sensitivity, specificity, and accuracy for the detection of liver transplantation complications, including hepatic artery stenosis, biliary leakage, and infection.
Conclusion
Multimodal sonographic evaluation is essential to identify postoperative complications in liver transplant recipients. Contrast-enhanced ultrasound may be of value in challenging cases, providing excellent anatomic delineation and reducing the risk of false-positive and false-negative diagnoses. A broad familiarity with appropriate applications of both nonenhanced and contrast-enhanced ultrasound may help radiologists optimize allograft assessment and improve patient outcomes.
Similar content being viewed by others
Explore related subjects
Discover the latest articles, news and stories from top researchers in related subjects.Avoid common mistakes on your manuscript.
Introduction
Ultrasound plays a central role in liver transplant evaluation, representing the mainstay imaging modality for assessment of the graft parenchyma, biliary tree, and vasculature. Acute complications of liver transplantation, including perihepatic hematoma and arterial thrombosis, are readily identified using conventional grayscale and color Doppler ultrasound. Delayed complications—including biliary stricture, hepatic arterial stenosis, and allograft rejection—are also frequently diagnosed on postoperative ultrasound. Contrast-enhanced ultrasound (CEUS) has further improved sonographic evaluation of liver transplants, providing exquisitely sensitive flow visualization in the hepatic artery and portal vein and allowing for early detection of vascular complications [1]. In addition, emerging evidence suggests CEUS may improve localization of biliary leakage and characterization of biliary strictures in select patients.
In this review, we describe the use of multiparametric ultrasound for liver transplant evaluation with a special emphasis on clinical applications of CEUS. In addition, we provide case examples from our institution that illustrate the advantages of ultrasound for the diagnosis of both common and atypical liver transplant complications. The preponderance of the evidence together with our clinical experience suggests that multiparametric ultrasound is invaluable for the detection of both early and late postoperative liver transplantation complications.
Discussion
Vascular
Liver transplantation involves the creation of multiple vascular anastomoses. The surgical approach is informed by both donor and recipient related factors, including the size of the donor allograft and the native hepatic arterial anatomy. An end-to-end hepatic arterial anastomosis between the donor common hepatic artery and recipient proper hepatic artery, described as a “fish mouth” anastomosis, is the most commonly employed technique [2, 3]. However, the presence of variant hepatic arterial anatomy or donor-recipient size mismatch may necessitate more complex reconstructions; an aortohepatic conduit or double anastomosis is often used for recipients with replaced or accessory hepatic arteries [4, 5]. Caval, portal, and hepatic venous anastomotic techniques may also vary by donor and recipient anatomy. A piggyback technique involving in situ anastomosis of the donor and recipient inferior vena cava with a concomitant end-to-end portal venous anastomosis represents the most common surgical approach, but a bicaval technique or interposition graft from the superior mesenteric vein may be required in some individuals [6].
Vascular complications may occur in relation to an anastomosis or proximal or distal to the anastomotic site. Hepatic artery stenosis is the most common postoperative arterial complication, occurring in 4 to 11% of transplant recipients, and nearly always occurs at or near an anastomosis [7]. The underlying cause is likely multifactorial and related to intraoperative trauma, vascular kinking, and extrinsic compression [8]. Inflammatory processes in the setting of acute cellular rejection may also play a contributory role in some patients. Hepatic artery stenosis may occur any time after transplantation, but most commonly develops within the first year, with a median time to diagnosis of three months [9].
The hallmark sonographic finding of hepatic artery stenosis is a diminished resistive index below 0.5 and a tardus parvus waveform, characterized by prolonged systolic acceleration and diminished systolic amplitude with rounding of the systolic peak [10]. Dodd et al. suggested that three quantitative parameters may be used to establish a probable diagnosis of arterial stenosis based on Doppler ultrasound waveform: (1) resistive index less than 0.5; (2) systolic acceleration time longer than 0.08 s; and (3) peak systolic velocity greater than 200 cm/sec at the anastomosis [11]. In a subsequent study by Park et al., authors aimed to establish an optimal peak systolic velocity threshold for the diagnosis of hepatic artery stenosis. The Park group found that, in the presence of a tardus parvus waveform, a peak systolic velocity less than or equal to 48 cm/sec was 69% sensitive and 99% specific for hepatic artery stenosis [12]. Other authors have proposed that more stringent criteria should be used to increase specificity. In a 2018 analysis by Zheng et al., authors showed that using a resistive index less than 0.4 and a systolic acceleration time longer than 0.12 s significantly decreased the false-positive rate without increasing the false-negative rate in patients with hepatic arterial stenosis [13]. However, a low resistive index and tardus parvus waveform can also be seen in the setting of hepatic arterial thrombosis and arterioportal fistula, among other etiologies, and direct sonographic visualization of the stenosis at or near the anastomosis is essential to establish a definitive diagnosis.
Direct visualization of a hepatic artery stenosis can be challenging. A peak systolic velocity greater than 200 cm/sec at the anastomosis can be used to identify the area of stenosis, but the specific site and degree of stenosis can be difficult to ascertain based on Doppler ultrasound alone given that the stenosis often lies outside the liver and may be challenging to visualize. The application of CEUS may be of value to delineate the type, degree, and specific sites of stenosis, which may inform endovascular intervention [14]. In addition, limited data suggest that CEUS is more sensitive than grayscale and color Doppler ultrasound for the detection of early low-grade arterial stenosis [15]. At our institution, CEUS is commonly used to confirm suspected hepatic artery stenosis and depict the type, length, and number of stenoses for preprocedural planning.
Hepatic arterial thrombosis represents the second most common arterial complication in the early postoperative setting, with an incidence of approximately 4.4% reported in the medical literature [16]. Notably, however, the incidence of perioperative hepatic arterial thrombosis at our institution has progressively decreased over time and is now relatively rare. Delayed hepatic arterial thrombosis occurs months to years after transplantation and is somewhat less common, but may occur in up to 1.7% of recipients [17]. Irrespective of the temporal onset, the mortality rate and risk of allograft loss is high; up to one-third of patients who develop hepatic arterial thrombosis will die and over half will require a repeat transplant. However, early diagnosis significantly increases the likelihood of successful revascularization and allograft salvage [18].
The sensitivity and specificity of grayscale and color Doppler ultrasound for hepatic arterial thrombosis varies based on the time frame relative to surgery. In the immediate and early postoperative period, the reported sensitivity and specificity of ultrasound may be as high as 92% and 88%, respectively [19,20,21]. However, sensitivity is significantly lower in the setting of delayed or late hepatic arterial thrombosis, likely due to collateralization that confounds the sonographic assessment of vascular flow [22].
The classic sonographic findings of early hepatic arterial thrombosis follow a relatively predictable pattern, which was first described by Nolten and Sproat and has since been confirmed in several analyses [19]. The earliest sign of early hepatic arterial thrombosis is diminished diastolic flow, manifesting as an elevated resistive index. A resistive index of 0.8 is commonly used as a cutoff value, although correlation with laboratory values and sonographic follow-up is required to distinguish early thrombosis from expected postoperative edema. There is subsequently dampening of the systolic peak, which will ultimately progress to complete loss of hepatic arterial flow. Late hepatic arterial thrombosis presents with distinct sonographic findings due to the common presence of arterial collaterals. Sonographic features are similar to hepatic artery stenosis; a resistive index below 0.5 and tardus parvus waveforms are classically observed in these cases. In both early and late hepatic arterial thrombosis, the complete absence of vascular flow is typically considered diagnostic (see Table 1).
Caution must be applied in regard to elevated resistive indices in the early postoperative period, as an elevated resistive index alone is a relatively common and self-limited finding of no clinical consequence. In the late postoperative period, an elevated resistive index may indicate an intrinsic parenchymal process, such as rejection, and should be interpreted with consideration of the clinical context. Progressive dampening of the systolic peak with eventual loss of arterial flow is a more specific finding that is highly-suggestive of thrombosis.
Grayscale and color Doppler ultrasound represent the first-line imaging modalities to assess for hepatic arterial thrombosis in both symptomatic and asymptomatic patients. However, although the sensitivity and specificity are high, false-positive and false-negative findings are not uncommon, particularly in the late postoperative setting. Common causes of false-positive cases include hepatic parenchymal edema, vasospasm, and systemic hypotension, which are frequently present in the early postoperative period [23]. High-grade hepatic artery stenosis can also mimic thrombosis. False-negative findings most often result from the development of periportal collateral arteries, which are inadequate to perfuse the liver parenchyma and intrahepatic biliary tree but produce a normal Doppler waveform that masks underlying thrombosis [22, 24].
A delayed diagnosis of hepatic arterial thrombosis can have devastating clinical consequences. The emergence of CEUS represents a paradigm shift in the evaluation of suspected hepatic arterial thrombosis, allowing for diagnosis with strikingly high sensitivity, specificity, and accuracy. Indeed, in a 2012 prospective study by Lu et al., authors found that CEUS provided a sensitivity, specificity, and accuracy of 100, 96.9, and 92.9% for diagnosing hepatic arterial thrombosis [25]. A subsequent study by Kim et al. established that CEUS shows higher specificity and positive predictive value than computed tomography angiography (CTA) for the diagnosis of hepatic arterial thrombosis [26].
A presumptive diagnosis of hepatic arterial thrombosis is typically confirmed using CEUS at our institution. Classic findings with CEUS are easily interpreted and include absent enhancement of the intrahepatic and extrahepatic arterial supply with early enhancement of the portal vein; in the setting of a patent hepatic artery, the arteries should enhance before the portal vein, whereas in thrombosis, the portal vein will be the only vessel showing enhancement (Figs. 1 and 2). In some cases, an abrupt cutoff of the affected hepatic artery can be seen, allowing for localization of the thrombus. Hepatic parenchymal infarcts are frequently present and will show absent enhancement on arterial, portal venous, and delayed phases. The presence of hepatic arterial enhancement virtually excludes the possibility of thrombosis, preventing unnecessary angiography or surgery. Advantages of CEUS over CTA and magnetic resonance angiography (MRA) include the ability to perform dynamic imaging, allowing for multiple acquisitions and direct interrogation of areas of concern over the course of a scan, which aids in problem-solving in challenging cases. In addition, there is no ionizing radiation exposure associated with sonography, and microbubble contrast agents have few contraindications and can be safely administered to patients with renal failure or iodinated contrast allergies.
Hepatic artery pseudoaneurysms are rare, occurring in only 0.3 to 3% of transplant recipients, but may be catastrophic [27]. The mortality rate has been reported to be as high as 2 to 3% and up to 70% in the setting of rupture [28]. The majority of pseudoaneurysms develop within the extrahepatic arterial supply and are caused by underlying infection, which may occur secondary to colonization of the subhepatic space by enteric pathogens in the setting of Roux-en-Y hepaticojejunostomy. Other recognized risk factors for extrahepatic pseudoaneurysms include untreated hepatic artery stenosis, bile leak, fungal infection, adhesions, and technical factors related to surgery [29, 30]. Intrahepatic pseudoaneurysms are relatively rare and typically represent iatrogenic injuries related to prior procedures, such as liver biopsy or percutaneous biliary drainage [31]. Complications of untreated pseudoaneurysms include rupture and fistulization, either of which may manifest with rapid decompensation and death [32]. Assessment for pseudoaneurysm therefore represents a priority in the postoperative setting.
Ultrasound is the first-line imaging modality to assess for hepatic artery pseudoaneurysm. Grayscale ultrasound typically reveals a rounded or saccular outpouching arising from the hepatic artery. Color Doppler ultrasound classically shows local bidirectional flow, often referred to as the “yin-yang sign,” which is caused by turbulence within the pseudoaneurysmal sac. A corresponding “to-and-fro” spectral waveform pattern indicating blood entering the pseudoaneurysmal sac during systole and exiting the sac during diastole is typically present (Fig. 3).
Conventional ultrasound is highly-specific for the diagnosis of hepatic artery pseudoaneurysm. However, sensitivity is limited. In one study by Kim et al., authors reported that a hepatic artery pseudoaneurysm was detected in only one of eight patients using grayscale and color Doppler ultrasound [30]. Other authors have described similarly low sensitivity for extrahepatic pseudoaneurysms, although the detection rate of intrahepatic pseudoaneurysms is reportedly significantly higher, likely due to the improved sonic window [33]. False-positives are relatively uncommon, but may occur if the focally dilated appearance of a fish mouth anastomosis is mistaken for an aneurysmal sac.
The sensitivity of ultrasound for hepatic artery pseudoaneurysms is considerably higher with contrast enhancement. In one retrospective study by Ren et al., investigators reported that sensitivity increased from 37.5% with conventional ultrasound to 75% with CEUS, rivaling that of CTA [34]. Contrast enhancement is also of value for delineating the contour of the fish mouth anastomosis, reducing the likelihood of false-positive findings. In addition, hepatic artery pseudoaneurysms may occasionally develop in association with the anastomosis; CEUS provides superior anatomic detail to identify the pseudoaneurysm origin for treatment planning. At our institution, CEUS is performed for patients with a clinical presentation concerning for pseudoaneurysm but normal or equivocal sonographic findings.
Portal venous and caval complications are relatively uncommon. However, venous thrombosis and stenosis may occur in the early and late postoperative setting. The incidence of portal vein thrombosis in liver transplant recipients ranges from 0.3 to 2.6%, with thrombosis most commonly occurring within three months of surgery [35, 36]. The clinical symptomatology is variable; thrombosis in the early postoperative period typically manifests with fulminant allograft dysfunction whereas delayed thrombosis presents with sequelae of portal hypertension, such as portosystemic collateralization and ascites. Grayscale and color Doppler ultrasound is 89% sensitive and 92% specific for a diagnosis of portal vein thrombosis [37]. However, although conventional sonography is highly accurate, emerging evidence suggests that CEUS may serve as an important adjunct in equivocal cases. In a retrospective analysis by Rennert et al., authors reported that CEUS was more sensitive than grayscale and color Doppler ultrasound alone, correctly diagnosing portal vein thrombosis in cases that were previously interpreted as negative [38]. CEUS can also be used to identify small thrombi in peripheral portal venous branches and quantify the severity of portal venous insufficiency by depicting the degree and pattern of parenchymal hypoperfusion [39]. In addition, hepatocellular carcinoma may rarely develop within an allograft, and CEUS can help distinguish bland thrombus from tumor in vein, the latter of which shows avid arterial enhancement with delayed phase washout (Fig. 4) [40].
Portal vein stenosis is rare and almost always occurs at the site of an end-to-end anastomosis or at the anastomosis of an interposition jump graft from the superior mesenteric vein. Sonographic findings may include a preanastomotic-to-anastomotic velocity ratio of 1:3 or a velocity change of greater than 60 cm/sec across an anastomosis. A velocity of greater than 125 cm/sec at an anastomosis is also highly suggestive of portal vein stenosis [41]. However, elevated velocity at an anastomosis is very common in the early postoperative period secondary to edema and other non-pathologic processes, and serial sonographic follow-up may be indicated to distinguish normal perioperative findings from true stenosis. Progression from portal vein stenosis to complete thrombosis may occur if left untreated. Grayscale and color Doppler ultrasound are typically adequate to establish a diagnosis of portal vein stenosis, but CEUS may be of value to distinguish stenosis from thrombosis and identify the specific location of stenosis, the degree of pre-stenotic dilatation, and the presence hepatic parenchymal hypoperfusion [38]. Management may involve venoplasty with balloon dilatation or stenting.
Caval and hepatic vein complications may occur in up to 3% of transplant recipients. A piggyback anastomosis between the donor and recipient inferior vena cava is a common site of stenosis, which can be identified on ultrasound by the presence of a monophasic waveform, venous pulsatility index lower than 0.45, and a three-fold or greater increase in velocity across the anastomosis [42]. A modified piggyback technique using a cuff of three suprahepatic veins has reportedly been associated with a lower risk of stenosis, although stenosis may still occur and will manifest with sonographic findings similar to those seen in a conventional piggyback technique. Hepatic vein and inferior vena cava thrombosis typically occur as a result of intraoperative trauma, vessel kinking, or in relation to an underlying hypercoagulable state. Sonographic findings include a monophasic waveform or reversal of flow with CEUS showing absent or decreased contrast enhancement [15]. Hepatic vein torsion is an exceedingly rare cause of venous outflow obstruction resulting from a significant donor-recipient allograft size mismatch or inadequate hepatopexy that is characterized by flow reversal or hepatic parenchymal hypoperfusion on CEUS [43].
Biliary
Biliary complications occur in up to 30% of patients undergoing liver transplantation [44]. Bile leakage is the most common complication in the early postoperative period, with an incidence of up to 25%, and typically occurs at the ductal anastomosis [45, 46]. The risk of bile leakage may vary based on the type of biliary reconstruction performed during surgery; limited evidence suggests that a Roux-en-Y choledochojejunostomy is associated with a significantly greater risk of postoperative biliary leakage as compared to an end-to-end ductal anastomosis or duct-to-duct choledochocholedochostomy [47]. Bile leakage may also occur from a cystic duct stump or at the ductal insertion of a T-tube in patients who require temporary external biliary drainage [48].
Ultrasound is the first-line imaging modality to assess for biliary leakage. Grayscale and color Doppler ultrasound typically reveal an avascular, predominantly anechoic intrahepatic or perihepatic collection. The term “biloma” is commonly used when the collection is organized or loculated. Assessment of echogenicity can be valuable to distinguish a biloma from other early postoperative complications; although bilomas frequently contain echogenic debris, a completely anechoic collection likely represents a biloma whereas a complex or mixed echogenicity collection is suggestive of hematoma or abscess. Nevertheless, it can be challenging to distinguish a gas-containing biloma from a hepatic abscess. Moreover, bilomas can become superinfected. Other tools that may be of value to distinguish a biloma from an abscess include CEUS; the presence of arterial phase rim enhancement or a honeycomb appearance with enhancement of intralesional septae suggests a diagnosis of abscess [49]. In addition, the presence of hepatic artery stenosis favors a diagnosis of abscess over biloma. However, careful correlation of the unenhanced ultrasound findings, CEUS, and the clinical context is required to establish a presumptive diagnosis. Nuclear medicine cholescintigraphy using an iminodiacetic acid analog or magnetic resonance imaging with a hepatocyte-specific contrast agent, such as gadoxetate disodium, is required for confirmation.
There is emerging evidence suggesting that CEUS may allow for localization of biliary leakage in select patients. In a case report by Mao et al., investigators used CEUS to identify the site of biliary leak in a patient with recent T-tube removal [50]. The Mao group performed ultrasound-guided percutaneous drainage of a presumed biloma and subsequently injected a microbubble contrast agent through the catheter. The CEUS delineated the biliary tree and localized the biliary leak to the common bile duct, helping to facilitate endoscopic treatment. Other authors have used CEUS to localize biliary leakage at an anastomosis. In a 2018 review by Huang et al., authors described a sonographic technique in which administration of a microbubble ultrasound contrast agent through a drainage catheter allowed for precise localization of a biliary leak with pooling of the contrast agent near the anastomosis [51].
Biliary strictures represent the most common biliary complication of liver transplantation and may occur months to years after surgery [52]. Strictures are broadly classified into two distinct categories. Anastomotic strictures are relatively common, involve the extrahepatic bile duct, and are easily treated with endoscopic balloon dilation and stent placement with a low risk of allograft loss [53]. Nonanastomotic strictures, in contrast, typically develop secondary to an underlying pathologic process, such as infection, ischemia, or recurrence of underlying primary sclerosing cholangitis, tend to be multifocal, are difficult to treat, and have been associated with a high risk of allograft loss. Nonanastomotic strictures also tend to present earlier in the postoperative course relative to anastomotic strictures and are usually diagnosed within six months of transplantation, manifesting with progressive transaminitis and hyperbilirubinemia [54].
Intrahepatic and extrahepatic biliary ductal dilatation with abrupt narrowing is the sonographic hallmark of a biliary stricture. Multifocal or long segment narrowing is often present in the setting of nonanastomotic strictures. Small, irregular biliary tree outpouchings can occasionally be seen in the setting of nonanastomotic strictures secondary to recurrence of primary sclerosing cholangitis. The use of CEUS may be of value to assess for active biliary epithelial and periductal inflammation, which is characterized by arterial phase hyperenhancement and delayed phase hypoenhancement [55]. Ultrasound is typically adequate to establish a diagnosis of anastomotic or nonanastomotic strictures, but magnetic resonance cholangiopancreatography (MRCP) is often useful for confirmation and further anatomic delineation.
Biliary ductal necrosis and biliary cast syndrome are uncommon liver transplantation complications that occur secondary to hypoperfusion. The bile ducts are supplied solely by the hepatic artery and thus severe stenosis or thrombosis may have catastrophic downstream effects on the biliary tree [56]. The sonographic features of biliary ductal necrosis are nonspecific and may include only diffuse intrahepatic biliary ductal dilatation; the presence of biliary ductal dilatation in the absence of an obvious stricture should therefore prompt interrogation of the hepatic artery for thrombosis or stenosis. Perfusion of the biliary tree can be further assessed with CEUS, which may show biliary wall hypoenhancement in the setting of ischemia [57].
Biliary cast syndrome is readily identified on grayscale ultrasound. Early biliary cast syndrome is characterized by small periportal branching structures that are isoechoic to the surrounding liver parenchyma, which represent bile ducts that are slightly distended by sludge. Progression of biliary cast syndrome will present with hyperechoic filling defects comprised of necrotic biliary mucosa, which distend the intrahepatic and extrahepatic bile ducts. Untreated biliary cast syndrome may result in the development of biliary leakage or stricture due to progressive inflammation and necrosis [58]. There is no established role for CEUS in the setting of biliary cast syndrome.
Parenchymal
Parenchymal complications of liver transplantation may occur any time over the lifespan of an allograft. Infectious and ischemic complications tend to occur in the early postoperative period and can be reliably diagnosed using grayscale and color Doppler ultrasound with application of CEUS for challenging cases. A hepatic abscess appears as a poorly-circumscribed, complex, predominantly hypoechoic collection, often containing internal gas and hyperechoic debris. Acute hepatic infarction may appear as an ill-defined, avascular hypoechoic region with indistinct borders. Internal locules of gas with associated dirty shadowing can often be seen in the setting of necrosis. The presence of hepatic artery thrombosis supports the diagnosis. The infarcted tissue will become progressively more anechoic or cystic and well-defined over time.
A gas-containing hepatic abscess is often indistinguishable from acute parenchymal infarction on grayscale and color Doppler ultrasound. However, the “bright band” sign, defined as multiple linear echogenic bands traversing a geographic region of hypoechogenicity, is highly suggestive of infarction rather than abscess [59, 60] (Fig. 5). In addition, CEUS can reliably differentiate the two entities. A hepatic abscess demonstrates arterial phase rim enhancement or a honeycomb appearance with avid enhancement of intralesional septae (Fig. 6) [49]. Acute infarction, in contrast, demonstrates hypoenhancement relative to the surrounding liver parenchyma on both arterial and delayed phases [15]. Hepatic abscess and parenchymal infarction require entirely different management strategies and thus correlation of the “bright band” sign and CEUS can significantly improve patient outcomes in the appropriate clinical setting.
Neoplastic complications of liver transplantation occur in the late postoperative period and may include hepatocellular carcinoma, cholangiocarcinoma, and post-transplant lympholiferative disorder (PTLD). Hepatocellular carcinoma classically presents as a hypoechoic mass with internal vascular flow and a peripheral hyperechoic halo. However, many benign and malignant neoplasms, such as focal nodular hyperplasia and hepatic adenoma, may demonstrate similar sonographic features. Recent clinical data suggest that CEUS is highly-specific for the diagnosis of hepatocellular carcinoma [61]. Indeed, the American College of Radiology recently endorsed a Liver Imaging Reporting and Data System (LI-RADS) specific to CEUS [62]. At our institution, CEUS has been used to distinguish hepatocellular carcinoma from focal nodular hyperplasia and other parenchymal masses (Fig. 7).
The diagnosis of PTLD can be challenging on account of its variable sonographic appearance. A well-defined echogenic mass with a peripheral hypoechoic rim and low vascular flow is classic, but lesions may also be hypoechoic or isoechoic without detectable vascular flow. One or multiple lesions may be present [63]. Notably, opportunistic infections, such as candidiasis, may mimic PTLD on ultrasound and affect a similar patient population. Emerging data suggest that CEUS may be useful to distinguish PTLD from other infectious and neoplastic processes. In a 2021 case report, Chen et al. described the use of CEUS in an immunocompromised patient who presented with multiple unusual, avascular hypoechoic hepatic nodules [64]. The nodules demonstrated a unique enhancement pattern with early homogeneous or heterogeneous arterial enhancement followed by gradual washout during portal venous phase. Other authors have reported applications of CEUS to evaluate for PTLD at other sites [65]. Although CEUS can not be used to establish a definitive diagnosis of PTLD, it appears to be useful to exclude infection and other sonographic mimics.
Limitations of multiparametic ultrasound
Multiparametric ultrasound is invaluable for the assessment of early and late postoperative complications related to liver transplantation. However, there are several inherent limitations. Clinical findings concerning for perioperative hemorrhage should be urgently assessed with multiphase computed tomography (CT) scan, which is superior to ultrasound for the detection and localization of active bleeding. In addition, although color and spectral Doppler ultrasound represents the first-line modality to screen for hepatic arterial stenosis, CTA is often required for confirmation and preprocedural planning.
The biliary tree can be characterized using unenhanced ultrasound with or without contrast enhancement. However, MRCP is typically necessary to delineate the entirety of the biliary tree, assess for multifocal strictures, and identify secondary causes of obstruction. Cross-sectional imaging may also be required for the assessment of large bilomas that extend beyond the sonographic field-of-view, particularly if there is concern for superinfection.
The data pertaining to multiparametic ultrasound for the assessment of post-transplant neoplastic processes, including PTLD, are somewhat limited. Positron emission tomography-computed tomography (PET-CT) is preferred for the characterization of most neoplasms and to assess for distant metastatic disease. Multiparametic ultrasound is highly sensitive and specific to evaluate for hepatocellular carcinoma using CEUS LI-RADS. However, although ultrasound may be useful for the initial assessment of other malignancies, it but should be considered a screening tool in most cases.
Conclusion
Ultrasound represents the mainstay imaging modality for the assessment of vascular, biliary, and parenchymal complications following liver transplantation. The addition of CEUS may provide valuable additional information to aid in prognostication and guide management. The continued evolution of advanced sonographic techniques and technologies, including contrast enhancement, will play an important role in transplant evaluation for the foreseeable future.
Data availability
No datasets were generated or analysed during the current study.
References
Hom BK, Shrestha R, Palmer SL, Katz MD, Selby RR, Asatryan Z, Wells JK, Grant EG. (2006) Prospective evaluation of vascular complications after liver transplantation: comparison of conventional and microbubble contrast-enhanced US. Radiology. 241(1):267-74, https://doi.org/10.1148/radiol.2411050597. PMID: 16990679.
Bhargava P, Vaidya S, Dick AA, Dighe M. (2011) Imaging of orthotopic liver transplantation: review. AJR Am J Roentgenol. https://doi.org/10.2214/AJR.09.7221. PMID: 21343537.
Quiroga S, Sebastià MC, Margarit C, Castells L, Boyé R, Alvarez-Castells A. (2001) Complications of orthotopic liver transplantation: spectrum of findings with helical CT. Radiographics. 21(5):1085-102. https://doi.org/10.1148/radiographics.21.5.g01se061085. PMID: 11553818.
Ishigami K, Zhang Y, Rayhill S, Katz D, Stolpen A. (2004) Does variant hepatic artery anatomy in a liver transplant recipient increase the risk of hepatic artery complications after transplantation? AJR Am J Roentgenol. 183(6):1577-84. https://doi.org/10.2214/ajr.183.6.01831577. PMID: 15547194.
Brookmeyer CE, Bhatt S, Fishman EK, Sheth S. (2022) Multimodality Imaging after Liver Transplant: Top 10 Important Complications. Radiographics. 42(3):702-721. https://doi.org/10.1148/rg.210108. Epub 2022 Mar 4. PMID: 35245104.
Belghiti J, Kianmanesh R. (2003) Surgical techniques used in adult living donor liver transplantation. Liver Transpl. https://doi.org/10.1053/jlts.2003.50226. PMID: 14528425.
Ueno T, Jones G, Martin A, Ikegami T, Sanchez EQ, Chinnakotla S, Randall HB, Levy MF, Goldstein RM, Klintmalm GB. (2006) Clinical outcomes from hepatic artery stenting in liver transplantation. Liver Transpl. 12(3):422-427. https://doi.org/10.1002/lt.20628. PMID: 16498642.
Frongillo F, Lirosi MC, Nure E, Inchingolo R, Bianco G, Silvestrini N, Avolio AW, De Gaetano AM, Cina A, Di Stasi C, Sganga G, Agnes S. (2015) Diagnosis and management of hepatic artery complications after liver transplantation. Transplant Proc. 47(7):2150-2155. https://doi.org/10.1016/j.transproceed.2014.11.068. PMID: 26361665.
Abbasoglu O, Levy MF, Vodapally MS, Goldstein RM, Husberg BS, Gonwa TA, Klintmalm GB. (1997) Hepatic artery stenosis after liver transplantation-incidence, presentation, treatment, and long term outcome. Transplantation. 63(2):250-5. https://doi.org/10.1097/00007890-199701270-00013. PMID: 9020326.
Choi EK, Lu DS, Park SH, Hong JC, Raman SS, Ragavendra N. (2013) Doppler US for suspicion of hepatic arterial ischemia in orthotopically transplanted livers: role of central versus intrahepatic waveform analysis. Radiology. 267(1):276-84. https://doi.org/10.1148/radiol.12120557. Epub 2013 Jan 7. PMID: 23297323.
Dodd GD 3rd, Memel DS, Zajko AB, Baron RL, Santaguida LA. (1994) Hepatic artery stenosis and thrombosis in transplant recipients: doppler diagnosis with resistive index and systolic acceleration time. Radiology. 192(3):657-661. https://doi.org/10.1148/radiology.192.3.8058930. PMID: 8058930.
Park YS, Kim KW, Lee SJ, Lee J, Jung DH, Song GW, Ha TY, Moon DB, Kim KH, Ahn CS, Hwang S, Lee SG. (2011) Hepatic arterial stenosis assessed with doppler US after liver transplantation: frequent false-positive diagnoses with tardus parvus waveform and value of adding optimal peak systolic velocity cutoff. Radiology. 260(3):884-891. https://doi.org/10.1148/radiol.11102257. Epub 2011 Jul 6. PMID: 21734158.
Zheng BW, Tan YY, Fu BS, Tong G, Wu T, Wu LL, Meng XC, Zheng RQ, Yi SH, Ren J. (2018) Tardus parvus waveforms in doppler ultrasonography for hepatic artery stenosis after liver transplantation: can a new cut-off value guide the next step? Abdom Radiol. 43(7):1634-1641. https://doi.org/10.1007/s00261-017-1358-2. PMID: 29063132; PMCID: PMC6061483.
Zheng RQ, Mao R, Ren J, Xu EJ, Liao M, Wang P, Lu MQ, Yang Y, Cai CJ, Chen GH. (2010) Contrast-enhanced ultrasound for the evaluation of hepatic artery stenosis after liver transplantation: potential role in changing the clinical algorithm. Liver Transpl. 16(6):729-735. https://doi.org/10.1002/lt.22054. PMID: 20517906.
Sharafi S, Foster BR, Fung A. (2021) Contrast-enhanced ultrasound for vascular complications in the transplant liver. Clin Liver Dis. 17(3):139-143. https://doi.org/10.1002/cld.1020. PMID: 33868654; PMCID: PMC8043700.
Bekker J, Ploem S, de Jong KP. (2009) Early hepatic artery thrombosis after liver transplantation: a systematic review of the incidence, outcome and risk factors. Am J Transplant. 9(4):746-57. https://doi.org/10.1111/j.1600-6143.2008.02541.x. Epub 2009 Mar 2. PMID: 19298450.
Gunsar F, Rolando N, Pastacaldi S, Patch D, Raimondo ML, Davidson B, Rolles K, Burroughs AK. (2003) Late hepatic artery thrombosis after orthotopic liver transplantation. Liver Transpl. 9(6):605-611. https://doi.org/10.1053/jlts.2003.50057. PMID: 12783403.
García-Criado A, Gilabert R, Nicolau C, Real I, Arguis P, Bianchi L, Vilana R, Salmerón JM, García-Valdecasas JC, Brú C. (2001) Early detection of hepatic artery thrombosis after liver transplantation by doppler ultrasonography: prognostic implications. J Ultrasound Med. 20(1):51-8. https://doi.org/10.7863/jum.2001.20.1.51. PMID: 11149529.
Nolten A, Sproat IA. (1996) Hepatic artery thrombosis after liver transplantation: temporal accuracy of diagnosis with duplex US and the syndrome of impending thrombosis. Radiology. 198(2):553-559. https://doi.org/10.1148/radiology.198.2.8596865. PMID: 8596865.
Harihara Y, Makuuchi M, Takayama T, Kawarasaki H, Kubota K, Ito M, Tanaka H, Aoyanagi N, Matsukura A, Kita Y, Saiura A, Sakamoto Y, Kobayashi T, Sano K, Hashizume K, Nakatsuka T. (1998) Arterial waveforms on doppler ultrasonography predicting or supporting hepatic arterial thrombosis in liver transplantation. Transplant Proc. 30(7):3188-3189. https://doi.org/10.1016/s0041-1345(98)00988-9. PMID: 9838409.
Flint EW, Sumkin JH, Zajko AB, Bowen A. (1988) Duplex sonography of hepatic artery thrombosis after liver transplantation. AJR Am J Roentgenol. 151(3):481-483. https://doi.org/10.2214/ajr.151.3.481. PMID: 3044034.
Horrow MM, Blumenthal BM, Reich DJ, Manzarbeitia C. (2007) Sonographic diagnosis and outcome of hepatic artery thrombosis after orthotopic liver transplantation in adults. AJR Am J Roentgenol. 189(2):346-351. https://doi.org/10.2214/AJR.07.2217. PMID: 17646460.
Crossin JD, Muradali D, Wilson SR. (2003) US of liver transplants: normal and abnormal. Radiographics. 23(5):1093-114. https://doi.org/10.1148/rg.235035031. PMID: 12975502.
La Barba G, Vivarelli M, Golfieri R, Tamè MR, Caputo M, Piscaglia F, Cavallari A. (2004) Hepatic artery thrombosis and graft ischemia in the presence of preserved arterial inflow: not a contradiction but a real possibility. Liver Transpl. 10(5):710-711. https://doi.org/10.1002/lt.20163. PMID: 15108267.
Lu Q, Zhong XF, Huang ZX, Yu BY, Ma BY, Ling WW, Wu H, Yang JY, Luo Y. (2012) Role of contrast-enhanced ultrasound in decision support for diagnosis and treatment of hepatic artery thrombosis after liver transplantation. Eur J Radiol. https://doi.org/10.1016/j.ejrad.2011.11.015. Epub 2011 Dec 5. PMID: 22153745.
Kim JS, Kim KW, Lee J, Kwon HJ, Kwon JH, Song GW, Lee SG. (2019) Diagnostic performance for hepatic artery occlusion after liver transplantation: computed tomography angiography versus contrast-enhanced ultrasound. Liver Transpl. 25(11):1651-1660. https://doi.org/10.1002/lt.25588. Epub 2019 Jul 19. PMID: 31206222.
Stange B, Settmacher U, Glanemann M, Nuessler NC, Bechstein WO, Neuhaus P. (2000) Aneurysms of the hepatic artery after liver transplantation. Transplant Proc. 32(3):533-4. https://doi.org/10.1016/s0041-1345(00)00877-0. PMID: 10812100.
Piardi T, Lhuaire M, Bruno O, Memeo R, Pessaux P, Kianmanesh R, Sommacale D. (2016) Vascular complications following liver transplantation: a literature review of advances in 2015. World J Hepatol. 8(1):36-57. https://doi.org/10.4254/wjh.v8.i1.36. PMID: 26783420; PMCID: PMC4705452.
Langnas AN, Marujo W, Stratta RJ, Wood RP, Shaw BW (1991) Vascular complications after orthotopic liver transplantation. Am J Surg. 161(1):76-82, https://doi.org/10.1016/0002-9610(91)90364-j. PMID: 1987861.
Kim HJ, Kim KW, Kim AY, Kim TK, Byun JH, Won HJ, Shin YM, Kim PN, Ha HK, Lee SG, Lee MG. (2005) Hepatic artery pseudoaneurysms in adult living-donor liver transplantation: efficacy of CT and Doppler sonography. AJR Am J Roentgenol. 184(5):1549-55, https://doi.org/10.2214/ajr.184.5.01841549. PMID: 15855114.
Zajko AB, Chablani V, Bron KM, Jungreis C. (1990) Hemobilia complicating transhepatic catheter drainage in liver transplant recipients: management with selective embolization. Cardiovasc Intervent Radiol. 13(5):285-288. https://doi.org/10.1007/BF02578626. PMID: 2124164.
Volpin E, Pessaux P, Sauvanet A, Sibert A, Kianmanesh R, Durand F, Belghiti J, Sommacale D. (2014) Preservation of the arterial vascularisation after hepatic artery pseudoaneurysm following orthotopic liver transplantation: long-term results. Ann Transplant. 19:346–352. https://doi.org/10.12659/AOT.890473. PMID: 25034853.
Marshall MM, Muiesan P, Srinivasan P, Kane PA, Rela M, Heaton ND, Karani JB, Sidhu PS. (2001) Hepatic artery pseudoaneurysms following liver transplantation: incidence, presenting features and management. Clin Radiol. 56(7):579-87. https://doi.org/10.1053/crad.2001.0650. Erratum in: Clin Radiol. 56(9):785. PMID: 11446757.
Ren X, Luo Y, Gao N, Niu H, Tang J. (2016) Common ultrasound and contrast-enhanced ultrasonography in the diagnosis of hepatic artery pseudoaneurysm after liver transplantation. Exp Ther Med. 12(2):1029-1033. https://doi.org/10.3892/etm.2016.3343. Epub 2016 May 17. PMID: 27446316; PMCID: PMC4950670.
Khalaf H. (2010) Vascular complications after deceased and living donor liver transplantation: a single-center experience. Transplant Proc. 42(3):865-870. https://doi.org/10.1016/j.transproceed.2010.02.037. PMID: 20430192.
Kyoden Y, Tamura S, Sugawara Y, Matsui Y, Togashi J, Kaneko J, Kokudo N, Makuuchi M. (2008) Portal vein complications after adult-to-adult living donor liver transplantation. Transpl Int. 21(12):1136-44. https://doi.org/10.1111/j.1432-2277.2008.00752.x. Epub 2008 Sep 1. PMID: 18764831.
Tessler FN, Gehring BJ, Gomes AS, Perrella RR, Ragavendra N, Busuttil RW, Grant EG. (1991 Diagnosis of portal vein thrombosis: value of color doppler imaging. AJR Am J Roentgenol. 157(2):293-6. https://doi.org/10.2214/ajr.157.2.1853809. PMID: 1853809.
Rennert J, Dornia C, Georgieva M, Roehrl S, Fellner C, Schleder S, Stroszczynski C, Jung EM. (2012) Identification of early complications following liver transplantation using contrast enhanced ultrasound (CEUS) First results. J Gastrointestin Liver Dis. 21(4):407-412. PMID: 23256124.
Lee SJ, Kim KW, Kim SY, Park YS, Lee J, Kim HJ, Lee JS, Song GW, Hwang S, Lee SG. (2013) Contrast-enhanced sonography for screening of vascular complication in recipients following living donor liver transplantation. J Clin Ultrasound. 41(5):305-312. https://doi.org/10.1002/jcu.22044. Epub 2013 Mar 28. PMID: 23553428.
Chen J, Zhu J, Zhang C, Song Y, Huang P. (2020) Contrast-enhanced ultrasound for the characterization of portal vein thrombosis vs tumor-in-vein in HCC patients: a systematic review and meta-analysis. Eur Radiol. 30(5):2871-2880. https://doi.org/10.1007/s00330-019-06649-z. Epub 2020 Feb 4. PMID: 32020403; PMCID: PMC7160216.
Mullan CP, Siewert B, Kane RA, Sheiman RG. (2010) Can doppler sonography discern between hemodynamically significant and insignificant portal vein stenosis after adult liver transplantation? AJR Am J Roentgenol. 195(6):1438-43. https://doi.org/10.2214/AJR.10.4636. PMID: 21098207.
Ko EY, Kim TK, Kim PN, Kim AY, Ha HK, Lee MG. (2003) Hepatic vein stenosis after living donor liver transplantation: evaluation with doppler US. Radiology. 229(3):806-810. https://doi.org/10.1148/radiol.2293020700. Epub 2003 Oct 23. PMID: 14576444.
Jeng KS, Huang CC, Lin CK, Lin CC, Chen KH. (2017) Graft calcification caused by a torsion of the hepatic vein after a living-related donor liver transplantation. Ann Hepatol. 16(1):164–168. https://doi.org/10.5604/16652681.1226954. PMID: 28051807.
Wadhawan M, Kumar A, Gupta S, Goyal N, Shandil R, Taneja S, Sibal A. (2013) Post-transplant biliary complications: an analysis from a predominantly living donor liver transplant center. J Gastroenterol Hepatol. 28(6):1056-60. https://doi.org/10.1111/jgh.12169. PMID: 23432435.
Kochhar G, Parungao JM, Hanouneh IA, Parsi MA. (2013) Biliary complications following liver transplantation. World J Gastroenterol. 19(19):2841–2846. https://doi.org/10.3748/wjg.v19.i19.2841. PMID: 23704818; PMCID: PMC3660810.
Senter-Zapata M, Khan AS, Subramanian T, Vachharajani N, Dageforde LA, Wellen JR, Shenoy S, Majella Doyle MB, Chapman WC. (2018) Patient and graft survival: biliary complications after liver transplantation. J Am Coll Surg. 226(4):484–494. https://doi.org/10.1016/j.jamcollsurg.2017.12.039. Epub 2018 Jan 31. PMID: 29360615.
Kasahara M, Egawa H, Takada Y, Oike F, Sakamoto S, Kiuchi T, Yazumi S, Shibata T, Tanaka K. (2006) Biliary reconstruction in right lobe living-donor liver transplantation: comparison of different techniques in 321 recipients. Ann Surg. 243(4):559–566. https://doi.org/10.1097/01.sla.0000206419.65678.2e. PMID: 16552210; PMCID: PMC1448968.
Greif F, Bronsther OL, Van Thiel DH, Casavilla A, Iwatsuki S, Tzakis A, Todo S, Fung JJ, Starzl TE. (1994) The incidence, timing, and management of biliary tract complications after orthotopic liver transplantation. Ann Surg. 219(1):40–45. https://doi.org/10.1097/00000658-199401000-00007. PMID: 8297175; PMCID: PMC1243088.
Popescu A, Sporea I, Şirli R, Dănilă M, Mare R, Grădinaru Taşcău O, Moga T. (2015) Does contrast enhanced ultrasound improve the management of liver abscesses? A single centre experience. Med Ultrason. 17(4):451–455. https://doi.org/10.11152/mu.2013.2066.174.deu. PMID: 26649338.
Mao R, Xu EJ, Li K, Zheng RQ. (2010) Usefulness of contrast-enhanced ultrasound in the diagnosis of biliary leakage following T-tube removal. J Clin Ultrasound. 38(1):38–40. https://doi.org/10.1002/jcu.20622. PMID: 19670237.
Huang DY, Yusuf GT, Daneshi M, Ramnarine R, Deganello A, Sellars ME, Sidhu PS. (2018) Contrast-enhanced ultrasound (CEUS) in abdominal intervention. Abdom Radiol. 43(4):960–976. https://doi.org/10.1007/s00261-018-1473-8. PMID: 29450615; PMCID: PMC5884902.
Valls C, Alba E, Cruz M, Figueras J, Andía E, Sanchez A, Lladó L, Serrano T. (2005) Biliary complications after liver transplantation: diagnosis with MR cholangiopancreatography. AJR Am J Roentgenol. 184(3):812–820. https://doi.org/10.2214/ajr.184.3.01840812. PMID: 15728602.
Ryu CH, Lee SK. (2011) Biliary strictures after liver transplantation. Gut Liver. 5(2):133–42. https://doi.org/10.5009/gnl.2011.5.2.133. Epub 2011 Jun 23. PMID: 21814591; PMCID: PMC3140656.
Guichelaar MM, Benson JT, Malinchoc M, Krom RA, Wiesner RH, Charlton MR. (2003) Risk factors for and clinical course of non-anastomotic biliary strictures after liver transplantation. Am J Transplant. 3(7):885–890. https://doi.org/10.1034/j.1600-6143.2003.00165.x. PMID: 12814481.
Xu HX. (2009) Contrast-enhanced ultrasound in the biliary system: Potential uses and indications. World J Radiol. 1(1):37–44. https://doi.org/10.4329/wjr.v1.i1.37. PMID: 21160719; PMCID: PMC2999303.
Seehofer D, Eurich D, Veltzke-Schlieker W, Neuhaus P. (2013) Biliary complications after liver transplantation: old problems and new challenges. Am J Transplant. 13(2):253–265. https://doi.org/10.1111/ajt.12034. Epub 2013 Jan 17. PMID: 23331505.
Zheng BW, Wu T, Ju JX, Wu LL, Zhang HJ, Lian YF, Tong G, Li QJ, Qiu C, Zhou HC, Zheng RQ, Ren J. (2021) Contrast-enhanced ultrasound for biliary ischemia: a possible new clinical indication. J Ultrasound Med. 40(9):1927–1934. https://doi.org/10.1002/jum.15577. Epub 2020 Dec 3. PMID: 33270273.
Hu B, Horrow MM. (2016) Ultrasound of biliary cast syndrome and its mimics. Ultrasound Q. 32(3):258–270. https://doi.org/10.1097/RUQ.0000000000000196. PMID: 26561220.
Whang G, Chopra S, Tchelepi H. (2019) Bright band sign a grayscale ultrasound finding in hepatic infarction. J Ultrasound Med. 38(9):2515–2520. https://doi.org/10.1002/jum.14939. Epub 2019 Jan 21. PMID: 30666665.
Llewellyn ME, Jeffrey RB, DiMaio MA, Olcott EW. (2014) The sonographic "bright band sign" of splenic infarction. J Ultrasound Med. 33(6):929–938. https://doi.org/10.7863/ultra.33.6.929. PMID: 24866600.
Malhi H, Grant EG, Duddalwar V. (2014) Contrast-enhanced ultrasound of the liver and kidney. Radiol Clin North Am. 52(6):1177–1190. https://doi.org/10.1016/j.rcl.2014.07.005. Epub 2014 Sep 10. PMID: 25444099.
Bartolotta TV, Taibbi A, Midiri M, Lagalla R. (2019) Contrast-enhanced ultrasound of hepatocellular carcinoma: where do we stand? Ultrasonography. 38(3):200–214. https://doi.org/10.14366/usg.18060. Epub 2019 Feb 25. PMID: 31006227; PMCID: PMC6595127.
Borhani AA, Hosseinzadeh K, Almusa O, Furlan A, Nalesnik M. (2009) Imaging of posttransplantation lymphoproliferative disorder after solid organ transplantation. Radiographics. 29(4):981–1000, https://doi.org/10.1148/rg.294095020. PMID: 19605652.
Chen W, Li J, Fan X, Zhang Y, Wang L, Liu Y, Cui A, Wang L. (2021) Application of contrast-enhanced ultrasound in the diagnosis of post-transplant lymphoproliferative disease after hematopoietic stem cell transplantation: a case report. Medicine. 100(2):e24047. https://doi.org/10.1097/MD.0000000000024047. PMID: 33466157; PMCID: PMC7808548.
Kazmierski BJ, Sharbidre KG, Robbin ML, Grant EG. (2020) Contrast-enhanced ultrasound for the evaluation of renal transplants. J Ultrasound Med. 39(12):2457–2468. https://doi.org/10.1002/jum.15339. Epub 2020 May 15. PMID: 32412688.
Funding
Open access funding provided by SCELC, Statewide California Electronic Library Consortium.
Author information
Authors and Affiliations
Contributions
S.C. performed data curation, acquired resources, and performed the formal analysis. B.D.B. wrote the original draft. J.M.T. performed data curation, acquired resources, and reviewed and edited the original draft. E.G.G. reviewed and edited the original draft. H.T. conceptualized the project, supervised the projected, and reviewed and edited the original draft.
Corresponding author
Ethics declarations
Conflict of interest
The authors have no relevant financial or non-financial interests to disclose. The authors have no competing interests to declare that are relevant to the content of this article.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Chau, S.S., Beutler, B.D., Grant, E.G. et al. Ultrasound innovations in abdominal radiology: multiparametic imaging in liver transplantation. Abdom Radiol (2024). https://doi.org/10.1007/s00261-024-04518-y
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/s00261-024-04518-y