Contrast Agents in Liver Imaging (Series in Radiology)


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However, the presence of intralesional fat was detected on out-of-phase T1-weighted sequence. The presence of intralesional fat is not usually found in FNH and suggests the diagnosis of adenoma — adenomatosis, in the present case —, with a very different prognosis and approach. On the other hand, the lesions showed homogeneous hepatobiliary contrast uptake, hence the highest likelihood of the diagnosis of multiple FNHs. Homogeneous hepatobiliary contrast uptake indicates the diagnosis of FNH.

Adenomas are well defined, homogeneous or heterogeneous lesions.

Introduction

MR Contrast Agents for Liver Imaging: What, When, How .. reported that, in at least one series, gadolinium-enhanced imaging was superior to .. 2 Current address: Department of Radiology, Fundación Santa Fe de Bogotá. Magnetic Resonance Imaging · Molecular Imaging · Musculoskeletal Radiology Hepatobiliary-specific contrast agents are one of several classes of contrast Contrast agent–enhanced MR imaging of the liver and biliary tree is routinely Hepatobiliary-specific agents show promise in increasing the.

The largest ones tend to present signal heterogeneity, with mild to moderate hypersignal on T2-weighted, hyposignal on T1-weighted sequences, homogeneous or heterogeneous arterial contrast-enhancement, late washout, and possible development of capsule Adenomas are composed of hepatocytes containing glycogen and lipids surrounded by a capsule. Although containing functioning hepatocytes, there is a lack of biliary ducts resulting in deficiency in bilirubin and hepatobiliary contrast excretion.

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Additionally, adenomas present smaller expression of membrane transporters such as OATP1 1 , 2. Thus, in the hepatobiliary phase, most adenomas are hypointense in relation to the surrounding parenchyma Figure 3. Rarely, there is hepatobiliary contrast uptake by adenomas and, in cases where it occurs, such an uptake tends to be preferentially peripheral in the hepatobiliary phase 1 , 2 , 4.

The smallest lesion arrowheads presents subtle hypersignal on T2-weighted and marked signal loss on out-of-phase T1-weighted sequence caused by the presence of intralesional fat. No hepatobiliary contrast uptake is observed.

4 Contrast Agents Part II

The presence of intralesional fat and the absence of hepatobiliary contrast uptake indicate a probable diagnosis of adenoma. The largest lesion arrows presents high signal intensity on T2-weighted, hyposignal on t1-weighted sequence, and nodular, peripheral and discontinuous uptake in the arterial-phase, and no hepatobiliary contrast uptake that is a typical hemangioma behavior. Hemangiomas do not contain functioning hepatocytes so uptake of this contrast medium is not observed. Also, in the delayed-phase, the fill-in pattern is not observed, which might occur with the utilization of hepatobiliary contrast agent.

Hemangiomas normally have a typical presentation at MRI with extracellular contrast and are not an indication for investigation with hepatobiliary contrast.

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At conventional MRI, hemangiomas present marked hypersignal on T2-weighted, hyposignal on T1-weighted sequences, discontinuous, nodular, peripheral contrast enhancement in the arterial phase, tending to centripetal fill-in by the contrast agent in the subsequent phases 13 , However, considering that hemangiomas are common lesions, they will be frequently present on images acquired with hepatobiliary contrast for several reasons. Hemangiomas present the same imaging findings at dynamic studies with hepatobiliary contrast; however, in the delayed phase, as the hepatobiliary contrast medium is leaving the interstitium and entering into the functioning hepatocytes, the hemangioma fill-in might or might not occur in this phase, differing from its usual behavior with the use of extracellular gadolinium Hemangiomas are formed by a clump of blood vessels and do not contain hepatocytes, therefore they do not present contrast enhancement during the hepatobiliary phase and appear hypointense in this phase 1 , 2 , 9 , 15 Figure 4.

A potential confusion factor is the fact that some hemangiomas may present subtle central contrast uptake during the early hepatobiliary phase because of the tendency to persistent centripetal enhancement at dynamic study, like in those with extracellular gadolinium 1. The caudate lobe lesion arrowheads presents subtle hypersignal on T2-weighted sequence and signal loss on T1-weighted out-of-phase sequence caused by the presence of intralesional fat. Such a lesion shows intense and homogeneous contrast uptake in the arterial-phase, with decay in the portal and delayed phases, presenting greater hepatobiliary contrast uptake than the adjacent parenchyma, suggesting FNH as the first diagnostic hypothesis.

Considering that the presence of intralesional fat in NFH is rare, the patient will be maintained under imaging follow-up. The lesions in segments VII and VIII arrows are similar, with marked hypersignal on T2-weighted, hyposignal on T1-weighted sequence, and nodular, peripheral and discontinuous uptake in the arterial phase, a characteristic of hemangiomas. In cirrhosis, the hepatobiliary contrast uptake by the nodules depends on their differentiation stage and on the presence of functioning hepatocytes.

Low-grade regenerative and dysplastic nodules present preferentially portal vascularization, contain functioning hepatocytes and, like the surrounding parenchyma, show hepatobiliary contrast uptake. High-degree dysplastic nodules lose the portal vascularization and start gaining abnormal arterial vascularization. Thus, high-grade dysplastic nodules tend to be hypovascular in the arterial and portal phases, but may also become hypervascular in the arterial phase in cases where the abnormal arterial vascularization is more developed.

High-grade dysplastic nodules contain functioning hepatocytes and also demonstrate hepatobiliary contrast uptake in the same way as the surrounding parenchyma Figure 5. Hepatobiliary contrast uptake by HCC also depends on its differentiation stage. Well-differentiated HCCs contain functioning hepatocytes and might show hepatobiliary contrast uptake. On the other hand, poorly-differentiated or undifferentiated hepatocarcinomas do not contain functioning hepatocytes and do not show hepatobiliary contrast uptake, remaining hypointense in relation to the surrounding parenchyma 2 , 10 , 17 - 19 Figure 6.

Small nodules are observed adjacent to the gallbladder, with hyposignal on T2-weighted sequence, without expression on the other sequences and on the conventional dynamic study, but with hepatobiliary contrast uptake, leading to the diagnosis of regenerative nodules. Well-differentiated HCCs show hepatobiliary contrast uptake, requiring imaging follow-up.

Two liver nodules are seen in the segment VIII arrows as well as a larger nodule, in the segment VI arrowheads , all of them contrast-enhanced in the arterial-phase, washout in the delayed-phase, and without uptake in the hepatobiliary-phase, characterizing HCCs. Poorly differentiated or undifferentiated HCCs do not contain functioning hepatocytes so hepatobiliary contrast uptake is not observed.

The different enhancement patterns depend on the histological grade of the HCCs and may be explained by the membrane transporters expression. Hepatobiliary contrast uptake by HCCs depends on the tumor differentiation stage and on the amount of functioning hepatocytes 2 , 4. The diagnostic performance of MRI in the detection of HCCs of all sizes increases with the utilization of hepatobiliary contrast agents 1 , However, in cases of advanced cirrhosis, the contrast uptake by the liver parenchyma may be compromised by decreased hepatocytes function, which would result in reduction of the method's accuracy to detect HCCs 4 , The differentiation between HCC and perfusion alterations may also represent a diagnostic challenge.

Perfusional alterations present a signal similar to the one of the remainder hepatic tissue during the portal and hepatobiliary phases, while most HCCs, except the well-differentiated ones, present hyposignal in the hepatobiliary phase The hepatobiliary phase may also be useful in the post-chemoembolization or post-radiofrequency ablation follow-up, considering that inflammatory reactions show hepatobiliary contrast uptake and residual HCC tends to not present contrast uptake Hepatobiliary contrast increases the method's sensitivity to detect liver metastasis, particularly the small-sized ones.

Metastases do not contain functioning hepatocytes or biliary ducts, and do not show contrast uptake during the hepatobiliary phase. As a result, the healthy hepatic tissue remains hyperintense and the metastasis, hypointense, which facilitates its detection 1 , 2. The utilization of such contrast agents increases the index of detection of hypo- and hypervascular metastases Figure 7. Additionally, hepatobiliary contrast agents contribute to the diagnosis of small, benign focal lesions frequently found in patients with neoplasias, particularly FNH Figure 8.

MR contrast agents

Like in cirrhosis, perfusional alterations in patients with metastasis show contrast uptake in the hepatobiliary phase, differently from metastases 1. Hypovascular metastases with diffusion restriction. In the hepatobiliary-phase, the liver parenchyma shows contrast uptake and becomes hyperintense. The metastatic implants that do not contain hepatocytes become hypointense. Note the capacity of hepatobiliary contrast to detect very small lesions which cannot be visualized on the other sequences.

Two hypervascular lesions arrows are seen with intermediate signal intensity on T1- and T2- weighted sequences, showing contrast uptake in the hepatobiliary-phase. Such lesions present functioning hepatocytes, suggesting FNHs as the main diagnostic hypothesis and ruling out the possibility of metastatic implants. The avascular lesion arrowhead is secondary to post-treatment alteration. The imaging evaluation of the biliary system has been approached by a series of publications in the Brazilian radiological literature 24 - The biliary excretion of hepatobiliary contrast agents allows for the anatomical and functional characterization of intra- and extrahepatic biliary tract.

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Such contrast agents shortens the T1 relaxation time of the bile and allows for the performance of a high-resolution T1-weighted cholangiography 4. The previous knowledge of the biliary anatomy and its variations becomes increasingly important in the preoperative planning, considering the complexity of the hepatic anatomy as well as of the more refined surgical techniques, which reduces the occurrence of postoperative complications 4.

Also, hepatobiliary contrast-enhanced cholangiography allows for the accurate detection of postoperative complications such as biliary fistulas and bilomas which present progressive fill-in during the hepatobiliary phase. In the postoperative follow-up, inadvertent ductal ligation can also be easily recognized in the hepatobiliary phase as an abrupt interruption of the biliary tract 4 , 5.

Other applications of hepatobiliary contrast agents include the evaluation of the biliary flow dynamics, the study of partial or complete biliary duct obstructions, and the localization of the stenosis site. The hepatobiliary contrast may contribute to the diagnosis of cholecystitis as the gallbladder is not filled by the contrast medium, differently from its habitual behavior with other contrast agents.

The diagnosis of sphincter of Oddi dysfunction can be based on the finding of absent or delayed passage of the hepatobiliary contrast thru the ampulla of Vater. Hepatobiliary contrast allows for the differentiation between biliary lesions and extrabiliary cysts, since it delineates the biliary tract, demonstrating the communication of biliary cystic lesions with the bile ducts, and extrabiliary cystic lesions that do not communicate with bile ducts, such as pseudocysts, duodenal diverticula and duodenal duplication cysts 5.

Several studies are evaluating the relation between the degree of hepatic fibrosis in patients with cirrhosis As well as the hepatobiliary contrast enhancement with the objective of reducing the necessity of biopsies currently considered a gold standard. Hepatocytes are responsible for the uptake and excretion of the hepatobiliary contrast medium, so their integrity is essential for the enhancement of the parenchyma in the hepatobiliary phase.

In cirrhosis, hepatocytes are progressively replaced by fibrotic tissue, so that the more advanced the fibrosis, the smaller the hepatic parenchyma enhancement in the hepatobiliary phase. Additionally, as compared with healthy livers, cirrhotic livers present later enhancement peak and slower washout 32 - Further potential hepatobiliary contrast applications include the evaluation of the functional hepatic reserve before partial hepatectomy; evaluation of live donor's hepatic function as well as evaluation of early liver failure after transplant 4.

In summary, hepatobiliary contrast increases the MRI accuracy and reduces the number of cases of undefined liver lesions. Imaging findings in the hepatobiliary findings should be always analyzed in the clinical context, considering the lesion signal characteristics on anatomical sequences. The utilization of hepatobiliary contrast agents may reduce the necessity of invasive diagnostic procedures as well as of further investigation with other imaging methods, and imaging follow-up, reducing costs and the anxiety of both patients and medical team.

This modifies their biological behaviour and makes the total size of the iron oxide particle substantially larger. Superparamagnetic iron oxide particles do not leak into the interstitium. They, therefore, act as intravascular contrast agents or blood pool agents as long as the vessel endothelium is intact and unaltered by any pathological process.

Their elimination from the blood is by uptake into the reticuloendothelial system cells in liver, spleen, bone marrow and lymph nodes and are phagocytosed by macrophages throughout the body. The superparamagnetic iron oxide particles agents are preferentially entrapped by the Kupffer cells in the liver and spleen and reduce their T2 relaxation time. Thus, normal liver appears dark on T2 weighted images. Most liver tumours which are usually deficient in Kupffer cells, do not exhibit superparamagnetic iron oxide particles agent uptake and appear relatively hyperintense.

However, well-differentiated tumours which have not lost all their Kupffer cells, will take up superparamagnetic iron oxide particles agents and exhibit reduced signal intensity. Hepatobiliary-specific MR contrast agents prolong the apparent "hepatobiliary phase", therefore there is no precise time requirement for imaging in this phase.

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A tailored examination for a confident non-invasive diagnosis of focal liverlesions. If the multiphasic imaging findings of haemangiomas are atypical with a hepatocellular contrast agent such as gadoxetic acid, the T 2 -weighted sequences are usually sufficiently discriminatory [ 81 ]. Review of hemipelvectomy endoprostheses: However, the relationship between liver function derangements and the degree of liver parenchyma enhancement is not yet accurately established. As the name implies, tissue-specific contrast agents are targeted at a specific tissue type eg, reticuloendothelial cell-specific or hepatocyte-specific or organ eg, blood-pool agents for the vascular system or enteral agents for bowel. Imaging and pathologic findings.

High-spatial-resolution sequences in separate breath holds can complete imaging and longer imaging time can be used if needed, for example to study bile leak or contrast agent washout. These features, combined with advances in MR imaging hardware and software, allow high-resolution images of the liver to be obtained.

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Liver-specific agents for contrast-enhanced MRI: role in oncological imaging

Articles Cases Courses Quiz. About Blog Go ad-free. Ray Ballinger et al. Gadolinium-based agents Manganese-based agents Superparamagnetic iron oxide particles Preferred MR protocol Related articles References.

Hepatobiliary-specific MR contrast agents: Jaypee Brothers Medical Pub. Read it at Google Books - Find it at Amazon 3. MR contrast agents for liver imaging: