Sequential use of gadolinium chelate and mangafodipir trisodium for the assessment of focal liver lesions: initial observations

Biocompatible and pH-sensitive PLGA encapsulated MnO nanocrystals for molecular and cellular MRI

Inorganic manganese-based particles are becoming attractive for molecular and cellular imaging, due to their ability to provide bright contrast on MRI, as opposed to the dark contrast generated from iron-based particles. Using a single emulsion technique, we have successfully fabricated pH-sensitive poly(lactic-co-glycolic acid) (PLGA)-encapsulated manganese oxide (MnO) nanocrystals. Two classes of particles were fabricated at ∼140 nm and 1.7 μm and incorporated 15 to 20 nm MnO nanocrystals with high encapsulation efficiencies. Intact particles at physiological pH cause little contrast in MRI, but following endocytosis into low pH compartments within the cells, the particles erode and MnO dissolves to release Mn(2+). This causes the cells to appear bright on MR images. The magnitude of the change in MRI properties is as high as 35-fold, making it the most dynamic "smart" MRI contrast agent yet reported. Possible applications of these MnO particles include slow release Mn(2+), tumor targeting, and confirmation of cell uptake.

Diagnosis and treatment of benign focal liver lesions

BACKGROUND

With the routine use of improved imaging modalities, more benign liver lesions are detected nowadays. An accurate characterization of these incidental lesions may be a challenge, and frequently a biopsy or even unnecessary surgery is being performed. However, these interventions are not always to the benefit of the patient.

METHODS

A Medline search of studies relevant to imaging diagnosis and management of the most common, benign, solid and non-solid liver lesions was undertaken. References from identified articles were handsearched for further relevant articles. The authors' own experiences with benign liver lesions were also taken into account.

RESULTS

Although atypical imaging features are the exception rather than the rule, it is sometimes difficult to differentiate between benign and malignant lesions, and knowledge of their imaging features is essential if unnecessary work-up is to be avoided. The use of tissue-specific contrast media, which has clearly improved the accuracy of highly advanced radiological techniques, may be helpful during differential diagnosis. Once having established an accurate diagnosis, surgery is rarely indicated for a benign liver lesion because of its asymptomatic nature.

CONCLUSION

Knowledge of imaging features and a clear management strategy during diagnostic work-up, emphasizing the indications for surgery, will minimize the number of patients who have to undergo biopsy or unnecessary surgery.

EVP-ABD-enhanced MRI to evaluate diffuse liver disease in a rat model

PURPOSE

To evaluate the feasibility of using manganese-based MR imaging contrast agent EVP-ABD to detect diffuse liver disease in an established rat hepatitis model.

MATERIALS AND METHODS

Hepatitis was induced by administration of CCl(4) in corn oil vehicle to rats intraperitoneally. MR images were acquired on a 3T scanner using a volume coil approximately 36 hours after the administration of CCl(4). EVP-ABD was administered via a tail vein at a dose of 10 mumol/kg. Multi-TI turboflash images were acquired to evaluate liver R1 (=1/T1) values before and after the EVP-ABD administration. Eighteen rats received various doses of CCl(4) and completed pre- and postcontrast MRI scans and liver histologic evaluation.

RESULTS

The liver R1 after the EVP-ABD administration and the change of the liver R1 before and after the administration, DeltaR1, show significant correlations with the CCl(4) dose. A significant correlation was also found between the histologic scores and the CCl(4) doses despite known variability in the relationship of CCl(4) dose to histology. A significant correlation was found between the histologic score and DeltaR1.

CONCLUSION

Our results indicate that EVP-ABD-enhanced MRI can detect diffuse liver disease generated by CCl(4) based on the significant correlation between proton R1 in liver following EVP-ABD and the CCl(4) doses as well as the histologic scores.

MR imaging of the liver

MR imaging is establishing a role as a primary diagnostic technique, with increasing evidence showing MR imaging to have advantages over CT regarding diagnostic sensitivity and specificity for many pathologies of solid organs, bile and pancreatic ducts, bowel, peritoneum, and retroperitoneum. In addition, there are increasing concerns regarding the risks of radiation and iodinated contrast associated with CT imaging of the abdomen. The incidence of contrast-induced nephropathy associated with iodinated contrast used for CT scanning is difficult to ascertain because reporting is spurious and variable in interpretation.

MR imaging of diffuse liver diseases

This article discusses MR imaging sequences that are used for the evaluation of diffuse liver diseases, including processes that lead to abnormal lipid metabolization, iron de-position disease, and perfusion abnormalities.

Magnetic Resonance Imaging of the Liver: Review of Techniques and Approach to Common Diseases

MR imaging examination of the liver should use a combination of single-shot T2W and breath-hold T1W images, and include gadolinium enhancement with acquisition of multiple phases. MR provides superior characterization of liver masses than CT, and multi-phase gadolinium enhancement including a properly timed arterial phase is critical. The T1 weighted pre-contrast images must include in-phase/out-of-phase acquisitions, to assess hepatic lipid and or iron content, and dynamically enhanced post-gadolinium images. Timing of the arterial phase images is also critical for demonstration of acute hepatitis. The timing of the venous and equilibrium phase images are less critical, and are important for grading more severe acute hepatitis, demonstration of fibrosis, and for delineating vascular abnormalities. In cirrhosis, dynamic post-gadolinium images are critical for detection and characterization of regenerative or dysplastic nodules, and HCC. The same sequences useful for liver evaluation provide a comprehensive evaluation of all the soft tissues of the abdomen, and allow depiction of most of the important diseases, thus facilitating use of a universal protocol for abdominal imaging.

Magnetic resonance imaging features of focal liver lesions after intervention

The aim of this article is to provide an overview of MRI features of primary and secondary liver lesions after intervention. Emphasis is given to T2- and T1-weighted pre and post intravenous gadolinium chelates appearance of successfully treated lesions and, from residual/recurrent tumors after therapy. In addition, complications after procedures are briefly cited. Liver resection, radiation therapy, systemic chemotherapy, transcatheter arterial chemoembolization, ablative therapies and liver transplantation are the methods discussed in this review. Among these methods, special attention is given to MRI findings after ablative therapies since radiofrequency ablation is commonly performed in our institution.

Modern hepatic imaging

This article provides a brief overview of the current status of commonly employed diagnostic techniques--US, CT, MR, and PET--for the evaluation of liver metastases and HCC as well as a description of imaging in RF ablation and liver transplantation. The various advantages and limitations of the techniques have been outlined. At the present time, at our center, MRI is used most often to evaluate these liver pathologies, due to its high accuracy for lesion detection and characterization.

Assessment of Sequential Enhancement Patterns of Focal Nodular Hyperplasia and Hepatocellular Carcinoma on Mangafodipir Trisodium Enhanced MR Imaging

RATIONALE AND OBJECTIVES

Sequential contrast changes of mangafodipir trisodium (Mn-DPDP)-enhanced magnetic resonance imaging (MRI) were evaluated in the differentiation of focal nodular hyperplasias (FNH) and hepatocellular carcinomas (HCC).

METHODS

Patients with FNH (n = 16) or HCC (n = 12) underwent MRI: T2-weighted fast spin echo before and T1-weighted gradient echo before and 1, 4, 14, and 22 hours after 5 micromol/kg Mn-DPDP. Homogeneity of enhancement and delineation of fibrous scars of FNHs were assessed qualitatively. Lesion-to-liver contrast changes of FNHs and HCCs were compared quantitatively (Mann-Whitney U).

RESULTS

Mn-DPDP improved detection of characteristic scars of FNHs from 50% before to 90% after contrast agent. Apart from fibrous tissue enhancement of FNHs was mostly homogeneous (90%). Time-dependent contrast changes were up to 20 times higher (after 4 hours) for FNHs than HCCs (P < 0.0001).

CONCLUSIONS

Mn-DPDP-enhanced MRI helps to delineate characteristic morphologic features of FNHs and can provide quantitative data differentiating FNH and HCC.

Atypical focal nodular hyperplasia of the liver: imaging features of nonspecific and liver-specific MR contrast agents

OBJECTIVE

The objective of our study was to describe the functional and differential uptake features of atypical focal nodular hyperplasia using different MR contrast agents and to evaluate their potential role in the diagnosis and characterization of focal nodular hyperplasia.

MATERIALS AND METHODS

Contrast-enhanced MR images of 45 patients with 85 focal nodular hyperplasia lesions were retrospectively reviewed. In these patients, sonographic findings were nonspecific (n = 37), or CT features were inconclusive (n = 8). Non-liver specific gadolinium chelates were used in 18 patients (48 lesions) suspected of having either focal nodular hyperplasia or hemangioma. The following liver-specific agents were used in patients with suspected focal nodular hyperplasia or metastases: mangafodipir trisodium, 30 patients (55 lesions); ferumoxides, six patients (16 lesions); and SHU 555 A, six patients (six lesions). Individual lesions were quantified by signal intensity and assessed qualitatively by homogeneity, contrast enhancement, and presence of a central scar.

RESULTS

At unenhanced MR imaging, the triad of homogeneity, isointensity, and central scar was found in 22% of the focal nodular hyperplasia lesions. On mangafodipir trisodium-enhanced T1-weighted images, all focal nodular hyperplasia lesions showed contrast uptake: in 64% of the lesions, uptake was equal to parenchyma; 25%, greater than the parenchyma; and 11%, less than the parenchyma. On iron oxide-enhanced T2-weighted images, all focal nodular hyperplasia lesions showed uptake of the contrast agent, but contrast uptake in the lesions was less than in the surrounding parenchyma. Dynamic gadolinium chelate-enhanced MR imaging showed early and vigorous enhancement of focal nodular hyperplasia lesions with rapid washout in 88%. Atypical imaging features of the lesions included hyperintensity on T1-weighted images, necrosis and hemorrhage, and inhomogeneous or only minimal contrast uptake.

CONCLUSION

For patients in whom the diagnosis of focal nodular hyperplasia cannot be established on unenhanced or gadolinium-enhanced MR imaging, homogeneous uptake of liver-specific contrast agent with better delineation of central scar may help to make a confident diagnosis of focal nodular hyperplasia.

T1 efficacy of EVP-ABD: a potential manganese-based MR contrast agent for hepatic vascular and tissue phase imaging

PURPOSE

To evaluate the T1 efficacy of EVP-ABD, a new manganese (Mn)-based contrast agent, for vascular and liver tissue enhancement in comparison with currently approved agents.

MATERIALS AND METHODS

Ten Yorkshire pigs (body weight, 26 -46 kg) were used for the efficacy evaluation, nine for kinetic T1 evaluation (three each agent) and one for post EVP-ABD imaging. With a fast imaging scheme to monitor T1 values of blood and liver, 10 micromol/kg EVP-ABD was injected intravenously and compared with gadopentetate dimeglumine (Magnevist, GdDTPA) and mangafodipir trisodium (Teslascan, mangafodipir trisodium) at routine clinical dosages. All were imaged with 3D T1 Gradient Recalled Echo (GRE) sequence (TR/TE/alpha = 3.8/1.6/25 degrees ) prior to and 10 minutes post injection using a 1.5-T whole-body scanner. Additional high-resolution 2D liver images (TR/TE/alpha = 50/4.6/40 degrees ) and arterial phase images of the upper aorta were acquired from the pig for post EVP-ABD imaging.

RESULTS

At 10 micromol/kg, EVP-ABD provided a dramatic decline in blood T1, comparable to 0.1 mmol/kg GdDTPA, followed by a rapid return to blood baseline T1 values. In addition to the blood enhancement phase, EVP-ABD achieved a 70% reduction in liver T1 within 2 minutes postadministration, with an imaging window of at least 2 hours. A substantially improved signal-to-noise ratio (SNR) was observed in both the 2D and 3D liver images postcontrast.

CONCLUSION

EVP-ABD demonstrated peak vascular enhancement similar to GdDTPA and prolonged specific liver enhancement exceeding mangafodipir trisodium. EVP-ABD has favorable T1 enhancing characteristics with the potential to allow for a comprehensive liver evaluation.

Contrast agents for hepatic magnetic resonance imaging

The current availability of liver-specific contrast media (LSCM) allows the possibility to obtain an accurate diagnosis when studying focal liver lesions (FLL). It is necessary to have an in-depth knowledge of the biologic and histologic characteristics of FLL and the enhancement mechanism of LSCM to gain significant accuracy in the differential diagnosis of FLL. It is possible to subdivide FLL into three main groups according to the kinetics of contrast enhancement: hypervascular FLL, hypovascular FLL, and FLL with delayed enhancement. Dynamic contrast-enhanced magnetic resonance imaging is an important tool in the identification and characterization of FLL. LSCM with a first phase of extracellular distribution give both dynamic (morphologic) and late phase (functional) information useful for lesion characterization. With LSCM it is possible to differentiate with high accuracy benign from malignant lesions and hepatocellular from nonhepatocellular lesions. To understand contrast behavior after injection of LSCM, it is necessary to correlate contrast enhancement with the biologic and histologic findings of FLL.

Contrast-enhanced MRI of the liver with mangafodipir trisodium: imaging technique and results

Magnetic resonance (MR) contrast agents are now routinely used for detecting and characterizing focal liver lesions. Liver specific, hepatobiliary, MRI contrast agent mangafodipir trisodium (Mn-DPDP) is taken up by the functioning hepatocytes and excreted by the biliary system. Contrast uptake leads to persistent elevation of T1-weighted signal of normal liver parenchyma within 10 minutes of injection. Most tumors of non-hepatocellular origin typically are hypointense relative to enhanced liver parenchyma on T1 weighted images and are more conspicuous than on unenhanced images. Whereas, tumors of hepatocellular origin such as focal nodular hyperplasia (FNH), adenoma, and well-differentiated hepatocellular carcinomas (HCC) have been shown to accumulate Mn-DPDP, providing characterization information to discriminate hepatocellular from non-hepatocellular tumors. The purpose of this pictorial essay is to illustrate the appearance of various liver tumors on mangafodipir enhanced liver MR imaging.

MR imaging of benign hepatic tumors

Use of a state-of-the-art pattern recognition approach and the combination of various MR sequences and contrast enhancement techniques makes it possible to diagnose most benign hepatic tumors with confidence.

Magnetic resonance imaging. Liver-specific contrast agents

MR imaging with new liver-specific contrast agents will probably be the imaging modality used in the future to detect focal liver lesions. The detection of HCC will probably be improved by using specific hepatobiliary agents, but the exact technique remains to be determined. New liver-specific contrast can differentiate some benign lesions from malignant ones and can assist in making a final diagnosis. In certain circumstances, liver-specific contrast agents can be used to evaluate hepatic vessels, the biliary tract, and hepatic function. New applications are also expected.

Contrast-enhanced magnetic resonance cholangiography versus heavily T2-weighted magnetic resonance cholangiography

RATIONALE AND OBJECTIVES

To investigate the feasibility of contrast-enhanced magnetic resonance cholangiography (CE-MRC) and compare it with single-shot turbo spin-echo magnetic resonance cholangiography (SSTSE-MRC).

METHODS

Fifteen patients with suspected metastatic liver disease (n = 10) or biliary tree abnormalities (n = 5) underwent a magnetic resonance imaging (1.5-T system) examination before and after mangafodipir administration. Contrast-enhanced MRC with a three-dimensional fast low-angle shot sequence after mangafodipir trisodium administration was compared with SSTSE-MRC. Four anatomic segments were evaluated: the intrapancreatic and extrapancreatic common bile duct segments, the cystic duct, and the area of hepatic bifurcation. Contrast-enhanced MRC and SSTSE-MRC were separately analyzed on a 5-point grading scale in terms of ductal segment visualization and lumen narrowing or dilatation.

RESULTS

There was no difference (P = 0.375) in segment visualization between CE-MRC and SSTSE-MRC; 56 of the 60 segments were visualized by both techniques. In the evaluation of ductal narrowing or dilatation, nonsignificant differences (P = 0.500) were observed. Contrast-enhanced MRC was not influenced by fluid superimposition and provided additional information from background tissues.

CONCLUSIONS

Contract-enhanced MRC is a feasible technique showing anatomic correlation with SSTSE-MRC, and it can in addition provide functional information. Contrast-enhanced MRC may be used in selected patients when traditional SSTSE-MRC is inconclusive.