MRT der Leber

Metal-Based Complexes as Pharmaceuticals for Molecular Imaging of the Liver

This article reviews the use of metal complexes as contrast agents (CA) and radiopharmaceuticals for the anatomical and functional imaging of the liver. The main focus was on two established imaging modalities: magnetic resonance imaging (MRI) and nuclear medicine, the latter including scintigraphy and positron emission tomography (PET). The review provides an overview on approved pharmaceuticals like Gd-based CA and ^99mTc-based radiometal complexes, and also on novel agents such as ⁶⁸Ga-based PET tracers. Metal complexes are presented by their imaging modality, with subsections focusing on their structure and mode of action. Uptake mechanisms, metabolism, and specificity are presented, in context with advantages and limitations of the diagnostic application and taking into account the respective imaging technique.

Investigations on the Ga(III) Complex of EOB-DTPA and Its 68Ga Radiolabeled Analogue

We demonstrate a method for the isolation of EOB-DTPA (3,6,9-triaza-3,6,9-tris(carboxymethyl)-4-(ethoxybenzyl)-undecanedioic acid) from its Gd(III) complex and protocols for the preparation of its novel non-radioactive, i.e., natural Ga(III) as well as radioactive (68)Ga complex. The ligand as well as the Ga(III) complex were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and elemental analysis. (68)Ga was obtained by a standard elution method from a (68)Ge/(68)Ga generator. Experiments to evaluate the (68)Ga-labeling efficiency of EOB-DTPA at pH 3.8-4.0 were performed. Established analysis techniques radio TLC (thin layer chromatography) and radio HPLC (high performance liquid chromatography) were used to determine the radiochemical purity of the tracer. As a first investigation of the (68)Ga tracers' lipophilicity the n-octanol/water distribution coefficient of (68)Ga species present in a pH 7.4 solution was determined by an extraction method. In vitro stability measurements of the tracer in various media at physiological pH were performed, revealing different rates of decomposition.

[Modern diagnostics of cystic liver lesions and hemangiomas]

CLINICAL ISSUE

Cystic liver lesions incorporate a broad heterogeneous group of mostly benign but also malignant abnormalities. The radiological aim is the non-invasive diagnosis with the use of different imaging modalities to determine the type of lesion.

STANDARD RADIOLOGICAL METHODS

The common generally asymptomatic incidental findings of cystic lesions on ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) must be classified on the basis of specific imaging features. Such a differentiation is essential because the clinical consequences and the appropriate therapy can vary depending on the underlying pathology. Due to the morphological overlap of many cystic lesions, conventional radiological methods are often insufficient.

METHODICAL INNOVATIONS

The huge advances in cross-sectional imaging (multidetector CT, MRI with special sequences and different contrast agents and MR cholangiopancreatography) in combination with the clinical history usually enable a non-invasive diagnosis. Pathognomonic morphological and hemodynamic lesion features, as well as a knowledge of the pathomechanisms, help to differentiate this broad spectrum of entities.

ACHIEVEMENTS

In this article the different entities of cystic liver lesions, together with the appropriate diagnostic method for detection and distinction and including their strengths and limitations, are demonstrated.

PRACTICAL RECOMMENDATIONS

A well-founded knowledge about the development of various cystic liver lesions and the suitable choice of imaging method facilitate a non-invasive diagnosis.

[Radiological diagnosis of primary hepatic malignancy]

Modern radiology offers countless opportunities both in the detection but also in the characterization of primary liver malignancies. Ultrasound remains usually the first exploratory overview study whereat using ultrasound contrast agent for a further characterization of liver lesions improves this technique considerably. Advanced cross-sectional imaging methods can, in most cases, already provide an exact diagnosis. Thus, the CT is already considered a standard technique for liver imaging and magnetic resonance imaging has gained in recent years due to liver-specific contrast agents and faster sequences a central role in liver imaging. The following article provides an overview of these various radiological procedures and describes the different primary liver malignancies and their imaging characteristics.

[Benign focal hepatic lesions]

A profound knowledge of the various benign focal hepatic lesions and selection of the most suitable radiological examination modality is essential for achieving an accurate characterization of a hepatic lesion and in turn will determine the further patient management. This will avoid unnecessary agitation to both patient and the referring clinician and limits time-consuming, costly and risky biopsies to an absolute minimum. The following article will discuss the typical and atypical appearances of the most frequent and clinically relevant benign focal hepatic lesions with ultrasound, computed tomography and magnetic resonance imaging.

[New developments in MRI of the liver]

Radiology has gained an exceptional position in medicine because a correct diagnosis is the most crucial issue in determining an accurate and personalized therapeutic strategy. This has a direct influence not only on the individual patient but also on the socio-economic aspects of healthcare services in terms of shortening the time interval to establish a diagnosis and to avoid risk-associated invasive diagnostic methods or long-term, cost-intensive follow-up. Magnetic resonance imaging (MRI) is an excellent example of this which due to continuous technological developments and emerging techniques allows a non-invasive diagnosis of the different hepatic diseases. In this article, we illustrate the direct correlation between the recent technical advances in MRI, such as 3.0 T, diffusion-weighted imaging, perfusion imaging, spectroscopy, texture analysis and MR elastography and obtaining a confident non-invasive diagnosis of focal and diffuse liver diseases.

Gadoxetate disodium-enhanced MRI of the liver: part 1, protocol optimization and lesion appearance in the noncirrhotic liver

OBJECTIVE

The purpose of this article is to review the pharmacokinetic and pharmacodynamic properties of gadoxetate disodium (Gd-EOB-DTPA), to describe a workflow-optimized pulse sequence protocol, and to illustrate the imaging appearance of focal lesions in the noncirrhotic liver.

CONCLUSION

Gd-EOB-DTPA allows a comprehensive evaluation of the liver with the acquisition of both dynamic and hepatocyte phase images. This provides potential additional information, especially for the detection and characterization of small liver lesions. However, protocol optimization is necessary for improved image quality and workflow.

Magnetic resonance imaging of liver malignancies

The histological structure of the liver is complex, consisting of hepatocytes, biliary epithelium, and mesenchymal cells. From this large variety of cells, a broad spectrum of benign and malignant liver lesions in originate. An accurate diagnosis of these lesions is mandatory for choosing an appropriate therapeutic approach. With the recent developments in hardware and software, magnetic resonance imaging (MRI) has emerged as the method of choice in the diagnostic workup of focal liver lesions, in particular in the pretherapeutic stage. The introduction of high-field MRI at 3.0 T in the routine workup and the selective use of liver-specific contrast agents, including hepatobiliary and reticuloendothelial agents, have also strengthened the role of MRI in liver imaging. In this overview article, we will review the recent developments in 3.0-T MRI and MRI contrast agents in the diagnostic workup of the most common malignant liver tumors.

Technology Insight: advances in liver imaging

The role of diagnostic imaging in the assessment of liver disease continues to gain in importance. The classic techniques used for liver imaging are ultrasonography, CT and MRI. In the past decade, there have been significant advances in all three techniques. In this article, we discuss the advances in ultrasonography, CT and MRI that have improved assessment of focal and diffuse liver disease, including the development of hardware, software, processing algorithms and procedural innovations.