MR contrast agents for liver imaging: what, when, how

Safe and Informed Use of Gadolinium-Based Contrast Agent in Body Magnetic Resonance Imaging: Where We Were and Where We Are

Gadolinium-based contrast agents (GBCAs) have helped to improve the role of magnetic resonance imaging (MRI) for the diagnosis and treatment of diseases. There are currently nine different commercially available gadolinium-based contrast agents (GBCAs) that can be used for body MRI cases, and which are classifiable according to their structures (cyclic or linear) or biodistribution (extracellular-space agents, target/specific-agents, and blood-pool agents). The aim of this review is to illustrate the commercially available MRI contrast agents, their effect on imaging, and adverse reaction on the body, with the goal to lead to their proper selection in different clinical contexts. When we have to choose between the different GBCAs, we have to consider several factors: (1) safety and clinical impact; (2) biodistribution and diagnostic application; (3) higher relaxivity and better lesion detection; (4) higher stability and lower tissue deposit; (5) gadolinium dose/concentration and lower volume injection; (6) pulse sequences and protocol optimization; (7) higher contrast-to-noise ratio at 3.0 T than at 1.5 T. Knowing the patient's clinical information, the relevant GBCAs properties and their effect on body MRI sequences are the key features to perform efficient and high-quality MRI examination.

Spatiotemporal knowledge teacher-student reinforcement learning to detect liver tumors without contrast agents

Detecting Liver tumors without contrast agents (CAs) has shown great potential to advance liver cancer screening. It enables the provision of a reliable liver tumor-detecting result from non-enhanced MR images comparable to the radiologists' results from CA-enhanced MR images, thus eliminating the high risk of CAs, preventing an experience gap between radiologists and simplifying clinical workflows. In this paper, we proposed a novel spatiotemporal knowledge teacher-student reinforcement learning (SKT-RL) as a safe, speedy, and inexpensive contrast-free technology for liver tumor detection. Our SKT-RL builds a teacher-student framework to realize the exploring of explicit liver tumor knowledge from a teacher network on clear contrast-enhanced images to guide a student network to detect tumors from non-enhanced images directly. Importantly, our STK-RL enables three novelties in aspects of construction, transferring, and optimization to tumor knowledge to improve the guide effect. (1) A new spatiotemporal ternary knowledge set enables the construction of accurate knowledge that allows understanding of DRL's behavior (what to do) and reason (why to do it) behind reliable detection within each state and between their related historical states. (2) A novel pixel momentum transferring strategy enables detailed and controlled knowledge transfer ability. It transfers knowledge at a pixel level to enlarge the explorable space of transferring and control how much knowledge is transferred to prevent over-rely of the student to the teacher. (3) A phase-trend reward function designs different evaluations according to different detection phases to optimal for each phase in high-precision but also allows reward trend to constraint the evaluation to improve stability. Comprehensive experiments on a generalized liver tumor dataset with 375 patients (including hemangiomas, hepatocellular carcinoma, and normal controls) show that our novel SKT-RL attains a new state-of-the-art performance (improved precision by at least 4% when comparing the six recent advanced methods) in the task of liver tumor detection without CAs. The results proved that our SKT-DRL has greatly promoted the development and deployment of contrast-free liver tumor technology.

Liver metastases: The role of magnetic resonance imaging

The liver is one of the organs most commonly involved in metastatic disease, especially due to its unique vascularization. It's well known that liver metastases represent the most common hepatic malignant tumors. From a practical point of view, it's of utmost importance to evaluate the presence of liver metastases when staging oncologic patients, to select the best treatment possible, and finally to predict the overall prognosis. In the past few years, imaging techniques have gained a central role in identifying liver metastases, thanks to ultrasonography, contrast-enhanced computed tomography (CT), and magnetic resonance imaging (MRI). All these techniques, especially CT and MRI, can be considered the non-invasive reference standard techniques for the assessment of liver involvement by metastases. On the other hand, the liver can be affected by different focal lesions, sometimes benign, and sometimes malignant. On these bases, radiologists should face the differential diagnosis between benign and secondary lesions to correctly allocate patients to the best management. Considering the above-mentioned principles, it's extremely important to underline and refresh the broad spectrum of liver metastases features that can occur in everyday clinical practice. This review aims to summarize the most common imaging features of liver metastases, with a special focus on typical and atypical appearance, by using MRI.

Biogenic Imaging Contrast Agents

Imaging contrast agents are widely investigated in preclinical and clinical studies, among which biogenic imaging contrast agents (BICAs) are developing rapidly and playing an increasingly important role in biomedical research ranging from subcellular level to individual level. The unique properties of BICAs, including expression by cells as reporters and specific genetic modification, facilitate various in vitro and in vivo studies, such as quantification of gene expression, observation of protein interactions, visualization of cellular proliferation, monitoring of metabolism, and detection of dysfunctions. Furthermore, in human body, BICAs are remarkably helpful for disease diagnosis when the dysregulation of these agents occurs and can be detected through imaging techniques. There are various BICAs matched with a set of imaging techniques, including fluorescent proteins for fluorescence imaging, gas vesicles for ultrasound imaging, and ferritin for magnetic resonance imaging. In addition, bimodal and multimodal imaging can be realized through combining the functions of different BICAs, which helps overcome the limitations of monomodal imaging. In this review, the focus is on the properties, mechanisms, applications, and future directions of BICAs.

Hydrophilic Copolymers with Hydroxamic Acid Groups as a Protective Biocompatible Coating of Maghemite Nanoparticles: Synthesis, Physico-Chemical Characterization and MRI Biodistribution Study

Superparamagnetic iron oxide nanoparticles (SPION) with a "non-fouling" surface represent a versatile group of biocompatible nanomaterials valuable for medical diagnostics, including oncology. In our study we present a synthesis of novel maghemite (γ-Fe₂O₃) nanoparticles with positive and negative overall surface charge and their coating by copolymer P(HPMA-co-HAO) prepared by RAFT (reversible addition-fragmentation chain-transfer) copolymerization of N-(2-hydroxypropyl)methacrylamide (HPMA) with N-[2-(hydroxyamino)-2-oxo-ethyl]-2-methyl-prop-2-enamide (HAO). Coating was realized via hydroxamic acid groups of the HAO comonomer units with a strong affinity to maghemite. Dynamic light scattering (DLS) demonstrated high colloidal stability of the coated particles in a wide pH range, high ionic strength, and the presence of phosphate buffer (PBS) and serum albumin (BSE). Transmission electron microscopy (TEM) images show a narrow size distribution and spheroid shape. Alternative coatings were prepared by copolymerization of HPMA with methyl 2-(2-methylprop-2-enoylamino)acetate (MMA) and further post-polymerization modification with hydroxamic acid groups, carboxylic acid and primary-amino functionalities. Nevertheless, their colloidal stability was worse in comparison with P(HPMA-co-HAO). Additionally, P(HPMA-co-HAO)-coated nanoparticles were subjected to a bio-distribution study in mice. They were cleared from the blood stream by the liver relatively slowly, and their half-life in the liver depended on their charge; nevertheless, both cationic and anionic particles revealed a much shorter metabolic clearance rate than that of commercially available ferucarbotran.

Medical Imaging Technology and Imaging Agents

Medical imaging is a technology that studies the interaction between human body and irradiations of X-ray, ultrasound, magnetic field, etc. and represents anatomical structures of human organs/tissues with the implication of irradiation attenuation in the form of grayscales. With these medical images, detailed information on health status and disease diagnosis may be judged by clinical physicians to determine an appropriate therapy approach. This chapter will give a systematic introduction on the modalities, classifications, basic principles, and biomedical applications of traditional medical imaging along with the types, construction, and major features of the corresponding contrast agents or imaging probes.

Contrast Agents for Hepatocellular Carcinoma Imaging: Value and Progression

Hepatocellular carcinoma (HCC) has the third-highest incidence in cancers and has become one of the leading threats to cancer death. With the research on the etiological reasons for cirrhosis and HCC, early diagnosis has been placed great hope to form a favorable prognosis. Non-invasive medical imaging, including the associated contrast media (CM)-based enhancement scan, is taking charge of early diagnosis as mainstream. Meanwhile, it is notable that various CM with different advantages are playing an important role in the different imaging modalities, or even combined modalities. For both physicians and radiologists, it is necessary to know more about the proper imaging approach, along with the characteristic CM, for HCC diagnosis and treatment. Therefore, a summarized navigating map of CM commonly used in the clinic, along with ongoing work of agent research and potential seeded agents in the future, could be a needed practicable aid for HCC diagnosis and prognosis.

Assessment of iron nanoparticle distribution in mouse models using ultrashort-echo-time MRI

Microscopic magnetic field inhomogeneities caused by iron deposition or tissue-air interfaces may result in rapid decay of transverse magnetization in MRI. The aim of this study is to detect and quantify the distribution of iron-based nanoparticles in mouse models by applying ultrashort-echo-time (UTE) sequences in tissues exhibiting extremely fast transverse relaxation. In 24 C57BL/6 mice (two controls), suspensions containing either non-oxidic Fe or AuFeO_x nanoparticles were injected into the tail vein at two doses (200 μg and 600 μg per mouse). Mice underwent MRI using a UTE sequence at 4.7 T field strength with five different echo times between 100 μs and 5000 μs. Transverse relaxation times T₂ * were computed for the lung, liver, and spleen by mono-exponential fitting. In UTE imaging, the MRI signal could reliably be detected even in liver parenchyma exhibiting the highest deposition of nanoparticles. In animals treated with Fe nanoparticles (600 μg per mouse), the relaxation time substantially decreased in the liver (3418 ± 1534 μs (control) versus 228 ± 67 μs), the spleen (2170 ± 728 μs versus 299 ± 97 μs), and the lungs (663 ± 101 μs versus 413 ± 99 μs). The change in transverse relaxation was dependent on the number and composition of the nanoparticles. By pixel-wise curve fitting, T₂ * maps were calculated showing nanoparticle distribution. In conclusion, UTE sequences may be used to assess and quantify nanoparticle distribution in tissues exhibiting ultrafast signal decay in MRI.

Platinum Nanoparticles in Biomedicine: Preparation, Anti-Cancer Activity, and Drug Delivery Vehicles

Cancer is the main cause of morbidity and mortality worldwide, excluding infectious disease. Because of their lack of specificity in chemotherapy agents are used for cancer treatment, these agents have severe systemic side effects, and gradually lose their therapeutic effects because most cancers become multidrug resistant. Platinum nanoparticles (PtNPs) are relatively new agents that are being tested in cancer therapy. This review covers the various methods for the preparation and physicochemical characterization of PtNPs. PtNPs have been shown to possess some intrinsic anticancer activity, probably due to their antioxidant action, which slows tumor growth. Targeting ligands can be attached to functionalized metal PtNPs to improve their tumor targeting ability. PtNPs-based therapeutic systems can enable the controlled release of drugs, to improve the efficiency and reduce the side effects of cancer therapy. Pt-based materials play a key role in clinical research. Thus, the diagnostic and medical industries are exploring the possibility of using PtNPs as a next-generation anticancer therapeutic agent. Although, biologically prepared nanomaterials exhibit high efficacy with low concentrations, several factors still need to be considered for clinical use of PtNPs such as the source of raw materials, stability, solubility, the method of production, biodistribution, accumulation, controlled release, cell-specific targeting, and toxicological issues to human beings. The development of PtNPs as an anticancer agent is one of the most valuable approaches for cancer treatment. The future of PtNPs in biomedical applications holds great promise, especially in the area of disease diagnosis, early detection, cellular and deep tissue imaging, drug/gene delivery, as well as multifunctional therapeutics.

Evaluation of Multisource Adaptive MRI Fusion for Gross Tumor Volume Delineation of Hepatocellular Carcinoma

Purpose

Tumor delineation plays a critical role in radiotherapy for hepatocellular carcinoma (HCC) patients. The incorporation of MRI might improve the ability to correctly identify tumor boundaries and delineation consistency. In this study, we evaluated a novel Multisource Adaptive MRI Fusion (MAMF) method in HCC patients for tumor delineation.

Methods

Ten patients with HCC were included in this study retrospectively. Contrast-enhanced T1-weighted MRI at portal-venous phase (T1W_PP), contrast-enhanced T1-weighted MRI at 19-min delayed phase (T1W_DP), T2-weighted (T2W), and diffusion-weighted MRI (DWI) were acquired on a 3T MRI scanner and imported to in-house-developed MAMF software to generate synthetic MR fusion images. The original multi-contrast MR image sets were registered to planning CT by deformable image registration (DIR) using MIM. Four observers independently delineated gross tumor volumes (GTVs) on the planning CT, four original MR image sets, and the fused MRI for all patients. Tumor contrast-to-noise ratio (CNR) and Dice similarity coefficient (DSC) of the GTVs between each observer and a reference observer were measured on the six image sets. Inter-observer and inter-patient mean, SD, and coefficient of variation (CV) of the DSC were evaluated.

Results

Fused MRI showed the highest tumor CNR compared to planning CT and original MR sets in the ten patients. The mean ± SD tumor CNR was 0.72 ± 0.73, 3.66 ± 2.96, 4.13 ± 3.98, 4.10 ± 3.17, 5.25 ± 2.44, and 9.82 ± 4.19 for CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively. Fused MRI has the minimum inter-observer and inter-patient variations as compared to original MR sets and planning CT sets. GTV delineation inter-observer mean DSC across the ten patients was 0.81 ± 0.09, 0.85 ± 0.08, 0.88 ± 0.04, 0.89 ± 0.08, 0.90 ± 0.04, and 0.95 ± 0.02 for planning CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively. The patient mean inter-observer CV of DSC was 3.3%, 3.2%, 1.7%, 2.6%, 1.5%, and 0.9% for planning CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively.

Conclusion

The results demonstrated that the fused MRI generated using the MAMF method can enhance tumor CNR and improve inter-observer consistency of GTV delineation in HCC as compared to planning CT and four commonly used MR image sets (T1W_PP, T1W_DP, T2W, and DWI). The MAMF method holds great promise in MRI applications in HCC radiotherapy treatment planning.

Treatment and diagnosis of chemotherapy-induced peripheral neuropathy: An update

When peripheral neuropathy occurs due to chemotherapy treatment, it is referred to as chemotherapy-induced peripheral neuropathy (CIPN). Typically, symptoms are sensory rather than motor and include reduced feeling and heightened sensitivity to pressure, pain, temperature, and touch. The pathophysiology of CIPN is very complex, and it involves multiple mechanisms leading to its development which will be described specifically for each chemotherapeutic class. There are currently no approved or effective agents for CIPN prevention, and Duloxetine is the only medication that is an effective treatment against CIPN. There is an unavoidable necessity to develop preventative and treatment approaches for CIPN due to its detrimental impact on patients' lives. The purpose of this review is to examine CIPN, innovative pharmacological and nonpharmacological therapy and preventive strategies for this illness, and future perspectives for this condition and its therapies.

Liver magnetic resonance imaging: how we do it

Magnetic resonance imaging is used for evaluating focal liver lesions, hepatic vascular diseases, biliary diseases and diffuse liver diseases in children. MRI examinations take a long time, often requiring sedation or anesthesia in smaller children. This makes it essential to understand the concepts and technique necessary to obtain an optimal examination for answering the clinical question while minimizing the need for sedation/anesthesia. We discuss key concepts including appropriate sequence selection, choice of contrast media, dynamic imaging, phases of contrast enhancement and protocol organization.

MR Imaging Contrast Agents: Role in Imaging of Chronic Liver Diseases

Contrast-enhanced MR imaging plays an important role in the evaluation of patients with chronic liver disease, particularly for detection and characterization of liver lesions. The two most commonly used contrast agents for liver MR imaging are extracellular agents (ECAs) and hepatobiliary agents (HBAs). In patients with liver disease, the main advantage of ECA-enhanced MR imaging is its high specificity for the diagnosis of progressed HCCs. Conversely, HBAs have an additional contrast mechanism, which results in high liver-to-lesion contrast and highest sensitivity for lesion detection in the hepatobiliary phase. Emerging data suggest that features depicted on contrast-enhanced MR imaging scans are related to tumor biology and are predictive of patients' prognosis, likely to further expand the role of contrast-enhanced MR imaging in the clinical care of patients with chronic liver disease.

Targeted Regulation of Blood-Brain Barrier for Enhanced Therapeutic Efficiency of Hypoxia-Modifier Nanoparticles and Immune Checkpoint Blockade Antibodies for Glioblastoma

Glioblastoma is the most destructive type of brain cancer. The blood-brain barrier (BBB) is a tremendous obstacle that hinders therapeutic agents, such as chemical drugs and antibodies, from reaching glioblastoma tissues. Meanwhile, the abnormal microenvironment of glioblastoma extremely restricts the expected therapeutic effects of accumulated drugs. Therefore, in the present study, BBB-regulating nanovesicles (BRN) are developed to achieve targeted and controlled BBB regulation, carrying adenosine 2A receptor (A_2AR) agonists and perfluorocarbon (PF). The red-blood-cell membrane (RBCM) is included on the outside to avoid the premature release of therapeutic agents. In the presence of ultrasonication (US), A_2AR agonists are released and induce effects on both F-actin and tight junctions of endothelial cells. Subsequently, BBB permeability is temporarily increased and enables small molecules and nanoparticles to enter brain parenchymal tissues. The high affinity between manganese dioxide and temozolomide (TMZ) is utilized to form multifunctional nanoparticles to ameliorate the hypoxic microenvironment, which yields improved glioblastoma inhibition combined with radiotherapy. Moreover, with the aid of targeted BBB regulation, programmed death ligand-1 (PD-L1) antibody induces a tumor-specific immune response. Taken together, the findings suggest that synergistic combination may have the potential in amplifying the therapeutic efficacies of clinical drugs and immune checkpoint blockade antibodies to overcome the therapeutic resistance of glioblastoma.

Parotid gland tumors: comparison of conventional and diffusion-weighted MRI findings with histopathological results

OBJECTIVES

The aim of this study was to investigate the relationship between pathological classification of parotid gland tumors and conventional MRI - diffusion-weighted imaging findings and also contribute the possible effect of apparent diffusion coefficient (ADC) to diagnosis.

METHODS

60 patients with parotid masses diagnosed using histopathology and/or cytology were enrolled in this retrospective study. All patients were evaluated using a 1.5 T MRI. Demographic features, conventional MRI findings, and ADC values (mean, minimum, maximum, and relative) were recorded. MRI findings and ADC values were compared between benign-malignant groups and pleomorphic adenoma vs Warthin's tumor groups.

RESULTS

60 tumors (48 benign, 12 malignant) were evaluated in a total of 60 patients (39 males, 21 females). The mean age was 59 (±14, 18-86) years old; the mean lesion size was 26 (±10, 11-61) mm. On the texture of conventional MRI, T2 dominantly hyperintense/with hypointensity signal was seen in 87% of pleomorphic adenomas and T2 dominantly hypointense/with hyperintesity signal was encountered in 64% of all Warthin's tumors. Seven (28%) Warthin's tumors were misdiagnosed as pleomorphic adenomas and two others (8%) as malignant tumors. The commonly used mean ADC value was 1.6 ± 0.6 × 10^-3 mm² s^-1 for benign tumors, 0.8 ± 0.3 × 10^-3 mm² s^-1 for malign tumors, 1 (0.9-1.8) × 10^-3 mm² s^-1 for Warthin's tumors, and 1.9 ± 0.3 × 10^-3 mm² s^-1 for pleomorphic adenomas. There was a statistically significant difference in ADC values between benign-malignant tumors and pleomorphic adenomas-Warthin's tumors.

CONCLUSIONS

Warthin's tumor may occasionally be misdiagnosed as pleomorphic adenoma and malignant tumor because of variable morphologic features. In addition to benign-malignant differentiation, the added ADC measurement may also be useful for differentiating Warthin's tumors from pleomorphic adenomas.

Quantification of liver function using gadoxetic acid-enhanced MRI

The introduction of hepatobiliary contrast agents, most notably gadoxetic acid (GA), has expanded the role of MRI, allowing not only a morphologic but also a functional evaluation of the hepatobiliary system. The mechanism of uptake and excretion of gadoxetic acid via transporters, such as organic anion transporting polypeptides (OATP1,3), multidrug resistance-associated protein 2 (MRP2) and MRP3, has been elucidated in the literature. Furthermore, GA uptake can be estimated on either static images or on dynamic imaging, for example, the hepatic extraction fraction (HEF) and liver perfusion. GA-enhanced MRI has achieved an important role in evaluating morphology and function in chronic liver diseases (CLD), allowing to distinguish between the two subgroups of nonalcoholic fatty liver diseases (NAFLD), simple steatosis and nonalcoholic steatohepatitis (NASH), and help to stage fibrosis and cirrhosis, predict liver transplant graft survival, and preoperatively evaluate the risk of liver failure if major resection is planned. Finally, because of its noninvasive nature, GA-enhanced MRI can be used for long-term follow-up and post-treatment monitoring. This review article aims to describe the current role of GA-enhanced MRI in quantifying liver function in a variety of hepatobiliary disorders.

Advances in functional and molecular MRI technologies in chronic liver diseases

MRI has emerged as the most comprehensive non-invasive diagnostic tool for liver diseases. In recent years, the value of MRI in hepatology has been significantly enhanced by a wide range of contrast agents, both clinically available and under development, that add functional information to anatomically detailed morphological images, or increase the distinction between normal and pathological tissues by targeting molecular and cellular events. Several classes of contrast agents are available for contrast-enhanced hepatic MRI, including i) conventional non-specific extracellular fluid contrast agents for assessing tissue perfusion; ii) hepatobiliary-specific contrast agents that are taken up by functioning hepatocytes and excreted through the biliary system for evaluating hepatobiliary function; iii) superparamagnetic iron oxide particles that accumulate in Kupffer cells; and iv) novel molecular contrast agents that are biochemically targeted to specific molecular/cellular processes for staging liver diseases or detecting treatment responses. The use of different functional and molecular MRI methods enables the non-invasive assessment of disease burden, progression, and treatment response in a variety of liver diseases. A high diagnostic performance can be achieved with MRI by combining imaging biomarkers.

New boundaries of liver imaging: from morphology to function

From an invisible organ to one of the most explored non-invasively, the liver is, today, one of the cornerstones for current cross-sectional imaging techniques and minimally invasive procedures. After the achievements of US, CT and, most recently, MRI in providing highly accurate morphological and structural information about the organ, a significant scientific development has gained momentum for the last decades, coupling morphology to liver function and contributing far most to what we know today as precision medicine. In fact, dedicated tailor-made investigations are now possible in order to detect and, most of all, quantify physiopathological processes with unprecedented certitude. It is the intention of this review to provide a better insight to the reader of several functional imaging techniques applied to liver imaging. Contrast enhanced imaging, diffusion weighted imaging, elastography, spectral computed tomography and fat and iron assessment techniques are commonly performed clinically. Diffusion kurtosis imaging, magnetic resonance spectroscopy, T1 relaxometry and radiomics remain largely limited to advanced clinical research. Each of them has its own value and place on the diagnostic armamentarium and provide unique qualitative and quantitative information regarding the pathophysiology of diseases, contributing at a large scale to model therapeutic decisions and patient follow-up. Therefore, state-of-the-art liver imaging acts today as a non-invasive surrogate biomarker of many focal and diffuse liver diseases.

Diagnostic approach in hepatic lymphoma: radiological imaging findings and literature review

PURPOSE

Imaging manifestations of hepatic lymphoma, both primary (PHL) and secondary (SHL), are extremely variable and non-specific, but some features are useful diagnostic clues in an appropriate clinical setting. Through a PubMed search, we found several published reviews focused on PHL and SHL diagnosis. However, to the best of our knowledge, few of them encompass a comprehensive analysis of all the diagnostic tools and relative radiological findings. The aim of this review is to provide a description of the radiological features of both PHL and SHL, by critically analyzing the available literature.

MATERIALS AND METHODS

An extensive review of published literature along with a description of personal case series of both PHL and SHL has been conducted.

RESULTS

SHL can be easily diagnosed with imaging techniques, as it is usually associated with node disease. On the contrary the diagnosis can be a challenge in PHL, often mimicking HCC or liver metastasis of adenocarcinoma. In this context, multiparametric MRI plays a fundamental role in the differential diagnosis. Both for PHL and SHL, liver involvement presents as solitary or multiple lesions or as diffuse infiltrative disease.

CONCLUSION

PHL and SHL may be correctly characterized using different radiological techniques. Both CT and MRI have showed a good correlation with histology, as they permit to distinguish between lymphomatous tissue, and necrotic and fibrotic areas.

Pearls and pitfalls in magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary hepatic malignancy, which usually arises in cirrhotic liver. When the typical enhancement pattern, consisting of late arterial hyperenhancement followed by washout, is present in nodules larger than 1 cm, HCC can be confidently diagnosed without the need for tissue biopsy. Nevertheless, HCC can display an atypical enhancement pattern, either as iso or hypovascular lesion, or hypervascular lesion without washout. Not only the enhancement pattern of HCC could be atypical, but also a variety of histological types of HCC, such as steatotic, scirrhous, fibrolamellar, or combined hepatocellular-cholangiocellular carcinoma could raise diagnostic dilemmas. In addition, distinct morphological types of HCC or different growth pattern can occur. Awareness of these atypical and rare HCC presentations on magnetic resonance imaging is important for accurate differentiation from other focal liver lesions and timely diagnosis, which allows optimal treatment of patients.

Comparison of diagnostic performance of non-contrast MRI and abbreviated MRI using gadoxetic acid in initially diagnosed hepatocellular carcinoma patients: a simulation study of surveillance for hepatocellular carcinomas

OBJECTIVE

This study was conducted in order to compare the diagnostic performance of noncontrast and abbreviated MRI using gadoxetic acid for detecting hepatocellular carcinoma (HCC) in initially diagnosed HCC patients.

METHODS

We identified 140 consecutive patients with newly diagnosed HCC (173 HCCs) within the Milan criteria, who underwent liver MRI using gadoxetic acid between 2015 and 2016. One hundred twenty-three consecutive patients without HCC who underwent liver MRI in the same period for HCC surveillance were enrolled for the control group. Two radiologists independently reviewed two MRI sets: a noncontrast set and an abbreviated set. The noncontrast set consists of T2 FSE/ssFSE, T1 in- and out-of-phase image, DWI, and the ADC map. The abbreviated set consists of T2 FSE/ssFSE, hepatobiliary phase image 20 min after gadoxetic acid injection, DWI, and the ADC map.

RESULTS

In a per-patient analysis, sensitivity of reviewer 1 for noncontrast and abbreviated sets was 85.7 and 90.0%, respectively. The specificity for both noncontrast and abbreviated sets was 92.7%. For reviewer 2, sensitivity of noncontrast and abbreviated sets was 86.4 and 89.3%, respectively. Per-patient specificity of reviewer 2 was 92.7% for both noncontrast and abbreviated sets. The sensitivity and specificity of two image sets were not significantly different for both reviewers. The per-tumor sensitivity of noncontrast and abbreviated sets was 81.5 and 84.4% for reviewer 1, respectively, and 79.8 and 84.4% for reviewer 2, respectively. There was no significant difference.

CONCLUSION

Noncontrast and abbreviated MRI using gadoxetic acid showed comparable diagnostic performance for detecting patients with HCCs in the early stage.

KEY POINTS

• Diagnostic performance of noncontrast MRI and abbreviated MRI using gadoxetic acid for detecting HCCs is comparable in patients with HCCs in the early stage. • Noncontrast MRI and abbreviated MRI showed high sensitivity and specificity for detecting HCCs in the early stage. • Outcomes of surveillance for HCC in high-risk patients can be improved by adopting these simplified and focused MRI protocols.

MRI of the liver: choosing the right contrast agent

Contrast enhanced MRI of the liver provides valuable information in the evaluation of both chronic liver disease and focal liver lesions. Currently, two classes of MRI contrast agents are available for clinical use, namely the extracellular contrast agent (ECA) and the hepatobiliary agent (HBA). The use of appropriate contrast agents for liver MRI requires knowledge of the clinical situation and question to be answered. ECAs have been used for decades since their introduction into clinical practice and provide excellent dynamic phase information that is useful in characterizing focal liver lesions. In the last decade, HBAs, particularly Gadoxetate, have been found useful for characterizing lesions with functioning hepatocytes and more importantly in evaluating the biliary tree. Gadoxetate, however, provides less satisfactory dynamic phase images compared to ECAs, particularly during the arterial phase. In this perspective article, we will discuss the various intravenous contrast agents used for liver MRI and their ideal utilization.

Differential characterization of hepatic tumors in MR imaging by burst-released Mn2+-ions from hollow manganese-silicate nanoparticles in the liver

Gd³⁺-based contrast agents monopolize in the clinical MR imaging-based diagnosis of hepatic tumors, however, the inherent toxicity by the released Gd³⁺-ions triggered an urgent demand for safer alternatives. Here, we demonstrate hollow manganese silicate nanoparticles (HMS), which exert burst-release of Mn²⁺-ions by switching to physiological acidic condition, exhibiting high effectiveness in hepatic tumor characterization as liver-specific MR contrast agent through the in-depth in vivo MR imaging study and immunohistochemical investigations with three hepatic tumor models (e.g., hepatocellular carcinoma, neuroendocrine carcinoma, adenocarcinoma). Their characteristic time-sequential enhancement patterns in HMS-enhanced MR imaging with improved conspicuity reflect their biological features such as vascularity, cellularity, mitochondrial activity and hepatocellular specificity, and thus allow the disease-specific characterization of various hepatic tumors. HMS-enhanced MR imaging with necrotic hepatocellular carcinoma model suggested the good correlation of the extent of tumor necrosis with residual mitochondrial activity. Such multi-responsive spatio-biological distribution and function of HMS resulting in time-dependent bioimaging coupled with low systemic toxicity sets the clinical potential to accurate diagnosis and therapeutic response in various hepatic tumors.

Hepatic tumor classification using texture and topology analysis of non-contrast-enhanced three-dimensional T1-weighted MR images with a radiomics approach

The purpose of this study is to evaluate the accuracy for classification of hepatic tumors by characterization of T1-weighted magnetic resonance (MR) images using two radiomics approaches with machine learning models: texture analysis and topological data analysis using persistent homology. This study assessed non-contrast-enhanced fat-suppressed three-dimensional (3D) T1-weighted images of 150 hepatic tumors. The lesions included 50 hepatocellular carcinomas (HCCs), 50 metastatic tumors (MTs), and 50 hepatic hemangiomas (HHs) found respectively in 37, 23, and 33 patients. For classification, texture features were calculated, and also persistence images of three types (degree 0, degree 1 and degree 2) were obtained for each lesion from the 3D MR imaging data. We used three classification models. In the classification of HCC and MT (resp. HCC and HH, HH and MT), we obtained accuracy of 92% (resp. 90%, 73%) by texture analysis, and the highest accuracy of 85% (resp. 84%, 74%) when degree 1 (resp. degree 1, degree 2) persistence images were used. Our methods using texture analysis or topological data analysis allow for classification of the three hepatic tumors with considerable accuracy, and thus might be useful when applied for computer-aided diagnosis with MR images.

Contrast Agents for MR Imaging

Contrast media are essential to the practice of MR imaging. An increasing variety of agents have been approved for clinical use, specific contrast agents can often be tailored to a specific clinical question. Compared with CT contrast media, MR imaging contrast is well tolerated with an excellent safety record and a low incidence of adverse events. In this article, we review the pharmacology, indications, and the common adverse events of the intravenous and oral MR contrast agents most commonly used in contemporary imaging practice, including gadolinium-based contrast, manganese and iron-based agents and the most common oral contrast agents.

Acoustically modulated magnetic resonance imaging of gas-filled protein nanostructures

Non-invasive biological imaging requires materials capable of interacting with deeply penetrant forms of energy such as magnetic fields and sound waves. Here, we show that gas vesicles (GVs), a unique class of gas-filled protein nanostructures with differential magnetic susceptibility relative to water, can produce robust contrast in magnetic resonance imaging (MRI) at sub-nanomolar concentrations, and that this contrast can be inactivated with ultrasound in situ to enable background-free imaging. We demonstrate this capability in vitro, in cells expressing these nanostructures as genetically encoded reporters, and in three model in vivo scenarios. Genetic variants of GVs, differing in their magnetic or mechanical phenotypes, allow multiplexed imaging using parametric MRI and differential acoustic sensitivity. Additionally, clustering-induced changes in MRI contrast enable the design of dynamic molecular sensors. By coupling the complementary physics of MRI and ultrasound, this nanomaterial gives rise to a distinct modality for molecular imaging with unique advantages and capabilities.

Contributions of Magnetic Resonance Imaging to Gastroenterological Practice: MRIs for GIs

MRI has transformed from the theoretical, investigative realm to mainstream clinical medicine over the past four decades and has become a core component of the diagnostic toolbox in the practice of gastroenterology (GI). Its success is attributable to exquisite contrast and the ability to isolate specific proton species through the use of different pulse sequences (i.e., T1-weighted, T2-weighted, diffusion-weighted) and exploiting extracellular and hepatobiliary contrast agents. Consequently, MRI has gained preeminence in various GI clinical applications: liver and pancreatic lesion evaluation and detection, liver transplantation evaluation, pancreatitis evaluation, Crohn's disease evaluation (using MR enterography) rectal cancer staging and perianal fistula evaluation. MR elastography, in concert with technical innovations allowing for fat and iron quantification, provides a noninvasive approach, or "MRI virtual liver biopsy" for diagnosis and management of chronic liver diseases. In the future, the arrival of ultra-high-field MR systems (7 T) and the ability to perform magnetic resonance spectroscopy in the abdomen promise even greater diagnostic insight into chronic liver disease.

Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications

Despite established clinical utilisation, there is an increasing need for safer, more inert gadolinium-based contrast agents, and for chelators that react rapidly with radiometals. Here we report the syntheses of a series of chiral DOTA chelators and their corresponding metal complexes and reveal properties that transcend the parent DOTA compound. We incorporated symmetrical chiral substituents around the tetraaza ring, imparting enhanced rigidity to the DOTA cavity, enabling control over the range of stereoisomers of the lanthanide complexes. The Gd chiral DOTA complexes are shown to be orders of magnitude more inert to Gd release than [GdDOTA]⁻. These compounds also exhibit very-fast water exchange rates in an optimal range for high field imaging. Radiolabeling studies with (Cu-64/Lu-177) also demonstrate faster labelling properties. These chiral DOTA chelators are alternative general platforms for the development of stable, high relaxivity contrast agents, and for radiometal complexes used for imaging and/or therapy.

MRI contrast agents containing the rare earth metal gadolinium are very effective, yet unstable and thus potentially hazardous. Here, the authors developed complexes between gadolinium and the scaffolding compound DOTA with increased stability, which also lend themselves to radiometal labelling.

Liver metastases: Detection and staging

The liver is more often involved with metastatic disease than primary liver tumors. The accurate detection and characterization of liver metastases are crucial since patient management depends on it. The imaging options, mainly consisting of contrast-enhanced ultrasound (CEUS), multidetector computed tomography (CT), magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI), extra-cellular contrast media and liver-specific contrast media as well as positron emission tomography/computed tomography (PET/CT), are constantly evolving. PET/MRI is a more recent hybrid method and a topic of major interest concerning liver metastases detection and characterization. This review gives a brief overview about the spectrum of imaging findings and focus on an update about the performance, advantages and potential limitations of each modality as well as current developments and innovations.

Interpreting body MRI cases: what you need to know to get started

Interpreting body MRI cases can seem overwhelming to an uninitiated radiologist. The standard study includes a variety of pulse sequences, the names of which vary depending on the MR vendor. Pulse sequences may be displayed haphazardly on the picture archiving and communication system (PACS), frequently not synchronized with the imaging protocol. Adding to the complexity is the use of different gadolinium-based contrast agents, which may affect the timing and diagnostic yield of each sequence. The following introductory primer for interpreting body MRI cases is meant to create a basic framework for efficiently reviewing body MRI cases to provide high quality interpretations, fully utilizing the diagnostic information of the modality. There are 4 components that need to be mastered when interpreting body MRI cases including: (1) recognizing the key sequences in a basic body MRI protocol, (2) learning how to best display the key pulse sequences on PACS, (3) understanding the technique and clinical utility of each sequence and learning how to utilize sequences to be an "MR Pathologist", and (4) understanding the key features of the different gadolinium based contrast agents.

FIRST BRAZILIAN CONSENSUS ON MULTIMODAL TREATMENT OF COLORECTAL LIVER METASTASES. MODULE 1: PRE-TREATMENT EVALUATION

Background

: Liver metastases of colorectal cancer are frequent and potentially fatal event in the evolution of patients with these tumors.

Aim

: In this module, was contextualized the clinical situations and parameterized epidemiological data and results of the various treatment modalities established.

Method:

Was realized deep discussion on detecting and staging metastatic colorectal cancer, as well as employment of imaging methods in the evaluation of response to instituted systemic therapy.

Results

: The next step was based on the definition of which patients would have their metastases considered resectable and how to expand the amount of patients elegible for modalities with curative intent.

Conclusion

: Were presented clinical, pathological and molecular prognostic factors, validated to be taken into account in clinical practice.

MRI contrast agents: Classification and application (Review)

Magnetic resonance imaging (MRI) contrast agents are categorised according to the following specific features: chemical composition including the presence or absence of metal atoms, route of administration, magnetic properties, effect on the magnetic resonance image, biodistribution and imaging applications. The majority of these agents are either paramagnetic ion complexes or superparamagnetic magnetite particles and contain lanthanide elements such as gadolinium (Gd3+) or transition metal manganese (Mn2+). These elements shorten the T1 or T2 relaxation time, thereby causing increased signal intensity on T1-weighted images or reduced signal intensity on T2-weighted images. Most paramagnetic contrast agents are positive agents. These agents shorten the T1, so the enhanced parts appear bright on T1-weighted images. Dysprosium, superparamagnetic agents and ferromagnetic agents are negative contrast agents. The enhanced parts appear darker on T2-weighted images. MRI contrast agents incorporating chelating agents reduces storage in the human body, enhances excretion and reduces toxicity. MRI contrast agents may be administered orally or intravenously. According to biodistribution and applications, MRI contrast agents may be categorised into three types: extracellular fluid, blood pool and target/organ-specific agents. A number of contrast agents have been developed to selectively distinguish liver pathologies. Some agents are also capable of targeting other organs, inflammation as well as specific tumors.

3-Aminopropylsilane-modified iron oxide nanoparticles for contrast-enhanced magnetic resonance imaging of liver lesions induced by Opisthorchis felineus

Purpose

Liver fluke causes severe liver damage in an infected human. However, the infection often remains neglected due to the lack of pathognomonic signs. Nanoparticle-enhanced magnetic resonance imaging (MRI) offers a promising technique for detecting liver lesions induced by parasites.

Materials and methods

Surface modification of iron oxide nanoparticles produced by coprecipitation from a solution of Fe³⁺ and Fe²⁺ salts using 3-aminopropylsilane (APS) was carried out. The APS-modified nanoparticles were characterized by transmission electron microscopy, fourier transform infrared spectroscopy, and thermogravimetric analysis. Magnetic resonance properties of MNPs were investigated in vitro and in vivo.

Results

The amount of APS grafted on the surface of nanoparticles (0.60±0.06 mmol g⁻¹) was calculated based on elemental analysis and infrared spectroscopy data. According to transmission electron microscopy data, there were no essential changes in the structure of nanoparticles during the modification. The APS-modified nanoparticles exhibit high magnetic properties; the calculated relaxivity r₂ was 271 mmol⁻¹ s⁻¹. To obtain suspension with optimal hydrodynamic characteristics, amino groups on the surface of nanoparticles were converted into an ionic form with HCl. Cellular uptake of modified nanoparticles by rat hepatoma cells and human monocytes in vitro was 74.1±4.5 and 10.0±3.7 pg [Fe] per cell, respectively. Low cytotoxicity of the nanoparticles was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Annexin V/7-aminoactinomycin D flow cytometry assays. For the first time, magnetic nanoparticles were applied for contrast-enhanced MRI of liver lesions induced by Opisthorchis felineus.

Conclusion

The synthesized APS-modified iron oxide nanoparticles showed high efficiency as an MRI contrast agent for the evaluation of opisthorchiasis-related liver damage.

Alternatives to GBCA: Are We There Yet?

Gadolinium has been widely used as the contrast agent of choice for magnetic resonance imaging (MRI). However, gadolinium administration is not always desired due to its inherent enhancement properties and potential side effects (nephrogenic systemic fibrosis). This article reviews gadolinium alternatives, iron-, and manganese- based agents, and their current clinical usage for contrast-enhanced MRI examinations.

Hepatoblastoma in Explanted Livers of Patients With Biliary Atresia

OBJECTIVES

Surveillance of hepatic nodules for malignant transformation to hepatocellular carcinoma is important in the monitoring of patients with biliary atresia (BA). To date, only 2 published case reports describe the finding of hepatoblastoma (HB) in this setting. The present study aimed to investigate this association of HB and BA, and to assess the utility of alpha-fetoprotein (aFP) as a marker in the diagnosis.

METHODS

A retrospective study of all patients who underwent isolated liver transplantation (LTx) for the primary diagnosis of BA at a single center, between January 1999 and June 2014, was conducted. Patient demographics, pre-LTx aFP levels, and histologic examination of native liver explants were reviewed.

RESULTS

One hundred two (44% men, median age 11 months) patients underwent LTx for BA. Two (2%) explants examinations were confirmatory for concomitant HB; both patients had abnormally elevated aFP. Overall, 56 (55%) patients had available pre-LTx aFP levels. Recipients with persistently abnormal aFP levels (n = 20, 36%) were older at hepatoportoenterostomy (107 vs 68 days, P = 0.02) and younger at LTx surgery (359 vs 1713 days, P < 0.01), compared to patients with constantly normal levels (n = 24, 43%).

CONCLUSIONS

In our cohort, HB was found to coexist in approximately 2% of patients with BA undergoing LTx, far exceeding the hypothetical anticipated incidence of 1:10 billion for the concomitant diagnoses. Elevated serum aFP levels may be sensitive but not specific for HB in this context. Further research is required to identify specific mechanisms and risk factors.

Contrast agents in diagnostic imaging: Present and future

Specific contrast agents have been developed for x ray examinations (mainly CT), sonography and Magnetic Resonance Imaging. Most of them are extracellular agents which create different enhancement on basis of different vascularization or on basis of different interstitial network in tissues, but some can be targeted to a particular cell line (e.g. hepatocyte). Microbubbles can be used as carrier for therapeutic drugs which can be released in specific targets under sonographic guidance, decreasing systemic toxicity and increasing therapeutic effect. Radiologists have to choose a particular contrast agent knowing its physical and chemical properties and the possibility of adverse reactions and balancing them with the clinical benefits of a more accurate diagnosis. As for any drug, contrast agents can cause adverse events, which are more frequent with Iodine based CA, but also with Gd based CA and even with sonographic contrast agents hypersensitivity reaction can occur.

Recent advances in the imaging of hepatocellular carcinoma

The role of imaging is crucial for the surveillance, diagnosis, staging and treatment monitoring of hepatocellular carcinoma (HCC). Over the past few years, considerable technical advances were made in imaging of HCCs. New imaging technology, however, has introduced new challenges in our clinical practice. In this article, the current status of clinical imaging techniques for HCC is addressed. The diagnostic performance of imaging techniques in the context of recent clinical guidelines is also presented.

Novel Mn3 [Co(CN)6]2@SiO2@Ag Core-Shell Nanocube: Enhanced Two-Photon Fluorescence and Magnetic Resonance Dual-Modal Imaging-Guided Photothermal and Chemo-therapy

The versatile Mn3[Co(CN)6]2@SiO2@Ag core-shell NCs are prepared by a simple coprecipitation method. Ag nanoparticles with an average diameter of 12 nm deposited on the surface of Mn3[Co(CN)6]2@SiO2 through S-Ag bonding are fabricated in ethanol solution by reducing silver nitrate (AgNO3 ) with NaBH4 . The NCs possess T1 -T2 dual-modal magnetic resonance imaging ability. The inner Prussian blue analogs (PBAs) Mn3[Co(CN)6]2 exhibit bright two-photon fluorescence (TPF) imaging when excited at 730 nm. Moreover, the TPF imaging intensity displays 1.85-fold enhancement after loading of Ag nanoparticles. Besides, the sample also has multicolor fluorescence imaging ability under 403, 488, and 543 nm single photon excitation. The as-synthesized Mn3[Co(CN)6]2@SiO2@Ag NCs show a DOX loading capacity of 600 mg g(-1) and exhibit an excellent ability of near-infrared (NIR)-responsive drug release and photothermal therapy (PTT) which is induced from the relative high absorbance in NIR region. The combined chemotherapy and PTT against cancer cells in vitro test shows high therapeutic efficiency. The multimodal treatment and imaging could lead to this material a potential multifunctional system for biomedical diagnosis and therapy.

Renal safety of intravenous gadolinium-enhanced magnetic resonance imaging in patients awaiting liver transplantation

Renal dysfunction in cirrhosis carries a high morbidity and mortality. Given the potential risk of contrast-induced nephropathy associated with iodinated intravenous contrast used in computed tomography (CT), alternate contrast modalities for abdominal imaging in liver transplant candidates need to be examined. The purpose of this study was to examine the renal safety of magnetic resonance imaging (MRI) with gadolinium in patients awaiting liver transplantation. The study involved a retrospective analysis of 352 patients of abdominal MRI with low-dose gadobenate dimeglumine (MultiHance) (0.05 mmol/kg) in patients with cirrhosis and without renal replacement therapy at a single center during the period from 2007 to 2013. For each case, serum creatinine before and within a few days after the MRI were compared. In addition, the patients were analyzed for the development of nephrogenic systemic fibrosis (NSF), a reported complication of gadolinium in chronic kidney disease. The pre-MRI serum creatinine values ranged from 0.36 to 4.86 mg/dL, with 70 patients (20%) having values ≥ 1.5 mg/dL. A comparison of the pre- and post-MRI serum creatinine values did not demonstrate a clinically significant difference (mean change = 0.017 mg/dL; P = 0.38), including those patients with a pre-MRI serum creatinine ≥ 1.5 mg/dL. In addition, no cases of NSF were noted. In conclusion, our findings suggest that MRI with low-dose gadobenate dimeglumine (MultiHance) is a nonnephrotoxic imaging modality in liver transplant candidates, and its use can be cautiously expanded to liver transplant candidates with concomitant renal insufficiency.

Superparamagnetic iron oxide nanoparticles for in vivo molecular and cellular imaging

In the last decade, the biomedical applications of nanoparticles (NPs) (e.g. cell tracking, biosensing, magnetic resonance imaging (MRI), targeted drug delivery, and tissue engineering) have been increasingly developed. Among the various NP types, superparamagnetic iron oxide NPs (SPIONs) have attracted considerable attention for early detection of diseases due to their specific physicochemical properties and their molecular imaging capabilities. A comprehensive review is presented on the recent advances in the development of in vitro and in vivo SPION applications for molecular imaging, along with opportunities and challenges.

Primary leiomyoma of the liver: a review of a rare tumour

Context. Primary leiomyoma of the liver is a rare tumour with uncertain pathogenesis with similar presentation with other tumours of the liver. Little is known about its clinical course. Objectives. To review the literature for case reports of primary leiomyoma of the liver. Methods. Extensive literature search was carried out for case reports of primary leiomyoma of the liver. Results. A total of 36 cases of primary leiomyoma of the liver were reviewed. The mean age of presentation is 43 years with slight female sex affectation; females accounted for 55.6% of the cases reported in the literature. The average size of the tumour is 8.7 cm. 34.4% of the cases reviewed were incidental finding with the mean follow-up time of 33 months with most cases reporting no evidence of disease. Conclusions. Primary leiomyoma of the liver is very rare tumour with complex pathogenesis which remains largely unknown. Imaging of the tumour does not allow for a tissue specific diagnosis; hence histological review of the tissue specimen and immunohistochemical stains are imperative for diagnosis. Surgical resection is both diagnostic and curative. The diagnosis of primary leiomyoma of the liver should be considered as a differential in the management of liver tumours.

High correlation between microbubble contrast-enhanced ultrasound, magnetic resonance and histopathology in the evaluation of hepatocellular carcinoma

OBJECTIVES

To evaluate the efficacy of microbubble contrast ultrasound in diagnosis of hepatocellular carcinoma and to compare its results with those of magnetic resonance and histopathology.

METHODS

A total of 29 patients suffering from chronic liver diseases and awaiting liver transplants at Hospital Israelita Albert Einstein were subject to magnetic resonance, microbubble contrast ultrasound, and excision liver biopsies.

RESULTS

Excellent agreement between magnetic resonance and microbubble contrast ultrasound was observed in this study. There was moderate agreement between both imaging methods and histopathology results.

CONCLUSION

Microbubble contrast ultrasound was as accurate as magnetic resonance to evaluate hepatocellular carcinoma. These results were confirmed by comparing both methods to histopathological diagnosis.