MRI Gadolinium-Based Contrast Media: Meeting Radiological, Clinical, and Environmental Needs

Gadolinium-based contrast agents (GBCAs) are routinely used in magnetic resonance imaging (MRI). They are essential for choosing the most appropriate medical or surgical strategy for patients with serious pathologies, particularly in oncologic, inflammatory, and cardiovascular diseases. However, GBCAs have been associated with an increased risk of nephrogenic systemic fibrosis in patients with renal failure, as well as the possibility of deposition in the brain, bones, and other organs, even in patients with normal renal function. Research is underway to reduce the quantity of gadolinium injected, without compromising image quality and diagnosis. The next generation of GBCAs will enable a reduction in the gadolinium dose administered. Gadopiclenol is the first of this new generation of GBCAs, with high relaxivity, thus having the potential to reduce the gadolinium dose while maintaining good in vivo stability due to its macrocyclic structure. High-stability and high-relaxivity GBCAs will be one of the solutions for reducing the dose of gadolinium to be administered in clinical practice, while the development of new technologies, including optimization of MRI acquisitions, new contrast mechanisms, and artificial intelligence may help reduce the need for GBCAs. Future solutions may involve a combination of next-generation GBCAs and image-processing techniques to optimize diagnosis and treatment planning while minimizing exposure to gadolinium. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3.

Using Adaptive Imaging Parameters to Improve PEGylated Ultrasmall Iron Oxide Nanoparticles-Enhanced Magnetic Resonance Angiography

The PEGylated ultrasmall iron oxide nanoparticles (PUSIONPs) exhibit longer blood residence time and better biodegradability than conventional gadolinium-based contrast agents (GBCAs), enabling prolonged acquisitions in contrast-enhanced magnetic resonance angiography (CE-MRA) applications. The image quality of CE-MRA is dependent on the contrast agent concentration and the parameters of the pulse sequences. Here, a closed-form mathematical model is demonstrated and validated to automatically optimize the concentration, echo time (TE), repetition time (TR) and flip angle (FA). The pharmacokinetic studies are performed to estimate the dynamic intravascular concentrations within 12 h postinjection, and the adaptive concentration-dependent sequence parameters are determined to achieve optimal signal enhancement during a prolonged measurement window. The presented model is tested on phantom and in vivo rat images acquired from a 3T scanner. Imaging results demonstrate excellent agreement between experimental measurements and theoretical predictions, and the adaptive sequence parameters obtain better signal enhancement than the fixed ones. The low-dose PUSIONPs (0.03 mmol kg-1 and 0.05 mmol kg-1) give a comparable signal intensity to the high-dose one (0.10 mmol kg-1) within 2 h postinjection. The presented mathematical model provides guidance for the optimization of the concentration and sequence parameters in PUSIONPs-enhanced MRA, and has great potential for further clinical translation.

Relationship of Dose and Signal Enhancement Properties of Gadoquatrane, a New Tetrameric, Macrocyclic Gadolinium-Based Contrast Agent, Compared With Gadobutrol: A Randomized Crossover Study in Healthy Adults

OBJECTIVES

To investigate the signal-enhancement properties of the tetrameric gadolinium-based contrast agent (GBCA) gadoquatrane in relation to the administered dose and compare its properties to those of a standard dose of gadobutrol, as a representative of the currently established macrocyclic GBCAs for magnetic resonance imaging.

MATERIALS AND METHODS

In this randomized, single-blind, 4 × 4 crossover study, 43 healthy adults (19-50 years of age) received 3 single IV injections of gadoquatrane (0.01, 0.03, and 0.06 mmol gadolinium/kg body weight) and 1 injection of gadobutrol (0.1 mmol gadolinium/kg body weight) in randomized sequence with 1-week washout periods between administrations. The relative signal enhancement (RSE) was determined in predefined areas of interest in magnetic resonance image sets of the head-neck region. RSE-vs-dose curves (dose-response curves) were established by linear regression, and comparator-equivalent doses were determined by Bayesian inverse regression analysis. Further, 3 blood samples were taken after each injection for pharmacokinetic analyses, and safety data were assessed.

RESULTS

The RSE increased with gadoquatrane dose. A linear function adequately fitted this relationship. In line with the more than 2-fold higher r1 relaxivity of gadoquatrane per gadolinium ion, gadobutrol-equivalent RSE was achieved with gadoquatrane at less than half the gadolinium dose and less than one eighth of the molecule dose.Administration of gadoquatrane and gadobutrol resulted in very similar dose-normalized gadolinium concentrations in plasma, indicating that the pharmacokinetic profiles are essentially the same. Both contrast agents were well tolerated. Adverse events were rare and not dependent on the dose administered.

CONCLUSIONS

Gadoquatrane has the potential to be an effective GBCA that can be used at substantially lower doses in clinical routine than the currently established macrocyclic GBCAs.

Pharmacokinetics, safety, and tolerability of the novel tetrameric gadolinium-based MRI contrast agent gadoquatrane in healthy Chinese and Japanese men: Two randomized dose-escalation studies including concentration-QTc modeling

PURPOSE

To investigate the pharmacokinetics, safety, and tolerability of the novel tetrameric high-relaxivity gadolinium-based contrast agent gadoquatrane in Japanese (Study 1) and Chinese men (Study 2).

PARTICIPANTS AND METHODS

In two similarly designed single-center, randomized, single-blind, placebo-controlled, consecutive-cohort dose-escalation studies, healthy volunteers were randomly assigned to intravenous administration of gadoquatrane (0.01-0.1 mmol gadolinium/kg body weight) or placebo. Study procedures included blood sampling and collection of urine for pharmacokinetic analyses and safety assessments.

RESULTS

Twenty-five healthy Japanese men (mean age ± standard deviation: 26±5.9 years) and 23 healthy Chinese men (31±7.6 years old) were evaluated. In both studies, the pharmacokinetic profile of gadoquatrane was characterized by rapid distribution of the drug into the extracellular space and fast renal elimination. Postdose gadolinium concentrations rapidly declined with a geometric mean effective half-life of 1.3-1.4 h. The exposure increased approximately dose-proportionally with dose. The body weight-normalized volume of distribution was constant across dose levels (0.21-0.24 L/kg). Total recovery of gadolinium in urine amounted to 82-95 % (Study 1) and 96-99 % (Study 2) of the dose administered. Only a few mild, transient adverse events were reported, none of which gave rise to any safety concerns. Exploratory drug concentration-QTc modeling indicated no risk of a clinically relevant QT/QTc prolongation at the anticipated diagnostic dose.

CONCLUSION

Gadoquatrane was safe and well tolerated at all doses tested. The pharmacokinetic profile was essentially the same as that of other extracellular macrocyclic gadolinium-based contrast agents and was consequentially also similar for Japanese and Chinese participants.

Lipophilic Group-Modified Manganese(II)-Based Contrast Agents for Vascular and Hepatobiliary Magnetic Resonance Imaging

Effective vascular and hepatic enhancement and better safety are the key drivers for exploring gadolinium-free hepatobiliary contrast agents. Herein, a facile strategy proposes that the high lipophilicity may be favorable to enhancing sequentially vascular and hepatobiliary signal intensity based on the structure-activity relationship that both hepatic uptake and interaction with serum albumins partly depend on lipophilicity. Therefore, 11 newly synthesized derivatives of manganese o-phenylenediamine-N,N,N',N'-tetraacetic acid (MnLs) were evaluated as vascular and hepatobiliary agents. The maximum signal intensities of the heart, liver, and kidneys were strongly correlated with log P, a key indicator of lipophilicity. The most lipophilic agent, MnL6, showed favorable relaxivity when binding with serum albumin, good vascular enhancement, rapid excretion, and reliable hepatobiliary phases comparable to a classic hepatobiliary agent, gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) for in vivo liver tumor imaging. Inhibition experiments confirmed the hepatic targeting of MnL6 is mediated by organic anion-transporting polypeptides.

Preparation and performance of biocompatible gadolinium polymer as liver-targeting magnetic resonance imaging contrast agent

A biocompatible macromolecule-conjugated gadolinium chelate complex (PAV2-EDA-DOTA-Gd) as a new liver-specific contrast agent for magnetic resonance imaging (MRI) was synthesized and evaluated. An aspartic acid-valine copolymer was used as a carrier and ethylenediamine as a chemical linker, and the aspartic acid-valine copolymer was covalently linked to the small molecule MRI contrast agent Gd-DOTA (Dotarem) to synthesize a large molecule contrast agent. In vitro MR relaxation showed that the T1-relaxivity of PAV2-EDA-DOTA-Gd (13.7 mmol-1 L s-1) was much higher than that of the small-molecule Gd-DOTA (4.9 mmol-1 L s-1). In vivo imaging of rats showed that the enhancement effect of PAV2-EDA-DOTA-Gd (55.37 ± 2.80%) on liver imaging was 2.6 times that of Gd-DOTA (21.12 ± 3.86%), and it produced a longer imaging window time (40-70 min for PAV2-EDA-DOTA-Gd and 10-30 min for Gd-DOTA). Preliminary safety experiments, such as cell experiments and tissue sectioning, showed that PAV2-EDA-DOTA-Gd had low toxicity and satisfactory biocompatibility. The results of this study indicated that PAV2-EDA-DOTA-Gd had high potential as a liver-specific MRI contrast agent.

Gadolinium contrast agents- challenges and opportunities of a multidisciplinary approach: Literature review

Contrast agents is used in magnetic resonance imaging (MRI) to improve the visibility of the details of the organ structures. Gadolinium-based contrast agent (GBCA) has been used since 1988 in MRI for diagnostic and follow-up of patients, the gadolinium good properties make it an effective choice for enhance the signal in MRI by increase its intensity and shortening the relaxation time of the proton. Recently, many studies show a gadolinium deposition in different human organs due to release of free gadolinium various body organs or tissue, which led to increased concern about the use of gadolinium agents, in this study, the potential diseases that may affect the patient and side effects that appear on the patient and related to accumulation of gadolinium were clarified, the study focused on the organs such as brain and bones in which gadolinium deposition was found and the lesions associated with it, and the diseases associated with gadolinium retention includes Nephrogenic Systemic Fibrosis (NSF) and Gadolinium deposition disease (GDD). Some studies tended to improve the contrast agents by developing a new non-gadolinium agents or development of next-generation gadolinium agents. In this review article the latest knowledge about MRI contrast agent.

Exploring atherosclerosis imaging with contrast-enhanced MRI using PEGylated ultrasmall iron oxide nanoparticles

Plaque rupture is a critical concern due to its potential for severe outcomes such as cerebral infarction and myocardial infarction, underscoring the urgency of noninvasive early diagnosis. Magnetic resonance imaging (MRI) has gained prominence in plaque imaging, leveraging its noninvasiveness, high spatial resolution, and lack of ionizing radiation. Ultrasmall iron oxides, when modified with polyethylene glycol, exhibit prolonged blood circulation and passive targeting toward plaque sites, rendering them conducive for MRI. In this study, we synthesized ultrasmall iron oxide nanoparticles of approximately 3 nm via high-temperature thermal decomposition. Subsequent surface modification facilitated the creation of a dual-modality magnetic resonance/fluorescence probe. Upon intravenous administration of the probes, MRI assessment of atherosclerotic plaques and diagnostic evaluation were conducted. The application of Flash-3D sequence imaging revealed vascular constriction at lesion sites, accompanied by a gradual signal amplification postprobe injection. T1-weighted imaging of the carotid artery unveiled a progressive signal ratio increase between plaques and controls within 72 h post-administration. Fluorescence imaging of isolated carotid arteries exhibited incremental lesion-to-control signal ratios. Additionally, T1 imaging of the aorta demonstrated an evolving signal enhancement over 48 h. Therefore, the ultrasmall iron oxide nanoparticles hold immense promise for early and noninvasive diagnosis of plaques, providing an avenue for dynamic evaluation over an extended time frame.

Novel manganese and polyester dendrimer-based theranostic nanoparticles for MRI and breast cancer therapy

Therapeutic nanoplatforms are widely used in the diagnosis and treatment of breast cancer due to the merits of enabling high soft-tissue resolution and the availability of numerous therapeutic nanoparticles. It is thus vital to develop multifunctional theranostic nanoparticles for the visualization and dynamic monitoring of tumor therapy. In this study, we designed a manganese-based and hypericin-loaded polyester dendrimer nanoparticle (MHD) for magnetic resonance imaging (MRI) and hypericin-based photodynamic therapy (PDT) enhancement. We found that MHD could greatly enhance MRI contrast with a longitudinal relaxivity of 5.8 mM^-1 s^-1 due to the Mn-based paramagnetic dendrimer carrier. Meanwhile, the MRI-guided PDT inhibition of breast tumors could be achieved by the hypericin-carrying MHD and further improved by Mn²⁺-mediated alleviation of the hypoxic microenvironment and the enhancement of cellular ROS. Besides, MHD showed excellent biocompatibility and biosafety with liver and kidney clearance mechanisms. Thus, the high efficiency in MRI contrast enhancement and excellent tumor-inhibiting effects indicate MHD's potential as a novel, stable, and multifunctional nanotheranostic agent for breast cancer.

19 F MRI Nanotheranostics for Cancer Management: Progress and Prospects

Fluorine magnetic resonance imaging (19 F MRI) is a promising imaging technique for cancer diagnosis because of its excellent soft tissue resolution and deep tissue penetration, as well as the inherent high natural abundance, almost no endogenous interference, quantitative analysis, and wide chemical shift range of the 19 F nucleus. In recent years, scientists have synthesized various 19 F MRI contrast agents. By further integrating a wide variety of nanomaterials and cutting-edge construction strategies, magnetically equivalent 19 F atoms are super-loaded and maintain satisfactory relaxation efficiency to obtain high-intensity 19 F MRI signals. In this review, the nuclear magnetic resonance principle underlying 19 F MRI is first described. Then, the construction and performance of various fluorinated contrast agents are summarized. Finally, challenges and future prospects regarding the clinical translation of 19 F MRI nanoprobes are considered. This review will provide strategic guidance and panoramic expectations for designing new cancer theranostic regimens and realizing their clinical translation.

Safety and Gadolinium Distribution of the New High-Relaxivity Gadolinium Chelate Gadopiclenol in a Rat Model of Severe Renal Failure

OBJECTIVE

The aim of this study was to investigate the toxicological profile of gadopiclenol, a new high-relaxivity macrocyclic gadolinium-based contrast agent (GBCA), in renally impaired rats, in comparison with 2 other macrocyclic GBCAs, gadoterate meglumine and gadobutrol, and 1 linear and nonionic GBCA, gadodiamide.

METHODS

Renal failure was induced by adding 0.75% wt/wt adenine to the diet for 3 weeks. During the second week of adenine-enriched diet, the animals (n = 8/group × 5 groups) received 5 consecutive intravenous injections of GBCA at 2.5 mmol/kg per injection, resulting in a cumulative dose of 12.5 mmol/kg or saline followed by a 3-week treatment-free period after the last injection. The total (elemental) gadolinium (Gd) concentration in different tissues (brain, cerebellum, femoral epiphysis, liver, skin, heart, kidney, spleen, plasma, urine, and feces) was measured by inductively coupled plasma mass spectrometry. Transmission electron microscopy (and electron energy loss spectroscopy analysis of metallic deposits) was used to investigate the presence and localization of Gd deposits in the skin. Relaxometry was used to evaluate the presence of dissociated Gd in the skin, liver, and bone. Skin histopathology was performed to investigate the presence of nephrogenic systemic fibrosis-like lesions.

RESULTS

Gadodiamide administrations were associated with high morbidity-mortality but also with macroscopic and microscopic skin lesions in renally impaired rats. No such effects were observed with gadopiclenol, gadoterate, or gadobutrol. Overall, elemental Gd concentrations were significantly higher in gadodiamide-treated rats than in rats treated with the other GBCAs for all tissues except the liver (where no significant difference was found with gadopiclenol) and the kidney and the heart (where statistically similar Gd concentrations were observed for all GBCAs). No plasma biochemical abnormalities were observed with gadopiclenol or the control GBCAs. Histopathology revealed a normal skin structure in the rats treated with gadopiclenol, gadoterate, and gadobutrol, contrary to those treated with gadodiamide. No evidence of Gd deposits on collagen fibers and inclusions in fibroblasts was found with gadopiclenol and its macrocyclic controls, unlike with gadodiamide. Animals of all test groups had Gd-positive lysosomal inclusions in the dermal macrophages. However, the textures differed for the different products (speckled texture for gadodiamide and rough-textured appearance for the 2 tested macrocyclic GBCAs).

CONCLUSIONS

No evidence of biochemical toxicity or pathological abnormalities of the skin was observed, and similar to other macrocyclic GBCAs, gadoterate and gadobutrol, tissue retention of Gd was found to be low (except in the liver) in renally impaired rats treated with the new high-relaxivity GBCA gadopiclenol.

Integration of PEG-conjugated gadolinium complex and superparamagnetic iron oxide nanoparticles as T 1-T 2 dual-mode magnetic resonance imaging probes

The T 1-T 2 dual-mode probes for magnetic resonance imaging (MRI) can non-invasively acquire comprehensive information of different tissues or generate self-complementary information of the same tissue at the same time, making MRI a more flexible imaging modality for complicated applications. In this work, three Gadolinium-diethylene-triaminepentaaceticacid (Gd-DTPA) complex conjugated superparamagnetic iron oxide (SPIO) nanoparticles with different Gd/Fe molar ratio (0.94, 1.28 and 1.67) were prepared as T 1-T 2 dual-mode MRI probes, named as SPIO@PEG-GdDTPA0.94, SPIO@PEG-GdDTPA1.28 and SPIO@PEG-GdDTPA1.67, respectively. All SPIO@PEG-GdDTPA nanocomposites with 8 nm spherical SPIO nanocrystals showed good Gd3+ chelate stability. SPIO@PEG-GdDTPA0.94 nanocomposites with lowest Gd/Fe molar ratio show no cytotoxicity to Raw 264.7 cells as compared to SPIO@PEG-GdDTPA1.28 and SPIO@PEG-GdDTPA1.67. SPIO@PEG-GdDTPA0.94 nanocomposites with r 1 (8.4 mM-1s-1), r 2 (83.2 mM-1s-1) and relatively ideal r 2/r 1 ratio (9.9) were selected for T 1-T 2 dual-mode MRI of blood vessels and liver tissue in vivo. Good contrast images were obtained for both cardiovascular system and liver in animal studies under a clinical 3 T scanner. Importantly, one can get high-quality contrast-enhanced blood vessel images within the first 2 h after contrast agent administration and acquire liver tissue anatomy information up to 24 h. Overall, the strategy of one shot of the dual mode MRI agent could bring numerous benefits not only for patients but also to the radiologists and clinicians, e.g. saving time, lowering side effects and collecting data of different organs sequentially.

Synthesis of a Thermal-Responsive Dual-Modal Supramolecular Probe for Magnetic Resonance Imaging and Fluorescence Imaging

Dual-modal imaging can integrate the advantages of different imaging technologies, which could improve the accuracy and efficiency of clinical diagnosis. Herein, a novel amphiphilic thermal-responsive copolymer obtained from three types of monomers, N-isopropyl acrylamide, 2-(acetoacetoxy) ethyl methacrylate, and propargyl methacrylate, by RAFT copolymerization, is reported. It can be grafted with β-cyclodextrin and aggregation-induced emission (AIE) luminogens tetraphenylethylene by click chemistry and Biginelli reaction. The multifunctional supramolecular polymer (P4) can be constructed by host-guest inclusion between the copolymer and the Gd-based contrast agent (CA) modified by adamantane [Ad-(DOTA-Gd)]. And it can form vesicles with a bilayer structure in aqueous which will enhance the AIE and magnetic resonance imaging effects. As fluorescent thermometer, P4 can enter HeLa cells for intracellular fluorescence imaging (FI) and is sensitive to temperature with detection limit value of 1.5 °C. As magnetic resonance CA, P4 exhibits higher relaxation compared to Magnevist, which can prolong the circulation time in vivo. In addition, Gd³⁺ in the polymer can be quickly released from the body by disassembly that reduced the biological toxicity. This work introduces new synthetic ideas for dual-modal probe, which has great potential for clinical diagnostic applications in bioimaging.

Coconut-shell-derived activated carbon for NIR photo-activated synergistic photothermal-chemodynamic cancer therapy

Exploiting new non-metal-based peroxidase-mimic nanoenzymes for chemodynamic therapy (CDT) in cancer treatment is an active and challenging field. Here, we found that activated carbon nanoparticles (denoted as ANs) fabricated from coconut shell have satisfactory peroxidase-mimic nanoenzyme activity. Based on this positive result, gadodiamide, a clinically used nuclear magnetic imaging contrast agent, was loaded inside the AN pores and encapsulated by polyvinylpyrrolidone (PVP) to obtain Gd@PANs. PANs (ANs modified using PVP) efficiently catalyze the massive decomposition of endogenous hydrogen peroxide (H2O2) inside cancer cells to produce toxic oxidized hydroxyl radicals (˙OH) for the CDT treatment of cancer, but they showed no toxicity toward normal cells. Additionally, under 808 nm laser irradiation, the photothermal conversion efficiency of the PANs reaches 45.20%, ensuring their effective photothermal therapy (PTT) treatment functionality. Simultaneously, during PTT treatment, the heating effect significantly enhances the peroxidase-mimic activity of the PANs to achieve an ideal PTT-CDT synergistic therapeutic outcome. Gd@PANs can also be used for the T1-magnetic resonance imaging (MRI) of tumors to integrate treatment and diagnosis.

Alternatives to Gadolinium-Based Contrast Agents

Gadolinium-based contrast agents have been used in hundreds of millions of patients in the past 30 years, with an exemplary safety record. However, assumptions made at their inception have been recently challenged, rekindling innovation efforts. This critical review outlines the motivations, technical obstacles, problems, and the most recent published progress toward the creation of alternatives to the existing gadolinium-based contrast agent.