Pre-clinical evaluation of gadobutrol: a new, neutral, extracellular contrast agent for magnetic resonance imaging

Skin-Related Adverse Reactions in Gadolinium-Based Contrast Agents-Induced Hypersensitivity: A Systematic Review of the Literature

Gadolinium-based contrast agents (GBCAs) have been used in clinical settings for several decades and in general they have established a good safety profile. Despite the use of chelating agents, some adverse reactions might occur when using these agents. This review aimed to assess the relationship between administered dose of Gadolinium-based contrast and the rate, duration, and severity of skin-related adverse reactions. Four electronic databases were searched using various relevant keywords. Duplicate records were removed, and the remaining records were retrieved and assessed for eligibility. The inclusion criteria were observational or experimental studies that analyzed the rate of immediate and/or delayed adverse reactions to GBCAs in magnetic resonance imaging. Data were extracted into a pre-designed spreadsheet. Ten studies were deemed eligible to be included in this review. A total of 691,007 GBCAs injections/patients were included in these studies. Six hundred seventy-nine skin-related adverse reactions were reported among the study participants, with a rate of 0.10%, urticaria was the most common (499 cases, 74.7%), while allergic dermatitis (three cases, 0.5%) and angioedema (four cases, 0.6%) were least frequent. In conclusion, the rate of these skin-related adverse reactions was low. The most commonly reported reactions were urticaria, rash, and pruritus. Most of these reported reactions were mild, no significant association was found in the volume of contrast agents and the risk for developing adverse reactions reported in the included studies.

Waiting times between examinations with intravascularly administered contrast media: a review of contrast media pharmacokinetics and updated ESUR Contrast Media Safety Committee guidelines

The pharmacokinetics of contrast media (CM) will determine how long safe waiting intervals between successive CT or MRI examinations should be. The Contrast Media Safety Committee has reviewed the data on pharmacokinetics of contrast media to suggest safe waiting intervals between successive contrast-enhanced imaging studies in relation to the renal function of the patient. CLINICAL RELEVANCE STATEMENT: Consider a waiting time between elective contrast-enhanced CT and (coronary) angiography with successive iodine-based contrast media administrations in patients with normal renal function (eGFR > 60 mL/min/1.73 m2) of optimally 12 h (near complete clearance of the previously administered iodine-based contrast media) and minimally 4 h (if clinical indication requires rapid follow-up). KEY POINTS: • Pharmacokinetics of contrast media will guide safe waiting times between successive administrations. • Safe waiting times increase with increasing renal insufficiency. • Iodine-based contrast media influence MRI signal intensities and gadolinium-based contrast agents influence CT attenuation.

Protein MRI Contrast Agents as an Effective Approach for Precision Molecular Imaging

ABSTRACT

Cancer and other acute and chronic diseases are results of perturbations of common molecular determinants in key biological and signaling processes. Imaging is critical for characterizing dynamic changes in tumors and metastases, the tumor microenvironment, tumor-stroma interactions, and drug targets, at multiscale levels. Magnetic resonance imaging (MRI) has emerged to be a primary imaging modality for both clinical and preclinical applications due to its advantages over other modalities, including sensitivity to soft tissues, nondepth limitations, and the use of nonionizing radiation. However, extending the application of MRI to achieve both qualitative and quantitative precise molecular imaging with the capability to quantify molecular biomarkers for early detection, staging, and monitoring therapeutic treatment requires the capacity to overcome several major challenges including the trade-off between metal-binding affinity and relaxivity, which is an issue frequently associated with small chelator contrast agents. In this review, we will introduce the criteria of ideal contrast agents for precision molecular imaging and discuss the relaxivity of current contrast agents with defined first shell coordination water molecules. We will then report our advances in creating a new class of protein-targeted MRI contrast agents (ProCAs) with contributions to relaxivity largely derived from the secondary sphere and correlation time. We will summarize our rationale, design strategy, and approaches to the development and optimization of our pioneering ProCAs with desired high relaxivity, metal stability, and molecular biomarker-targeting capability, for precision MRI. From first generation (ProCA1) to third generation (ProCA32), we have achieved dual high r1 and r2 values that are 6- to 10-fold higher than clinically approved contrast agents at magnetic fields of 1.5 T, and their relaxivity values at high field are also significantly higher, which enables high resolution during small animal imaging. Further engineering of multiple targeting moieties enables ProCA32 agents that have strong biomarker-binding affinity and specificity for an array of key molecular biomarkers associated with various chronic diseases, while maintaining relaxation and exceptional metal-binding and selectivity, serum stability, and resistance to transmetallation, which are critical in mitigating risks associated with metal toxicity. Our leading product ProCA32.collagen has enabled the first early detection of liver metastasis from multiple cancers at early stages by mapping the tumor environment and early stage of fibrosis from liver and lung in vivo, with strong translational potential to extend to precision MRI for preclinical and clinical applications for precision diagnosis and treatment.

American Society of Regional Anesthesia and Pain Medicine contrast shortage position statement

The medical field has been experiencing numerous drug shortages in recent years. The most recent shortage to impact the field of interventional pain medicine is that of iodinated contrast medium. Pain physicians must adapt to these changes while maintaining quality of care. This position statement offers guidance on adapting to the shortage.

Nephrogenic Systemic Fibrosis in Patients with Chronic Kidney Disease after the Use of Gadolinium-Based Contrast Agents: A Review for the Cardiovascular Imager

Gadolinium-enhanced cardiac magnetic resonance has revolutionized cardiac imaging in the last two decades and has emerged as an essential and powerful tool for the characterization and treatment guidance of a wide range of cardiovascular diseases. However, due to the high prevalence of chronic renal dysfunction in patients with cardiovascular conditions, the risk of nephrogenic systemic fibrosis (NSF) after gadolinium exposure has been a permanent concern. Even though the newer macrocyclic agents have proven to be much safer in patients with chronic kidney disease and end-stage renal failure, clinicians must fully understand the clinical characteristics and risk factors of this devastating pathology and maintain a high degree of suspicion to prevent and recognize it. This review aimed to summarize the existing evidence regarding the physiopathology, clinical manifestations, diagnosis, and prevention of NSF related to the use of gadolinium-based contrast agents.

Gadolinium: pharmacokinetics and toxicity in humans and laboratory animals following contrast agent administration

Gadolinium-based contrast agents (GBCAs) have transformed magnetic resonance imaging (MRI) by facilitating the use of contrast-enhanced MRI to allow vital clinical diagnosis in a plethora of disease that would otherwise remain undetected. Although over 500 million doses have been administered worldwide, scientific research has documented the retention of gadolinium in tissues, long after exposure, and the discovery of a GBCA-associated disease termed nephrogenic systemic fibrosis, found in patients with impaired renal function. An understanding of the pharmacokinetics in humans and animals alike are pivotal to the understanding of the distribution and excretion of gadolinium and GBCAs, and ultimately their potential retention. This has been well studied in humans and more so in animals, and recently there has been a particular focus on potential toxicities associated with multiple GBCA administration. The purpose of this review is to highlight what is currently known in the literature regarding the pharmacokinetics of gadolinium in humans and animals, and any toxicity associated with GBCA use.

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.

Symptoms Associated with Gadolinium Exposure (SAGE): A Suggested Term

In this article, members of the American College of Radiology Committee on Drugs and Contrast Media propose a new term for symptoms reported after intravascular exposure to gadolinium-based contrast agents-Symptoms Associated with Gadolinium Exposure, or SAGE. This term is advocated in lieu of other proposed nomenclature that presumes a causal relationship that has not yet been scientifically verified. The purpose of this new term, SAGE, is to assist researchers and clinical providers in describing such symptoms without prematurely causally attributing them to a disease and to standardize reporting of these symptoms to allow for coherent interpretation of related studies.

Functional and histologic imaging of urinary bladder wall after exposure to psychological stress and protamine sulfate

To quantify the urinary bladder wall T1 relaxation time (T1) before and after the instillation contrast mixture in rats previously subjected to water avoidance stress (WAS) and/or acute exposure to protamine sulfate (PS). Female Wistar rats were randomized to receive either sham (control) or 1 h of WAS for ten consecutive days before the evaluation of nocturnal urination pattern in metabolic cages. T1 mapping of urinary bladder wall at 9.4 T was performed pre- and post- instillation of 4 mM Gadobutrol in a mixture with 5 mM Ferumoxytol. Subsequently, either T1 mapping was repeated after brief intravesical PS exposure or the animals were sacrificed for histology and analyzing the mucosal levels of mRNA. Compared to the control group, WAS exposure decreased the single void urine volume and shortened the post-contrast T1 relaxation time of mucosa- used to compute relatively higher ingress of instilled Gadobutrol. Compromised permeability in WAS group was corroborated by the urothelial denudation, edema and ZO-1 downregulation. PS exposure doubled the baseline ingress of Gadobutrol in both groups. These findings confirm that psychological stress compromises the paracellular permeability of bladder mucosa and its non-invasive assay with MRI was validated by PS exposure.

Interaction of macrocyclic gadolinium-based MR contrast agents with Type I collagen. Equilibrium and kinetic studies

The interactions of gadoterate meglumine, gadobutrol, gadoteridol and Gd(HB-DO3A) with bovine Type I collagen were investigated by ultrafiltration and dialysis. The affinity of the four agents to collagen is similar. However, the maximum adsorbed amount of GdIII-complexes decreases in the following order: gadoterate meglumine > gadobutrol > gadoteridol > Gd(HB-DO3A). Calculations with the open three-compartment model reveal that the structural homologs gadoteridol and Gd(HB-DO3A) have a lower adsorption onto collagen, which may explain the less prolonged in vivo retention of gadoteridol observed in soft tissues of rats.

The Use of Contrast Agents in Interventional Pain Procedures: A Multispecialty and Multisociety Practice Advisory on Nephrogenic Systemic Fibrosis, Gadolinium Deposition in the Brain, Encephalopathy After Unintentional Intrathecal Gadolinium Injection, and Hypersensitivity Reactions

This Practice Advisory presents a comprehensive and evidence-based set of position statements and recommendations for the use of contrast media in interventional pain procedures. The advisory was established by an international panel of experts under the auspices of 11 multinational and multispecialty organizations based on a comprehensive review of the literature up to December 31, 2019. The advisory discusses the risks of using gadolinium-based contrast agents. These include nephrogenic systemic fibrosis, gadolinium brain deposition/retention, and encephalopathy and death after an unintentional intrathecal gadolinium injection. The advisory provides recommendations on the selection of a specific gadolinium-based contrast agent in patients with renal insufficiency, those who had multiple gadolinium-enhanced magnetic resonance imaging examinations, and in cases of paraspinal injections. Additionally, recommendations are made for patients who have a history of mild, moderate, or severe hypersensitivity reactions to contrast medium.

An In Vitro Model of Nonattached Biofilm-Like Bacterial Aggregates Based on Magnetic Levitation

Chronic infections are associated with the formation of nonattached biofilm-like aggregates. In vitro models of surface-attached biofilms do not always accurately mimic these processes. Here, we tested a new approach to create in vitro nonattached bacterial aggregates using the principle of magnetic levitation of biological objects placed into a magnetic field gradient. Bacteria grown under magnetic levitation conditions formed nonattached aggregates that were studied with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) and characterized quantitatively. Nonattached aggregates consisted of bacteria submerged into an extracellular matrix and demonstrated features characteristic of biofilms, such as a polymeric matrix that binds Ruby Red and Congo red dyes, a prerequisite of bacterial growth, and increased resistance to gentamicin. Three quantitative parameters were explored to characterize strain-specific potential to form nonattached aggregates: geometric sizes, relative quantities of aggregated and free-swimming bacteria, and Congo red binding. Among three tested Escherichia coli strains, one strain formed nonattached aggregates poorly, and for this strain, all three of the considered parameters were different from those of the other two strains (P < 0.05). Further, we characterized biofilm formation on plastic and agar surfaces by these strains and found that good biofilm formation ability does not necessarily indicate good nonattached aggregate formation ability, and vice versa. The model and quantitative methods can be applied for in vitro studies of nonattached aggregates and modeling bacterial behavior in chronic infections, as it is important to increase our understanding of the role that nonattached bacterial aggregates play in the pathogenesis of chronic diseases.IMPORTANCE An increasing amount of evidence indicates that chronic infections are associated with nonattached biofilm-like aggregates formed by pathogenic bacteria. These aggregates differ from biofilms because they form under low-shear conditions within the volume of biological fluids and they do not attach to surfaces. Here, we describe an in vitro model that provides nonattached aggregate formation within the liquid volume due to magnetic levitation. Using this model, we demonstrated that despite morphological and functional similarities of nonattached aggregates and biofilms, strains that exhibit good biofilm formation might exhibit poor nonattached aggregate formation, suggesting that mechanisms underlying the formation of biofilms and nonattached aggregates are not identical. The magnetic levitation approach can be useful for in vitro studies of nonattached aggregate formation and simulation of bacterial behavior in chronic infections.

Physicochemical and Pharmacokinetic Profiles of Gadopiclenol: A New Macrocyclic Gadolinium Chelate With High T1 Relaxivity

Objectives

We aimed to evaluate gadopiclenol, a newly developed extracellular nonspecific macrocyclic gadolinium-based contrast agent (GBCA) having high relaxivity properties, which was designed to increase lesion detection and characterization by magnetic resonance imaging.

Methods

We described the molecular structure of gadopiclenol and measured the r₁ and r₂ relaxivity properties at fields of 0.47 and 1.41 T in water and human serum. Nuclear magnetic relaxation dispersion profile measurements were performed from 0.24 mT to 7 T. Protonation and complexation constants were determined using pH-metric measurements, and we investigated the acid-assisted dissociation of gadopiclenol, gadodiamide, gadobutrol, and gadoterate at 37°C and pH 1.2. Applying the relaxometry technique (37°C, 0.47 T), we investigated the risk of dechelation of gadopiclenol, gadoterate, and gadodiamide in the presence of ZnCl₂ (2.5 mM) and a phosphate buffer (335 mM). Pharmacokinetics studies of radiolabeled ¹⁵³Gd-gadopiclenol were performed in Beagle dogs, and protein binding was measured in rats, dogs, and humans plasma and red blood cells.

Results

Gadopiclenol [gadolinium chelate of 2,2′,2″-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,6,9-triyl)tris(5-((2,3-dihydroxypropyl)amino)-5-oxopentanoic acid); registry number 933983-75-6] is based on a pyclen macrocyclic structure. Gadopiclenol exhibited a very high relaxivity in water (r₁ = 12.2 mM⁻¹·s⁻¹ at 1.41 T), and the r₁ value in human serum at 37°C did not markedly change with increasing field (r₁ = 12.8 mM⁻¹·s⁻¹ at 1.41 T and 11.6 mM⁻¹·s⁻¹ at 3 T). The relaxivity data in human serum did not indicate protein binding. The nuclear magnetic relaxation dispersion profile of gadopiclenol exhibited a high and stable relaxivity in a strong magnetic field. Gadopiclenol showed high kinetic inertness under acidic conditions, with a dissociation half-life of 20 ± 3 days compared with 4 ± 0.5 days for gadoterate, 18 hours for gadobutrol, and less than 5 seconds for gadodiamide and gadopentetate. The pharmacokinetic profile in dogs was typical of extracellular nonspecific GBCAs, showing distribution in the extracellular compartment and no metabolism. No protein binding was found in rats, dogs, and humans.

Conclusions

Gadopiclenol is a new extracellular and macrocyclic Gd chelate that exhibited high relaxivity, no protein binding, and high kinetic inertness. Its pharmacokinetic profile in dogs was similar to that of other extracellular nonspecific GBCAs.

Inter-individual Comparison of Gadobutrol and Gadoteridol Tissue Time-intensity Profiles for Dynamic Susceptibility Contrast Perfusion MR Imaging

Purpose:

Gadobutrol is a gadolinium-based contrast material (GBCM) with a high concentration of gadolinium and high relaxivity. Our purpose was to evaluate the signal intensity profiles in brain tissue for the bolus width and degree of signal change after bolus injection using an echo planar dynamic susceptibility contrast (DSC) sequence. We compared gadobutrol to gadoteridol using various injection speeds and saline flush volumes.

Methods:

We studied 97 patients who underwent brain MRI. Datasets for perfusion studies were acquired using a 3T scanner with an echo planar imaging (EPI) sequence. The injection protocols were set up with combinations of injection speed and saline flush volume for both gadobutrol and gadoteridol. The full width at half maximum (FWHM) and the maximum signal change ratio (SCR_max ) of the time intensity curves were measured.

Results:

The FWHM did not show a statistically significant difference according to injection speed, flush volume, or type of GBCM. The SCR_max showed a greater change with a faster injection speed, larger saline flush, and gadobutrol administration. The difference between gadobutrol and gadoteridol became smaller with a faster injection speed and a larger saline flush.

Conclusion:

The maximum signal drop was larger with gadobutrol when the injection speed was slow and the saline flush was small. Thus, gadobutrol may be useful to obtain a better profile for DSC perfusion MRI in conditions requiring a slower injection speed and/or a smaller volume of saline flush.

Gadolinium Deposition in the Brain: A Systematic Review of Existing Guidelines and Policy Statement Issued by the Canadian Association of Radiologists

Emerging evidence has confirmed that, following administration of a gadolinium-based contrast agent (GBCA), very small amounts of gadolinium will deposit in the brain of humans with intact blood-brain barriers. The literature is evolving rapidly and the degree to which gadolinium will deposit for a particular GBCA or class of GBCAs remains undetermined. Several studies suggest that linear GBCAs deposit more gadolinium in the brain compared with macrocyclic GBCAs; however, our understanding of the molecular composition of deposited gadolinium is preliminary, and the clinical significance of gadolinium deposition remains unknown. To date, there is no conclusive evidence linking gadolinium deposition in the brain with any adverse patient outcome. A panel of radiologists representing the Canadian Association of Radiologists was assembled to assist the Canadian medical imaging community in making informed decisions regarding the issue of gadolinium deposition in the brain. The objectives of the working group were: 1) to review the evidence from animal and human studies; 2) to systematically review existing guidelines and position statements issued by other organizations and health agencies; and 3) to formulate an evidence-based position statement on behalf of the Canadian Association of Radiologists. Based on our appraisal of the evidence and systematic review of 9 guidelines issued by other organizations, the working group established the following consensus statement. GBCA administration should be considered carefully with respect to potential risks and benefits, and only used when required. Standard dosing should be used and repeat administrations should be avoided unless necessary. Gadolinium deposition is one of several issues to consider when prescribing a particular GBCA. Currently there is insufficient evidence to recommend one class of GBCA over another. The panel considered it inappropriate to withhold a linear GBCA if a macrocyclic agent is unavailable, if hepatobiliary phase imaging is required, or if there is a history of severe allergic reaction to a macrocyclic GBCA. Further study in this area is required, and the evidence should be monitored regularly with policy statements updated accordingly.

Gadolinium Retention: A Research Roadmap from the 2018 NIH/ACR/RSNA Workshop on Gadolinium Chelates

Gadolinium-based contrast agents (GBCAs) have revolutionized MRI, enabling physicians to obtain crucial life-saving medical information that often cannot be obtained with other imaging modalities. Since initial approval in 1988, over 450 million intravenous GBCA doses have been administered worldwide, with an extremely favorable pharmacologic safety profile; however, recent information has raised new concerns over the safety of GBCAs. Mounting evidence has shown there is long-term retention of gadolinium in human tissues. Further, a small subset of patients have attributed a constellation of symptoms to GBCA exposure, although the association of these symptoms with GBCA administration or gadolinium retention has not been proven by scientific investigation. Despite evidence that macrocyclic GBCAs show less gadolinium retention than linear GBCAs, the safety implications of gadolinium retention are unknown. The mechanism and chemical forms of gadolinium retention, as well as the biologic activity and clinical importance of these retained gadolinium species, remain poorly understood and underscore the need for additional research. In February 2018, an international meeting was held in Bethesda, Md, at the National Institutes of Health to discuss the current literature and knowledge gaps about gadolinium retention, to prioritize future research initiatives to better understand this phenomenon, and to foster collaborative standardized studies. The greatest priorities are to determine (a) if gadolinium retention adversely affects the function of human tissues, (b) if retention is causally associated with short- or long-term clinical manifestations of disease, and (c) if vulnerable populations, such as children, are at greater risk for experiencing clinical disease. The purpose of the research roadmap is to highlight important information that is not known and to identify and prioritize needed research. ©RSNA, 2018 Online supplemental material is available for this article .

Immediate Allergic Reactions to Gadolinium-based Contrast Agents: A Systematic Review and Meta-Analysis

Purpose To perform a systematic review and meta-analysis to determine if there are differences in rates of immediate allergic events between classes of gadolinium-based contrast agents (GBCAs). Materials and Methods PubMed and Google Scholar databases were searched for studies in which rates of immediate adverse events to GBCAs were reported. The American College of Radiology classification system was used to characterize allergic-like events as mild, moderate, or severe, and the total number of administrations of each GBCA was recorded. Where necessary, authors of studies were contacted to clarify data and eliminate physiologic reactions. Relative risks of GBCA types were estimated by using the Mantel-Haenszel type method. Results Nine studies in which immediate reactions to GBCA were recorded from a total of 716 978 administrations of GBCA met the criteria for inclusion and exclusion. The overall rate of patients who had immediate allergic-like reactions was 9.2 per 10 000 administrations and the overall rate of severe immediate allergic-like reactions was 0.52 per 10 000 administrations.. The nonionic linear chelate gadodiamide had the lowest rate of reactions, at 1.5 (95% confidence interval [CI]: 0.74, 2.4) per 10 000 administrations, which was significantly less than that of linear ionic GBCAs at 8.3 (95% CI: 7.5, 9.2) per 10 000 administrations (relative risk, 0.19 [95% CI: 0.099, 0.36]; P < .00001) and less than that for nonionic macrocyclic GBCAs at 16 (95% CI: 14, 19) per 10 000 administrations (relative risk, 0.12 [95% CI: 0.05, 0.31]; P < .001). GBCAs known to be associated with protein binding had a higher rate of reactions, at 17 (95% CI: 15, 20) per 10 000 administrations compared with the same chelate classification without protein binding, at 5.2 (95% CI: 4.5, 6.0) per 10 000 administrations (relative risk, 3.1 [95% CI: 2.4, 3.8]; P < .0001). Conclusion These data show the lowest rate of immediate allergic adverse events with use of the nonionic linear GBCA gadodiamide in comparison with those of ionic linear or nonionic macrocyclic GBCAs. A higher rate of immediate allergic adverse events was associated with ionicity, protein binding, and macrocyclic structure. © RSNA, 2017 An earlier incorrect version of this article appeared online. This article was corrected on August 31, 2017.

Basic MR relaxation mechanisms and contrast agent design

The diagnostic capabilities of magnetic resonance imaging (MRI) have undergone continuous and substantial evolution by virtue of hardware and software innovations and the development and implementation of exogenous contrast media. Thirty years since the first MRI contrast agent was approved for clinical use, a reliance on MR contrast media persists, largely to improve image quality with higher contrast resolution and to provide additional functional characterization of normal and abnormal tissues. Further development of MR contrast media is an important component in the quest for continued augmentation of diagnostic capabilities. In this review we detail the many important considerations when pursuing the design and use of MR contrast media. We offer a perspective on the importance of chemical stability, particularly kinetic stability, and how this influences one's thinking about the safety of metal-ligand-based contrast agents. We discuss the mechanisms involved in MR relaxation in the context of probe design strategies. A brief description of currently available contrast agents is accompanied by an in-depth discussion that highlights promising MRI contrast agents in the development of future clinical and research applications. Our intention is to give a diverse audience an improved understanding of the factors involved in developing new types of safe and highly efficient MR contrast agents and, at the same time, provide an appreciation of the insights into physiology and disease that newer types of responsive agents can provide.

Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch

We present a fully reversible and highly efficient on-off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100,000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced.

Safety and Efficacy of Gadobutrol for Contrast-enhanced Magnetic Resonance Imaging of the Central Nervous System: Results from a Multicenter, Double-blind, Randomized, Comparator Study

PURPOSE

Contrast-enhanced magnetic resonance imaging (MRI) of the central nervous system (CNS) with gadolinium-based contrast agents (GBCAs) is standard of care for CNS imaging and diagnosis because of the visualization of lesions that cause blood–brain barrier breakdown. Gadobutrol is a macrocyclic GBCA with high concentration and high relaxivity. The objective of this study was to compare the safety and efficacy of gadobutrol 1.0 M vs unenhanced imaging and vs the approved macrocyclic agent gadoteridol 0.5 M at a dose of 0.1 mmol/kg bodyweight.

MATERIALS AND METHODS

Prospective, multicenter, double-blind, crossover trial in patients who underwent unenhanced MRI followed by enhanced imaging with gadobutrol or gadoteridol. Three blinded readers assessed the magnetic resonance images. The primary efficacy variables included number of lesions detected, degree of lesion contrast-enhancement, lesion border delineation, and lesion internal morphology.

RESULTS

Of the 402 treated patients, 390 patients received study drugs. Lesion contrast-enhancement, lesion border delineation, and lesion internal morphology were superior for combined unenhanced/gadobutrol-enhanced imaging vs unenhanced imaging (P < 0.0001 for all). Compared with gadoteridol, gadobutrol was non-inferior for all primary variables and superior for lesion contrast-enhancement, as well as sensitivity and accuracy for detection of malignant disease. The percentage of patients with at least one drug-related adverse event was similar for gadobutrol (10.0%) and gadoteridol (9.7%).

CONCLUSION

Gadobutrol is an effective and well-tolerated macrocyclic contrast agent for MRI of the CNS. Gadobutrol demonstrates greater contrast-enhancement and improved sensitivity and accuracy for detection of malignant disease than gadoteridol, likely because of its higher relaxivity.

Brain tumours at 7T MRI compared to 3T--contrast effect after half and full standard contrast agent dose: initial results

OBJECTIVES

To compare the contrast agent effect of a full dose and half the dose of gadobenate dimeglumine in brain tumours at 7 Tesla (7 T) MR versus 3 Tesla (3T).

METHODS

Ten patients with primary brain tumours or metastases were examined. Signal intensities were assessed in the lesion and normal brain. Tumour-to-brain contrast and lesion enhancement were calculated. Additionally, two independent readers subjectively graded the image quality and artefacts.

RESULTS

The enhanced mean tumour-to-brain contrast and lesion enhancement were significantly higher at 7 T than at 3T for both half the dose (91.8 ± 45.8 vs. 43.9 ± 25.3 [p = 0.010], 128.1 ± 53.7 vs. 75.5 ± 32.4 [p = 0.004]) and the full dose (129.2 ± 50.9 vs. 66.6 ± 33.1 [p = 0.002], 165.4 ± 54.2 vs. 102.6 ± 45.4 [p = 0.004]). Differences between dosages at each field strength were also significant. Lesion enhancement was higher with half the dose at 7 T than with the full dose at 3T (p = .037), while the tumour-to-brain contrast was not significantly different. Subjectively, contrast enhancement, visibility, and lesion delineation were better at 7 T and with the full dose. All parameters were rated as good, at the least.

CONCLUSION

Half the routine contrast agent dose at 7 T provided higher lesion enhancement than the full dose at 3T which indicates the possibility of dose reduction at 7 T.

KEY POINTS

• The contrast effect of gadobenate dimeglumine was assessed at 7 T and 3T. • In brain tumours, contrast effect was higher at 7 T than at 3T. • Tumour-to-brain contrast at 7 T half dose and 3T full dose were comparable. • 7 T half dose lesion enhancement was higher than 3T full dose enhancement. • Our results indicate the possibility of contrast agent dose reduction at 7 T.

Neurotoxic effects of indocyanine green -cerebellar granule cell culture viability study

The aim of this study was to examine neurotoxicity indocyanine green (ICG). We assessed viability of primary cerebellar granule cell culture (CGC) exposed to ICG to test two mechanisms that could be the first triggers causing neuronal toxicity: imbalance in calcium homeostasis and the degree of oligomerization of ICG molecules. We have observed this imbalance in CGC after exposure to 75-125μΜ ICG and dose and application sequence dependent protective effect of Gadovist on surviving neurons in vitro when used with ICG. Spectroscopic studies suggest the major cause of toxicity of the ICG is connected with oligomers formation. ICG at concentration of 25 μM (which is about 4 times higher than the highest concentration of ICG in the brain applied in in-vivo human studies) is not neurotoxic in the cell culture.

Intraindividual comparison of T1 relaxation times after gadobutrol and Gd-DTPA administration for cardiac late enhancement imaging

PURPOSE

To evaluate T1-relaxation times of chronic myocardial infarction (CMI) using gadobutrol and gadopentetate dimeglumine (Gd-DTPA) over time and to determine the optimal imaging window for late enhancement imaging with both contrast agents.

MATERIAL AND METHODS

Twelve patients with CMI were prospectively included and examined on a 1.5 T magnetic resonance (MR) system using relaxivity-adjusted doses of gadobutrol (0.15 mmol/kg) and Gd-DTPA (0.2 mmol/kg) in random order. T1-relaxation times of remote myocardium (RM), infarcted myocardium (IM), and left ventricular cavity (LVC) were assessed from short-axis TI scout imaging using the Look-Locker approach and compared intraindividually using a Wilcoxon paired signed-rank test (α<0.05).

RESULTS

Within 3 min of contrast agent administration (CA), IM showed significantly lower T1-relaxation times than RM with both contrast agents, indicating beginning cardiac late enhancement. Differences between gadobutrol and Gd-DTPA in T1-relaxation times of IM and RM were statistically not significant through all time points. However, gadobutrol led to significantly higher T1-relaxation times of LVC than Gd-DTPA from 6 to 9 min (220 ± 15 ms vs. 195 ± 30 ms p<0.01) onwards, resulting in a significantly greater ΔT1 of IM to LVC at 9-12 min (-20 ± 35 ms vs. 0 ± 35 ms, p<0.05) and 12-15 min (-25 ± 45 ms vs. -10 ± 60 ms, p<0.05). Using Gd-DTPA, comparable ΔT1 values were reached only after 25-35 min.

CONCLUSION

This study indicates good delineation of IM to RM with both contrast agents as early as 3 min after administration. However, we found significant differences in T1 relaxation times with greater ΔT1 IM-LVC using 0.15 mmol/kg gadobutrol compared to 0.20 mmol/kg Gd-DTPA after 9-15 min post-CA suggesting earlier differentiability of IM and LVC using gadobutrol.

Physicochemical characterization of a novel graphene-based magnetic resonance imaging contrast agent

We report the synthesis and characterization of a novel carbon nanostructure-based magnetic resonance imaging contrast agent (MRI CA); graphene nanoplatelets intercalated with manganese (Mn²⁺) ions, functionalized with dextran (GNP-Dex); and the in vitro assessment of its essential preclinical physicochemical properties: osmolality, viscosity, partition coefficient, protein binding, thermostability, histamine release, and relaxivity. The results indicate that, at concentrations between 0.1 and 100.0 mg/mL, the GNP-Dex formulations are hydrophilic, highly soluble, and stable in deionized water, as well as iso-osmolar (upon addition of mannitol) and iso-viscous to blood. At potential steady-state equilibrium concentrations in blood (0.1–10.0 mg/mL), the thermostability, protein-binding, and histamine-release studies indicate that the GNP-Dex formulations are thermally stable (with no Mn²⁺ ion dissociation), do not allow non-specific protein adsorption, and elicit negligible allergic response. The r₁ relaxivity of GNP-Dex was 92 mM⁻¹s⁻¹ (per-Mn²⁺ ion, 22 MHz proton Larmor frequency); ~20- to 30-fold greater than that of clinical gadolinium (Gd³⁺)- and Mn²⁺-based MRI CAs. The results open avenues for preclinical in vivo safety and efficacy studies with GNP-Dex toward its development as a clinical MRI CA.

Toxicological safety evaluation of gadobutrol

OBJECTIVES

Gadobutrol (Gadovist/Gadavist, Bayer Pharma AG, Berlin, Germany) is a nonionic, macrocyclic, gadolinium-based contrast agent for magnetic resonance imaging of the central nervous system as well as liver and kidneys and for contrast enhancement in magnetic resonance angiography. For risk assessment of the single diagnostic use in humans, the toxicity of this compound was evaluated with a series of preclinical studies.

MATERIALS AND METHODS

Preclinical studies into acute, repeated-dose, reproductive, and developmental toxicity as well as genotoxicity, local tolerance, contact-sensitizing potential, and antigenicity were performed.

RESULTS

In rodents, lethality was observed after a single intravenous administration of 20 mmol/kg, representing doses at least 2 orders of magnitude higher than the standard single diagnostic dose in humans (0.1 mmol/kg). The no observed adverse effect levels after repeated (daily) administrations over the course of 4 weeks exceeded the single diagnostic dose in humans by a factor of 12 in rats and 10 in dogs (calculated on the basis of body weight), and no unexpected organ toxicity was observed. The most salient finding of repeated dosing in both rats and dogs was vacuolization of renal tubular epithelium without concomitant effect on kidney function, which represents a well-known finding for this class of compounds. Gadobutrol was not teratogenic in rats, rabbits, and monkeys even when given repeatedly during organogenesis at maximum dose levels tested, being 25 to 100 times (based on body weight) above the diagnostic dose in humans. No indications of potential genotoxic, contact allergenic, or immunotoxic effects were observed. In local tolerance testing, gadobutrol was well tolerated after intravenous administration.

CONCLUSIONS

Gadobutrol was well tolerated with high safety margins between the single diagnostic dose of 0.1 mmol/kg in humans and the doses showing effects in animal studies.

Efficacy and Safety of Gadobutrol (1.0 M) versus Gadopentetate Dimeglumine (.5 M) for Enhanced Mri of Cns Lesions: A Phase Iii, Multicenter, Single-blind, Randomized Study in Chinese Patients

The aim of this study was to compare the efficacy and safety of macrocyclic gadobutrol (1.0 M) with linear gadopentetate dimeglumine (0.5 M) for contrast-enhanced magnetic resonance imaging (MRI) of central nervous system (CNS) lesions in Chinese patients (N = 147) with known or suspected CNS lesions, who were enrolled in this single-blind, randomized, parallel-group study. Three blinded independent readers evaluated all efficacy variables. The primary efficacy variable was the difference between the two agents for the change in contrast-to-noise ratio (CNR) between non-enhanced and contrast-enhanced scans of lesions. Secondary outcomes included mean change in number of lesions detected before and after contrast enhancement, diagnostic confidence, and safety and tolerability parameters. Gadobutrol was non-inferior to gadopentetate dimeglumine in respect to the difference in the mean change in CNR (6.94; 95% confidence interval [CI] lower limit: -3.90; predefined maximum 95% CI lower limit: -6.52). The mean change in the number of CNS lesions detected was greater with gadobutrol versus gadopentetate dimeglumine (1.2 vs. 0.2 lesions). Diagnostic confidence was classified as ‘high’ for more patients with gadobutrol versus gadopentetate dimeglumine by the investigators (58.8% vs. 55.4%) and by the three blinded readers (63.6% vs. 55.7%, 23.7% vs. 18.0% and 81.7% vs. 81.0%). Both agents were well tolerated by participating patients. We concluded that in Chinese patients with CNS lesions, gadobutrol (1.0 M) was as effective and well tolerated in contrast-enhanced MRI as gadopentetate dimeglumine (0.5 M). Gadobutrol provided improved visualization of CNS lesions compared with gadopentetate dimeglumine, with a comparable tolerability profile.

Gadobutrol for magnetic resonance imaging of chronic myocardial infarction: intraindividual comparison with gadopentetate dimeglumine

OBJECTIVES

To compare 0.15 mmol/kg gadobutrol with 0.20 mmol/kg gadopentetate dimeglumine with regard to late gadolinium enhancement (LGE) of infarcted myocardium at magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Twenty patients with history of chronic myocardial infarction underwent 2 cardiac MR examinations at 1.5 Tesla. For the evaluation of myocardial infarction, late gadolinium enhancement (LGE) imaging was performed with an inversion recovery-prepared gradient-echo sequence 15 minutes after administration of either gadobutrol (r1 = 5.2 mmol(-1)s(-1)) or gadopentetate dimeglumine (r1 = 4.1 mmol(-1)s(-1)). The dose of the contrast agents was adjusted based on the relaxivity of both contrast agents. Hence, gadobutrol and gadopentetate dimeglumine were administered at 0.15 mmol/kg and 0.20 mmol/kg, respectively. Contrast-to-noise ratios (CNR) between infarcted myocardium and remote myocardium (CNR remote) and between infarcted myocardium and left ventricular lumen (CNR lumen) were assessed by 2 independent readers. Additionally, infarct size was assessed semiautomatically by using a threshold of 5 standard deviations above the mean signal intensity of remote myocardium.

RESULTS

Subendocardial or transmural LGE was present in 16 of 20 (80%) patients. The optimal inversion time for LGE imaging did not differ significantly between gadobutrol and gadopentetate dimeglumine (275 ± 21 milliseconds [range, 240-320 milliseconds] and 282 ± 23 milliseconds [range, 240-330 milliseconds], respectively; P = 0.32). The CNR remote after administration of gadobutrol (40.0 ± 4.6; 95% confidence interval [CI]: 30.3; 49.7) and gadopentetate dimeglumine (40.6 ± 4.6; 95% CI: 30.9; 50.3) did not show significant differences (P = 0.90), whereas gadobutrol yielded a significantly higher CNR lumen (6.2 ± 3.6; 95% CI: -1.5; 13.9) compared with gadopentetate dimeglumine (0.8 ± 3.6; 95% CI: -6.9; 8.5). Infarct size after administration of gadobutrol (23.7 ± 4.7 mL; 95% CI: 13.6; 33.7) and gadopentetate dimeglumine (23.7 ± 4.7 mL;95% CI: 13.7; 33.8) was not statistically different (P = 0.94). There was an excellent correlation between gadobutrol- and gadopentetate dimeglumine-enhanced assessment of infarct size (Spearman r = 0.99 and r = 0.97 for reader 1 and 2, respectively).

CONCLUSION

This pilot study shows that 0.15 mmol/kg gadobutrol is an effective contrast agent for LGE imaging with better delineation of infarcted myocardium from left ventricular lumen than 0.20 mmol/kg gadopentetate dimeglumine.

Does higher gadolinium concentration play a role in the morphologic assessment of brain tumors? Results of a multicenter intraindividual crossover comparison of gadobutrol versus gadobenate dimeglumine (the MERIT Study)

BACKGROUND AND PURPOSE

Gadobenate dimeglumine has proved advantageous compared with other gadolinium-based contrast agents for contrast-enhanced brain MR imaging. Gadobutrol is a more highly concentrated agent (1.0 mol/L). This study intraindividually compared 0.1-mmol/kg doses of these agents for qualitative and quantitative evaluation of brain tumors.

MATERIALS AND METHODS

Adult patients with suspected or known brain tumors underwent 2 identical MR imaging examinations at 1.5T, 1 with gadobenate dimeglumine and the other with gadobutrol, both at a dose of 0.1-mmol/kg body weight. The agents were injected in randomized order separated by 3-14 days. Imaging sequences and acquisition timing were identical for the 2 examinations. Three blinded readers evaluated images qualitatively for diagnostic information (lesion extent, delineation, morphology, enhancement, global preference) and quantitatively for CNR and LBR.

RESULTS

One hundred fourteen of 123 enrolled patients successfully underwent both examinations. Final diagnoses were intra-axial tumors, metastases, extra-axial tumors, "other" tumors, and "nontumor" (49, 46, 8, 7, and 4 subjects, respectively). Readers 1, 2, and 3 demonstrated preference for gadobenate dimeglumine in 46 (40.7%), 54 (47.4%), and 49 (43.0%) patients, respectively, compared with 6, 7, and 7 patients for gadobutrol (P < .0001, all readers). Highly significant (P < .0001, all readers) preference for gadobenate dimeglumine was demonstrated for all other qualitative end points. Inter-reader agreement was good for all evaluations (κ = 0.414-0.629). Significantly superior CNR and LBR were determined for gadobenate dimeglumine (P < .019, all readers).

CONCLUSIONS

Significantly greater morphologic information and lesion enhancement are achieved on brain MR imaging with 0.1-mmol/kg gadobenate dimeglumine compared with gadobutrol at an equivalent dose.

Convenient Synthesis and Evaluation of Heptadentate Bifunctional Ligand for Radioimmunotherapy Applications

An efficient synthetic route to a bifunctional chelating agent C-NE3TA-NCS for antibody-targeted radioimmunotherapy (RIT) applications was developed. Various synthetic methods centered on the key reaction steps including bimolecular cyclization, ring opening reactions of aziridine and aziridinium cations, and reductive aminiation were explored to optimize the preparation of a tetraaza-based chelate TANPA and C-NE3TA analogues. Heptadentate C-NE3TA-NCS was conjugated to a tumor targeting antibody and compared to hexadentate C-NOTA-NCS for radiolabeling reaction kinetics with lanthanides for RIT. C-NE3TA-antibody conjugate displayed significantly enhanced complexation kinetics with 90Y as compared to C-NOTA-antibody conjugate. The synthetic methods for TANPA and C-NE3TA-NCS reported herein have broad applications for preparation of bifunctioanl macrocyclic chelating agents.

Cyanine dyes as contrast agents for near-infrared imaging in vivo: acute tolerance, pharmacokinetics, and fluorescence imaging

We compare pharmacokinetic, tolerance, and imaging properties of two near-IR contrast agents, indocyanine green (ICG) and 1,1(')-bis-(4-sulfobutyl) indotricarbocyanine-5,5(')-dicarboxylic acid diglucamide monosodium salt (SIDAG). ICG is a clinically approved imaging agent, and its derivative SIDAG is a more hydrophilic counterpart that has recently shown promising imaging properties in preclinical studies. The rather lipophilic ICG has a very short plasma half-life, thus limiting the time available to image body regions during its vascular circulation (e.g., the breast in optical mammography where scanning over several minutes is required). In order to change the physicochemical properties of the indotricarbocyanine dye backbone, several derivatives were synthesized with increasing hydrophilicity. The most hydrophilic dye SIDAG is selected for further biological characterization. The acute tolerance of SIDAG in mice is increased up to 60-fold compared to ICG. Contrary to ICG, the pharmacokinetic properties of SIDAG are shifted toward renal elimination, caused by the high hydrophilicity of the molecule. N-Nitrosomethylurea (NMU)-induced rat breast carcinomas are clearly demarcated, both immediately and 24 h after intravenous administration of SIDAG, whereas ICG shows a weak tumor contrast under the same conditions. Our findings demonstrate that SIDAG is a high potential contrast agent for optical imaging, which could increase the sensitivity for detection of inflamed regions and tumors.

Diagnostic yield of double-dose gadobutrol in the detection of brain metastasis: intraindividual comparison with double-dose gadopentetate dimeglumine

BACKGROUND AND PURPOSE

Accurate assessment of the number and lesion characteristics of brain metastasis is very important in GKS. The purpose of this study was to compare the diagnostic efficacy of DD gadobutrol in the detection of brain metastases compared with a DD 0.5-mol/L gadolinium contrast, gadopentetate dimeglumine.

MATERIALS AND METHODS

Records of 27 patients (male to female ratio, 15:12; mean age, 57.1 years) diagnosed with brain metastasis and having undergone GKS were retrospectively analyzed. All patients underwent the first 3D-T1-GRE MR imaging with a DD of gadopentetate dimeglumine. The second MR imaging with a DD of gadobutrol was performed during GKS by using the same parameters used for the first scan. Two neuroradiologists counted the number of enhancing lesions on 2 consecutive MR imaging examinations and reached consensus. Lesion-brain CNR was measured from 45 lesions, and paired t test analysis was performed between DD gadopentetate dimeglumine and gadobutrol MR imaging.

RESULTS

On DD gadopentetate dimeglumine-enhanced images, a total of 130 lesions were detected visually. With DD gadobutrol, 25 additional lesions were detected on GKS MR imaging. There was no missing lesion on DD gadobutrol MR imaging. The mean lesion-brain CNR was higher on DD gadobutrol MR imaging than on DD gadopentetate dimeglumine imaging (2.17 +/- 0.19 versus 1.90 +/- 0.26; P = .00011, paired t test, 2-tailed). Only 2 cases showed lower CNR on DD gadobutrol images: 1 with hemorrhagic metastasis from renal cell carcinoma and the other with steroid treatment after the first MR imaging.

CONCLUSIONS

DD 1.0-mol/L gadobutrol provides higher lesion conspicuity and enhances lesion detection in brain metastasis compared with DD 0.5-mol/L gadolinium contrast agents.