Revisiting the Pharmacokinetic Profiles of Gadolinium-Based Contrast Agents: Differences in Long-Term Biodistribution and Excretion

Gadolinium Contrast Agent Deposition in Children

Over the past few years, a large number of studies have evidenced increased signal intensity in the deep brain nuclei on unenhanced T1-MRI images achieved by the application of gadolinium-based contrast agents (GBCAs). The deposition of gadolinium in the brain, bone, and other tissues following administration of GBCAs has also been confirmed in histological studies in rodents and in necropsy studies in adults and children. Given the distinct physiological characteristics of children, this review focuses on examining the current research on gadolinium deposition in children, particularly studies utilizing novel methods and technologies. Furthermore, the article compares safety research findings of linear GBCAs and macrocyclic GBCAs in children, with the aim of offering clinicians practical guidance based on the most recent research outcomes. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Gadolinium Elimination in a Gadolinium Deposition Disease Population After a Single Exposure to Gadolinium-Based Contrast Agents

PURPOSE

This study documents the gadolinium (Gd) content in urine over time after the administration of a single dose of Gd-based contrast agent (GBCA) in patients diagnosed with Gd deposition disease.

MATERIALS AND METHODS

In this retrospective observational study, 45 subjects with normal renal function who had performed 1 contrast-enhanced magnetic resonance imaging and had a nonprovoked (native) 24-hour urine test for Gd quantification after the examination were evaluated. The GBCA brand and the time interval in days between the GBCA administration and 24-hour urine Gd measurements were recorded. Log-log plot visualization of time points for urine Gd content was obtained.

RESULTS

Time points collected for urine Gd content showed that Gd was above the reference levels for 3 months postinjection. The urinary concentration of Gd was similar for all agents, including linear and macrocyclic. The urinary content decreased in a dog-leg fashion. Gd urine content was substantially elevated at 1 month and decreased to remain above the accepted normal range by 3 months.

CONCLUSIONS

Gd is retained in the body and shows demonstrable continued spontaneous elimination in urine for at least several months after administration, including the most stable macrocyclic agents. The Gd elimination pattern shows a logarithmic decrease pattern between 1 and 3 months for all agents, regardless of their structure.

Gadolinium-Based Contrast Agents and Free Gadolinium Inhibit Differentiation and Activity of Bone Cell Lineages

OBJECTIVES

Administration of gadolinium-based contrast agents (GBCA) in magnetic resonance imaging results in the long-term retention of gadolinium (Gd) in tissues and organs, including the bone, and may affect their function and metabolism. This study aims to investigate the effects of Gd and GBCA on the proliferation/survival, differentiation, and function of bone cell lineages.

MATERIALS AND METHODS

Primary murine osteoblasts (OB) and osteoclast progenitor cells (OPC) isolated from C57BL/6J mice were used to test the effects of Gd 3+ (12.5-100 μM) and GBCA (100-2000 μM). Cultures were supplemented with the nonionic linear Gd-DTPA-BMA (gadodiamide), ionic linear Gd-DTPA (gadopentetic acid), and macrocyclic Gd-DOTA (gadoteric acid). Cell viability and differentiation were analyzed on days 4-6 of the culture. To assess the resorptive activity of osteoclasts, the cells were grown in OPC cultures and were seeded onto layers of amorphous calcium phosphate with incorporated Gd.

RESULTS

Gd 3+ did not affect OB viability, but differentiation was reduced dose-dependently up to 72.4% ± 6.2%-73.0% ± 13.2% (average ± SD) at 100 μM Gd 3+ on days 4-6 of culture as compared with unexposed controls ( P < 0.001). Exposure to GBCA had minor effects on OB viability with a dose-dependent reduction up to 23.3% ± 10.2% for Gd-DTPA-BMA at 2000 μM on day 5 ( P < 0.001). In contrast, all 3 GBCA caused a dose-dependent reduction of differentiation up to 88.3% ± 5.2% for Gd-DTPA-BMA, 49.8% ± 16.0% for Gd-DTPA, and 23.1% ± 8.7% for Gd-DOTA at 2000 μM on day 5 ( P < 0.001). In cultures of OPC, cell viability was not affected by Gd 3+ , whereas differentiation was decreased by 45.3% ± 9.8%-48.5% ± 15.8% at 100 μM Gd 3+ on days 4-6 ( P < 0.05). Exposure of OPC to GBCA resulted in a dose-dependent increase in cell viability of up to 34.1% ± 11.4% at 2000 μM on day 5 of culture ( P < 0.001). However, differentiation of OPC cultures was reduced on day 5 by 24.2% ± 9.4% for Gd-DTPA-BMA, 47.1% ± 14.0% for Gd-DTPA, and 38.2% ± 10.0% for Gd-DOTA ( P < 0.001). The dissolution of amorphous calcium phosphate by mature osteoclasts was reduced by 36.3% ± 5.3% upon incorporation of 4.3% Gd/Ca wt/wt ( P < 0.001).

CONCLUSIONS

Gadolinium and GBCA inhibit differentiation and activity of bone cell lineages in vitro. Thus, Gd retention in bone tissue could potentially impair the physiological regulation of bone turnover on a cellular level, leading to pathological changes in bone metabolism.

Analytical interference of intravascular contrast agents with clinical laboratory tests: a joint guideline by the ESUR Contrast Media Safety Committee and the Preanalytical Phase Working Group of the EFLM Science Committee

The Contrast Media Safety Committee of the European Society of Urogenital Radiology has, together with the Preanalytical Phase Working Group of the EFLM Science Committee, reviewed the literature and updated its recommendations to increase awareness and provide insight into these interferences. CLINICAL RELEVANCE STATEMENT: Contrast Media may interfere with clinical laboratory tests. Awareness of potential interference may prevent unwanted misdiagnosis. KEY POINTS: • Contrast Media may interfere with clinical laboratory tests; therefore awareness of potential interference may prevent unwanted misdiagnosis. • Clinical Laboratory tests should be performed prior to radiological imaging with contrast media or alternatively, blood or urine collection should be delayed, depending on kidney function.

Meningeal contrast enhancement in multiple sclerosis: Assessment of field strength, acquisition delay, and clinical relevance

BACKGROUND/PURPOSE

Leptomeningeal enhancement (LME) on post-contrast FLAIR is described as a potential biomarker of meningeal inflammation in multiple sclerosis (MS). Here we report an assessment of the impact of MRI field strength and acquisition timing on meningeal contrast enhancement (MCE).

METHODS

This was a cross-sectional, observational study of 95 participants with MS and 17 healthy controls (HC) subjects. Each participant underwent an MRI of the brain on both a 7 Tesla (7T) and 3 Tesla (3T) MRI scanner. 7T protocols included a FLAIR image before, soon after (Gd+ Early 7T FLAIR), and 23 minutes after gadolinium (Gd+ Delayed 7T FLAIR). 3T protocol included FLAIR before and 21 minutes after gadolinium (Gd+ Delayed 3T FLAIR).

RESULTS

LME was seen in 23.3% of participants with MS on Gd+ Delayed 3T FLAIR, 47.4% on Gd+ Early 7T FLAIR (p = 0.002) and 57.9% on Gd+ Delayed 7T FLAIR (p < 0.001 and p = 0.008, respectively). The count and volume of LME, leptomeningeal and paravascular enhancement (LMPE), and paravascular and dural enhancement (PDE) were all highest for Gd+ Delayed 7T FLAIR and lowest for Gd+ Delayed 3T FLAIR. Non-significant trends were seen for higher proportion, counts, and volumes for LME and PDE in MS compared to HCs. The rate of LMPE was different between MS and HCs on Gd+ Delayed 7T FLAIR (98.9% vs 82.4%, p = 0.003). MS participants with LME on Gd+ Delayed 7T FLAIR were older (47.6 (10.6) years) than those without (42.0 (9.7), p = 0.008).

CONCLUSION

7T MRI and a delay after contrast injection increased sensitivity for all forms of MCE. However, the lack of difference between groups for LME and its association with age calls into question its relevance as a biomarker of meningeal inflammation in MS.

Toxicity Mechanisms of Gadolinium and Gadolinium-Based Contrast Agents-A Review

Gadolinium-based contrast agents (GBCAs) have been used for more than 30 years to improve magnetic resonance imaging, a crucial tool for medical diagnosis and treatment monitoring across multiple clinical settings. Studies have shown that exposure to GBCAs is associated with gadolinium release and tissue deposition that may cause short- and long-term toxicity in several organs, including the kidney, the main excretion organ of most GBCAs. Considering the increasing prevalence of chronic kidney disease worldwide and that most of the complications following GBCA exposure are associated with renal dysfunction, the mechanisms underlying GBCA toxicity, especially renal toxicity, are particularly important. A better understanding of the gadolinium mechanisms of toxicity may contribute to clarify the safety and/or potential risks associated with the use of GBCAs. In this work, a review of the recent literature concerning gadolinium and GBCA mechanisms of toxicity was performed.

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.

Analytical interference of intravascular contrast agents with clinical laboratory tests: a joint guideline by the ESUR Contrast Media Safety Committee and the Preanalytical Phase Working Group of the EFLM Science Committee

The Contrast Media Safety Committee of the European Society of Urogenital Radiology has, together with the Preanalytical Phase Working Group of the EFLM Science Committee, reviewed the literature and updated its recommendations to increase awareness and provide insight into these interferences.

Meningeal contrast enhancement in multiple sclerosis: assessment of field strength, acquisition delay, and clinical relevance

Background/Purpose

Leptomeningeal enhancement (LME) on post-contrast FLAIR is described as a potential biomarker of meningeal inflammation in multiple sclerosis (MS). Here we report a comprehensive assessment of the impact of MRI field strength and acquisition timing on meningeal contrast enhancement (MCE).

Methods

This was a cross-sectional, observational study of 95 participants with MS and 17 healthy controls (HC) subjects. Each participant underwent an MRI of the brain on both a 7 Tesla (7T) and 3 Tesla (3T) MRI scanner. 7T protocols included a FLAIR image before, soon after (Gd+ Early 7T FLAIR), and 23 minutes after gadolinium (Gd+ Delayed 7T FLAIR). 3T protocol included FLAIR before and 21 minutes after gadolinium (Gd+ Delayed 3T FLAIR).

Results

LME was seen in 23.3% of participants with MS on Gd+ Delayed 3T FLAIR, 47.4% on Gd+ Early 7T FLAIR (p = 0.002) and 57.9% on Gd+ Delayed 7T FLAIR (p < 0.001 and p = 0.008, respectively). The count and volume of LME, leptomeningeal and paravascular enhancement (LMPE), and paravascular and dural enhancement (PDE) were all highest for Gd+ Delayed 7T FLAIR and lowest for Gd+ Delayed 3T FLAIR. Non-significant trends were seen for higher proportion, counts, and volumes for LME and PDE in MS compared to HCs. The rate of LMPE was different between MS and HCs on Gd+ Delayed 7T FLAIR (98.9% vs 82.4%, p = 0.003). MS participants with LME on Gd+ Delayed 7T FLAIR were older (47.6 (10.6) years) than those without (42.0 (9.7), p = 0.008).

Conclusion

7T MRI and a delay after contrast injection increased sensitivity for all forms of MCE. However, the lack of difference between groups for LME and its association with age calls into question its relevance as a biomarker of meningeal inflammation in MS.

Safety, Tolerability, and Pharmacokinetics of a Novel Macrocyclic Gadolinium-Based Contrast Agent, HNP-2006, in Healthy Subjects

OBJECTIVES

Gadolinium-based contrast agents (GBCAs) are indispensable in contrast-enhanced magnetic resonance imaging. A higher risk of gadolinium deposition in linear GBCAs required the introduction of macrocyclic GBCAs with a stable molecular structure. We conducted the first-in-human study to evaluate the safety, tolerability, and pharmacokinetics (PKs) of HNP-2006, a novel macrocyclic GBCA, in healthy male subjects.

MATERIALS AND METHODS

A randomized, placebo-controlled, double-blind, single-ascending dose study was conducted. Subjects received either a single intravenous bolus injection of HNP-2006 or its matching placebo with a treatment-to-placebo ratio of 6:2 at the dose level of 0.02, 0.05, 0.1, 0.2, and 0.3 mmol/kg. Safety was assessed through routine clinical assessments. Blood sampling and urine collection were performed up to 72 hours postdose for PK assessments. Noncompartmental methods were used to calculate PK parameters, and a population PK model was constructed.

RESULTS

Overall, 40 subjects completed the study. Fourteen subjects reported 22 treatment-emergent adverse events (TEAEs). The severity of all TEAEs was mild, and the HNP-2006 dose was associated with the incidence of TEAEs. The most common TEAEs included nausea and dizziness, which occurred within an hour of administration. HNP-2006 was rapidly eliminated by urinary excretion with a half-life of 1.8-2.0 hours and showed a dose-proportional PK. A 2-compartment model had the best fit with the population PK analysis.

CONCLUSIONS

A single intravenous dose of HNP-2006 was well-tolerated and safe up to 0.30 mmol/kg. HNP-2006 was rapidly excreted in urine and exhibited dose-independent PK profiles.

Review of strategies to reduce the contamination of the water environment by gadolinium-based contrast agents

Gadolinium-based contrast agents (GBCA) are essential for diagnostic MRI examinations. GBCA are only used in small quantities on a per-patient basis; however, the acquisition of contrast-enhanced MRI examinations worldwide results in the use of many thousands of litres of GBCA per year. Data shows that these GBCA are present in sewage water, surface water, and drinking water in many regions of the world. Therefore, there is growing concern regarding the environmental impact of GBCA because of their ubiquitous presence in the aquatic environment. To address the problem of GBCA in the water system as a whole, collaboration is necessary between all stakeholders, including the producers of GBCA, medical professionals and importantly, the consumers of drinking water, i.e. the patients. This paper aims to make healthcare professionals aware of the opportunity to take the lead in making informed decisions about the use of GBCA and provides an overview of the different options for action.In this paper, we first provide a summary on the metabolism and clinical use of GBCA, then the environmental fate and observations of GBCA, followed by measures to reduce the use of GBCA. The environmental impact of GBCA can be reduced by (1) measures focusing on the application of GBCA by means of weight-based contrast volume reduction, GBCA with higher relaxivity per mmol of Gd, contrast-enhancing sequences, and post-processing; and (2) measures that reduce the waste of GBCA, including the use of bulk packaging and collecting residues of GBCA at the point of application.Critical relevance statement This review aims to make healthcare professionals aware of the environmental impact of GBCA and the opportunity for them to take the lead in making informed decisions about GBCA use and the different options to reduce its environmental burden.Key points• Gadolinium-based contrast agents are found in sources of drinking water and constitute an environmental risk.• Radiologists have a wide spectrum of options to reduce GBCA use without compromising diagnostic quality.• Radiology can become more sustainable by adopting such measures in clinical practice.

Preclinical Safety Assessment of Gadopiclenol: A High-Relaxivity Macrocyclic Gadolinium-Based MRI Contrast Agent

OBJECTIVE

Gadopiclenol is a new high-relaxivity macrocyclic gadolinium-based contrast agent for magnetic resonance imaging of the central nervous system and other body regions. The product has been approved by US Food and Drug Administration and is currently being evaluated by European Medicines Agency. For risk assessment of the single diagnostic use in humans, the safety profile of gadopiclenol was evaluated with a series of preclinical studies.

MATERIALS AND METHODS

With exception of dose-ranging studies, all safety pharmacology and toxicology studies were performed in compliance with Good Laboratory Practice principles. Safety pharmacology studies were conducted to assess potential effects on cardiovascular (in vitro and in dogs), respiratory (in rats and guinea pigs), neurological (in rats), and renal endpoints (in rats). Toxicology studies were also performed to investigate acute toxicity (in rats and mice), extended single-dose (in rats and dogs) and repeated-dose toxicity (in rats and dogs), reproductive (in rats), developmental (in rats and rabbits) and juvenile toxicity (in rats), as well as genotoxicity (in vitro and in rats), local tolerance (in rabbits), potential immediate hypersensitivity (in guinea pigs), and potential tissue retention of gadolinium (in rats).

RESULTS

Safety pharmacology studies conducted at high intravenous (IV) doses showed a satisfactory tolerance of gadopiclenol in the main body systems. After either single or repeated IV dosing (14 and 28 days) in rats and dogs, gadopiclenol was well tolerated even at high doses. The no-observed-adverse-effect level values (ie, the highest experimental dose without adverse effects) representing between 8 times in rats and 44 times in dogs (based on the exposure), the exposure achieved in humans at the intended diagnostic dose, provide a high safety margin. No or only minor and reversible effects on body weight, food consumption, clinical signs, clinical pathology parameters, or histology were observed at the highest doses. The main histological finding consists in renal tubular vacuolations (exacerbated after repeated exposure), which supports a well-known finding for this class of compounds that has no physiological consequence on kidney function. Reproductive toxicity studies showed no evidence of effects on reproductive performance, fertility, perinatal and postnatal development in rats, or reproductive development in rats or rabbits. The safety profile of gadopiclenol in juvenile rats was satisfactory like in adults. Gadopiclenol was not genotoxic in vitro in the Ames test, a mouse lymphoma assay, and a rat in vivo micronucleus test. There were no signs of local intolerance at the injection site after IV and intra-arterial administration in rabbits. However, because of minor signs of intolerance after perivenous administration, misadministration must be avoided. Gadopiclenol exhibited no signs of potential to induce immediate hypersensitivity in guinea pigs.

CONCLUSIONS

High safety margins were observed between the single diagnostic dose of 0.05 mmol/kg in humans and the doses showing effects in animal studies. Gadopiclenol is, therefore, well tolerated in various species (mice, rats, dogs, rabbits, and guinea pigs). All observed preclinical data support the clinical approval.

Ten years of gadolinium retention and deposition: ESMRMB-GREC looks backward and forward

In 2014, for the first time, visible hyperintensities on unenhanced T1-weighted images in the nucleus dentatus and globus pallidus of the brain were associated with previous Gadolinium-based contrast agent (GBCA) injections and gadolinium deposition in patients with normal renal function. This led to a frenzy of retrospective studies with varying methodologies that the European Society of Magnetic Resonance in Medicine and Biology Gadolinium Research and Educational Committee (ESMRMB-GREC) summarised in 2019. Now, after 10 years, the members of the ESMRMB-GREC look backward and forward and review the current state of knowledge of gadolinium retention and deposition. CLINICAL RELEVANCE STATEMENT: Gadolinium deposition is associated with the use of linear GBCA but no clinical symptoms have been associated with gadolinium deposition. KEY POINTS : • Traces of Gadolinium-based contrast agent-derived gadolinium can be retained in multiple organs for a prolonged time. • Gadolinium deposition is associated with the use of linear Gadolinium-based contrast agents. • No clinical symptoms have been associated with gadolinium deposition.

Crown-hydroxylamines are pH-dependent chelating N,O-ligands with a potential for aerobic oxidation catalysis

Despite the rich coordination chemistry, hydroxylamines are rarely used as ligands for transition metal coordination compounds. This is partially because of the instability of these complexes that undergo decomposition, disproportionation and oxidation processes involving the hydroxylamine motif. Here, we design macrocyclic poly-N-hydroxylamines (crown-hydroxylamines) that form complexes containing a d-metal ion (Cu(II), Ni(II), Mn(II), and Zn(II)) coordinated by multiple (up to six) hydroxylamine fragments. The stability of these complexes is likely to be due to a macrocycle effect and strong intramolecular H-bonding interactions between the N-OH groups. Crown-hydroxylamine complexes exhibit interesting pH-dependent behavior where the efficiency of metal binding increases upon deprotonation of the hydroxylamine groups. Copper complexes exhibit catalytic activity in aerobic oxidation reactions under ambient conditions, whereas the corresponding complexes with macrocyclic polyamines show poor or no activity. Our results show that crown-hydroxylamines display anomalous structural features and chemical behavior with respect to both organic hydroxylamines and polyaza-crowns.

Where does the gadolinium go? A review into the excretion and retention of intravenous gadolinium

Gadolinium-based contrast agents (GBCAs) are commonly used in medical imaging. Most intravenously (IV) administered gadolinium is excreted via the kidneys, and pathological retention in renal failure leading to nephrogenic systemic fibrosis (NSF) is well described. More recently, retention of gadolinium in the body in the absence of renal disease has been identified, with unknown clinical consequences. Many patients are aware of this, either through the media or via comprehensive consent documentation. Some internet sites, without hard evidence, have suggested a constellation of possible symptoms associated with GBCA retention. Recent experience with patients ascribing symptoms to a contrast-enhanced MRI examination prompted this review of the fate of injected GBCA after MRI study, and of information available to patients online regarding gadolinium retention.

Intracerebral gadolinium deposition following blood-brain barrier disturbance in two different mouse models

To evaluate the influence of the blood-brain barrier on neuronal gadolinium deposition in a mouse model after multiple intravenous applications of the linear contrast agent gadodiamide. The prospective study held 54 mice divided into three groups: healthy mice (A), mice with iatrogenic induced disturbance of the blood-brain barrier by glioblastoma (B) or cerebral infarction (C). In each group 9 animals received 10 iv-injections of gadodiamide (1.2 mmol/kg) every 48 h followed by plain T1-weighted brain MRI. A final MRI was performed 5 days after the last contrast injection. Remaining mice underwent MRI in the same time intervals without contrast application (control group). Signal intensities of thalamus, pallidum, pons, dentate nucleus, and globus pallidus-to-thalamus and dentate nucleus-to-pons ratios, were determined. Gadodiamide complex and total gadolinium amount were quantified after the last MR examination via LC-MS/MS and ICP-MS. Dentate nucleus-to-pons and globus pallidus-to-thalamus SI ratios showed no significant increase over time within all mice groups receiving gadodiamide, as well as compared to the control groups at last MR examination. Comparing healthy mice with group B and C after repetitive contrast administration, a significant SI increase could only be detected for glioblastoma mice in globus pallidus-to-thalamus ratio (p = 0.033), infarction mice showed no significant SI alteration. Tissue analysis revealed significantly higher gadolinium levels in glioblastoma group compared to healthy (p = 0.013) and infarction mice (p = 0.029). Multiple application of the linear contrast agent gadodiamide leads to cerebral gadolinium deposition without imaging correlate in MRI.

Current state of pediatric neuro-oncology imaging, challenges and future directions

Imaging plays a central role in neuro-oncology including primary diagnosis, treatment planning, and surveillance of tumors. The emergence of quantitative imaging and radiomics provided an uprecedented opportunity to compile mineable databases that can be utilized in a variety of applications. In this review, we aim to summarize the current state of conventional and advanced imaging techniques, standardization efforts, fast protocols, contrast and sedation in pediatric neuro-oncologic imaging, radiomics-radiogenomics, multi-omics and molecular imaging approaches. We will also address the existing challenges and discuss future directions.

Elemental Imaging of Long-term Gadolinium Retention in Rodent Femur

Background The use of gadolinium-based contrast agents (GBCAs) is linked to gadolinium retention in the skeleton of healthy individuals. The mechanism of gadolinium incorporation into bone tissue is not fully understood and requires spatially resolved analysis to locate the gadolinium. Purpose To compare the quantitative distribution of gadolinium retained over time in rodent femur following the administration of gadodiamide and gadobutrol at three different time points. Materials and Methods In this animal study conducted between May 2018 and April 2020, 108 9-week-old healthy rats were repeatedly injected with either gadodiamide, gadobutrol, or saline solution and were killed 1, 3, or 12 months after the last injection. The femurs of six female and six male rats per each group and time point were collected. Quantitative elemental imaging of gadolinium in longitudinal thin sections was performed on one sample per sex with use of laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Gadolinium concentration was determined with use of ICP-MS on the samples of all animals (six per group). Mann-Whitney U tests were applied on pairwise comparisons to determine potential sex effect and GBCA effect on gadolinium concentrations. Results The highest gadolinium retention was observed in the gadodiamide group (concentration, 97-200 nmol · g^-1), exceeding the mean concentration in the gadobutrol group (6.5-17 nmol · g^-1). However, the gadolinium distribution pattern was similar for both contrast agents, showing prominent gadolinium retention at endosteal surfaces, in the bone marrow, and in small tissue pores. Gadolinium distribution in cortical bone changed over time, initially showing a thin rim of higher concentration close to the periosteum, which appeared to grow wider and move toward the interior of the femur over 1 year. Conclusion For both gadolinium-based contrast agents, gadolinium retention in rat bone was initially located close to the periosteum and bone cavities and changed with bone remodeling processes. The relevance to long-term storage of gadolinium in humans remains to be determined. © RSNA, 2022 Online supplemental material is available for this article.

Evaluation of Physicochemical Properties, Pharmacokinetics, Biodistribution, Toxicity, and Contrast-Enhanced Cancer MRI of a Cancer-Targeting Contrast Agent, MT218

OBJECTIVES

Preclinical assessments were performed according to the US Food and Drug Administration guidelines to determine the physicochemical properties, pharmacokinetics, clearance, safety, and tumor-specific magnetic resonance (MR) imaging of MT218, a peptidic gadolinium-based MR imaging agent targeting to extradomain B fibronectin for MR molecular imaging of aggressive tumors.

MATERIALS AND METHODS

Relaxivity, chelation stability, binding affinity, safety-related target profiling, and effects on CYP450 enzymes and transporters were evaluated in vitro. Magnetic resonance imaging was performed with rats bearing prostate cancer xenografts, immunocompetent mice bearing murine pancreatic cancer allografts, and mice bearing lung cancer xenografts at different doses of MT218. Pharmacological effects on cardiovascular, respiratory, and central nervous systems were determined in rats and conscious beagle dogs. Pharmacokinetics were tested in rats and dogs. Biodistribution and excretion were studied in rats. Single and repeated dosing toxicity was evaluated in rats and dogs. In vitro and in vivo genotoxicity, in vitro hemolysis, and anaphylactic reactivity were also performed.

RESULTS

At 1.4 T, the r1 and r2 relaxivities of MT218 were 5.43 and 7.40 mM -1 s -1 in pure water, 6.58 and 8.87 mM -1 s -1 in phosphate-buffered saline, and 6.54 and 8.70 mM -1 s -1 in aqueous solution of human serum albumin, respectively. The binding affinity of MT218 to extradomain B fragment is 3.45 μM. MT218 exhibited no dissociation of the Gd(III) chelates under physiological conditions. The peptide degradation half-life ( t1/2 ) of MT218 was 1.63, 5.85, and 2.63 hours in rat, dog, and human plasma, respectively. It had little effect on CYP450 enzymes and transporters. MT218 produced up to 7-fold increase of contrast-to-noise ratios in the extradomain B fibronectin-rich tumors with a dose of 0.04 mmol/kg for at least 30 minutes. MT218 had little pharmacological effect on central nervous, cardiovascular, or respiratory systems. MT218 had a mean plasma elimination half-life ( t1/2 ) of 0.31 and 0.89 hours in rats and dogs at 0.1 mmol/kg, respectively. No detectable Gd deposition was observed in the brain at 6 hours postinjection of MT218 at 0.1 mmol/kg in rats. MT218 was not mutagenic and had no mortality or morbidity in the rats or dogs up to 1.39 and 0.70 mmol/kg/d, respectively. The no observed adverse effect level of MT218 in Sprague-Dawley rats was 1.39 mmol/kg for single dosing and 0.46 mmol/kg/d for repeated dosing. The no observed adverse effect level in dogs was 0.07 mmol/kg/d. MT218 exhibited no genotoxicity, hemolysis, and anaphylactic reactivity.

CONCLUSION

The preclinical assessments showed that the targeted contrast agent MT218 has high r1 and r2 relaxivities, satisfactory physicochemical properties, pharmacokinetic, and safety profiles and produces effective tumor enhancement in multiple cancer types in rats and mice at reduced doses.

Preclinical Profile of Gadoquatrane: A Novel Tetrameric, Macrocyclic High Relaxivity Gadolinium-Based Contrast Agent

OBJECTIVES

The aim of this report was to characterize the key physicochemical, pharmacokinetic (PK), and magnetic resonance imaging (MRI) properties of gadoquatrane (BAY 1747846), a newly designed tetrameric, macrocyclic, extracellular gadolinium-based contrast agent (GBCA) with high relaxivity and stability.

MATERIALS AND METHODS

The r1-relaxivities of the tetrameric gadoquatrane at 1.41 and 3.0 T were determined in human plasma and the nuclear magnetic relaxation dispersion profiles in water and plasma. The complex stability was analyzed in human serum over 21 days at pH 7.4 at 37°C and was compared with the linear GBCA gadodiamide and the macrocyclic GBCA (mGBCA) gadobutrol. In addition, zinc transmetallation assay was performed to investigate the kinetic inertness. Protein binding and the blood-to-plasma ratio were determined in vitro using rat and human plasma. The PK profile was evaluated in rats (up to 7 days postinjection). Magnetic resonance imaging properties were investigated using a glioblastoma (GS9L) rat model.

RESULTS

The new chemical entity gadoquatrane is a macrocyclic tetrameric Gd complex with one inner sphere water molecule per Gd ( q = 1). Gadoquatrane showed high solubility in buffer (1.43 mol Gd/L, 10 mM Tris-HCl, pH 7.4), high hydrophilicity (logP -4.32 in 1-butanol/water), and negligible protein binding. The r1-relaxivity of gadoquatrane in human plasma per Gd of 11.8 mM -1 ·s -1 (corresponding to 47.2 mM -1 ·s -1 per molecule at 1.41 T at 37°C, pH 7.4) was more than 2-fold (8-fold per molecule) higher compared with established mGBCAs. Nuclear magnetic relaxation dispersion profiles confirmed the more than 2-fold higher r1-relaxivity in human plasma for the clinically relevant magnetic field strengths from 0.47 to 3.0 T. The complex stability of gadoquatrane at physiological conditions was very high. The observed Gd release after 21 days at 37°C in human serum was below the lower limit of quantification. Gadoquatrane showed no Gd 3+ release in the presence of zinc in the transmetallation assay. The PK profile (plasma elimination, biodistribution, recovery) was comparable to that of gadobutrol. In MRI, the quantitative evaluation of the tumor-to-brain contrast in the rat glioblastoma model showed significantly improved contrast enhancement using gadoquatrane compared with gadobutrol at the same Gd dose administered (0.1 mmol Gd/kg body weight). In comparison to gadoterate meglumine, similar contrast enhancement was reached with gadoquatrane with 75% less Gd dose. In terms of the molecule dose, this was reduced by 90% when compared with gadoterate meglumine. Because of its tetrameric structure and hence lower number of molecules per volume, all prepared formulations of gadoquatrane were iso-osmolar to blood.

CONCLUSIONS

The tetrameric gadoquatrane is a novel, highly effective mGBCA for use in MRI. Gadoquatrane provides favorable physicochemical properties (high relaxivity and stability, negligible protein binding) while showing essentially the same PK profile (fast extracellular distribution, fast elimination via the kidneys in an unchanged form) to established mGBCAs on the market. Overall, gadoquatrane is an excellent candidate for further clinical development.

Use of Real-Life Safety Data From International Pharmacovigilance Databases to Assess the Importance of Symptoms Associated With Gadolinium Exposure

OBJECTIVE

Recent scientific publications have reported cases of patients who complained from a variety of symptoms after they received a gadolinium-based contrast agent (GBCA). The aim of this study was to appreciate the importance of these clinical manifestations in the overall population by assessing the weight of "symptoms associated with gadolinium exposure" (SAGE) among the bulk of safety experiences reported to major health authorities.

MATERIALS AND METHODS

Symptoms associated with gadolinium exposure were identified from a review of the scientific literature, and the corresponding preferred terms were searched in each system organ class (SOC) category recorded in the European and North American pharmacovigilance databases EudraVigilance (EV) and FDA Adverse Event Reporting System (FAERS), respectively. The numbers of SAGE per preferred term, and cumulatively per SOC, were recorded and their weights in the overall spectrum of adverse events (AEs) were determined for each GBCA.

RESULTS

The analysis of the selected AEs revealed a significantly higher SAGE weight for gadobenate dimeglumine (EV: 25.83%, FAERS: 32.24%) than for gadoteridol (EV: 15.51%; FAERS: 21.13%) and significantly lower SAGE weights for gadobutrol (EV: 7.75%; FAERS: 13.31%) and gadoterate meglumine (EV: 8.66%; FAERS: 12.99%). A similar ranking was found for most of the SOCs except for "nervous system disorders," probably owing to a limitation in the methods of data selection. Furthermore, this analysis showed a greater percentage of reports mentioning a decrease in the quality of life of the patients when they were exposed to gadobenate dimeglumine or gadoteridol than to gadobutrol or gadoterate meglumine.

CONCLUSION

This study showed that SAGE represent a significant percentage of the bulk of AEs reported to the health authorities for each GBCA. It provided real-life arguments suggesting that SAGE may be more prevalent with linear than macrocyclic GBCAs and that gadoteridol may present a higher SAGE risk than the other macrocyclic 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.

Gadolinium retention: should pediatric radiologists be concerned, and how to frame conversations with families

Gadolinium retention in the brain and other organs has recently been identified by imaging and confirmed histologically. No direct clinical effects of gadolinium retention, which occurs after gadolinium-based contrast agent (GBCA) administration for MRI, have been scientifically accepted at this time. However, there is understandable concern among medical professionals and the public about the potential effects of gadolinium retention, particularly in the brain. Part of this concern might stem from the identification of nephrogenic systemic fibrosis caused by GBCAs in people with severe renal failure in 2006. This article briefly describes the characteristics of GBCAs; reviews and differentiates gadolinium retention, nephrogenic systemic fibrosis, and "gadolinium deposition disease" or "gadolinium toxicity"; and discusses societal guidelines and current usage in children. With the belief that GBCAs should not be withheld for appropriate indications in the absence of evidence of its potential risks, we offer a framework for determining when GBCA use is appropriate and suggestions for discussing its risks and benefits with children and their families.

Altered Functional Mitochondrial Protein Levels in Plasma Neuron-Derived Extracellular Vesicles of Patients With Gadolinium Deposition

The retention of the heavy metal, gadolinium, after a Gadolinium-Based Contrast Agent-assisted MRI may lead to a symptom cluster termed Gadolinium Deposition Disease. Little is known of the disorder's underlying pathophysiology, but a recent study reported abnormally elevated serum levels of pro-inflammatory cytokines compared to normal controls. As a calcium channel blocker in cellular plasma and mitochondrial membranes, gadolinium also interferes with mitochondrial function. We applied to sera from nine Gadolinium Deposition Disease and two Gadolinium Storage Condition patients newly developed methods allowing isolation of plasma neuron-derived extracellular vesicles that contain reproducibly quantifiable levels of mitochondrial proteins of all major classes. Patients' levels of five mitochondrial functional proteins were statistically significantly lower and of two significantly higher than the levels in normal controls. The patterns of differences between study patients and controls for mitochondrial dynamics and mitochondrial proteins encompassing neuronal energy generation, metabolic regulation, ion fluxes, and survival differed from those seen for patients with first episode psychosis and those with Major Depressive Disorder compared to their controls. These findings suggest that mitochondrial dysfunction due to retained gadolinium may play a role in causing Gadolinium Deposition Disease. Larger samples of both GDD and GSC patients are needed to allow not only testing the repeatability of our findings, but also investigation of relationships of specific mitochondrial protein deficiencies or excesses and concurrent cytokine, genetic, or other factors to GDD's neurological and cognitive symptoms. Studies of neuronal mitochondrial proteins as diagnostic markers or indicators of treatment effectiveness are also warranted.

Whole-body magnetic resonance imaging (WBMRI) versus whole-body computed tomography (WBCT) for myeloma imaging and staging

Myeloma-associated bone disease (MBD) develops in about 80-90% of patients and severely affects their quality of life, as it accounts for the majority of mortality and morbidity. Imaging in multiple myeloma (MM) and MBD is of utmost importance in order to detect bone and bone marrow lesions as well as extraosseous soft-tissue masses and complications before the initiation of treatment. It is required for determination of the stage of disease and aids in the assessment of treatment response. Whole-body low-dose computed tomography (WBLDCT) is the key modality to establish the initial diagnosis of MM and is now recommended as reference standard procedure for the detection of lytic destruction in MBD. In contrast, whole-body magnetic resonance imaging (WBMRI) has higher sensitivity for the detection of focal and diffuse plasma cell infiltration patterns of the bone marrow and identifies them prior to osteolytic destruction. It is recommended for the evaluation of spinal and vertebral lesions, while functional, diffusion-weighted MRI (DWI-MRI) is a promising tool for the assessment of treatment response. This review addresses the current improvements and limitations of WBCT and WBMRI for diagnosis and staging in MM, underlining the fact that both modalities offer complementary information. It further summarizes the corresponding radiological findings and novel technological aspects of both modalities.

GdClean: removal of Gadolinium contamination in mass cytometry data

MOTIVATION

Mass cytometry (Cytometry by Time-Of-Flight, CyTOF) is a single-cell technology that is able to quantify multiplex biomarker expressions and is commonly used in basic life science and translational research. However, the widely used Gadolinium (Gd)-based contrast agents (GBCAs) in magnetic resonance imaging (MRI) scanning in clinical practice can lead to signal contamination on the Gd channels in the CyTOF analysis. This Gd contamination greatly affects the characterization of the real signal from Gd-isotope-conjugated antibodies, severely impairing the CyTOF data quality and ruining downstream single-cell data interpretation.

RESULTS

We first in-depth characterized the signals of Gd isotopes from a control sample that was not stained with Gd-labeled antibodies but was contaminated by Gd isotopes from GBCAs, and revealed the collinear intensity relationship across Gd contamination signals. We also found that the intensity ratios of detected Gd contamination signals to the reference Gd signal were highly correlated with the natural abundance ratios of corresponding Gd isotopes. We then developed a computational method named by GdClean to remove the Gd contamination signal at the single-cell level in the CyTOF data. We further demonstrated that the GdClean effectively cleaned up the Gd contamination signal while preserving the real Gd-labeled antibodies signal in Gd channels. All of these shed lights on the promising applications of the GdClean method in preprocessing CyTOF datasets for revealing the true single-cell information.

AVAILABILITY AND IMPLEMENTATION

The R package GdClean is available on GitHub at https://github.com/JunweiLiu0208/GdClean.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Optimal sequences and sequence parameters for GBCA-enhanced MRI of the glymphatic system: a systematic literature review

BACKGROUND

The glymphatic system (GS) is a recently discovered waste clearance system in the brain.

PURPOSE

To evaluate the most promising magnetic resonance imaging (MRI) sequence(s) and the most optimal sequence parameters for glymphatic MRI (gMRI) 4-24 h after administration of gadolinium-based contrast agent (GBCA).

MATERIAL AND METHODS

Multiple literature databases were systematically searched for articles regarding gMRI or MRI of the perilymph in the inner ear until 11 May 2020. All relevant MRI sequence parameters were tabulated for qualitative analysis. Their potential was assessed based on detection of low dose GBCA, primarily measured as signal intensity (SI) ratio.

RESULTS

Thirty articles were included in the analysis. Three-dimensional fluid attenuated inversion recovery (3D-FLAIR), 3D Real Inversion Recovery (3D-Real IR), and multiple 3D T1-weighted gradient echo sequences were used. In perilymph, 3D-FLAIR with a TE of at least 400 ms yielded the highest SIRs. In the qualitative analysis of inner ear studies using 3D-FLAIR, TR was in the range of 4400-10,000 ms, TI 1500-2600 ms, refocusing flip angle (rFA) (range 120°-180°), and echo train length (ETL) 23-173. In the gMRI studies, quantitative analysis was not possible. In the qualitative analysis, 3D-FLAIR was used in the majority (8/12) of the studies, usually with TR 4800-9000 ms, TI 1650-2500 ms, TE 311-561 ms, rFA 90°-120°, and ETL 167-278.

CONCLUSION

Long TE 3D-FLAIR is the most promising sequence for detection of low-dose GBCA in the GS. Clinical and/or phantom studies on other MRI parameters are needed for further optimization of gMRI.

Mild Dissolution/Recomplexation Strategy for Speciation Analysis of Gadolinium from MR Contrast Agents in Bone Tissues by Means of HPLC-ICP-MS

A species-dependent and total gadolinium quantification strategy for the analysis of bone and bone marrow samples was developed and applied to femurs of rats previously treated with different gadolinium-based contrast agents (GBCAs). A combined mild dissolution/recomplexation strategy allows the quantification of total Gd as well as the quantification of intact GBCA in bones within one analysis for the first time. Samples of rat bones and bone marrow were dissolved in low concentrations of hydrochloric acid and diethylenetriamine pentaacetate (DTPA). This is followed by the addition of excess In(III) to recomplex all free ligands, previously added DTPA as well as the ligands of GBCAs that were not stable during the dissolution step. Separation and quantification were carried out by means of high-performance liquid chromatography (HPLC) on a hydrophilic interaction liquid chromatography (HILIC) column with subsequent inductively coupled plasma-mass spectrometry (ICP-MS). The results show that the investigated GBCA with a macrocyclic ligand shows a higher tendency to stay intact in the bone tissues over time, while a GBCA with a linear ligand is decomplexed more rapidly four weeks after GBCA administration. Additionally, for all macrocyclic GBCAs, a similar limited gadolinium accumulation was observed in the bone and bone marrow. Whereas linear GBCAs showed a higher gadolinium accumulation, a difference was observed between bone and bone marrow, indicating a different biodistribution behavior.

MR Imaging Safety Considerations of Gadolinium-Based Contrast Agents: Gadolinium Retention and Nephrogenic Systemic Fibrosis

Gadolinium (Gd)-based contrast agents (GBCAs) have revolutionized of MR imaging, enabling physicians to obtain life-saving medical information that often cannot be obtained with unenhanced MR imaging or other imaging modalities. Since regulatory approval in 1988, more than 450 million intravenous GBCA doses have been administered worldwide, with an extremely favorable pharmacologic safety profile. Recent evidence has demonstrated, however, that a small fraction of Gd is retained in human tissues. No direct correlation between Gd retention and clinical effects has been confirmed; however, a subset of patients have attributed various symptoms to GBCA exposure. This review details current knowledge regarding GBCA safety.

Acute Chelation Therapy-Associated Changes in Urine Gadolinium, Self-reported Flare Severity, and Serum Cytokines in Gadolinium Deposition Disease

OBJECTIVES

The aim of this study was to determine the following in patients who have undergone magnetic resonance imaging with gadolinium-based contrast agents (GBCAs) and meet the proposed diagnostic criteria for gadolinium deposition disease (GDD): (1) the effectiveness of chelation therapy (CT) with intravenous Ca-diethylenetriaminepentaacetic acid in removing retained gadolinium (Gd) and factors affecting the amount removed; (2) the frequency of CT-induced Flare, that is, GDD diagnostic symptom worsening, and factors affecting Flare intensity; (3) whether, as reported in a separate cohort, GDD patients' serum cytokine levels differ significantly from those in healthy normal controls and change significantly in response to CT; and (4) whether urine Gd, Flare reaction, and serum cytokine findings in GDD patients are mimicked in non-ill patients described as having gadolinium storage condition (GSC).

MATERIALS AND METHODS

Twenty-one GDD subjects and 3 GSC subjects underwent CT. Patients provided pre-CT and post-CT 24-hour urine samples for Gd content determination along with pre-CT and 24-hour post-CT serum samples for cytokine analysis. Patients rated potential Flare 24 hours after CT. Pre-CT and post-CT 24-hour urine Gd analyses and Luminex serum cytokine assays were performed blind to patients' GDD and GSC status and all other data except age and sex. Serum cytokine levels in a healthy normal control group of age- and sex-matched subjects drawn from Stanford influenza vaccination studies were measured once, contemporaneously with those of GDD and GSC patients, using the same Luminex assay.

RESULTS

Urine Gd amounts increased post-CT by 4 times or more after 87% of the 30 CT sessions. The most important factors appeared to be the time since the last GBCA dose and the cumulative dose received. Urine Gd amounts for GDD and GSC patients fell in the same ranges. All GDD patients, and no GSC patient, reported a Flare 24 hours post-CT. Linear regression found that Flare intensity was significantly predicted by a model including pre- and post-CT Gd amounts and the number of GBCA-enhanced magnetic resonance imaging. Post-CT, multiple cytokines showed strong positive relationships with GDD patients' Flare intensity in multivariable models. The pre-CT serum levels of 12 cytokines were significantly different in GDD patients compared with healthy flu vaccine controls. The small number of GSC patients precluded analogous statistical testing. Post-CT, GDD patients' serum levels of 20 cytokines were significantly decreased, and 2 cytokines significantly increased. These cytokines did not exhibit the same change pattern in the 3 GSC patients. The small number of GSC patients precluded statistical comparisons of GSC to GDD patients' results.

CONCLUSIONS

In this preliminary study, 24-hour urine Gd content increased markedly and similarly in GDD and GSC patients after Ca-diethylenetriaminepentaacetic acid CT. Post-CT Flare reaction developed only in GDD patients. The current study is the second finding significantly different serum cytokine levels in GDD patients compared with healthy normal controls. These differences and the difference between GDD and GSC patients' Flare and cytokine responses to CT suggest some inflammatory, immunologic, or other physiological differences in patients with GDD. Further research into the treatment and physiological underpinnings of GDD is warranted.

The Macrocyclic Gadolinium-Based Contrast Agents Gadobutrol and Gadoteridol Show Similar Elimination Kinetics From the Brain After Repeated Intravenous Injections in Rabbits

MATERIALS AND METHODS

Male white New Zealand rabbits (2.4-3.1 kg) in 2 study groups (n = 21 each) received 3 injections of either gadobutrol or gadoteridol at 0.9 mmol Gd/kg within 5 days (total dose, 2.7 mmol Gd/kg). Animals in one control group (n = 9) received 3 injections of saline (1.8 mL/kg). After 2, 6, and 12 weeks, 7 animals from each study group and 3 from the control group were killed and the Gd concentrations in the cerebellum, cerebrum, in blood and in urine were determined by inductively coupled plasma mass spectrometry. The chemical species of excreted Gd in urine were determined by high pressure liquid chromatography.

RESULTS

No significant (P > 0.05) differences in the Gd concentrations in the brain of rabbits were observed between the 2 macrocyclic GBCAs gadoteridol and gadobutrol at all time points. In the gadobutrol group, the mean Gd concentrations in the cerebellum and cerebrum decreased from 0.26 and 0.21 nmol Gd/g after 2 weeks, to 0.040 and 0.027 nmol Gd/g after 12 weeks, respectively, and in the gadoteridol group, from 0.25 and 0.21, to 0.037 and 0.023 nmol Gd/g, respectively. The plasma levels decreased from 0.11 and 0.13 nmol Gd/mL at 2 weeks for gadobutrol and gadoteridol to below the limit of quantification (<0.005 nmol Gd/mL) at 12 weeks. The urine concentration dropped in a biphasic course from 2 to 6 and from 6 to 12 weeks for both agents. The Gd excreted after 12 weeks was still present in the urine in the chemical form of the intact Gd complex for both agents.

CONCLUSIONS

Contrary to what had been reported in rats, no significant differences in the elimination kinetics from brain tissue in rabbits were observed after intravenous injection of multiple doses of the macrocyclic GBCAs gadobutrol and gadoteridol.

Gray Matter Nucleus Hyperintensity After Monthly Triple-Dose Gadopentetate Dimeglumine With Long-term Magnetic Resonance Imaging

OBJECTIVES

Gadolinium deposition is widely believed to occur, but questions regarding accumulation pattern and permanence remain. We conducted a retrospective study of intracranial signal changes on monthly triple-dose contrast-enhanced magnetic resonance imaging (MRI) examinations from the previously published Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial (N = 67) to characterize the dynamics of gadolinium deposition in several deep brain nuclei and track persistence versus washout of gadolinium deposition on long-term follow-up (LTFU) examinations (N = 28) obtained approximately 10 years after enrollment in the Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial.

MATERIALS AND METHODS

Using T2 and proton density images and using image analysis software (ITK-SNAP), manual regions of interest were created ascribing boundaries of the caudate nucleus, dentate nucleus, globus pallidus, pulvinar, putamen, white matter, and air. Intensity analysis was conducted on T1-weighted fat-saturated (fat-sat) images using the FSL package. A linear rigid-body transform was calculated from the fat-sat image at each target time point to the region of interest segmentation reference time point fat-sat image. Serial MRI signal was analyzed using linear mixed regression modeling with random intercept. Annual MRI signal changes including LTFU scans were assessed with t test.

RESULTS

During monthly scanning, all gray matter structures demonstrated a significant (P < 0.0001) increase in contrast-to-noise ratio. Yearly changes in deposition showed distinctive patterns for the specific nucleus: globus pallidus showed complete retention, pulvinar showed partial washout, while dentate, caudate, and putamen returned to baseline (ie, complete washout).

CONCLUSIONS

Monthly increased contrast-to-noise ratio in gray matter nuclei is consistent with gadolinium deposition over time. The study also suggests that some deep gray matter nuclei permanently retain gadolinium, whereas others demonstrate washout of soluble gadolinium.

An Ultrahigh-Field-Tailored T1 -T2 Dual-Mode MRI Contrast Agent for High-Performance Vascular Imaging

The assessment of vascular anatomy and functions using magnetic resonance imaging (MRI) is critical for medical diagnosis, whereas the commonly used low-field MRI system (≤3 T) suffers from low spatial resolution. Ultrahigh field (UHF) MRI (≥7 T), with significantly improved resolution and signal-to-noise ratio, shows great potential to provide high-resolution vasculature images. However, practical applications of UHF MRI technology for vascular imaging are currently limited by the low sensitivity and accuracy of single-mode (T1 or T2 ) contrast agents. Herein, a UHF-tailored T1 -T2 dual-mode iron oxide nanoparticle-based contrast agent (UDIOC) with extremely small core size and ultracompact hydrophilic surface modification, exhibiting dually enhanced T1 -T2 contrast effect under the 7 T magnetic field, is reported. The UDIOC enables clear visualization of microvasculature as small as ≈140 µm in diameter under UHF MRI, extending the detection limit of the 7 T MR angiography. Moreover, by virtue of high-resolution UHF MRI and a simple double-checking process, UDIOC-based dual-mode dynamic contrast-enhanced MRI is successfully applied to detect tumor vascular permeability with extremely high sensitivity and accuracy, providing a novel paradigm for the precise medical diagnosis of vascular-related diseases.

Gadolinium Retention as a Safety Signal: Experience of a Manufacturer

Objectives

The purpose of this manuscript is to review the successive regulatory actions and decisions following the initial publication by Kanda and colleagues in 2014 regarding gadolinium retention in the human brain after multiple gadolinium-based contrast agents (GBCAs) administrations.

Materials and Methods

Starting from 2014, the actions and decisions made by all regulatory authorities were collected and summarized region by region. Volumes of GBCA sales in 2018 per region and main countries are also presented as an indicator of patients’ exposure to those products.

Results

All regulatory authorities agreed on the absence of evidence of any harmful effect of gadolinium retention in humans. However, based on the same amount of preclinical and clinical evidence available in adults and children, regulatory authorities used different approaches resulting in different actions and decisions regarding the labeling and market authorizations of GBCAs, as well as the specific actions requested to the manufacturers.

Conclusions

The manufacturers of GBCAs had to face different situations according to the countries, due to the different positions and expectations from regulatory agencies. They have adapted their responses to the different positions of the regulatory agencies and conducted specific preclinical and clinical investigations to provide the expected evidence. It is also their responsibility to continuously monitor the benefit-risk balance of the products and to propose risk minimization measures to the regulatory agencies.

Rapid Detection of Gadolinium-Based Contrast Agents in Urine with a Chelated Europium Luminescent Probe

Gadolinium-based contrast agents are widely used in magnetic resonance imaging procedures to enhance image contrast. Despite their ubiquitous use in clinical settings, gadolinium is not an innocuous element, as suggested by several disorders associated with its use. Therefore, novel analytical technologies capable of tracking contrast agent excretion through urine are necessary for optimizing patient safety after imaging procedures. Here, we describe an assay to detect and quantify contrast agents in urine based on the luminescence quenching of a metal chelate probe, Eu³⁺-3,4,3-LI(1,2-HOPO), which only requires 10 min incubation before measurement. Gadolinium-based contrast agents prevent the formation of the Eu³⁺-3,4,3-LI(1,2-HOPO) complex, subsequently decreasing the luminescence of the assay solution. Three commercial contrast agents, Magnevist, Multihance, and Omniscan, were used to demonstrate the analytical concept in synthetic human urine, and subsequent quantification of mouse urine samples. To the best of our knowledge, this is the first assay capable of detecting and quantifying gadolinium-based contrast agents in urine without sample preparation or digestion.

Erythrocyte membrane concealed paramagnetic polymeric nanoparticle for contrast-enhanced magnetic resonance imaging

Recent progress in bioimaging nanotechnology has a great impact on the diagnosis, treatment, and prevention of diseases by enabling early intervention. Among different types of bioimaging modalities, contrast-enhanced magnetic resonance imaging using paramagnetic gadolinium-based molecular contrast agents (GBCAs) are most commonly used in clinic. However, molecular GBCAs distribute rapidly between plasma and interstitial spaces with short half-lives limiting its clinical impacts. To improve the properties of GBCAs, herein an effort has been put forth by incorporating GBCA into nanoscale system mimicking the property of red blood cell (RBC) that could facilitate contrast enhancement and prolong intraluminal retention in the body. The proposed nanoconstruct is made up of polymeric-core labeled with lipid conjugated GBCA followed by the imprint of the RBC membrane concealment layer to enhance stability and biocompatibility. Meanwhile, the confinement strategy of GBCA was implemented to accelerate magnetic properties of nanoconstruct providing longitudinal-relaxivity (r₁) to 12.78 ± 0.29 (mM s)^-1. Such improvement in r₁ was further confirmed by enhanced contrast in the vascular angiography of the murine model. Given higher colloidal stability and tunable magnetic properties, nanoconstruct proposed herein is a promising platform technology for the applications where enhanced plasma residence time and magnetic properties are necessary for diagnosis and therapy.

Decreased native renal T1 up to one week after gadobutrol administration in healthy volunteers

Background

Gadolinium‐based contrast agents (GBCAs) are widely used in MRI, despite safety concerns regarding deposition in brain and other organs. In animal studies gadolinium was detected for weeks after administration in the kidneys, but this has not yet been demonstrated in humans.

Purpose

To find evidence for the prolonged presence of gadobutrol in the kidneys in healthy volunteers.

Study Type

Combined retrospective and prospective analysis of a repeatability study.

Population

Twenty‐three healthy volunteers with normal renal function (12 women, age range 40–76 years), of whom 21 were used for analysis.

Field Strength/Sequence

Inversion recovery‐based T₁ map at 3T.

Assessment

T₁ maps were obtained twice with a median interval of 7 (range: 4–16) days. The T₁ difference (ΔT₁) between both scans was compared between the gadolinium group (n = 16, 0.05 mmol/kg gadobutrol administered after T₁ mapping during both scan sessions) and the control group (n = 5, no gadobutrol). T₁ maps were analyzed separately for cortex and medulla.

Statistical Tests

Mann–Whitney U‐tests to detect differences in ΔT₁ between groups and linear regression to relate time between scans and estimated glomerular filtration rate (eGFR) to ΔT₁.

Results

ΔT₁ differed significantly between the gadolinium and control group: median ΔT₁ cortex –98 vs. 7 msec (P < 0.001) and medulla –68 msec vs. 19 msec (P = 0.001), respectively. The bias corresponds to renal gadobutrol concentrations of 8 nmol/g tissue (cortex) and 4 nmol/g tissue (medulla), ie, ~2.4 μmol for both kidneys (0.05% of original dose). ΔT₁ correlated in the gadolinium group with duration between acquisitions for both cortex (regression coefficient (β) 16.5 msec/day, R² 0.50, P < 0.001) and medulla (β 11.5 msec/day, R² 0.32, P < 0.001). Medullary ΔT₁ correlated with eGFR (β 1.13 msec/(ml/min) R² 0.25, P = 0.008).

Data Conclusion

We found evidence of delayed renal gadobutrol excretion after a single contrast agent administration in subjects with normal renal function. Even within this healthy population, elimination delay increased with decreasing kidney function.

Level of Evidence: 3

Technical Efficacy: Stage 3

J. Magn. Reson. Imaging 2020;52:622–631.

Advances in Contrast Agents for Contrast-Enhanced Magnetic Resonance Imaging

INTRODUCTION

Magnetic resonance imaging (MRI) is a well-established medical invention in modern medical technology diagnosis. It is a nondestructive, versatile, and sensitive technique with a high spatial resolution for medical diagnosis. However, MRI has some limitations in differentiating certain tissues, particularly tiny blood vessels, pathological to healthy tissues, specific tumors, and inflammatory conditions such as arthritis, atherosclerosis, and multiple sclerosis. The contrast agent (CA) assisted imaging is the best possible solution to resolve the limitations of MRI.

METHOD

The literature review was carried out using the keywords, "MRI, T1&T2 relaxation, MRI CAs, delivery and adverse effects, classification of CAs." The tools used for the literature search were PubMed, Scopus, and Google Scholar.

RESULT AND DISCUSSION

The literature findings focus on MRI technique, limitations, and possible solutions. Primarily, the review focuses on the mechanism of CAs in image formation with detailed explanations of T1 and T2 relaxations, the mechanism of the MRI-CA image formations. This review presents the adverse effects of CA as well as available marketed formulations and recent patents to extent complete information about the MRI-CA.

CONCLUSION

MRI generates detailed visual information of various tissues with high resolution and contrast. The proton present in the biological fluid plays a crucial role in MR image formation, and it is unable to distinguish pathological conditions in many cases. The CAs are the best solution to resolve the limitation by interacting with native protons. The present review discusses the mechanism of CAs in contrast enhancement and its broad classification with the latest literature. Furthermore, the article presents information about CA biodistribution and adverse effects. The review concludes with an appropriate solution for adverse effects and presents the future prospective for researchers to develop advanced formulations.

Impact of Treatment With Chelating Agents Depends on the Stability of Administered GBCAs: A Comparative Study in Rats

Objective

This study investigated the potential effect of the chelating agent calcium trisodium pentetate (Ca-DTPA) on the urinary excretion of gadolinium and the subsequent elimination of gadolinium (Gd) in the brain after a single intravenous administration of either a linear (gadodiamide) or a macrocyclic (gadobutrol) Gd-based contrast agent in rats.

Materials and Methods

Rats received either a single injection of gadodiamide or gadobutrol (1.8 mmol/kg, each) or saline (n = 18 per group). Seven weeks after the injection, 6 animals of each group were killed before the treatment period. From the remaining 12 animals, 6 received either 3 intravenous injections of Ca-DTPA (180 μmol/kg) or saline. Urine was collected daily for 3 days after each infusion. Gadolinium measurements by ICP-MS were performed in urine and tissue samples.

Results

In animals that initially received the linear gadodiamide, Ca-DTPA infusion increased the urinary excretion of Gd by a factor of 10 (cumulative amount of 114 ± 21 nmol Gd vs 10 ± 4 nmol Gd after saline infusion, P ≤ 0.0001). In contrast, animals that received the macrocyclic gadobutrol exhibited a higher spontaneous urinary excretion of Gd (33 ± 12 nmol after saline infusion) and Ca-DTPA had no impact (30 ± 11 nmol Gd, P = 0.68).

The urinary excretion of Gd was associated with Gd brain content. Seven weeks after the initial Gd-based contrast agent administration, a total amount of 0.74 ± 0.053 nmol Gd was quantified in the brain after administration of gadodiamide. The Gd brain burden was partially reduced at the end of the treatment period in the animals that were repeatedly infused with Ca-DTPA (0.56 ± 0.13 nmol Gd, P = 0.009) but not with saline (0.66 ± 0.081 nmol, P = 0.32). In contrast, the total amount of macrocyclic gadobutrol measured in the brain was lower (0.11 ± 0.029 nmol Gd) and still spontaneously cleared during the 3-week saline infusion period (0.057 ± 0.019 nmol Gd (P = 0.003). Gadolinium quantified in the brain after infusions with Ca-DTPA did not differ from saline-infused animals (0.049 ± 0.014 nmol Gd).

Conclusions

Administration of the chelating agent Ca-DTPA 7 weeks after injection of linear gadodiamide induced relevant urinary Gd excretion. In parallel, the Gd amount in the brain tissue decreased. This indicates a dechelated pool among the chemical Gd forms present in the rat brain after linear gadodiamide administration that can be mobilized by chelation with Ca-DTPA. In contrast, Ca-DTPA did not mobilize Gd in animals that received macrocyclic gadobutrol, indicating that the Gd measured is intact gadobutrol.