Gadolinium Deposition and Chronic Toxicity

Clinicians, radiologists, and patients should be aware of the most up-to-date data on the risks of gadolinium-based contrast agent (GBCA) administration. In this review, we discuss in vivo gadolinium retention, particularly brain tissue retention, and potential toxic effects. GBCA pharmacokinetics and biodistribution are reviewed briefly. Based on the more recent published literature and society guidelines, general safety recommendations for clinical practice are provided.

Spatially resolved quantification of gadolinium deposited in the brain of a patient treated with gadolinium-based contrast agents

Due to its paramagnetic properties resulting from seven unpaired f-electrons, Gd is frequently applied in magnetic resonance imaging examinations. Due to the acute toxicity of free Gd³⁺, ligand ions based on polyaminocarboxylic acids are used to create thermodynamically stable linear or macrocyclic complexes. The highly water soluble Gd-based contrast agents (GBCAs) are known to be excreted fast and unmetabolized, mostly via the kidneys. Nevertheless, recent studies showed that Gd traces persists not only in animal but also in human brain. Aim of this study was the development and application of an analytical method for the spatially resolved quantification of gadolinium traces in human brain thin sections of a patient treated with GBCAs. For this retrospective study different human brain regions were selected to analyze the distribution of gadolinium. An additional patient served as control sample, as no GBCA was administered. Deep-frozen brain thin sections were analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and matrix-matched gelatin standards were prepared to quantify the gadolinium deposits via an external calibration. LA-ICP-MS analyses with high spatial resolution showed gadolinium deposits in different brain regions with highest concentrations above 800ngg^-1 more than two years after the last application of a GBCA. An excellent limit of quantification of 7ngg^-1, which is far below the limits of detection of MRI methods, could be achieved. The found concentrations confirm recent reports on gadolinium depositions in human brain, which were obtained without high spatial resolution. LA-ICP-MS provides limits of quantification, which are well suited to detect ultratrace amounts of gadolinium in human brain. Therefore, it provides valuable information on the distribution of gadolinium traces in the human brain even after single administration of GBCAs.

Gadolinium-based contrast agents induce gadolinium deposits in cerebral vessel walls, while the neuropil is not affected: an autopsy study

Recent studies showed gadolinium depositions following serial administrations of gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging examinations in various parts of the brain with the dentate nucleus (DN) being most affected. Even though no clinical correlates of the deposits are known yet, an intensive debate developed if this might be harmful. The aim of the current study was to specify the gadolinium distribution in brain tissue of patients who received serial injections of GBCAs in the low-µm range and to explore any potential pathological tissue changes caused by gadolinium deposits. Thirteen autopsy cases-eight receiving GBCA administrations, five serving as controls-were identified and analyzed. For all patients, total gadolinium quantification after acidic digestion by means of inductively coupled plasma-mass spectrometry (ICP-MS) was performed. Six cases were utilized for the spatially resolved quantification of gadolinium within the cerebellum and the basal ganglia by means of high-resolution laser ablation (LA)-ICP-MS. Histopathological and immunohistochemical examinations were performed to determine tissue reactions. LA-ICP-MS revealed gadolinium depositions in the walls of small blood vessels of the DN in all GBCA exposed patients, while no gadolinium was found in the control group. Additionally, the detection of phosphorus and metals like copper, zinc and iron provides evidence that transmetalation reactions might have occurred. No significant pathological changes of the brain tissue in the vicinity of the DN with respect to micro-/astrogliosis and neuronal loss were found in any of the patients. This notably holds true even for a patient who died from nephrogenic systemic fibrosis exhibiting extremely high gadolinium concentrations within the DN. The findings show that gadolinium depositions in the brain are restricted to blood vessel walls, while the neuropil is spared and apparent cellular reactions are absent.

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.

LA-ICP-MS/MS improves limits of detection in elemental bioimaging of gadolinium deposition originating from MRI contrast agents in skin and brain tissues

A novel analytical method to detect the retention of gadolinium from contrast agents for magnetic resonance imaging (MRI) in tissue samples of patients is presented. It is based on laser ablation - inductively coupled plasma - triple quadrupole - mass spectrometry (LA-ICP-MS/MS). Both Gd and P were monitored with a mass shift of +16, corresponding to mono-oxygenated species, as well as Zn, Ca, and Fe on-mass. This method resulted in a significantly reduced background and improved limits of detection not only for phosphorus, but also for gadolinium. These improvements were essential to perform elemental bioimaging with improved resolution of 5 μm x 5 μm, allowing the detection of small Gd deposits in fibrotic skin and brain tumour tissue with diameters of approximately 50 μm. Detailed analyses of these regions revealed that most Gd was accompanied with P and Ca, indicating co-precipitation.

Confirming improved detection of gadolinium in bone using in vivo XRF

The safety of using Gd in MRI contrast agents has recently been questioned, due to recent evidence of the retention of Gd in individuals with healthy renal function. Bone has proven to be a storage site for Gd, as unusually high concentrations have been measured in femoral heads of patients undergoing hip replacement surgery, as well as in autopsy samples. All previous measurements of Gd in bone have been invasive and required the bone to be removed from the body. X-ray fluorescence (XRF) offers a non-invasive and non-destructive method for carrying out in vivo measurements of Gd in humans. An updated XRF system provides improved detection limits in a short measurement time of 30-min. A new four-detector system and higher activity Cd-109 excitation source of 5GBq results in minimum detection limits (MDLs) of 1.64-1.72μgGd/g plaster for an average overlaying tissue thickness of the tibia. These levels are well within the range of previous in vitro Gd measurements. Additional validation through comparison with ICP-MS measurements has confirmed the ability of the XRF system for detecting Gd further, proving it is a feasible system to carry out human measurements.

The use of a binary chelate formulation: Could gadolinium based linear contrast agents be rescued by the addition of zinc selective chelates?

Tissue and bone retention of gadolinium based contrast agents (GBCAs) has become a clinical concern because of the potential short and long term toxic effects of free gadolinium. This is a critical problem for most open-chain agents that more readily transmetallate in vivo, in comparison to macrocyclic compounds. Gadolinium diethylene tri-aminepentaacetic acid bis-glucosamide (Gd-DTPA-BIGA) is an experimental, open-chain contrast agent which has a significantly increased relaxivity coefficient in comparison to other GBCAs. This results in greater signal intensity and improved contrast enhancement. These superior imaging qualities initiated a search for a solution to the transmetallation of this agent. Plasma zinc is a well-known GBCA transmettalation agent. Since the base chelate of Gadodiamide (Gd-DPTA-Bis-Methylamide or Omniscan), DTPA-Bis-Methylamide (DTPA-BMA), readily transmettalates with and binds serum zinc, we hypothesized that a plasma "zinc sink," may significantly reduce transmetallation of linear agents. 5% DTPA-BMA was added to a formulation of Gd-DTPA-BIGA, which was tested against the original formulation of Gd-DTPA-BIGA with 0.2% of the base chelate DTPA-BIGA. These formulations, including gadodiamide, were labeled with ¹⁵³GdCl₃ followed by infusion into cohorts of Sprague Dawley rats which were sacrificed at 1, 30 and 60 days. Internal organs were harvested, along with blood, skin and femur, and analyzed for residual gadolinium. A subset of tissues were also interrogated with ICP-MS. Labeled Gadodiamide and saline where used as controls. Conclusion: The addition of 5% DTPA-BMA, as a zinc binding agent, reduced the transmetallation of the linear agent Gd-DTPA-BIGA, in comparison to its original formulation supplemented with 0.2% BIGA. This result indicates that supplementing linear GBCAs with ancillary chelates may hold promise for reducing, or eliminating the biological archiving of gadolinium in tissues. In addition, this paper provides valuable animal data on the long term retention of gadolinium from linear based contrast agents.

Visible T1-hyperintensity of the dentate nucleus after multiple administrations of macrocyclic gadolinium-based contrast agents: yes or no?

OBJECTIVES

To investigate the appearance of visible dentate nucleus (DN) T1-hyperintensity and quantify changes in DN/pons (DN/P) signal intensity (SI) ratio in MS patients after the exclusive administration of macrocyclic GBCAs.

MATERIALS AND METHODS

One hundred forty-nine patients with confirmed MS were evaluated. Patients received at least two administrations of gadobutrol (n = 63), gadoterate (n = 57), or both (n = 29). Two experienced neuroradiologists in consensus evaluated unenhanced T1-weighted MR images from all examinations in each patient for evidence of visible DN hyperintensity. Thereafter, SI measurements were made in the left and right DN and pons on unenhanced T1-weighted images from the first and last scans. A two-sample t test compared the DN/P SI ratios for patients with and without visible T1-hyperintensity.

RESULTS

Visible T1-hyperintensity was observed in 42/149 (28.2%) patients (19 after gadobutrol only, 15 after gadoterate only, 8 after both), typically at the 4th or 5th follow-up exam at 3-4 years after the initial examination. Significant increases in DN/P SI ratio from first to last examination were determined for patients with visible T1-hyperintensity (0.998 ± 0.002 to 1.153 ± 0.016, p < 0.0001 for gadobutrol; 1.003 ± 0.004 to 1.110 ± 0.014, p < 0.0001 for gadoterate; 1.004 ± 0.011 to 1.163 ± 0.032, p = 0.0004 for both) but not for patients without visible T1-hyperintensity (p > 0.05; all groups).

CONCLUSION

Multiple injections of gadobutrol and/or gadoterate can lead to visible and quantifiable increases in DN/P SI ratio in some patients with MS.

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.

Analysis of the Gadolinium retention in the Experimental Autoimmune Encephalomyelitis (EAE) murine model of Multiple Sclerosis

OBJECTIVES

The aim of this study is to quantitatively investigate, at the preclinical level, the extent of Gd retention in the CNS, and peripheral organs, of immune-mediated murine models (Experimental Autoimmune Encephalomyelitis -EAE) of Multiple Sclerosis, compared to control animals, upon the injection of gadodiamide. The influence of the Gadolinium Based Contrast Agent administration timing during the course of EAE development is also monitored.

METHODS

EAE mice were injected with three doses (1.2 mmol/kg each) of gadodiamide at three different time points during the EAE development and sacrificed after 21 or 39 days. Organs were collected and the amount of Gd was quantified through Inductively Coupled Plasma-Mass Spectrometry. Transmission electron microscopy (TEM) and MRI techniques were applied to add spatial and qualitative information to the obtained results.

RESULTS

In the spinal cord of EAE group, 21 days after gadodiamide administration, a significantly higher accumulation of Gd occurred. Conversely, in the encephalon, a lower amount of Gd retention was reached, even if differences emerged between EAE and controls mice. After 39 days, the amounts of retained Gd markedly decreased. TEM validated the presence of Gd in CNS. MRI of the encephalon at 7.1T did not highlight any hyper intense region.

CONCLUSION

In the spinal cord of EAE mice, which is the mostly damaged region in this specific animal model, a preferential but transient accumulation of Gd is observed. In the encephalon, the Gd retention could be mostly related to inflammation occurring upon immunization rather than to demyelination.

MRI contrast agents and retention in the brain: review of contemporary knowledge and recommendations to the future

Gadolinium-based contrast agents (GBCA) were introduced with high expectations for favorable efficacy, low nephrotoxicity, and minimal allergic-like reactions. Nephrogenic systemic fibrosis and proven gadolinium retention in the body including the brain has led to the restriction of linear GBCAs and a more prudent approach regarding GBCA indication and dosing. In this review, we present the chemical, physical, and clinical aspects of this topic and aim to provide an equanimous and comprehensive summary of contemporary knowledge with a perspective of the future. In the first part of the review, we present various elements and compounds that may serve as MRI contrast agents. Several GBCAs are further discussed with consideration of their relaxivity, chelate structure, and stability. Gadolinium retention in the brain is explored including correlation with the presence of metalloprotein ferritin in the same regions where visible hyperintensity on unenhanced T1-weighted imaging occurs. Proven interaction between ferritin and gadolinium released from GBCAs is introduced and discussed, as well as the interaction of other elements with ferritin; and manganese in patients with impaired liver function or calcium in Fahr disease. We further present the concept that only high-molecular-weight forms of gadolinium can likely visibly change signal intensity on unenhanced T1-weighted imaging. Clinical data are also presented with respect to potential neurological manifestations originating from the deep-brain nuclei. Finally, new contrast agents with relatively high relaxivity and stability are introduced. CRITICAL RELEVANCE STATEMENT: GBCA may accumulate in the brain, especially in ferritin-rich areas; however, no adverse neurological manifestations have been detected in relation to gadolinium retention. KEY POINTS: Gadolinium currently serves as the basis for MRI contrast agents used clinically. No adverse neurological manifestations have been detected in relation to gadolinium retention. Future contrast agents must advance chelate stability and relativity, facilitating lower doses.