Gadolinium-Based MRI Contrast Agents Induce Mitochondrial Toxicity and Cell Death in Human Neurons, and Toxicity Increases With Reduced Kinetic Stability of the Agent:

Novel Gd-DTPA-peptide for targeted breast tumor magnetic resonance imaging

The prevalence of breast cancer underscores the imperative for early diagnosis in guiding treatment decisions. This study introduces a novel contrast agent, Gd-DTPA-VGB3, derived from the peptide VGB3 targeting vascular endothelial growth factor receptor-1 (VEGFR1) and VEGFR2, to enhance the contrast of conventional drug Magnevist in breast tumor MRI. The MRI contrast agent was synthesized on rink amide resin via Fmoc strategy, incorporating amino acids, and coupling to diethylenetriaminepentaacetic acid (DTPA). Gadolinium (Gd)-DTPA-VGB3 displayed specific binding to VEGFR1/2 in a displacement binding assay. Gd-DTPA-VGB3 exhibited minimal cytotoxicity to normal MCF-10 cells while inhibiting 4T1 mammary carcinoma cell proliferation. Compared to Magnevist, Gd-DTPA-VGB3 demonstrated a 2.8-fold increase in contrast-to-noise ratio (CNR) (355 vs. 125). Gd-DTPA-VGB3 exhibited enhanced accumulation in 4T1 tumor-bearing mice, resulting in significant signal intensity improvement. The findings highlight Gd-DTPA-VGB3's specific binding to VEGFRs, substantiating its potential as a candidate for enhancing MRI contrast in breast cancer diagnostics.

Gadolinium-based contrast agents aggravate mechanical and thermal hyperalgesia in a nitroglycerine-induced migraine model in male mice

In the diagnosis of migraine, which is a neurovascular disease, gadolinium-based contrast agents (GBCAs) are used to rule out more serious conditions. On the other hand, it remains unclear as a scientific gap whether GBCAs may trigger migraine-related pain. The aim of this study was to investigate the effect of GBCAs on mechanical and thermal pain behaviour in a nitroglycerin (NTG)-induced migraine model in mice. NTG (10 mg/kg) was administered intraperitoneally to adult (6-8weeks old) BALB/c mice 2 h before behavioral tests 5 times every other day on days 1st, 3rd, 5th and 9th to induce migraine model (N = 50). As GBCAs, gadobenate dimeglumine (linear-ionic), Gadodiamide (linear-nonionic), and gadobutrol (macrocyclic-nonionic) were delivered intravenously through the tail vein of mice for 5 days on test days. Mechanical pain threshold (plantar and facial withdrawal threshold) was evaluated by plantar von Frey and periorbital von Frey tests on days 1st, 5th, and 9th, and thermal pain threshold (latency) was evaluated by hot plate and cold plate tests on days 3rd and 7th. There was a statistically significant increase in mechanical and thermal hyperalgesia in NTG administered groups compared to the control group. Gadodiamide, gadobutrol and gadobenate dimeglumine administration significantly decreased latency, paw and facial withdrawal threshold (0.18 ± 0.05, 0.17 ± 0.07, 0.16 ± 0.09; 9th day values respectively) compared to NTG group (0.27 ± 0.05). The results of this in vivo study show that GBCAs produce effects that may trigger migraine attacks in migraine. It is recommended that these effects be further investigated and supported by further clinical studies.

Artificial T1-Weighted Postcontrast Brain MRI: A Deep Learning Method for Contrast Signal Extraction

OBJECTIVES

Reducing gadolinium-based contrast agents to lower costs, the environmental impact of gadolinium-containing wastewater, and patient exposure is still an unresolved issue. Published methods have never been compared. The purpose of this study was to compare the performance of 2 reimplemented state-of-the-art deep learning methods (settings A and B) and a proposed method for contrast signal extraction (setting C) to synthesize artificial T1-weighted full-dose images from corresponding noncontrast and low-dose images.

MATERIALS AND METHODS

In this prospective study, 213 participants received magnetic resonance imaging of the brain between August and October 2021 including low-dose (0.02 mmol/kg) and full-dose images (0.1 mmol/kg). Fifty participants were randomly set aside as test set before training (mean age ± SD, 52.6 ± 15.3 years; 30 men). Artificial and true full-dose images were compared using a reader-based study. Two readers noted all false-positive lesions and scored the overall interchangeability in regard to the clinical conclusion. Using a 5-point Likert scale (0 being the worst), they scored the contrast enhancement of each lesion and its conformity to the respective reference in the true image.

RESULTS

The average counts of false-positives per participant were 0.33 ± 0.93, 0.07 ± 0.33, and 0.05 ± 0.22 for settings A-C, respectively. Setting C showed a significantly higher proportion of scans scored as fully or mostly interchangeable (70/100) than settings A (40/100, P < 0.001) and B (57/100, P < 0.001), and generated the smallest mean enhancement reduction of scored lesions (-0.50 ± 0.55) compared with the true images (setting A: -1.10 ± 0.98; setting B: -0.91 ± 0.67, both P < 0.001). The average scores of conformity of the lesion were 1.75 ± 1.07, 2.19 ± 1.04, and 2.48 ± 0.91 for settings A-C, respectively, with significant differences among all settings (all P < 0.001).

CONCLUSIONS

The proposed method for contrast signal extraction showed significant improvements in synthesizing postcontrast images. A relevant proportion of images showing inadequate interchangeability with the reference remains at this dosage.

Uptake of Gadolinium-Based Contrast Agents by Blood Cells During Contrast-Enhanced MRI Examination

OBJECTIVES

Gadolinium-based contrast agents (GBCAs) are routinely used in magnetic resonance imaging (MRI) examinations. However, there is limited knowledge about the interaction with and distribution of the drug in human cells. This lack of knowledge is surprising, given that the first interaction of the drug occurs with blood cells. Moreover, recent studies reported gadolinium (Gd) deposition within organs, such as the brain. Hence, this study is aiming to determine the uptake of GBCA in blood cells of patients undergoing contrast-enhanced MRI (ce-MRI) examination.

MATERIALS AND METHODS

Human blood was exposed to either gadoterate meglumine (Gd-DOTA) or Eu-DOTA in vitro or was collected from patients undergoing ce-MRI with Gd-DOTA. Uptake of contrast agents (CAs) by blood cells was quantified by Gd measurements using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS) or, to confirm Gd-DOTA uptake, by a complementary method using Eu-DOTA by time-resolved fluorescence spectroscopy, respectively.

RESULTS

Uptake of Gd-DOTA or Eu-DOTA into white blood cells (WBCs) ex vivo was detectable by SC-ICP-MS and time-resolved fluorescence spectroscopy. The intracellular concentrations were estimated to be in the range of 1-3 μM. However, no CA uptake into erythrocytes was detected with either method. In total, 42 patients between 30 and 84 years old (24 men, 18 women) were enrolled. White blood cells' uptake of Gd was measured by SC-ICP-MS. Isolated WBCs from patients who underwent ce-MRI examination showed substantial Gd uptake; however, the studied patient group showed an inhomogeneous distribution of Gd uptake. Measurements immediately after MRI examination indicated 21-444 attogram/WBC, corresponding to an intracellular Gd concentration in the range from 0.2 to 5.5 μM.

CONCLUSIONS

This study confirms the ex vivo uptake of GBCA by WBCs and provides the first evidence that GBCA is indeed taken up by WBCs in vivo by patients undergoing ce-MRI examination. However, the observed Gd uptake in WBCs does not follow a log-normal distribution commonly observed in the fields of environmental studies, biology, and medicine. Whether cellular uptake of GBCA is linked to the observed deposition of Gd remains unclear. Therefore, studying the interaction between GBCA and human cells may clarify crucial questions about the effects of Gd on patients after MRI examinations.

Toxic Effects of Rare Earth Elements on Human Health: A Review

Rare earth elements (REEs) are a new type of material resource which have attracted significant attention in recent years. REEs have emerged as essential metals in modern-day technology due to their unique functions. The long-term, large-scale mining and utilization of rare earths has caused serious environmental pollution and constitutes a global health issue, which has raised concerns regarding the safety of human health. However, the toxicity profile of suspended particulate matter in REEs in the environment, which interacts with the human body, remains largely unknown. Studies have shown that REEs can enter the human body through a variety of pathways, leading to a variety of organ and system dysfunctions through changes in genetics, epigenetics, and signaling pathways. Through an extensive literature search and critical analysis, we provide a comprehensive overview of the available evidence, identify knowledge gaps, and make recommendations for future research directions.

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.

Data mining and analysis of the adverse events derived signals of 4 gadolinium-based contrast agents based on the US Food and drug administration adverse event reporting system

BACKGROUND

To detect and analyze risk signals of the drug-related adverse events (AEs) of 4 gadolinium-based contrast agents (GBCAs) (gadopentetate dimeglumine (Gd-DTPA), gadobenate dimeglumine (Gd-BOPTA), gadoteridol (Gd-HP-DO3A), and gadobutrol (Gd-BT-DO3A)) according to the US Food and Drug Administration Adverse Event Reporting System (FAERS) database and ensure the clinical safety.

RESEARCH DESIGN AND METHODS

The AEs that are associated with the 4 GBCAs were collected from the FAERS database from 2004Q1 to 2022Q3. The risk signals were mined using reporting odds ratio (ROR) and proportional reporting ratio (PRR).

RESULTS

424 risk signals were excavated, in which 151 risk signals were associated with Gd-DTPA, 93 risk signals were related to Gd-BOPTA, 79 risk signals were relevant to Gd-HP-DO3A, and 101 risk signals were associated with Gd-BT-DO3A. The AE signals involved 20 system organ classes (SOCs). Two of the top four SOCs were identical, namely 'skin and subcutaneous tissue disorders' and 'general disorders and administration site conditions.'

CONCLUSIONS

The safety signals of 4 GBCAs were detected, and the SOCs associated with the AEs of the 4 GBCAs were different. Besides, some AEs obtained in this study were not mentioned in the package inserts, which need more attention and research to ensure the clinical safety.

Protease-Mediated T1 Contrast Enhancement of Multilayered Magneto-Gadolinium Nanostructures for Imaging and Magnetic Hyperthermia

In this work, we constructed a multifunctional composite nanostructure for combined magnetic hyperthermia therapy and magnetic resonance imaging based on T1 and T2 signals. First, iron oxide nanocubes with a benchmark heating efficiency for magnetic hyperthermia were assembled within an amphiphilic polymer to form magnetic nanobeads. Next, poly(acrylic acid)-coated inorganic sodium gadolinium fluoride nanoparticles were electrostatically loaded onto the magnetic nanobead surface via a layer-by-layer approach by employing a positively charged enzymatic-cleavable biopolymer. The positive-negative multilayering process was validated through the changes occurring in surface ζ-potential values and structural characterization by transmission electron microscopy (TEM) imaging. These nanostructures exhibit an efficient heating profile, in terms of the specific absorption rates under clinically accepted magnetic field conditions. The addition of protease enzyme mediates the degradation of the surface layers of the nanostructures with the detachment of gadolinium nanoparticles from the magnetic beads and exposure to the aqueous environment. Such a process is associated with changes in the T1 relaxation time and contrast and a parallel decrease in the T2 signal. These structures are also nontoxic when tested on glioblastoma tumor cells up to a maximum gadolinium dose of 125 μg mL-1, which also corresponds to a iron dose of 52 μg mL-1. Nontoxic nanostructures with such enzyme-triggered release mechanisms and T1 signal enhancement are desirable for tracking tumor microenvironment release with remote T1-guidance and magnetic hyperthermia therapy actuation to be done at the diseased site upon verification of magnetic resonance imaging (MRI)-guided release.

Divalent Manganese Complexes as Potential Replacements for Gadolinium-Based Contrast Agents

ABSTRACT

Recent safety concerns surrounding the use of gadolinium-based contrast agents (GBCAs) have spurred research into identifying alternatives to GBCAs for use with magnetic resonance imaging. This review summarizes the molecular and pharmaceutical properties of a GBCA replacement and how these may be achieved. Complexes based on high-spin, divalent manganese (Mn 2+ ) have shown promise as general purpose and liver-specific contrast agents. A detailed description of the complex Mn-PyC3A is provided, describing its physicochemical properties, its behavior in different animal models, and how it compares with GBCAs. The review points out that, although there are parallels with GBCAs in how the chemical properties of Mn 2+ complexes can predict in vivo behavior, there are also marked differences between Mn 2+ complexes and GBCAs.

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

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

Depolymerizing self-immolative polymeric lanthanide chelates for vascular imaging

Medical imaging is widely used clinically and in research to understand disease progression and monitor responses to therapies. Vascular imaging enables the study of vascular disease and therapy, but exogenous contrast agents are generally needed to distinguish the vasculature from surrounding soft tissues. Lanthanide-based agents are commonly employed in MRI, but are also of growing interest for micro-CT, as the position of their k-edges allows them to provide enhanced contrast and also to be employed in dual-energy micro-CT, a technique that can distinguish contrast-enhanced blood vessels from tissues such as bone. Small molecule Gd3+ chelates are available, but are excreted too rapidly. At the same time, a lack of rapid clearance from the body for long-circulating agents presents toxicity concerns. To address these challenges, we describe here the use of self-immolative polymers for the development of new degradable chelates that depolymerize completely from end-to-end following the cleavage of a single end-cap from the polymer terminus. We demonstrate that tuning the end-cap allows the rate of depolymerization to be controlled, while tuning the polymer length enables the polymer to exhibit long circulation times in the blood of mice. After successfully providing one hour of blood contrast, depolymerization led to excretion of the resulting small molecule chelates into the bladder. Despite the high doses required for micro-CT, the agents were well tolerated in mice. Thus, these self-immolative polymeric chelates provide a new platform for the development of medical imaging contrast agents. STATEMENT OF SIGNIFICANCE: Vascular imaging is used clinically to diagnose and monitor vascular disease and in research to understand the progression of disease and study responses to new therapies. For techniques such as magnetic resonance imaging and x-ray computed tomography (CT), long circulating contrast agents are needed to differentiate the vasculature from surrounding tissues. However, if these agents are not rapidly excreted from the body, they can lead to toxicity. We present here a new polymeric system that can chelate hundreds of lanthanide ions for imaging contrast and can circulate for one hour in the blood, but then after end-cap cleavage breaks down completely into small molecules for excretion. The successful application of this system in micro-CT in mice is demonstrated.

Gadolinium-based contrast agents suppress adipocyte differentiation in 3T3-L1 cells

Gadolinium-based contrast agents (GBCAs) are widely used in magnetic resonance imaging (MRI) to improve the sensitivity and enhance diagnostic performance. GBCAs are mostly eliminated from the body through the kidney after administration; however small amounts of gadolinium are retained in the brain and other tissues. Although there is increasing concern about the adverse health effects of gadolinium, the cellular effects of GBCAs remains poorly understood. Here, we elucidated the potential cytotoxicity of the GBCAs Omniscan and Gadovist in 12 different cell lines, especially 3T3-L1 adipocyte cell line. Omniscan and Gadovist treatments significantly increased intracellular gadolinium levels in 3T3-L1 cells in a time- and dose-dependent manner. Additionally, Omniscan and Gadovist treatments downregulated the expression of adipocyte differentiation markers, including peroxisome proliferator-activated receptor γ (PPARG), adiponectin (ADIPOQ), and fatty acid-binding protein (FABP4), in 3T3-L1 cells, especially during early differentiation (day 0-2). Moreover, histological analysis using Oil red O staining showed that gadolinium chloride (GdCl₃) treatment suppressed lipid droplet accumulation and the expression of adipocyte differentiation markers. Overall, the results showed that Omniscan and Gadovist treatment suppressed adipocyte differentiation in 3T3-L1 cells, contributing to the understanding of the potential toxic effects of GBCA exposure.

Comparison between 2D FSE T2-weighted Dixon MRI and contrast-enhanced 2D FSE and 3D FSPGR T1-weighted Dixon MRI to quantify inflammation in hands of patients with early rheumatoid arthritis

PURPOSE

The purpose of this study was to compare two-dimensional (2D) T2-weighted, contrast-enhanced 2D T1-weighted and contrast-enhanced three-dimensional (3D) T1-weighted Dixon MRI sequences to assess disease activity using the RAMRIS scoring system in hands of patients with early rheumatoid arthritis.

MATERIALS AND METHODS

Twenty-five patients (19 women, 6 men; mean age 51.4 years ± 12.7 years [SD], age range: 28-70 years) with rheumatoid arthritis prospectively underwent MRI examination of both hands at 1.5 T using 2D fast spin-echo (FSE) T2-weighted, contrast-enhanced 2D FSE T1-weighted and contrast-enhanced 3D fast spoiled gradient echo (FSPGR) T1-weighted Dixon sequences. Three radiologists independently assessed disease activity according to RAMRIS using Dixon water-only and fat-only images. Intraclass correlation coefficients (ICC) were calculated to assess inter-technique and interobserver agreements.

RESULTS

Agreement to assess total RAMRIS score was very good between the MRI protocols (mean ICC ranging from 0.81 to 0.93) and between readers (mean ICC ranging from 0.91 to 0.94). Mean total RAMRIS scores of the three readers were significantly greater with contrast-enhanced 3D FSPGR T1-weighted (42.73 ± 29.39) than with contrast-enhanced 2D FSE T1-weighted (35.81 ± 25.48) and 2D FSE T2-weighted (32.20 ± 25.06) Dixon sequences.

CONCLUSION

2D FSE T2-weighted, contrast-enhanced 2D FSE T1-weighted Dixon and contrast-enhanced 3D FSPGR T1-weighted Dixon protocols are reproducible alternatives for the RAMRIS scoring in hands of patients with early rheumatoid arthritis. Coupling contrast-enhanced 3D FSPGR T1-weighted and 2D FSE T2-weighted sequences might be the most efficient option to completely assess the rheumatoid arthritis -related synovial and bone changes with the Dixon method.

Elemental bioimaging and transcriptomics reveal unchanged gene expression in mouse cerebellum following a single injection of Gadolinium-based contrast agents

Gadolinium (Gd) deposition in the brain, first and foremost in the dentate nucleus in the cerebellum, following contrast enhanced MRI, rose awareness of potential adverse effects of gadolinium-based contrast agent (GBCA) administration. According to previous in vitro experiments, a conceivable side-effect of Gd deposition could be an alteration of gene expression. In the current study, we aimed to investigate the influence of GBCA administration on gene expression in the cerebellum of mice using a combination of elemental bioimaging and transcriptomics. In this prospective animal study, three groups of eight mice each were intravenously injected with either linear GBCA gadodiamide, macrocyclic GBCA gadoterate (1 mmol GBCA/kg body weight) or saline (NaCl 0.9%). Animals were euthanized four weeks after injection. Subsequently, Gd quantification via laser ablation-ICP-MS and whole genome gene expression analysis of the cerebellum were performed. Four weeks after single application of GBCAs to 24-31 days old female mice, traces of Gd were detectable in the cerebellum for both, the linear and macrocyclic group. Subsequent transcriptome analysis by RNA sequencing using principal component analysis did not reveal treatment-related clustering. Also differential expression analysis did not reveal any significantly differentially expressed genes between treatments.

Multiple directional DWI combined with T2WI in predicting muscle layer and Ki-67 correlation in bladder cancer in 3.0-T MRI

OBJECTIVE

To investigate the value of 3.0T MRI multi-directional diffusion-weighted imaging (DWI) combined with T2WI morphological features and lesion distribution in preoperative prediction of muscle layer invasion of bladder cancer (BC) and the correlation with postoperative Ki-67.

MATERIALS AND METHODS

This retrospective study enrolled patients with BC between 2019 and 2021. Patients with muscular invasive bladder cancer (MIBC) or non-muscular invasive BC (NMIBC) were also analyzed by preoperative 3.0T MRI aFostic efficacy.

RESULTS

A total of 186 patients were enrolled. About 27 patients with MIBC (35 lesions in total) and 62 with NMIBC (99 lesions in total). We found the tumor with a larger size, a wide base, and a smaller apparent dispersion coefficient (ADC) value and normalized ADC(nADC) value, without a stalk, presenting a greater risk of muscle invasion. ADC value, nADC value, maximum diameter, and stalk were independently associated with muscle invasion. Lesions located at the bladder fundus or involvement of multiple sites were independently associated with muscle invasion compared to the bladder body. In combination with morphological features, the AUCs of ADC and nADC showed accuracies of 0.925 and 0.947-0.951, respectively. TADC and nTADC showed the best diagnostic efficacy in multiple respects. KI-67 LI was negatively correlated with ADC and nADC values.

CONCLUSIONS

This is the first report in which we found Multi-directional DWI combined with T2WI in 3.0T MRI can be used to predict the muscle layer invasion of bladder cancer. ADC values reflect the muscular invasion of bladder cancer and show a moderate negative correlation with Ki-67. It is especially suitable for bladder cancer patients with renal insufficiency or tumor recurrence.

MRI detection of brain gadolinium retention in multiple sclerosis: Magnetization transfer vs. T1-weighted imaging

BACKGROUND AND PURPOSE

Evidence of brain gadolinium retention has affected gadolinium-based contrast agent usage. It is, however, unclear to what extent macrocyclic agents are retained and whether their in vivo detection may necessitate nonconventional MRI. Magnetization transfer (MT) could prove suitable to detect gadolinium-related signal changes since dechelated gadolinium ions bind to macromolecules. Therefore, this study aimed to investigate associations of prior gadolinium administrations with MT and T1 signal abnormalities.

METHODS

A cohort of 23 persons with multiple sclerosis (MS) (18 females, 5 males, 57 ± 8.0 years) with multiple past gadolinium administrations (median 6, range 3-12) and 23 age- and sex-matched healthy controls underwent 1.5 Tesla MRI with MT, T1-weighted 2-dimensional spin echo, and T1-weighted 3-dimensional gradient echo. The signal intensity index was assessed by MRI in gadolinium retention predilection sites.

RESULTS

There were dose-dependent associations of the globus pallidus signal on gradient echo (r = .55, p < .001) and spin echo (r = .38, p = .013) T1-weighted imaging, but not on MT. Relative to controls, MS patients had higher signal intensity index in the dentate nucleus on T1-weighted gradient echo (1.037 ± 0.040 vs. 1.016 ± 0.023, p = .04) with a similar trend in the globus pallidus on T1-weighted spin echo (1.091 ± 0.034 vs. 1.076 ± 0.014, p = .06). MT detected no group differences.

CONCLUSIONS

Conventional T1-weighted imaging provided dose-dependent associations with gadolinium administrations in MS, while these could not be detected with 2-dimensional MT. Future studies could explore newer MT techniques like 3D and inhomogenous MT. Notably, these associations were identified with conventional MRI even though most patients had not received gadolinium administrations in the preceding 9 years, suggestive of long-term retention.

Different Impact of Gadopentetate and Gadobutrol on Inflammation-Promoted Retention and Toxicity of Gadolinium Within the Mouse Brain

OBJECTIVES

Using a murine model of multiple sclerosis, we previously showed that repeated administration of gadopentetate dimeglumine led to retention of gadolinium (Gd) within cerebellar structures and that this process was enhanced with inflammation. This study aimed to compare the kinetics and retention profiles of Gd in inflamed and healthy brains after application of the macrocyclic Gd-based contrast agent (GBCA) gadobutrol or the linear GBCA gadopentetate. Moreover, potential Gd-induced neurotoxicity was investigated in living hippocampal slices ex vivo.

MATERIALS AND METHODS

Mice at peak of experimental autoimmune encephalomyelitis (EAE; n = 29) and healthy control mice (HC; n = 24) were exposed to a cumulative dose of 20 mmol/kg bodyweight of either gadopentetate dimeglumine or gadobutrol (8 injections of 2.5 mmol/kg over 10 days). Magnetic resonance imaging (7 T) was performed at baseline as well as at day 1, 10, and 40 post final injection (pfi) of GBCAs. Mice were sacrificed after magnetic resonance imaging and brain and blood Gd content was assessed by laser ablation-inductively coupled plasma (ICP)-mass spectrometry (MS) and ICP-MS, respectively. In addition, using chronic organotypic hippocampal slice cultures, Gd-induced neurotoxicity was addressed in living brain tissue ex vivo, both under control or inflammatory (tumor necrosis factor α [TNF-α] at 50 ng/μL) conditions.

RESULTS

Neuroinflammation promoted a significant decrease in T1 relaxation times after multiple injections of both GBCAs as shown by quantitative T1 mapping of EAE brains compared with HC. This corresponded to higher Gd retention within the EAE brains at 1, 10, and 40 days pfi as determined by laser ablation-ICP-MS. In inflamed cerebellum, in particular in the deep cerebellar nuclei (CN), elevated Gd retention was observed until day 40 after last gadopentetate application (CN: EAE vs HC, 55.06 ± 0.16 μM vs 30.44 ± 4.43 μM). In contrast, gadobutrol application led to a rather diffuse Gd content in the inflamed brains, which strongly diminished until day 40 (CN: EAE vs HC, 0.38 ± 0.08 μM vs 0.17 ± 0.03 μM). The analysis of cytotoxic effects of both GBCAs using living brain tissue revealed an elevated cell death rate after incubation with gadopentetate but not gadobutrol at 50 mM. The cytotoxic effect due to gadopentetate increased in the presence of the inflammatory mediator TNF-α (with vs without TNF-α, 3.15% ± 1.18% vs 2.17% ± 1.14%; P = 0.0345).

CONCLUSIONS

In the EAE model, neuroinflammation promoted increased Gd retention in the brain for both GBCAs. Whereas in the inflamed brains, efficient clearance of macrocyclic gadobutrol during the investigated time period was observed, the Gd retention after application of linear gadopentetate persisted over the entire observational period. Gadopentetate but not gadubutrol appeared to be neurotoxic in an ex vivo paradigm of neuronal inflammation.

Does Gadolinium Deposition Lead to Metabolite Alteration in the Dentate Nucleus? An MRS Study in Patients with MS

BACKGROUND AND PURPOSE

Repeat contrast-enhanced MR imaging exposes patients with relapsing-remitting MS to frequent administration of gadolinium-based contrast agents. We aimed to investigate the potential metabolite and neurochemical alterations of visible gadolinium deposition on unenhanced T1WI in the dentate nucleus using MRS.

MATERIALS AND METHODS

This prospective study was conducted in a referral university hospital from January 2020 to July 2021. The inclusion criteria for case and control groups were as follows: 1) case: patients with relapsing-remitting MS, visible gadolinium deposition in the dentate nucleus (ribbon sign), >5 contrast-enhanced MR images obtained; 2) control 1: patients with relapsing-remitting MS without visible gadolinium deposition in the dentate nucleus, >5 contrast-enhanced MR images obtained; 3) control 2: patients with relapsing-remitting MS without visible gadolinium deposition in the dentate nucleus, <5 contrast-enhanced-MR images obtained; and 4) control 3: adult healthy individuals, with no contrast-enhanced MR imaging. Dentate nucleus and pontine single-voxel 12 × 12 × 12 MRS were analyzed using short TEs.

RESULTS

Forty participants (10 per group; 27 [67.5%] female; mean age, 35.6 [SD, 9.6] years) were enrolled. We did not detect any significant alteration in the levels of NAA and choline between the studied groups. The mean concentrations of mIns were 2.7 (SD, 0.73) (case), 1.5 (SD, 0.8) (control 1), 2.4 (SD, 1.2) (control 2), and 1.7 (SD, 1.2) (control 3) (P = .04). The mean concentration of Cr and mIns (P = .04) and the relative metabolic concentration (dentate nucleus/pons) of lipid 1.3/Cr (P = .04) were significantly higher in the case-group than in healthy individuals (controls 1-3). Further analyses compared the case group with cumulative control 1 and 2 groups and showed a significant increase in lactate (P = .02), lactate/Cr (P = .04), and Cr (dentate nucleus/pons) (P = .03) in the case group.

CONCLUSIONS

Although elevated concentrations of Cr, lactate, mIns, and lipid in the dentate nucleus of the case group indicate a metabolic disturbance, NAA and choline levels were normal, implying no definite neuronal damage.

Augmented T1 -weighted steady state magnetic resonance imaging

T₁ contrasts obtained using short-TR incoherent steady state gradient echo (GRE) methods are generally suboptimal, to which non-T₁ factors in the signals play a major part. In this work, we proposed an augmented T₁ -weighted (aT₁ W) method to extract the signal ratio between routine GRE T₁ W and proton density-weighted signals that effectively removes the non-T₁ effects from the original T₁ W signals, including proton density, T₂ * decay, and coil sensitivity. A recently proposed multidimensional integration (MDI) technique was incorporated in the aT₁ W calculation for better signal-to-noise ratio (SNR) performance. For comparison between aT₁ W and T₁ W results, Monte Carlo noise analysis was performed via simulation and on scanned data, and region-of-interest (ROI) analysis and comparison was performed on the system phantom. For brain scans, the image contrast, noise behavior, and SNR of aT₁ W images were compared with routine GRE and inversion-recovery-based T₁ W images. The proposed aT₁ W method yielded saliently improved T₁ contrasts (potentially > 30% higher contrast-to-noise ratio [CNR]) than routine GRE T₁ W images. Good spatial homogeneity and signal consistency as well as high SNR/CNR were achieved in aT₁ W images using the MDI technique. For contrast-enhanced (CE) imaging, aT₁ W offered stronger post-CE contrast and better boundary delineation than T₁ MPRAGE images while using a shorter scan time.

Arterial spin labeling of nasopharyngeal carcinoma shows early therapy response

OBJECTIVE

This study aimed to determine the value of arterial spin labeling (ASL) perfusion imaging in assessing the early efficacy of chemoradiotherapy for nasopharyngeal carcinoma (NPC).

METHODS

Fifty-five patients with locoregionally advanced NPC underwent conventional 3.0-T magnetic resonance imaging (MRI) and ASL before and after chemoradiotherapy (prescribed dose reached 40 Gy). Based on the response evaluation criteria for solid tumors (RECIST 1.1), the patients were divided into the partial response and stable disease groups. MRI re-examination was performed one month after chemoradiotherapy completion, and patients were divided into residual and non-residual groups. We investigated inter-group differences in ASL-based tumor blood flow (TBF) parameters (pre-treatment tumor blood flow, post-treatment tumor blood flow, and changes in tumor blood flow, i.e., Pre-TBF, Post-TBF, ΔTBF), correlation between TBF parameters and tumor atrophy rate, and value of TBF parameters in predicting sensitivity to chemoradiotherapy.

RESULTS

There were differences in Pre-TBF, Post-TBF, and ΔTBF between the partial response and stable disease groups (p < 0.01). There were also differences in Pre-TBF and ΔTBF between the residual and non-residual groups (p < 0.01). Pre-TBF and ΔTBF were significantly correlated with the tumor atrophy rate; the correlation coefficients were 0.677 and 0.567, respectively (p < 0.01). Pre-TBF had high diagnostic efficacies in predicting sensitivity to chemoradiotherapy and residual tumors, with areas under the curve of 0.845 and 0.831, respectively.

CONCLUSION

ASL permits a noninvasive approach to predicting the early efficacy of chemoradiotherapy for NPC.

Assessment of genetic damage induced by gadolinium-based radiocontrast agents

BACKGROUND

Today, although gadolinium based contrast agents have been frequently used in the field of medicine, there is limited data available whether gadolinium based agents affect the genome.

AIM

The present study aimed to investigate the genotoxic and cytotoxic potentials of gadoteric acid and gadoversetamide used as gadolinium-based contrast agents for magnetic resonance (MR) imaging.

MATERIAL AND METHODS

The cytokinesis-block micronucleus assay was applied to human peripheral blood lymphocytes to assess the genotoxicity measured as micronucleus (MN), nucleoplasmic bridge (NPBs) and nuclear bud (NBUDs) frequencies. Furthermore, cytokinesis-block proliferation index (CBPI) was calculated to determine cytostasis. Lymphocytes were treated with gadoteric acid at concentrations of 1.0, 2.5, 5.0, and 25 mM and with gadoversetamide at concentrations of 0.25, 1.0, 2.5, and 5.0 mM for 48 h.

RESULTS

Gadoteric acid did not cause significant increase in MN, NBPs and NBUDs frequencies and CBPI values at any concentration. Gadoversetamide induced significantly increase MN formation at concentration of 2.5 mM, NBP formation at concentrations of 1.0 and 2.5 mM, and NBUD formation at concentrations of 0.25, 1.0 and 2.5 mM. Additionally, gadoversetamide exposure resulted in statistically significant decrease in CBPI values compared to the control at concentrations of 2.5 and 5.0 mM. In addition, CBPI levels in response to concentrations of gadoversetamide was negatively and significantly associated with concentration.

CONCLUSION

These findings show that gadoteric acid does not have genotoxic or cytotoxic potential, while gadoversetamide might have both genotoxic and cytotoxic potential on human peripheral blood lymphocytes. As a comparison, gadoversetamide was found more genotoxic and cytotoxic.

Genotoxic effects of gadobutrol and gadoversetamide active substances used in magnetic resonance imaging in human peripheral lymphocytes in vitro

Gadobutrol and gadoversetamide are gadolinium-based contrast agents (GBCAs) widely used during magnetic resonance imaging examination. In this study, the genotoxicity of two GBCAs, gadobutrol and gadoversetamide, was investigated by using different endpoints: chromosome aberration (CAs), sister chromatid exchange (SCEs), and micronucleus (MNi). Human peripheral lymphocytes (PBLs) were treated with five concentrations (7 000, 14 000, 28 000, 56 000, and 112 000 μg/mL) of both agents. While a few concentrations of gadobutrol significantly increased abnormal cell frequency and CA/Cell, nearly all the concentrations of gadoversetamide significantly elevated the same aberrations. Similarly, the effect of gadoversetamide on the formation of SCEs was higher than those of gadobutrol. Only one concentration of gadoversetamide significantly increased MN% but no gadobutrol. The comet assay was applied for the only gadobutrol which induced a significant increase in tail intensity at the highest concentration only. On the other hand, significantly decreased mitotic index (MI) was observed following both substances, again gadoversetamide was slightly higher than those of the gadobutrol. The results revealed that both the contrast agents are likely to induce genotoxic risk in PBLs. However, different concentrations and treatment periods should be examined in vitro and specifically in vivo with different test systems for the safer usage of these contrast agents.

Can Deep Learning Replace Gadolinium in Neuro-Oncology?: A Reader Study

MATERIALS AND METHODS

This monocentric retrospective study leveraged 200 multiparametric brain MRIs acquired between November 2019 and February 2020 at Gustave Roussy Cancer Campus (Villejuif, France). A total of 145 patients were included: 107 formed the training sample (55 ± 14 years, 58 women) and 38 the separate test sample (62 ± 12 years, 22 women). Patients had glioma, brain metastases, meningioma, or no enhancing lesion. T1, T2-FLAIR, diffusion-weighted imaging, low-dose, and standard-dose postcontrast T1 sequences were acquired. A deep network was trained to process the precontrast and low-dose sequences to predict "virtual" surrogate images for contrast-enhanced T1. Once trained, the deep learning method was evaluated on the test sample. The discrepancies between the predicted virtual images and the standard-dose MRIs were qualitatively and quantitatively evaluated using both automated voxel-wise metrics and a reader study, where 2 radiologists graded image qualities and marked all visible enhancing lesions.

RESULTS

The automated analysis of the test brain MRIs computed a structural similarity index of 87.1% ± 4.8% between the predicted virtual sequences and the reference contrast-enhanced T1 MRIs, a peak signal-to-noise ratio of 31.6 ± 2.0 dB, and an area under the curve of 96.4% ± 3.1%. At Youden's operating point, the voxel-wise sensitivity (SE) and specificity were 96.4% and 94.8%, respectively. The reader study found that virtual images were preferred to standard-dose MRI in terms of image quality (P = 0.008). A total of 91 reference lesions were identified in the 38 test T1 sequences enhanced with full dose of contrast agent. On average across readers, the brain lesion SE of the virtual images was 83% for lesions larger than 10 mm (n = 42), and the associated false detection rate was 0.08 lesion/patient. The corresponding positive predictive value of detected lesions was 92%, and the F1 score was 88%. Lesion detection performance, however, dropped when smaller lesions were included: average SE was 67% for lesions larger than 5 mm (n = 74), and 56% with all lesions included regardless of their size. The false detection rate remained below 0.50 lesion/patient in all cases, and the positive predictive value remained above 73%. The composite F1 score was 63% at worst.

CONCLUSIONS

The proposed deep learning method for virtual contrast-enhanced T1 brain MRI prediction showed very high quantitative performance when evaluated with standard voxel-wise metrics. The reader study demonstrated that, for lesions larger than 10 mm, good detection performance could be maintained despite a 4-fold division in contrast agent usage, unveiling a promising avenue for reducing the gadolinium exposure of returning patients. Small lesions proved, however, difficult to handle for the deep network, showing that full-dose injections remain essential for accurate first-line diagnosis in neuro-oncology.

Altered Plasma Mitochondrial Metabolites in Persistently Symptomatic Individuals after a GBCA-Assisted MRI

Despite the impressive safety of gadolinium (Gd)-based contrast agents (GBCAs), a small number of patients report the onset of new, severe, ongoing symptoms after even a single exposure-a syndrome termed Gadolinium Deposition Disease (GDD). Mitochondrial dysfunction and oxidative stress have been repeatedly implicated by animal and in vitro studies as mechanisms of Gd/GBCA-related toxicity, and as pathogenic in other diseases with similarities in presentation. Here, we aimed to molecularly characterize and explore potential metabolic associations with GDD symptoms. Detailed clinical phenotypes were systematically obtained for a small cohort of individuals (n = 15) with persistent symptoms attributed to a GBCA-enhanced MRI and consistent with provisional diagnostic criteria for GDD. Global untargeted mass spectroscopy-based metabolomics analyses were performed on plasma samples and examined for relevance with both single marker and pathways approaches. In addition to GDD criteria, frequently reported symptoms resembled those of patients with known mitochondrial-related diseases. Plasma differences compared to a healthy, asymptomatic reference cohort were suggested for 45 of 813 biochemicals. A notable proportion of these are associated with mitochondrial function and related disorders, including nucleotide and energy superpathways, which were over-represented. Although early evidence, coincident clinical and biochemical indications of potential mitochondrial involvement in GDD are remarkable in light of preclinical models showing adverse Gd/GBCA effects on multiple aspects of mitochondrial function. Further research on the potential contributory role of these markers and pathways in persistent symptoms attributed to GBCA exposure is recommended.

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.

MRI of Hands with Early Rheumatoid Arthritis: Usefulness of Three-Point Dixon Sequences to Quantitatively Assess Disease Activity

The use of efficient treatment with a treat-to-target strategy combined with early detection of the disease completely changed the imaging presentation and outcome of newly diagnosed rheumatoid arthritis (RA) patients. Magnetic Resonance Imaging (MRI) has become the reference technique in clinical research to detect and quantify inflammatory involvement of the soft tissues (synovitis and tenosynovitis) and bone marrow (osteitis) along with structural damages of the bone (erosions) in hands of patients with RA. Three-point Dixon MRI may be a valuable alternative to the currently recommended sequences as it yields effective fat signal suppression, high imaging quality and reproducible assessment of disease activity.

Heparin-coated iron oxide nanoparticles: application as liver contrast agent, toxicity and pharmacokinetics

The newly prepared heparin-coated iron oxide nanoparticles (Hep-IONPs) contrasted cholangioma tumors in the liver in T2 MRI. NPs were not toxic to rats and rabbits after 14 days of consecutive...

Dynamic Serial Cytokine Measurements During Intravenous Ca-DTPA Chelation in Gadolinium Deposition Disease and Gadolinium Storage Condition: A Pilot Study

PURPOSE

The aim of this study was to investigate the feasibility of measuring early changes in serum cytokine levels after intravenous diethylenetriaminepentaacetic acid (Ca-DTPA) chelation in patients manifesting either gadolinium deposition disease (GDD) or gadolinium storage condition (GSC) and the possible usefulness of this method in further research.

METHODS

Four patients with recent-onset GDD (≤1 year) and 2 patients with long-standing GSC (4 and 9 years) underwent chelation with intravenous bolus administration of Ca-DTPA. Multiple blood draws were performed to measure serum cytokines: at T = 0 (before Ca-DTPA injection) and 1, 5, 10, 30, 60 minutes, and 24 hours after Ca-DTPA injection. Patients rated the severity of GDD symptom flare at 24 hours. The 24-hour urine Gd amounts were measured prechelation and for the 24 hours after chelation. Serum samples were analyzed blind to whether patients had GDD or GSC but with knowledge of the time points characterizing each sample.

RESULTS

Urine samples for both GDD and GSC patients showed increases in Gd postchelation. All GDD patients experienced flare reactions postchelation; the 2 GSC patients did not. Two cytokines, EGF and sCD40L, peaked at 30 minutes postchelation in at least 4 of the 6 participants. Three cytokines, ENA78/CXCL5, EOTAXIN/CCL11, and LEPTIN, peaked at 24 hours in at least 4 of the 6 participants. Two participants were high outliers for a large number of cytokines across time points. No clear distinction between GDD and GSC was apparent from the cytokine patterns, although differences were present.

CONCLUSIONS

This pilot study describes precise temporal resolution (in the range of minutes) after a cytokine-inciting event. Select cytokines exhibited peak values at different time points. At this preliminary stage of investigation, peak cytokine release seems to reflect the amount of Gd mobilized rather than the severity of the patient symptomatic reaction. Too few subjects were studied to support statistical analysis between GDD and GSC groups, although differences were observed through visual data analysis.

The Role of Ferrous Ion in the Effect of the Gadolinium-Based Contrast Agents (GBCA) on the Purkinje Cells Arborization: An In Vitro Study

Gadolinium deposition in the brain has been observed in areas rich in iron, such as the dentate nucleus of the cerebellum. We investigated the role of Fe2+ in the effect of gadolinium-based contrast agents (GBCA) on thyroid hormone-mediated Purkinje cell dendritogenesis in a cerebellar primary culture. The study comprises the control group, Fe2+ group, GBCA groups (gadopentetate group or gadobutrol group), and GBCA+Fe2+ groups. Immunocytochemistry was performed with an anti-calbindin-28K (anti-CaBP28k) antibody, and the nucleus was stained with 4',6-diamidino-2-phenylindole (DAPI). The number of Purkinje cells and their arborization were evaluated with an analysis of variance with a post-hoc test. The number of Purkinje cells was similar to the control groups among all treated groups. There were no significant differences in dendrite arborization between the Fe2+ group and the control groups. The dendrite arborization was augmented in the gadopentetate and the gadobutrol groups when compared to the control group (p < 0.01, respectively). Fe2+ significantly increased the effect of gadopentetate on dendrite arborization (p < 0.01) but did not increase the effect of gadobutrol. These findings suggested that the chelate thermodynamic stability and Fe2+ may play important roles in attenuating the effect of GBCAs on the thyroid hormone-mediated dendritogenesis of Purkinje cells in in vitro settings.

Investigation of Effects of Gadolinium-Based Contrast Agents on Uterine Contractility Using Isolated Rat Myometrium

BACKGROUND

Despite concerns about safety, gadolinium-based contrast agents (GBCAs) are still used for abdominal and pelvic imaging during pregnancy. Researchers have mainly focused on teratogenicity, while very little is known about their possible direct effects on uterine contractility, yet free gadolinium potentially impacts contractility through interaction with calcium channels.

PURPOSE

To investigate possible effects of selected GBCAs (namely gadoteridol, gadoversetamide, gadobutrol, gadoterate meglumine, and gadoxetic acid) on the contractility of rat myometrium.

STUDY TYPE

In vitro organ bath study.

ANIMAL MODEL

Myometria were isolated from adult (10-12 weeks old) Sprague Dawley rats, both pregnant (N = 8) and nonpregnant (N = 36).

FIELD STRENGTH/SEQUENCE

NA.

ASSESSMENT

Myometrial strips were suspended in tissue bath containing physiological saline and isometric contractions were recorded. GBCAs were added to the tissue bath cumulatively, and their effects on contractility parameters (quantified by amplitude, frequency, and area under contractility curve [AUC]) were evaluated by 10-minute intervals.

STATISTICAL TESTS

Normality data, checked by Shapiro-Wilk test, were transformed by arcsine when needed. One- or two-way analysis of variance was performed, where appropriate, followed by Student-Newman-Keuls test. A P value of <0.05 was considered statistically significant.

RESULTS

All of the assayed GBCAs elicited some alterations in the myometrial contractility in a concentration-dependent manner. Gadoterate meglumine, gadoxetic acid, and gadoversetamide caused a concentration-dependent significant attenuation in AUC (oxytocin-induced, from 100% during control period to 45.1 ± 9.0% (nonpregnant) and 59.9 ± 8.5% (pregnant), for 90 μM gadoterate meglumine; respectively), and frequency of the spontaneous and oxytocin-induced contractions. Gadobutrol and gadoteridol at highest dose significantly attenuated mean AUC and frequency of oxytocin-induced contractions of nonpregnant myometrium.

DATA CONCLUSION

Results from this in vitro study indicate that GBCAs elicit modulation of myometrial contractions at clinically relevant concentrations. These effects may account, at least partially, for the known potential side effects (rare cases of miscarriages and elective abortion) of these agents.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 5.

Gadolinium Tissue Distribution in a Large-Animal Model after a Single Dose of Gadolinium-based Contrast Agents

Background There is an ongoing scientific debate about the degree and clinical importance of gadolinium deposition in the brain and other organs after administration of gadolinium-based contrast agents (GBCAs). While most published data focus on gadolinium deposition in the brain, other organs are rarely investigated. Purpose To compare gadolinium tissue concentrations in various organs 10 weeks after one injection (comparable to a clinically applied dose) of linear and macrocyclic GBCAs in a large-animal model. Materials and Methods In this prospective animal study conducted from March to May 2018, 36 female Swiss-Alpine sheep (age range, 4-10 years) received one injection (0.1 mmol/kg) of macrocyclic GBCAs (gadobutrol, gadoteridol, and gadoterate meglumine), linear GBCAs (gadodiamide and gadobenate dimeglumine), or saline. Ten weeks after injection, sheep were sacrificed and tissues were harvested. Gadolinium concentrations were quantified with inductively coupled plasma mass spectrometry (ICP-MS). Histologic staining was performed. Data were analyzed with nonparametric tests. Results At 10 weeks after injection, linear GBCAs resulted in highest mean gadolinium concentrations in the kidney (502 ng/g [95% CI: 270, 734]) and liver (445 ng/g [95% CI: 202, 687]), while low concentrations were found in the deep cerebellar nuclei (DCN) (30 ng/g [95% CI: 20, 41]). Tissue concentrations of linear GBCAs were three to 21 times higher compared with those of macrocyclic GBCAs. Administered macrocyclic GBCAs resulted in mean gadolinium concentrations of 86 ng/g (95% CI: 31, 141) (P = .08) in the kidney, 21 ng/g (95% CI: 4, 39) (P = .15) in liver tissue, and 10 ng/g (95% CI: 9, 12) (P > .99) in the DCN, which were not significantly elevated when compared with concentrations in control animals. No histopathologic alterations were observed irrespective of tissue concentrations within any examined organ. Conclusion Ten weeks after one injection of a clinically relevant dose of gadolinium-based contrast agents, the liver and kidney appeared to be reservoirs of gadolinium; however, despite gadolinium presence, no tissue injury was detected. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Clément in this issue.

Improved Delivery Methods for Gene Therapy and Cell Transplantation in Parkinson's Disease

A number of cell transplantation and gene therapy trials have been performed over the last three decades in an effort to restore function in Parkinson’s disease. Much has been learned about optimizing delivery methods for these therapeutics. This is particularly true in gene therapy, which has predominated the clinical trial landscape in recent years; however, cell transplantation for Parkinson’s disease is currently undergoing a renaissance. Innovations such as cannula design, iMRI-guided surgery and an evolution in delivery strategy has radically changed the way investigators approach clinical trial design. Future therapeutic strategies may employ newer delivery methods such as chronically implanted infusion devices and focal opening of the blood brain barrier with focused ultrasound.

Investigation of suspected gadolinium neurotoxicity in a dog

Gadolinium-based contrast agents are used across species to better visualize abnormalities during MRI and are considered generally safe in clinical practice. The aim of this study was to investigate central nervous system (CNS) gadolinium deposition in 11 dogs that had an MRI performed, received 0.22 mL/kg (0.1 mmol/kg) of gadopentetate dimeglumine, and were necropsied on the same hospital admission. The index case was a 5-year-old castrated male Australian Shepherd that presented for ataxia and following MRI developed seizure-like activity that became refractory to anticonvulsant therapy. Gadolinium concentration was quantified in CNS tissues by inductively-coupled plasma mass spectrometry and was 43-fold higher in the index case. These findings suggest the possibility of gadolinium toxicity in select patients.

Effects of Gadolinium Deposits in the Cerebellum: Reviewing the Literature from In Vitro Laboratory Studies to In Vivo Human Investigations

Gadolinium (Gd)-based contrast agents (GBCAs) are chemicals injected intravenously during magnetic resonance imaging (MRI) to enhance the diagnostic yield. The repeated use of GBCAs can cause their deposition in the brain, including the cerebellum. Such deposition may affect various cell subsets in the brain and consequently cause behavioral alterations due to neurotoxicity. Caution should thus be exercised in using these agents, particularly in patients who are more likely to have repeated enhanced MRIs during their lifespan. Further studies are required to clarify the toxicity of GBCAs, and potential mechanisms causing neurotoxicity have recently been reported. This review introduces the effects of GBCAs in the cerebellum obtained from in vitro and in vivo studies and considers the possible mechanisms of neurotoxicity involved.

Delayed Gadolinium Leakage in Ocular Structures: A Potential Marker for Age- and Vascular Risk Factor-Related Small Vessel Disease?

BACKGROUND

Gadolinium leakage in ocular structures (GLOS) was recently observed in fluid-attenuated inversion recovery (FLAIR) images obtained the day after an initial gadolinium injection in stroke patients. The specificity of GLOS to stroke and its mechanisms remain unclear.

OBJECTIVE

We investigated the factors associated with GLOS in a cohort of patients presenting with acute neurological deficits.

MATERIALS AND METHODS

This retrospective study included consecutive patients admitted to our stroke unit for acute neurological deficit between July 2017 and August 2018 who underwent baseline brain magnetic resonance imaging with the injection of a macrocyclic gadolinium agent and another scan without injection within 72 hours. The patients were separated into a stroke group and a stroke mimic group based on diffusion-weighted images. Gadolinium leakage in ocular structures was defined as a bright signal in the vitreous in follow-up FLAIR compared with baseline FLAIR (pregadolinium). Clinical data were collected together with imaging features from the baseline scans, including the volume of the infarct and of hypoperfusion if applicable, white matter hyperintensities, the number of lacunes, and the number of microbleeds, which were combined to yield a small vessel disease (SVD) score. We compared the prevalence of GLOS in both groups using the χ2 test. In the entire cohort, univariate and multivariate regression models were used to test the associations between GLOS and the collected data.

RESULTS

Among the 467 patients included in the study, GLOS was observed in similar proportions in the stroke group (32.2%, 136/422) and the stroke mimic group (28.9%, 13/45; mean difference, 3.3%; 95% confidence interval, -10.9 to 17.6; P = 0.65). In univariate analysis, GLOS was associated with older age, increased prevalence of vascular risk factors, brain imaging features of SVD (white matter hyperintensities, lacunes, microbleeds), as well as with impairment of renal function and increased dose of gadolinium. No associations were found with factors related to stroke, such as its volume, acute treatment, or rate of recanalization. Multivariate analyses showed that aging (P < 0.001), diabetes (P = 0.010), severe renal failure (P = 0.004), and increased dose of gadolinium (P < 0.001) were independent contributors to GLOS.

CONCLUSIONS

Gadolinium leakage in ocular structures, which occurs more commonly at higher concentrations of gadolinium, is not specific to stroke and may represent increased permeability of the blood-retinal barrier associated with age- and vascular risk factor-related SVD.

The inhibition of gadolinium ion (Gd3+) on the mitochondrial F1FO-ATPase is linked to the modulation of the mitochondrial permeability transition pore

The mitochondrial permeability transition pore (PTP), which drives regulated cell death when Ca²⁺ concentration suddenly increases in mitochondria, was related to changes in the Ca²⁺-activated F₁F_O-ATPase. The effects of the gadolinium cation (Gd³⁺), widely used for diagnosis and therapy, and reported as PTP blocker, were evaluated on the F₁F_O-ATPase activated by Mg²⁺ or Ca²⁺ and on the PTP. Gd³⁺ more effectively inhibits the Ca²⁺-activated F₁F_O-ATPase than the Mg²⁺-activated F₁F_O-ATPase by a mixed-type inhibition on the former and by uncompetitive mechanism on the latter. Most likely Gd³⁺ binding to F₁, is favoured by Ca²⁺ insertion. The maximal inactivation rates (k_inact) of pseudo-first order inactivation are similar either when the F₁F_O-ATPase is activated by Ca²⁺ or by Mg²⁺. The half-maximal inactivator concentrations (K_I) are 2.35 ± 0.35 mM and 0.72 ± 0.11 mM, respectively. The potency of a mechanism-based inhibitor (k_inact/K_I) also highlights a higher inhibition efficiency of Gd³⁺ on the Ca²⁺-activated F₁F_O-ATPase (0.59 ± 0.09 mM^-1∙s^-1) than on the Mg²⁺-activated F₁F_O-ATPase (0.13 ± 0.02 mM^-1∙s^-1). Consistently, the PTP is desensitized in presence of Gd³⁺. The Gd³⁺ inhibition on both the mitochondrial Ca²⁺-activated F₁F_O-ATPase and the PTP strengthens the link between the PTP and the F₁F_O-ATPase when activated by Ca²⁺ and provides insights on the biological effects of Gd³⁺.

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.

Human Hair as a Possible Surrogate Marker of Retained Tissue Gadolinium: A Pilot Autopsy Study Correlating Gadolinium Concentrations in Hair With Brain and Other Tissues Among Decedents Who Received Gadolinium-Based Contrast Agents

OBJECTIVES

We used laser ablation inductively coupled plasma mass spectrometry to quantify gadolinium in hair samples from autopsy cases with gadolinium-based contrast agent (GBCA) exposure. Hair gadolinium data were correlated with gadolinium concentrations in brain, skin, and bone tissues from the same case to investigate a potential noninvasive method for gadolinium quantification and monitoring.

MATERIALS AND METHODS

Medical records from autopsy cases at our institution were screened for history of GBCA exposure. Cases with exposure to a single type of GBCA with the most recent injection occurring within 1 year were identified and included in the study. The concentration of gadolinium in hair samples was analyzed by laser ablation inductively coupled plasma mass spectrometry, and brain (globus pallidus, dentate nucleus, white matter), bone, and skin tissues were analyzed by bulk inductively coupled plasma mass spectrometry. The mean of the maximum value in the hair samples was used to generate a representative measurement of the hair gadolinium concentration for each case. A linear regression analysis between each tissue type and hair was conducted to assess for possible correlation.

RESULTS

Tissue and hair samples from 18 autopsies (16 cases with exposure to GBCA, 2 controls) were included in the study. Comparing the different tissues revealed good correlation between some tissue types. The best model fit occurred between white matter and hair (R = 0.83; P < 0.0001) followed by the comparison between dentate nucleus and hair (R = 0.72; P < 0.0001) and dentate nucleus and skin (R = 0.70; P < 0.0001).

CONCLUSIONS

A significant correlation in this study between hair gadolinium concentrations and brain and skin gadolinium concentrations suggests that hair may serve as a safe and effective biomonitoring tissue for patients who receive GBCA injections.

Is Small Fiber Neuropathy Induced by Gadolinium-Based Contrast Agents?

OBJECTIVES

In recent years, complaints of patients about burning pain in arms and legs after the injection of gadolinium-based contrast agents (GBCAs) have been reported. In the current study, we investigated changes of small fibers in the epidermis as a potential cause of the patient complaints in a mouse model.

METHODS

Six groups of 8 mice were intravenously injected with either a macrocyclic GBCA (gadoteridol, gadoterate meglumine, gadobutrol), a linear GBCA (gadodiamide or gadobenate dimeglumine) (1 mmol/kg body weight), or saline (NaCl 0.9%). Four weeks after injection, animals were euthanized, and footpads were assessed using immunofluorescence staining. Intraepidermal nerve fiber density (IENFD) was calculated, and the median number of terminal axonal swellings (TASs) per IENFD was determined.

RESULTS

Nonparametric Wilcoxon signed-rank test revealed significantly lower IENFDs for all GBCAs compared with the control group (P < 0.0001) with the linear GBCAs showing significantly lower IENFDs than the macrocyclic GBCAs (P < 0.0001). The linear GBCAs presented significantly more TAS per IENFD than the control group (P < 0.0001), whereas no significant increase of TAS per IENFD compared with the control group was found for macrocyclic GBCAs (P < 0.237).

INTERPRETATION

It is unclear whether or at what dosage the decrease of IENFDs and the increase of TAS per IENFD found in the current animal model will appear in humans and if it translates into clinical symptoms. However, given the highly significant findings of the current study, more research in this field is required.

Pre-examinations Improve Automated Metastases Detection on Cranial MRI

MATERIALS AND METHODS

Our local ethics committee approved this retrospective monocenter study.First, a dual-time approach was assessed, for which the CNN was provided sequences of the MRI that initially depicted new MM (diagnosis MRI) as well as of a prediagnosis MRI: inclusion of only contrast-enhanced T1-weighted images (CNNdual_ce) was compared with inclusion of also the native T1-weighted images, T2-weighted images, and FLAIR sequences of both time points (CNNdual_all).Second, results were compared with the corresponding single time approaches, in which the CNN was provided exclusively the respective sequences of the diagnosis MRI.Casewise diagnostic performance parameters were calculated from 5-fold cross-validation.

RESULTS

In total, 94 cases with 494 MMs were included. Overall, the highest diagnostic performance was achieved by inclusion of only the contrast-enhanced T1-weighted images of the diagnosis and of a prediagnosis MRI (CNNdual_ce, sensitivity = 73%, PPV = 25%, F1-score = 36%). Using exclusively contrast-enhanced T1-weighted images as input resulted in significantly less false-positives (FPs) compared with inclusion of further sequences beyond contrast-enhanced T1-weighted images (FPs = 5/7 for CNNdual_ce/CNNdual_all, P < 1e-5). Comparison of contrast-enhanced dual and mono time approaches revealed that exclusion of prediagnosis MRI significantly increased FPs (FPs = 5/10 for CNNdual_ce/CNNce, P < 1e-9).Approaches with only native sequences were clearly inferior to CNNs that were provided contrast-enhanced sequences.

CONCLUSIONS

Automated MM detection on contrast-enhanced T1-weighted images performed with high sensitivity. Frequent FPs due to artifacts and vessels were significantly reduced by additional inclusion of prediagnosis MRI, but not by inclusion of further sequences beyond contrast-enhanced T1-weighted images. Future studies might investigate different change detection architectures for computer-aided detection.

Variability in hair gadolinium concentrations among decedents who received gadolinium-based contrast agents

This study utilized laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to quantify gadolinium in the hair of autopsy cases that had received gadolinium-based contrast agents (GBCAs) before death. Consecutive autopsy cases were reviewed for GBCA injections and subjects who received a single type of GBCA in the year before death were included. Hair samples were analyzed using LA-ICP-MS as a line scan technique and parameters were optimized to maximize instrument sensitivity, accuracy, and precision. Linear regression analyses between hair measures and gadolinium dose were executed. LA-ICP-MS analysis produced a time-resolved record of GCBA exposure, with the position of the gadolinium peak maxima along the hair shaft providing a good estimate for the day that GBCA injection occurred (R2 = 0.46; p = 0.0022); however, substantial within and between subject variation in the position of the GBCA peak was observed. Average area under the curve for gadolinium peaks in the hair samples was a better predictor of gadolinium dose (R2 = 0.41; p = 0.0046), compared to the average of peak maxima concentration. Correlation between area under the curve and dose suggests that LA-ICP-MS analysis of hair may be an effective method to evaluate gadolinium levels in subjects in vivo after exposure to GBCAs. This study demonstrates that analysis of human hair using techniques with high spatial resolution such as LA-ICP-MS has excellent potential to reveal time-dependent signatures of past exposures.

Ischemic Stroke Increased Gadolinium Deposition in the Brain and Aggravated Astrocyte Injury After Gadolinium-Based Contrast Agent Administration: Linear Versus Macrocyclic Agents

BACKGROUND

Gadolinium (Gd)-based contrast agents (GBCAs) have been widely used in MRI. However, several studies have reported Gd deposition in the brain, which has raised concerns about safety.

PURPOSE

To investigate the effects of ischemic stroke on Gd deposition in the brain after repeated administration of linear or macrocyclic GBCAs and to determine whether GBCAs aggravate astrocyte injury after stroke.

STUDY TYPE

Animal study.

ANIMAL MODEL

Twenty-seven male Sprague-Dawley rats were randomized to an exposure group (n = 24) and a healthy control group (n = 3). Half of the exposure group (n = 12) underwent transient middle cerebral artery occlusion (tMCAO) and half (n = 12) had a sham procedure. In each subgroup (tMCAO or sham), the rats had repeated gadopentetate (n = 6) or gadobutrol (n = 6) injections. Oxygen-glucose deprivation and reoxygenation (OGD/R) was used as an in vitro model of stroke.

ASSESSMENT

On day 3 and day 28 after the last injection (p.i.), the Gd concentration in the cerebrum was quantified by inductively coupled plasma mass spectrometry. Cell viability, reactive oxygen species (ROS), and mitochondrial membrane potential (MMP) were analyzed in vitro.

STATISTICAL TESTS

One-way analysis of variance and two-sample t-tests were performed.

RESULTS

The Gd concentration in the ipsilateral hemisphere homogenates of tMCAO group was significantly higher than that in the brain homogenates of the sham group on day 3 p.i. of either gadobutrol (0.065 ± 0.006 vs. 0.042 ± 0.007 μg/g, P < 0.05) or gadopentetate (0.093 ± 0.010 vs. 0.069 ± 0.008 μg/g, P < 0.05). Increased Gd deposition was also found in the ipsilateral hemisphere homogenates of the tMCAO group compared with the brain homogenates of the sham group on day 28 p.i. of gadopentetate (0.075 ± 0.012 vs. 0.044 ± 0.003 μg/g, P < 0.05), but not gadobutrol (0.012 ± 0.007 vs. 0.010 ± 0.001 μg/g, P = 0.80). The Gd concentration in the ipsilateral hemisphere in the tMCAO group was significantly higher for gadopentetate than gadobutrol on both day 3 p.i. (0.085 ± 0.006 vs. 0.049 ± 0.005 μg/g, P < 0.05) and day 28 p.i (0.075 ± 0.012 vs. 0.012 ± 0.007 μg/g, P < 0.05). Additionally, compared with gadobutrol, gadopentetate decreased viability, increased ROS accumulation, and decreased MMP in OGD/R-induced astrocytes (all P < 0.05).

DATA CONCLUSION

Administration of GBCAs after an animal model of ischemic stroke increased Gd deposition in the brain and aggravated astrocyte injury. The effect of gadopentetate appeared to be more pronounced than that of gadobutrol.

Alternatives to Gadolinium-Based Contrast Agents

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

Albumin-based nanoparticles as contrast medium for MRI: vascular imaging, tissue and cell interactions, and pharmacokinetics of second-generation nanoparticles

This multidisciplinary study examined the pharmacokinetics of nanoparticles based on albumin-DTPA-gadolinium chelates, testing the hypothesis that these nanoparticles create a stronger vessel signal than conventional gadolinium-based contrast agents and exploring if they are safe for clinical use. Nanoparticles based on human serum albumin, bearing gadolinium and designed for use in magnetic resonance imaging, were used to generate magnet resonance images (MRI) of the vascular system in rats ("blood pool imaging"). At the low nanoparticle doses used for radionuclide imaging, nanoparticle-associated metals were cleared from the blood into the liver during the first 4 h after nanoparticle application. At the higher doses required for MRI, the liver became saturated and kidney and spleen acted as additional sinks for the metals, and accounted for most processing of the nanoparticles. The multiple components of the nanoparticles were cleared independently of one another. Albumin was detected in liver, spleen, and kidneys for up to 2 days after intravenous injection. Gadolinium was retained in the liver, kidneys, and spleen in significant concentrations for much longer. Gadolinium was present as significant fractions of initial dose for longer than 2 weeks after application, and gadolinium clearance was only complete after 6 weeks. Our analysis could not account quantitatively for the full dose of gadolinium that was applied, but numerous organs were found to contain gadolinium in the collagen of their connective tissues. Multiple lines of evidence indicated intracellular processing opening the DTPA chelates and leading to gadolinium long-term storage, in particular inside lysosomes. Turnover of the stored gadolinium was found to occur in soluble form in the kidneys, the liver, and the colon for up to 3 weeks after application. Gadolinium overload poses a significant hazard due to the high toxicity of free gadolinium ions. We discuss the relevance of our findings to gadolinium-deposition diseases.

MRI contrast enhancement of liver pre-neoplasia using iron-tannic nanoparticles

The most challenging part of liver cancer detection is finding it in the very early stages. It has been argued that liver preneoplasia is found at the very earliest stages of liver cancer. The presence of a lesion is closely related to the development of HCC. We report herein a new class of iron-based T₁ MRI contrast agents which are nanoparticles of iron–tannic complexes (so-called Fe–TA NPs) that can be used for detecting liver preneoplasia. Preliminary assessment of their toxicity in healthy rats provides suitable imaging dose ranges with acceptable toxicity. In diethylnitrosamine (DEN) induced rats, it is shown that Fe–TA NPs are capable of enhancing MRI signals in rat livers having pre-neoplastic lesions within 60 minutes post-injection. The enhancement efficacy is strongly dependent on the characteristics of pre-neoplastic foci (GST-P+ foci). The highest enhancement was in good correlation with the size of GST-P+ foci and amount of Fe–TA NPs accumulated in the liver, and might be caused by the dysfunction of liver sinusoids along with cellular uptake capability of pre-neoplastic hepatocytes. Our results show that Fe–TA NPs are of great interest to develop as an efficient MRI imaging agent for risk assessment of liver cancer.

Imaging liver preneoplasia could be considered beneficial in first-line assessment of early stage liver cancer.

Increased T1 Signal Intensity of the Anterior Pituitary Gland on Unenhanced Magnetic Resonance Images After Chronic Exposure to Gadodiamide

OBJECTIVE

The aim of this study was to assess the signal intensity of the anterior pituitary (AP) gland on unenhanced T1-weighted images in patients with history of serial intravenous injections of gadodiamide and normal renal function.

MATERIALS AND METHODS

We included 53 patients who had undergone at least 5 injections of gadodiamide and a control group of 15 subjects who underwent at least 5 brain magnetic resonance imaging without gadolinium-based contrast agents. Using unenhanced sagittal T1-weighted images, values of mean signal intensity of the AP and of the central pons were obtained. Anterior pituitary-to-pons signal intensity ratios were calculated dividing the values of the AP by those of the pons. Then, the ratios were compared between the first and the last magnetic resonance imaging scans for all the subjects. To assess the difference between the first and the last ratios, nonparametric Wilcoxon signed-rank test with Monte Carlo resampling was applied. A P value less than 0.05 was considered as statistically significant.

RESULTS

The comparison between the first and the last scan revealed a statistically significant increase of AP-to-pons ratio in the last scan for the gadolinium-exposed group (P < 0.001), whereas nonsignificant results were found for the control group (P = nonsignificant).

CONCLUSIONS

We found an increased signal intensity of the AP on unenhanced T1-weighted images in patients with history of serial intravenous injections of gadodiamide and normal renal function, suggesting gadolinium deposition or long-term retention within the AP gland. Our findings need to be confirmed by further histochemical analysis of AP gland tissue samples.