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The aim of this study was to investigate the presence and chemical forms of residual gadolinium (Gd) in rat brain after a single dose of Gd-based contrast agent. Methods: Four groups of healthy rats (2 sacrifice time-points, n = 10/group, 80 rats in total) were randomized to receive a single intravenous injection of 1 of the 3 Gd-based contrast agents (GBCAs) (gadoterate meglumine, gadobenate dimeglumine, or gadodiamide) or the same volume of 0.9% saline solution. The injected concentration was 0.6 mmol/kg, corresponding to a concentration of 0.1 mmol/kg in humans after body surface normalization between rats and humans (according to the US Food and Drug Administration recommendations). Animals were sacrificed at 2 washout times: 1 (M1) and 5 (M5) months after the injection. Total Gd concentrations were determined in cerebellum by inductively coupled plasma mass spectrometry. Gadolinium speciation was analyzed by size-exclusion chromatography coupled to inductively coupled plasma mass spectrometry after extraction from cerebellum. Results: A single injection of a clinically relevant dose of GBCA resulted in the detectable presence of Gd in the cerebellum 1 and 5 months after injection. The cerebellar total Gd concentrations after administration of the least stable GBCA (gadodiamide) were significantly higher at both time-points (M1: 0.280 ± 0.060 nmol/g; M5: 0.193 ± 0.023 nmol/g) than those observed for macrocyclic gadoterate (M1: 0.019 ± 0.004 nmol/g, M5: 0.004 ± 0.002 nmol/g; P < 0.0001). Gadolinium concentrations after injection of gadobenate were significantly lower at both time-points (M1: 0.093 ± 0.020 nmol/g; M5: 0.067 ± 0.013 nmol/g; P < 0.05) than the Gd concentration measured after injection of gadodiamide. At the 5-month time-point, the Gd concentration in the gadoterate group was also significantly lower than the Gd concentration in the gadobenate group (P < 0.05). Gadolinium speciation analysis of the watersoluble fraction showed that, after injection of the macrocyclic gadoterate, Gd was still detected only in its intact, chelated form 5 months after injection. In contrast, after a single dose of linear GBCAs (gadobenate and gadodiamide), 2 different forms were detected: intact GBCA and Gd bound to soluble macromolecules (above 80 kDa). Elimination of the intact GBCA form was also observed between the first and fifth month, whereas the amount of Gd present in the macromolecular fraction remained constant 5 months after injection. Conclusions: A single injection of a clinically relevant dose of GBCA is sufficient to investigate long-term Gd retention in the cerebellar parenchyma. Administration of linear GBCAs (gadodiamide and gadobenate) resulted in higher residual Gd concentrations than administration of the macrocyclic gadoterate. Speciation analysis of the water-soluble fraction of cerebellum confirmed washout of intact GBCA over time. The quantity of Gd bound to macromolecules, observed only with linear GBCAs, remained constant 5 months after injection and is likely to represent a permanent depo...

A fter brain metastasis, primary central nervous system (CNS) tumors are the most common malignant brain lesions (1); more than 40 000 are malignant, and 60% of all malignant CNS tumors are gliomas (2). With less than 10% of patients surviving at 5 years, early and accurate diagnosis of brain tumors is crucially important. Glioblastoma multiforme leads to 255 000 deaths per year worldwide (3). With gadolinium-based contrast agents (GBCA), contrast material-enhanced MRI is the first-line diagnostic approach for the detection and characterization of primary CNS tumors. This technique dramatically improves the diagnostic accuracy of brain MRI. Clinical management of brain tumors is highly dependent on the information provided by contrast-enhanced MRI, including the location, the size, and the precise border delineation of the lesion. Moreover, contrast material uptake is a surrogate marker for distinguishing between low-grade glioma (no contrast material uptake) and high-grade glioma (contrast enhancement). The common clinical dosage for GBCAs is 0.1 mmol per kilogram of body weight, which has a very high benefit-to-risk ratio (4). A higher GBCA dose leads to better brain lesion detection (5), but a concern is the dose-dependent long-term retention of gadolinium in tissue, especially after injection of less thermodynamically stable (ie, linear