Background

T1-weighted MRI and quantitative longitudinal relaxation rate (R1) mapping have been used to evaluate gadolinium retention in the brain after gadolinium-based contrast agent (GBCA) administration. Whether MRI measures accurately reflect gadolinium regional distribution and concentration in the brain remains unclear.

Purpose

To compare gadolinium retention in rat forebrain measured with in vivo quantitative MRI R1 and ex vivo laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping after gadobenate, gadopentetate, gadodiamide, or gadobutrol administration.

Materials and Methods

Adult female Sprague-Dawley rats were randomly assigned to one of five groups (eight per group) and administered gadobenate, gadopentetate, gadodiamide, gadobutrol (2.4 mmol/kg per week for 5 weeks), or saline (4.8 mL/kg per week for 5 weeks). MRI R1 mapping was performed at baseline and 1 week after the final injection to determine R1 and ΔR1. Postmortem brains from the same rats were analyzed with LA-ICP-MS elemental mapping to determine regional gadolinium concentrations. Student t tests were performed to compare results between GBCA and saline groups.

Results

Rats that were administered gadobenate showed gadolinium-related MRI ΔR1 in 39.5% of brain volume (ΔR1 = 0.087 second⁻¹ ± 0.051); gadopentetate, 20.6% (ΔR1 = 0.069 second⁻¹ ± 0.018); gadodiamide, 5.4% (ΔR1 = 0.055 second⁻¹ ± 0.019); and gadobutrol, 2.2% (ΔR1 = 0.052 second⁻¹ ± 0.041). Agent-specific gadolinium-related ΔR1 was detected in multiple forebrain regions (neocortex, hippocampus, dentate gyrus, thalamus, and caudate-putamen) in rats treated with gadobenate or gadopentetate, whereas rats treated with gadodiamide showed gadolinium-related ΔR1 in caudate-putamen. By contrast, LA-ICP-MS elemental mapping showed a similar regional distribution pattern of heterogeneous retained gadolinium in the forebrain of rats treated with gadobenate, gadopentetate, or gadodiamide, with the average gadolinium concentration of 0.45 μg · g⁻¹ ± 0.07, 0.50 μg · g⁻¹ ± 0.10, and 0.60 μg · g⁻¹ ± 0.11, respectively. Low levels (0.01 μg · g⁻¹ ± 0.00) of retained gadolinium were detected in the forebrain of gadobutrol-treated rats.

Conclusion

Differences in in vivo MRI longitudinal relaxation rate versus ex vivo elemental mass spectrometry measures of retained gadolinium in rat forebrains suggest that some forms of retained gadolinium may escape detection with MRI.

© RSNA, 2022

Online supplemental material is available for this article.

中文翻译：

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用定量 MRI 与元素质谱法测量大鼠脑中的钆沉积

背景

T1 加权 MRI 和定量纵向弛豫率 (R1) 映射已用于评估基于钆的造影剂 (GBCA) 给药后大脑中的钆保留。MRI 测量是否能准确反映大脑中钆的区域分布和浓度仍不清楚。

目的

比较使用体内定量 MRI R1 和体外激光消融电感耦合等离子体质谱 (LA-ICP-MS) 测绘在给予钆贝酸、钆喷酸、钆双胺或钆布醇后的大鼠前脑中的钆保留。

材料和方法

成年雌性 Sprague-Dawley 大鼠被随机分配到五组中的一组（每组八只）并给予钆贝酸、钆喷酸、钆双胺、钆布醇（每周 2.4 毫摩尔/千克，持续 5 周）或生理盐水（每周 4.8 毫升/千克，持续 5 周） 5 周）。在基线和最后一次注射后 1 周进行 MRI R1 映射以确定 R1 和 ΔR1。使用 LA-ICP-MS 元素图谱分析同一只大鼠的死后大脑，以确定局部钆浓度。进行学生t检验以比较 GBCA 和盐水组之间的结果。

结果

施用钆贝酸盐的大鼠在 39.5% 的脑容量中显示出与钆相关的 MRI ΔR1（ΔR1 = 0.087 秒^-1 ± 0.051）；钆喷酸，20.6%（ΔR1 = 0.069 秒^-1 ± 0.018）；钆双胺，5.4%（ΔR1 = 0.055 秒^-1 ± 0.019）；和钆布醇，2.2%（ΔR1 = 0.052 秒^-1± 0.041)。在用钆贝酸或钆喷酸处理的大鼠的多个前脑区域（新皮质、海马、齿状回、丘脑和尾状壳核）检测到与药物特异性钆相关的 ΔR1，而用钆双胺处理的大鼠在尾状壳核中显示与钆相关的 ΔR1 . 相比之下，LA-ICP-MS 元素图谱显示，用钆贝酸、钆喷酸或钆双胺处理的大鼠前脑中异质保留钆的区域分布模式相似，平均钆浓度为 0.45 μg·g -1 ± 0.07 ^, 0.50 μg·g ^-1 ± 0.10 和 0.60 μg·g ^-1 ± 0.11。低浓度 (0.01 μg · g ⁻¹在接受钆布醇治疗的大鼠的前脑中检测到 ± 0.00) 残留的钆。

结论

体内 MRI 纵向弛豫率与大鼠前脑中残留钆的离体元素质谱测量的差异表明，某些形式的残留钆可能逃脱 MRI 检测。

©北美放射学会，2022

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