核磁共振成像MRI造影剂可以分为纵向弛豫造影剂 (T1制剂)和横向弛豫造影剂（T2制剂）。T1制剂是通过水分子中的氢核和顺磁性金属离子直接作用来缩短T1，从而增强信号，图像较亮；T2制剂是通过对外部局部磁性环境的不均匀性进行干扰，使邻近氢质子在弛豫中很快产生相(diphase)来缩短T2，从而减弱信号，图像较暗。
弛豫效率是MRI造影剂关键指标之一。弛豫效率高的样品，可以使用最少的量达到最好的效果；在造影剂研究领域，纽迈专门开发了小型的核磁共振成像分析仪，可测试方便的测试造影剂T1、T2弛豫时间，并可对试管样品进行成像，提供定量和定性评价数据，为造影剂产品的研发与改进提供快速可靠的检测手段。
目前市面上的T1造影剂产品是Gd钆及Gd的衍生物产品，最常用的就是Gd-DTPA钆喷替酸葡甲胺。
Magnetic resonance imaging (MRI) is an imaging technique usedprimarily in medical research to produce high quality images of in vivosystems. To track materials within in vivo systems, compounds-of-interest aretagged with materials that possess magnetic properties. These materials, aswell as MRI contrast agents, generally fall into two classes. The first issoluble gadolinium compounds that act through the T1 relaxation process and arebrightening agents. The second is particulate iron oxides that act through theT2 relaxation process and are darkening agents. Each type of contrast agent hasits benefits.
