Magnetic resonance imaging (MRI) often requires contrast agents to improve the visualization in some tissues and organs, including the gastrointestinal tract. In this latter case, instead of intravascular administration, oral agents can be used. Natural oral contrast agents, such as fruit juice, have the advantages of better taste, tolerability, and lower price with respect to the artificial agents. We have characterized the relaxometry profiles of pineapple juice in order to understand the origin of the increase in relaxation rates (and thus of the MRI contrast) in reference to its content of manganese ions. Furthermore, we have characterized the relaxometry profiles of pineapple juice in the presence of alginate in different amounts; the interaction of the manganese ions with alginate slows down their reorientation time to some extent, with a subsequent increase in the relaxation rates. The relaxometry profiles were also compared with those of manganese(II) solutions in 50 mmol/dm³ sodium acetate solution (same pH of pineapple juice), which revealed sizable differences, mostly in the number of water molecules coordinated to the metal ion, their lifetimes, and in the constant of the Fermi-contact interaction. Finally, the fit of the transverse relaxivity shows that the increased viscosity in the hydrogel formulations can improve significantly the negative contrast of pineapple juice at the magnetic fields relevant for clinical MRI.

中文翻译：

---

菠萝汁天然和水凝胶配方中MRI对比的起源

磁共振成像（MRI）通常需要造影剂，以改善某些组织和器官（包括胃肠道）的可视性。在后一种情况下，代替血管内给药，可以使用口服剂。天然口服造影剂，例如果汁，相对于人造试剂具有更好的味道，耐受性和更低的价格的优点。我们已经对菠萝汁的弛豫测定曲线进行了表征，以了解其锰离子含量引起的弛豫率增加的原因（进而是MRI对比）。此外，我们已经描述了在藻酸盐含量不同的情况下菠萝汁的弛豫测定曲线。锰离子与藻酸盐的相互作用在一定程度上减慢了其重新定向的时间，随后放松率增加。还比较了50mmol / dm的弛豫谱曲线与锰（II）溶液的弛豫谱曲线³醋酸钠溶液（菠萝汁的pH值相同），显示出相当大的差异，主要在于与金属离子配位的水分子数量，其寿命以及费米接触相互作用的常数。最后，横向弛豫的拟合表明，在与临床MRI相关的磁场下，水凝胶制剂中粘度的增加可以显着改善菠萝汁的负对比度。