Origin of the MRI Contrast in Natural and Hydrogel Formulation of Pineapple Juice

Abstract

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.

Not only manganese, but fruit component effects dictate the efficiency of fruit juice as an oral magnetic resonance imaging contrast agent

“…The profiles previously collected for pineapple juice are also reported. 16 1 H R 2 profiles at 400 MHz in the centrifuged blueberry juice (blue stars) and pineapple juice (black stars) are also shown identical profiles were also obtained in the absence of oxalate (Figure S1). The relaxation rates have very little dependence on the magnetic field, ranging from 0.50 to 0.43 s À1 on passing from low fields to 1 T, at 25 C. The water proton relaxivity due to manganese(II) ions in the centrifuged blueberry juice was then calculated from the differences between the relaxation rates of the juice and those of the Fe (NO 3 ) 3 solution, normalized to a manganese concentration of 1 mmol/dm 3 (Figure 2).…”

“…Interestingly, there is very good agreement at the intermediate magnetic fields, whereas the longitudinal relaxation rates are smaller than expected at low magnetic fields and higher at high magnetic fields. These effects were also observed for pineapple juice upon the addition of alginate, and are ascribed to the larger viscosity of the solution resulting from juice concentration and to transient interactions of manganese(II) ions, with possible confinement in a restricted environment, in such a way as to reduce their mobility 16 . This is confirmed by the appearance of a small relaxivity peak at about 25 MHz.…”

“…These effects were also observed for pineapple juice upon the addition of alginate, and are ascribed to the larger viscosity of the solution resulting from juice concentration and to transient interactions of manganese(II) ions, with possible confinement in a restricted environment, in such a way as to reduce their mobility. 16 This is confirmed by the appearance of a small relaxivity peak at about 25 MHz. The increase in the tumbling time is paralleled by a reduction of Fermi-contact relaxation (due to a smaller fraction of manganese aqua ions, a smaller electron relaxation time at low fields and/or a smaller contact coupling constant), which is also causing a decrease in the observed transverse relaxation rate at 400 MHz with respect to the prediction from the intact blueberry juice data.…”

“…23 Figure 1 also shows the relaxation rates measured for pineapple juice (black symbols), which was determined to contain 0.45 mmol/dm 3 of manganese. 16 The shape of the profiles for the two fruit juices are similar, as a result of the leading contribution from this paramagnetic ion. The lower relaxation rates measured for blueberry juice are in agreement with the lower manganese concentration expected in this juice, 11 where water was added to the blueberry puree, with respect to that of the pineapple juice.…”

“…The relaxivity profiles were fitted using the Solomon-Bloembergen-Morgan model [26][27][28][29] (see the supporting information) and the best fit parameters are reported in Table 1 together with those previously obtained for the pineapple juice and the manganese aqua ion. 16 The best fit profiles are shown in Figure 2, and the different contributions to the relaxivity (inner-sphere dipole-dipole relaxation modulated by slow mobility and by fast mobility, Fermi-contact relaxation, and outer-sphere relaxation) in Figure 3. Clearly, Fermi-contact relaxation provides a very large contribution to the longitudinal relaxivity at low fields, whereas at high fields the longitudinal relaxivity is determined by dipole-dipole interactions.…”