Paramagnetic pillared bentonites — The new digestive tract MRI contrast agents Miloš Mojović a, ⁎, Marko Daković a , Predrag Banković b , Zorica Mojović b a Faculty of Physical Chemistry, University of Belgrade, Belgrade, Studentski trg 12–16, 11000, Serbia b Institute of Chemistry Technology and Metallurgy, University of Belgrade, Department of Catalysis and Chemical Engineering, Belgrade, Njegoševa 12, 11000, Serbia abstract article info Article history: Received 10 July 2009 Received in revised form 23 November 2009 Accepted 23 November 2009 Available online 29 November 2009 Keywords: Bentonites Pillaring MRI contrast Digestive tract The availability of sophisticated diagnostic methods such as MRI has contributed to the increased use of imaging technologies in therapy and diagnostic studies. However, gastrointestinal tract MRI generally shows poor results because of the lack of suitable contrast agents. The iron oxide is traditionally popular material for MRI gastrointestinal studies because of its well-known superparamagnetic properties. On the other hand, it has many disadvantages which include black bowel, side effects of diarrhea and, from an important analytical standpoint, the presence of artifacts arising from clumping. When paramagnetic iron concentrates, it may become ferromagnetic, drastically altering its imaging properties. Other paramagnetic species, represented by gadolinium, also seem to be potentially suitable agents for these studies. Nevertheless, this metal itself cannot be used in humans because of its toxic properties. Therefore, there is clearly a need for orally effective, well tolerated agents that can be used in humans for digestive imaging studies. This MRI contrast should be useful for visualizing the anatomy of the digestive tract and particularly to differentiate between normal and pathological states, such as tumors. The solution has been proposed as zeolites or smectites (hectorite and montmorillonite) enclosing of paramagnetic metal ions obtained by ion-exchange methods. However, such materials could have problems of leakage of paramagnetic ions causing the appearance of the number side-effects. We propose the usage of the pillaring method for paramagnetic metal encapsulation in bentonites. By that way, paramagnetic cations like Fe +3 , Mn +2 and Gd +3 are introduced between clay mineral layers as polyoxo cations. After calcination, these polyoxo cations grow to be pillars (oxides of these metals) which are incorporated into the clay mineral matrix which prevents ion-leaching and dangerous side-effects. In this study we show that paramagnetic-pillared bentonites could be successfully used as MRI digestive tract non- leaching contrast agents, altering the longitudinal relaxation times of fluids in contact with the clay minerals. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The MRI (Magnetic Resonance Imaging) technique enables the direct electronic visualization of internal organs in living beings and is therefore powerful help and guide in prognosis, medical treatment and surgery. This technique can often advantageously supplement or replace X-ray tomography as well as the use of radioactive tracer compounds which may have obvious undesirable side effects. The useful parameters pertaining thereto, i.e. the relaxation time factors T1 and T2 of the water protons in the direct environment of the organs under investigation are usually not sufficiently differentiated to provide sharp images when the measurements are carried out in the absence of contrast agents. However, the differences of the relaxation time constants between protons in various parts of the organs can be enhanced in the presence, in the environment of the hydrated molecules under excitation, of a variety of magnetic species, e.g. paramagnetic (which mainly affect T1) and ferromagnetic or superparamagnetic (which mainly affect the T2 response). The paramagnetic substances include some metals in the ionic or organo-metallic state (e.g. Fe +3 , Mn +2 , Gd +3 and the like, particularly in the form of chelates to decrease the intrinsic toxicity of the free metal ions). Ferromagnetic and superparamagnetic contrast substances preferably include magnetic particles of micronic or submicronic size, i.e. from a few microns down to a few nanometers, for instance particles of magnetite (Fe 3 O 4 ), ferrites and other magnetic mineral compounds of transition elements. Application of contrast-enhancing agents in clinical MRI is indispensable in contemporary medical diagnosis. Roughly, about 20% of MRIs are ordered with contrast. MRI contrast agents designed for imaging the digestive tract mostly include solid magnetic materials generally in particular form. This is so because to be effective, the contrast agents should more or less line the walls of the digestive tract, thus requiring bulk. Obviously paramagnetic species in water-soluble molecular form would not fit the foregoing requirements and, if used, they should be associated with bulk carriers. A number of agents have been tried in humans for the purpose of distinguishing bowel from adjacent tissues (Bryant and Listinsky, 1990; Applied Clay Science 48 (2010) 191–194 ⁎ Corresponding author. Tel.: +381 112630796, +391641128379 (mobile); fax: +381 112187133. E-mail address: milos@ffh.bg.ac.rs (M. Mojović). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.11.041 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay