First ex-vivo MRI co-localization of two LIPOCEST agents.

One of the major advantages of the CEST methodology deals with the possibility of visualizing more probes in the same MR image voxels. This is a unique property within the contrast media that act on the (1)H-NMR signal of water protons, and it might considerably improve the potential of the technique. In addition to displaying sufficiently different resonance frequencies of their mobile protons, it is also important that the CEST agents designed for this application are highly sensitive. LIPOCEST agents represent the most sensitive class of CEST systems developed so far. On this basis, two LIPOCEST samples, a spherical one and an osmotically shrunken nonspherical one, endowed with markedly different resonance frequencies of their intraliposomal water protons, 3 ppm and 15 ppm, respectively, were prepared and tested both in vitro and in ex-vivo on a bovine muscle used as tissue-surrogate. The response of the two agents did not interfere each other, thus allowing the multiple visualization of the two agents present at nanomolar concentrations in the same image voxels.