Sodium lanthanide tungstate-based nanoparticles as bimodal probes for T1-T2 magnetic resonance imaging and X-ray computed tomography

Magnetic resonance imaging (MRI) is one of the most used imaging techniques for diagnosis in clinics. Often, magnetically-active substances, called contrast agents (CAs), have to be used, which increase contrast by shortening the longitudinal (T1) (resulting in signal enhancement in T1-weigthed images) and/or transverse (T2) (resulting in signal decay in T2-weighted images) relaxation times of the water protons present in biological tissues. A further strategy to improve diagnostic accuracy is recording both kinds of images (T1-weighted and T2-weighted) using dual T1-T2 CAs, which facilitates the exclusion of false positives. The traditional T1 or T2 contrast agents are not suitable for such a purpose. This paper deals with the development of double sodium lanthanide tungstate-based nanoparticles containing Gd3+ and Dy3+ cations, which are dispersible in physiological media, do not show appreciable in vitro (for human fibroblast cells) and in vivo (for C-elegans) toxicity and present appropriate relaxivity values for their use as a dual T1-T2 contrast agent for magnetic resonance imaging. In addition, they show an excellent X-ray attenuation capacity, thanks, mainly, to their tungsten content, which makes them also useful for X-ray computed tomography. Hence, the developed nanoparticles are ideal multimodal probes to be used as a dual T1-T2 contrast agent for magnetic resonance imaging and as a contrast agent for X-ray computed tomography.