Sodium lanthanide tungstate-based nanoparticles as bimodal probes for <i>T</i> ₁ – <i>T</i> ₂ magnetic resonance imaging and X-ray computed tomography

Magnetic resonance imaging (MRI) is one of the most commonly 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 (<i>T</i>₁) (resulting in signal enhancement in <i>T</i>₁-weighted images) and/or transverse (<i>T</i>₂) (resulting in signal decay in <i>T</i>₂-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 (<i>T</i>₁-weighted and <i>T</i>₂-weighted) using dual <i>T</i>₁-<i>T</i>₂ CAs, which facilitates the exclusion of false positives. The traditional <i>T</i>₁ or <i>T</i>₂ 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 <i>in vitro</i> (for human fibroblast cells) and <i>in vivo</i> (for <i>C. elegans</i>) toxicity and present appropriate relaxivity values for their use as a dual <i>T</i>₁-<i>T</i>₂ 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 <i>T</i>₁-<i>T</i>₂ contrast agent for magnetic resonance imaging and as a contrast agent for X-ray computed tomography.