High-tech contrast agents for biomedical imaging

Using medical imaging to diagnose and assess treatment efficacy

Biomedical imaging enables the non-invasive diagnosis and monitoring of tumors, as well as the evaluation of treatment efficacy. Magnetic resonance imaging (MRI) is one of the most commonly used techniques for diagnosis and follow-up, while the use of intraoperative near-infrared fluorescence spectrometry (NIRF) is constantly progressing. The former provides anatomical, functional and metabolic information, and often requires the use of gadolinium (Gd3+)-based contrast agents to enhance contrast between tumors and surrounding tissue. Fluorescence imaging, with its high sensitivity but more limited tissue penetration, is increasingly used in the operating room to guide surgery. It requires the use of specific near-infrared dyes (NIRF).

Enhancing measurement sensitivity and specificity

Combining these two techniques should make it possible to increase the sensitivity and specificity of measurements. To achieve this, scientists from the Centre interdisciplinaire de nanoscience de Marseille and the Centre de résonance magnétique biologique et médicale have devised nanosystems that can act as both contrast agents for MRI and dyes for NIRF. They have chosen amphiphilic dendrimers, tree-like molecules whose multiple endings can bind Gd3+ ions. In the core of nanoparticles assembled from these dendrimers, they then encapsulated a specific NIRF dye, enabling them to combine MRI and NIRF measurements. In this way, they obtained high-quality "bimodal" images of a pancreatic tumor.

Double the contrast and signal intensity

These dendrimers showed a twofold improvement in contrast in tumors compared with adjacent healthy muscle, and a twofold increase in fluorescence signal intensity. What's more, these systems were shown to be effective even at Gd3+ concentrations corresponding to 1/10 of the standard clinical dose, which could prevent potential risks of Gd3+-related toxicity.

These dendrimer-based nanosystems, described in the journal Advanced Materials, offer a promising nanotechnological platform for the development of multimodal imaging probes for biomedical applications.