A Northwestern University study shows that coupling a magnetic resonance imaging (MRI) contrast agent to a nanodiamond results in dramatically enhanced signal intensity and thus vivid image contrast.
‘The results are a leap and not a small one – it is a game-changing event for sensitivity,’ said Thomas J Meade, the Eileen Foell Professor in Cancer Research in the Weinberg College of Arts and Sciences and the Feinberg School of Medicine. ‘The complex is far more sensitive than anything else I’ve seen.’
Meade led the study with Dean Ho, assistant professor of biomedical engineering and mechanical engineering in the McCormick School of Engineering and Applied Science.
Ho has already demonstrated that the nanodiamonds have excellent biocompatibility and can be used for efficient drug delivery. This new work paves the way for the clinical use of nanodiamonds to deliver therapeutics and remotely track the activity and location of the drugs.
The study, to the best of the researchers’ knowledge, is the first published report of nanodiamonds being imaged by MRI technology. The ability to image nanodiamonds in vivo would be useful in biological studies where long-term cellular fate mapping is critical, such as tracking beta islet cells or tracking stem cells.
MRI is a medical imaging technique that uses an intravenous contrast agent to produce detailed images of internal structures in the body. MRI is capable of deep tissue penetration, achieves an efficient level of soft tissue contrast with high spatial and time-related resolution, and does not require ionising radiation.
Contrast agents are used in MRI because they alter the relaxivity (contrast efficacy indicator) and improve image resolution. Gadolinium (Gd) is the material most commonly used as an MRI contrast agent, but its contrast efficacy can be improved.
Meade, Ho and their colleagues developed a gadolinium(III)-nanodiamond complex that, in a series of tests, demonstrated a significant increase in relaxivity and, in turn, a significant increase in contrast enhancement.
The Gd(III)-nanodiamond complex demonstrated a greater than 10-fold increase in relaxivity – among the highest per Gd(III) values reported to date. This represents an important advance in the efficiency of MRI contrast agents.
Ho and Meade imaged a variety of nanodiamond samples, including nanodiamonds decorated with various concentrations of Gd(III), undecorated nanodiamonds and water. The intense signal of the Gd(III)-nanodiamond complex was brightest when the Gd(III) level was highest.
‘Nanodiamonds have been shown to be effective in attracting water molecules to their surface, which can enhance the relaxivity properties of the Gd(III)-nanodiamond complex,’ said Ho. ‘This might explain why these complexes are so bright and such good contrast agents.’