r e v i e w Gadonanotubes as new high-performance Mri contrast agents Balaji Sitharaman Lon J w ilson Department of Chemistry, r ichard e Smalley institute for Nanoscale Science and Technology, Center for Biological and environmental Nanotechnology, MS 60, r ice University, Houston, TX, USA Correspondence: Lon J w ilson Department of Chemistry, r ichard e Smalley institute for Nanoscale Science and Technology, r ice University, Houston, TX 77251-1892, USA Tel +1 713 348 3268 Fax +1 713 348 5155 durango@rice.edu Abstract: Gadolinium-based carbon nanostructures are poised to make a significant impact as advanced contrast agents (CAs) for magnetic resonance imaging (MRI) in medicine. This paper reviews and forecasts gadonanotubes as synthons for the design of high-performance MRI CA probes with efficacies up to 100 times greater than current clinical CAs. This level of performance is vital for achieving the goal of cellular and molecular imaging with MRI. These new materials will be useful for in vivo MRI applications as circulating drug nanocapsules because of their low toxicities, extremely high relaxivities, and potential for cellular targeting and induced cell death by magnetic hyperthermia. Keywords: nanotechnology, carbon nanotubes, gadonanotubes, MRI contrast agents Introduction Magnetic resonance imaging (MRI) is one of the most powerful and central techniques in diagnostic medicine and biomedical research (Mansfield 2004). Primarily, MRI non-invasively produces anatomical details for improved diagnosis of many diseases. Secondly, MRI also provides valuable information about the physiochemical state of tissues and blood flow. Thus, MRI is the method of choice for the diagnosis of many types of injuries and conditions, and it is not surprising that the use of MRI scanners is growing at an explosive rate. Today more than 22 000 MRI systems operate worldwide. In clinical MRI, the nuclear magnetic resonance signal from water protons in living tissue are used to image organs and disease sites, such as tumors, in 3D. The intensity of this MR signal depends on three important intrinsic tissue factors: the proton density, the longitudinal relaxation time, T1, and the transverse relaxation time, T2. Thus, various mathematical techniques have been developed to highlight the differences in T1 or T2 to obtain good contrast, ie, the difference in appearance of different tissues in an MR image. Otherwise, MR images would be fairly featureless since the amount of water does not vary significantly in the various tissues of in the body. The development of MRI has also concurrently led to the development of chemical contrast-enhancement products called contrast agents (CAs). MRI CAs are used primarily to improve disease detection by increasing sensitivity and diagnostic confidence. There are several types of MRI CAs including extracellular fluid space (ECF) agents, extended-residence-intravascular agents (blood pool), and tissue (organ)-specific agents. Nearly all commercial CAs available today are ECF agents that distribute extracellularly and excrete exclusively via the kidney. Annually, approximately 60 million MRI procedures are performed worldwide; 30–35% of these procedures use MRI CAs. international Journal of Nanomedicine 2006:1(3) 291–295 © 2006 Dove Medical Press Limited.All rights reserved 291