How MRI Works
MRI stands for Magnetic Resonance Imaging. By placing a patient within a strong magnetic field it is possible to synchronously align the protons on all the water molecules along the direction of the magnetic field. The instrument detects the radio waves that are produced when those water protons relax after synchronization. An electromagnetic pulse specifically tuned to the magnetic frequency of the protons sends them reeling. The instrument detects the radio waves that are produced when those water protons relax after being "pinged." Through a complex mathematical analysis it is possible to measure the spatial distribution of water, which is effectively a 3-D map of soft tissues within the body. Learn more about MRI.
MRI has become a pillar for physicians ability to diagnose what is going on inside the body from without. However, it is only natural to wish to see things that can't be visualized with MRI. One successful approach has been the development of injected agents that increase the image contrast during an MRI procedure.
MRI essentially measures the orientation of the magnetic fields on the protons of water molecules. If there are magnetic atoms present nearby, these will alter the relaxation of the water protons, which has the effect of increasing the MRI signal and thereby improving contrast. Body compartments that have the metal atoms will appear whiter relative to those which do not.
The catch is that heavy metals that have the appropriate magnetic properties, like Gadolinium (Gd), are toxic to animals. The solution to the toxicity problem is to wrap the Gd in a chelate, which encloses it and protects the body from the metal toxicity.
A chelate is an organic compound that contains charged groups which bind positively charged metals. The effect is to wrap the Gd so that it doesn't get out of the chelate. These chelates have been used successfully to boost MRI contrast for more than a decade.
Contrast agents, made of Gadolinium chelates, are injected into a patient prior to the MRI procedure to enhance the image. This compound enables radiologists to visualize irregularities inside the body that cannot be seen otherwise. Contrast media are used in about 40% of MRI procedures. Most patients who receive these agents experience no problems. However, with all these chelates it is best to get them out of the body as rapidly as possible to limit the possibility of the Gadolinium escaping. All chelates are eliminated by glomerular filtration in the kidney. Patients who may have impaired renal function are most at risk for problems with these contrast agents.
Gadolinium chelates are small molecules and diffuse rapidly out of the circulatory system by osmotic diffusion into the interstitial tissue, dissipating the image enhancement. This means that the available timing for image collection is limited to a few minutes after the chelate is injected. In practice, it is difficult to coordinate the administration with the image gathering and the failure rate is high. Practitioners sometimes try to control this by setting the patient up with an intravenous feed that releases the chelate remotely, while the patient is lying in the magnet.
Another challenge with chelates is they do not provide sufficient improvement in relativity to visualize everything the physician wishes to observe. Because of difficulties with experimental conditions, altered physiology of the patient, or limitations of the contrast there are many settings where the image isn't sufficient.
Luna nanoWorks believes we have found a 25-fold better relativity of Gadolinium in our proprietary TRIMETASPHERE® carbon nanomaterials, which will enable the radiologist to see things that are not visible using today's tools.
Additionally, Luna's nanomaterial-based contrast agent increases safety as the metal ions remain encapsulated in the carbon cage and can not escape unless temperatures rise above 900 degrees. In the body, this situation will not occur.