Magnetic resonance imaging (MRI) machines are employed to locate cancerous tumors and aid in the development of treatment plans, while nuclear magnetic resonance (NMR) machines are used to examine the atomic-scale structure and chemistry of drug compounds and other molecules. Diamonds are the key to a technique that could provide a very-low-cost alternative to these expensive medical imaging and drug discovery devices.
Defects in nanoscale and microscale diamonds were exploited to enhance the sensitivity of MRI and NMR systems while eliminating the need for their costly and bulky superconducting magnets. The technique could lead to the direct use of these tiny diamonds for rapid and enhanced biological imaging. Researchers also seek to transfer this special tuning, known as spin polarization, to a harmless fluid such as water, and to inject the fluid into a patient for faster MRI scans. The high surface area of the tiny particles is key in this effort.
Enhancing this spin polarization in the electrons of the diamonds’ atoms can be likened to aligning some compass needles pointing in many different directions to the same direction. These “hyperpolarized” spins could provide a sharper contrast for imaging than conventional superconducting magnets.
Scientists had struggled to overcome a problem in properly orienting the diamonds to achieve a more uniform spin polarization, and this problem was even more pronounced in collections of very small diamonds that presented a chaotic jumble of orientations. Earlier efforts, for example, had explored whether drilling tiny features into diamond samples could aid in controlling their spin polarization.
The tunable spin properties in diamonds with defects known as nitrogen vacancies — in which nitrogen atoms take the place of carbon atoms in the crystal structure of diamonds — have also been studied for potential use in quantum computing. In those applications, scientists seek to control the spin polarization of electrons as a way to transmit and store information like the ones and zeros in more conventional magnetic computer data storage.
By zapping a collection of microscale diamonds with green laser light, subjecting it to a weak magnetic field, and sweeping across the sample with a microwave source, this controllable spin polarization property could be enhanced in the diamonds by hundreds of times compared with conventional MRI and NMR machines.
A large measurement tool was developed for the new technique that proved instrumental in confirming and fine-tuning the spin polarization properties of the diamond samples. The device helped determine a good size for the diamond crystals; at first, crystals that measured about 100 microns, or 100 millionths of an inch across, were used. The tiny samples of pinkish diamonds resemble fine red sand. After testing, diamonds measuring about 1 to 5 microns performed about twice as well.
The tiny diamonds can be manufactured in economical processes by converting graphite into diamond, for example. A miniaturized system was developed that uses off-the-shelf components to produce the laser light, microwave energy, and magnetic field required to produce the spin polarization in the diamond samples. Existing NMR magnets could be retrofitted with one of these systems.