| Magnetic resonance imaging (MRI) has revolutionized modern medicine by providing non-invasive, chemically selective, three-dimensional imaging of living organisms. Industrial-scale MRI has the capability to image with millimeter-scale spatial resolution and has the sensitivity to detect as few as 1014 nuclear spins. Increasing spatial resolution to the atomic scale and sensitivity to the single-spin level would enable a wide array of applications most notably including imaging molecular structur. However, conventional MRI methods are already highly optimized, and further order-of-magnitude-scale improvements cannot be reasonably expected without employing fundamentally different technologies.;This thesis presents an alternative approach to conventional MRI that pushes resolution and sensitivity to the individual atom and molecular level. The guiding principle for achieving multiple order-of-magnitude improvements is to miniaturize the key components of MRI: the detector and the source of magnetic-field gradients. By scaling down the physical size of these components to the nano- and atomic- scales, the signals from individual spins become measurable and resolvable.;To miniature the detector, we employ an optically-active, paramagnetic atomic defect in diamond---a nitrogen-vacancy (NV) center---as our sensor. Owing to its optical readout, long coherence times, atomic-size, and room-temperature compatibility, NV centers in diamond have the capability to measure the magnetic fields from individual spins, provided the sensor can be placed sufficiently close to a target to be measured. This thesis describes the experimental realization of a microscope that can perform sensitive magnetometry experiments using a single NV center that magnetically images by spatially scanning the NV center within a few nanometers of magnetic targets. With this technique we are able to demonstrate the first room-temperature magnetic imaging of individual electron spins.;For miniaturizing the magnetic-field gradient source, we use scanning nanoscale magnets, building off the success of those used in magnetic resonance force microscopy. By shrinking the magnetic field source to tens of nanometers in size, the magnitude of the magnetic field gradients can be increased by more than a factor of 105 compared to conventional MRI field gradients coils, which increases spatial resolution correspondingly. With these tips optimized for compatibility with NV-based measurements, we are able to achieve sub-nanometer resolution in MRI imaging. |
