Creation of images of objects such as the body by use of the nuclear magnetic resonance phenomenon. The immediate practical application involves imaging the distribution of hydrogen nuclei (protons) in the body. The image brightness in a given region depends on the spin density and the relaxation times, with their relative importance determined by the particular imaging technique employed. Image brightness is also affected by motion such as blood flow.

See also Zeugmatography and Magnetic Resonance Imaging MRI.

(fMRI) Functional magnetic resonance imaging is a technique used to determine the dynamic brain function, often based on echo planar imaging, but can also be performed by using contrast agents and observing their first pass effects through brain tissue. Functional magnetic resonance imaging allows insights in a dysfunctional brain as well as into the basic workings of the brain.
The in functional brain MRI most frequently used effect to assess brain function is the blood oxygenation level dependent contrast (BOLD) effect, in which differential changes in brain perfusion and their resultant effect on the regional distribution of oxy- to deoxyhaemoglobin are observable because of the different 'intrinsic contrast media' effects of the two haemoglobin forms. Increased brain activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated haemoglobin. Because deoxygenated haemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity.
Functional imaging relates body function or thought to specific locations where the neural activity is taking place. The brain is scanned at low resolution but at a fast rate (typically once every 2-3 seconds). Structural MRI together with fMRI provides an anatomical baseline and best spatial resolution.
Interactions can also be seen from the motor cortex to the cerebellum or basal ganglia in the case of a movement disorder such as ataxia. For example: by a finger movement the briefly increase in the blood circulation of the appropriate part of the brain controlling that movement, can be measured.

(I MRA) In MR imaging, inflowing non-saturated fluid gives a higher signal intensity than stationary tissue. This effect makes it especially useful for imaging of flowing blood. Other factors such as susceptibility and spin saturation, can affect the signal of the blood within the vessels. Furthermore turbulence is part of normal blood flow and can decrease signal intensity.

See also Time of Flight Angiography.

Form of NMR spectroscopy in which an additional dimension is added to the conventional chemical shift dimension by allowing varying amounts of different interactions between spin systems (such as Nuclear Overhauser Effect, spin spin coupling or exchange).

With an open configuration MRI system neurosurgical procedures can be performed using image guidance. Open MRI can be used to guide interventional treatments or procedures, such as a biopsy.
Intraoperative MRI allows lesions to be precisely localized and targeted. Constantly updated images, correlated with images obtained pre-operatively, help to eliminate errors that can arise during framed and frameless stereotactic surgery when anatomic structures alter their position due to shifting or displacement of, e.g. brain parenchyma.
Intraoperative MRI can help with the identification of normal structures, such as blood vessels and is helpful in optimizing surgical approaches, achieving complete resection of intracerebral lesions, determining tumor margins and monitoring potential intraoperative complications.