The atoms are excited by a radio frequency (RF) pulse and the resultant signal is measured by a receiving coil. Scanning with X and Y gradient coils causes a selected region of the patient to experience the exact magnetic field required for the energy to be absorbed. First, energy from an oscillating magnetic field is temporarily applied to the patient at the appropriate resonance frequency. To perform a study, the person is positioned within an MRI scanner that forms a strong magnetic field around the area to be imaged. Given that the protons are affected by fields from other atoms to which they are bonded, it is possible to separate responses from hydrogen in specific compounds. In most medical applications, hydrogen nuclei, which consist solely of a proton, that are in tissues create a signal that is processed to form an image of the body in terms of the density of those nuclei in a specific region. Schematic of construction of a cylindrical superconducting MR scanner The sustained increase in demand for MRI within health systems has led to concerns about cost effectiveness and overdiagnosis. Diffusion MRI and functional MRI extend the utility of MRI to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. While MRI is most prominently used in diagnostic medicine and biomedical research, it also may be used to form images of non-living objects, such as mummies. Since its development in the 1970s and 1980s, MRI has proven to be a versatile imaging technique. By varying the parameters of the pulse sequence, different contrasts may be generated between tissues based on the relaxation properties of the hydrogen atoms therein. Pulses of radio waves excite the nuclear spin energy transition, and magnetic field gradients localize the polarization in space. For this reason, most MRI scans essentially map the location of water and fat in the body. Hydrogen atoms are naturally abundant in humans and other biological organisms, particularly in water and fat. In clinical and research MRI, hydrogen atoms are most often used to generate a macroscopic polarization that is detected by antennas close to the subject being examined. Certain atomic nuclei are able to absorb radio frequency energy when placed in an external magnetic field the resultant evolving spin polarization can induce a RF signal in a radio frequency coil and thereby be detected. MRI was originally called NMRI (nuclear magnetic resonance imaging), but 'nuclear' was dropped to avoid negative associations. Additionally, implants and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an MRI examination safely. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube, though 'Open' MRI designs mostly relieve this. Compared to CT, MRI provides better contrast in images of soft-tissues, e.g. MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. Magnetic resonance imaging ( MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. Nuclear magnetic resonance imaging (NMRI), magnetic resonance tomography (MRT) Para-sagittal MRI of the head, with aliasing artifacts (nose and forehead appear at the back of the head)

Relax synonyms