tesla clinical MRI scanner. The<unk>  (MRI) concerns fundamental<unk> l considerations of MRI techniques and technological aspects of MRI devices. MRI is a medical<unk>  technique mostly used in radiology and nuclear medicine in order to investigate the anatomy and physiology of the body, and to detect pathologies including tumors, inflammation, neurological conditions such as stroke, disorders of muscles and joints, and abnormalities in the heart and blood vessels among others. Contrast agents may be injected intravenously or into a joint to enhance the image and facilitate diagnosis. Unlike CT and X-ray, MRI uses no ionizing radiation and is, therefore, a safe procedure suitable for diagnosis in children and repeated runs. Patients with specific non-ferromagnetic metal implants, cochlear implants, and cardiac pacemakers nowadays may also have an MRI in spite of effects of the strong<unk>  fields. This does not apply on older devices, details for medical professionals are provided by the device's manufacturer. Certain atomic nuclei are able to absorb and emit radio frequency energy when placed in an external<unk>  field. In clinical and research MRI, hydrogen atoms are most often used to generate a detectable radio-frequency signal that is received by antennas in close proximity to the anatomy being examined. Hydrogen atoms are naturally abundant in people and other biological organisms, particularly in water and fat. For this reason, most MRI scans essentially map the location of water and fat in the body. Pulses of radio waves excite the nuclear spin energy transition, and<unk>  field gradients localize the signal in space. 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. When inside the<unk>  field (B0) of the scanner, the<unk>  moments of the protons align to be either parallel or anti-parallel to the direction of the field. While each individual proton can only have one of two alignments, the collection of protons appear to behave as though they can have any alignment. Most protons align parallel to B0 as this is a lower energy state. A radio frequency pulse is then applied, which can excite protons from parallel to anti-parallel alignment, only the latter are relevant to the rest of the discussion. In response to the force bringing them back to their equilibrium orientation, the protons undergo a rotating motion (precession), much like a spun wheel under the effect of gravity. The protons will return to the low energy state by the process of spin-lattice relaxation. This appears as a<unk>  flux, which yields a changing voltage in receiver coils to give the signal. The frequency at which a proton or group of protons in a voxel resonates depends on the strength of the local<unk>  field around the proton or group of protons, a stronger field corresponds to a larger energy difference and higher frequency photons. By applying additional<unk>  fields (gradients) that vary linearly over space, specific slices to be imaged can be selected, and an image is obtained by taking the 2-D Fourier transform of the spatial frequencies of the signal (k-space). Due to the<unk>  Lorentz force from B0 on the current flowing in the gradient coils, the gradient coils will try to move producing loud knocking sounds, for which patients require hearing protection.
Physics of magnetic resonance imaging
Bone conduction
Instruments used in pathology
Gastrointestinal physiology
Composition of the human body
Anatomical terms of motion
Instruments used in radiology
Pain in animals