A small linear magnetic field applied in addition to (superimposed on) the large static magnetic field in a MRI scanner. The strength (amplitude) and direction of the gradient fields change during the scan, which allows each small volume element (voxel) within the imaging volume to resonate at a different frequency. In this way, spatial encoding may be performed.

MRI hardware includes the electrical and mechanical components of a scanning device.
The main hardware components for the MRI machine are:
The magnet establishing the B0 field to align the spins.
Within the magnet are the gradient coils for producing variations in B0 in the X, Y, and Z directions to make a localization of the received data possible.
Within the gradient coil or directly on the object being imaged is the radio frequency (RF) coil. This RF coil is used to establish the B1 magnetic field necessary to excite the spinning nuclei. The RF coil also detects the signal emitted from the spins within the object being imaged.
The RF amplifier increases the power of the pulses.
The analog to digital converter converts the received analog raw data into digital values.
Depending on the design of the device and the body part being imaged the patient is positioned inside the magnet (e.g. on a movable table or standing upright).
The MRI scan room is surrounded by a RF shield (Faraday cage).
In addition, a computer console, a display, and a film printer belong to the MRI equipment.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'

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Hitachi Medical Systems America, Inc. (HMSA), was a major provider of magnetic resonance imaging systems in the United States. Hitachi had more than 2300 installed permanent magnet MR imaging systems worldwide. As a full-line supplier of medical imaging equipment in Japan, Hitachi Medical Corporation (HMC) founded HMSA to provide a direct link to the U.S. marketplace. Altaireâ„¢ , the open MR system from Hitachi, extends the family of open MRI products.

In December 2019 Japan's Fujifilm announced the acquisition of Hitachi's diagnostic imaging business for 179 billion yen ($1.63 billion). This includes Hitachi’s CT, MRI, X-ray, and ultrasound imaging operations, also its electronic health record business. Fujifilm expects the deal to close in July 2020 subject to regulatory clearances.

MRI Scanners:

0.3T to 0.7T:
1.5T:

IMRIS® is a Canadian manufacturer of Magnetic Resonance Imaging Systems for use in neurosurgical operating rooms. The 1.5T intra-operative system, developed by IMRIS, is the only system of its kind in the world. This patented, intra-operative system, is designed so that the magnet moves over the patient for imaging (before, during and after surgery), and then is retracted to allow complete surgical access to the patient.

MRI Scanners:

1.5T:

ISOL Technology participated in the pioneering the Korea's MRI development since the early 1980's. In spite of the rapidly changing business environment, and severe competition in the overall medical market, ISOL Technology has grown steadily each year and has established itself as a major provider of Magnetic Resonance(MR) Imaging Systems in Korea.
ISOL Technology also has the largest market share of the domestic bone densitometry equipment sales and is currently in the early stages of development of the 61 channel MCG (Magnetocardiography) system with the R and D funds from the Korean Ministry of Commerce, Industry and Energy.

MRI Scanners:

0.35T to 0.5T:
1.5T:
3T: