The principal advantage of MRI at high field is the increase in signal to noise ratio. This can be used to improve anatomic and/or temporal resolution and reduce scan time while preserving image quality. MRI devices for whole body imaging for human use are available up to 3 tesla (3T). Functional MRI (fMRI) and MR spectroscopy (MRS) benefit significantly. In addition, 3T machines have a great utility in applications such as TOF MRA and DTI. Higher field strengths are used for imaging of small parts of the body or scientific animal experiments. Higher contrast may permit reduction of gadolinium doses and, in some cases, earlier detection of disease.
Using high field MRI//MRS, the RF-wavelength and the dimension of the human body complicating the development of MR coils. The absorption of RF power causes heating of the tissue. The energy deposited in the patient's tissues is fourfold higher at 3T than at 1.5T. The specific absorption rate (SAR) induced temperature changes of the human body are the most important safety issue of high field MRI//MRS.
Susceptibility and chemical shift dispersion increase like T1, therefore high field MRI occasionally exhibits imaging artifacts. Most are obvious and easily recognized but some are subtle and mimic diseases. A thorough understanding of these artifacts is important to avoid potential pitfalls. Some imaging techniques or procedures can be utilized to remove or identify artifacts.

See also Diffusion Tensor Imaging.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

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:

From Philips Medical Systems;
Philips continues to expand the frontiers of utra high field MRI with the introduction of the new Intera Achieva 3.0T™. Its powerful future-safe platform shares all the advantages of the Achieva family and covers applications throughout the whole body.

The Larmor precession frequency is the rate of precession of a spin packet under the influence of a magnetic field. The frequency of an RF signal, which will cause a change in the nucleus spin energy level, is given by the Larmor equation. The frequency is determined by the gyro magnetic ratio of atoms and the strength of the magnetic field. The gyromagnetic ratio is different for each nucleus of different atoms.
The stronger the magnetic field, the higher the precessional frequency. If an RF pulse at the Larmor frequency is applied to the nucleus of an atom, the protons will alter their alignment from the direction of the main magnetic field to the direction opposite the main magnetic field. As the proton tries to realign with the main magnetic field, it will emit energy at the Larmor frequency. By varying the magnetic field across the body with a magnetic field gradient, the corresponding variation of the Larmor frequency can be used to encode the position. For protons (hydrogen nuclei), the Larmor frequency is 42.58 MHz/Tesla.

See also Larmor Equation.

From Siemens Medical Systems;
The MAGNETOM 7T is designed as an open research platform. 7T MRI provides anatomical detail at the submillimiter scale, enhanced contrast mechanisms, outstanding spectroscopy performance, ultra-high resolution functional imaging (fMRI), multinuclear whole-body MRI and functional information.
This ultra high field (UHF) MRI device is a research system and not cleared, approved or licensed in any jurisdiction for patient examinations.