(MR) Resonance phenomenon resulting in the absorption and/or emission of electromagnetic energy by nuclei (for that reason also nuclear magnetic resonance) or electrons in a static magnetic field, after excitation by a suitable RF magnetic field.
The peak resonance frequency is proportional to the magnetic field, and is given by the Larmor equation. Only unpaired electrons or nuclei with a spin exhibit magnetic resonance. The absorption or emission of energy by atomic nuclei in an external magnetic field after the application of RF excitation pulses using frequencies, which satisfy the conditions of the Larmor equation.
The magnetic resonance phenomenon may be used in one of these ways:
By manipulation of the external field (application of gradient fields), the resonance frequency can become dependent on spatial location, and hence images may be generated (MRI).
The effect of the electron cloud in any atom or molecule is to slightly shield the nucleus from the external field, thus giving any chemical species a characteristic frequency. This gives rise to 'spectra' where nuclei in a molecule give rise to specific signals, thus facilitating the detection of individual chemicals by means of their frequency spectra (MRS)

Controlling the frequency spectrum (bandwidth) of a RF pulse (via tailoring) while imposing a magnetic field gradient on spins, such that only a desired region will have an appropriate resonant frequency to be excited.
Originally used to excite all but a desired region; now often used to select only a desired region, such as a plane, for excitation. Used without simultaneous magnetic field gradients, tailored RF pulses can be used to selectively excite a particular spectral line or group of lines. RF and gradient pulse combinations can be designed to select both spatial regions and spectral frequencies.

A generally smooth background curve, only the data above the baseline/background will be included in the calculation. Either the integrals or peak heights of the resonance spectral lines in the spectrum are measured. For BOLD imaging it is a non-activated image, in contrast to an activated image.

(MR mammography) Magnetic resonance imaging of the breast is particularly useful in evaluation of newly diagnosed breast cancer, in women whose breast tissue is mammographically very dense and for screening in women with a high lifetime risk of breast cancer because of their family history or genetic disposition.
Breast MRI can be performed on all standard whole body magnets at a field strength of 0.5 T - 1.5 Tesla. Powerful gradient strengths over 15 mT/m will help to improve the balance between spatial resolution, scanning speed, and volume coverage. The use of a dedicated bilateral breast coil is obligatory.
Malignant lesions release angiogenic factors that increase local vessel density and vessel permeability. Breast cancer is detectable due to the strong enhancement in dynamic breast imaging that peaks early (about 1-2 min.) after contrast medium injection. If breast cancer is suspected, a breast biopsy may be necessary to secure the diagnosis.

See also Magnetic Resonance Imaging MRI, Biopsy and MR Guided Interventions.

Requirements in breast MRI procedures:
For Ultrasound Imaging (USI) see Breast Ultrasound at Medical-Ultrasound-Imaging.com.

See also the related poll result: 'MRI will have replaced 50% of x-ray exams by'

MRI computer can be divided into central processing unit (CPU), consisting of instruction, interpretation and arithmetic unit plus fast access memory, and peripheral devices such as bulk data storage and input and output devices (including, via the interface, the spectrometer). The computer controls the RF pulses and gradients necessary to acquire data, and process the data to produce spectra or images. (Devices such as the spectrometer may themselves incorporate small computers.)

See also Digital to Analog Converter, Analog to Digital Converter, Transformer, Pulse Programmer, Array Processor, Detector.

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