This is a list of some of the commonly used terms in MRI.
Adiabatic pulses are special RF pulses used when the RF field is inhomogeneous, as one might see with using a surface coil rather than a volume coil for excitation of spins. The flip angles produced with conventional RF pulses are sensitive to the B1 or RF field homogeneity. The flip angles produced with adiabatic pulses are relatively insensitive. These special pulses are produced by sweeping the frequency of an irradiating RF pulse through the Larmor frequency. Conventional pulses use a constant frequency pulse at the Larmor frequency. The disadvantage of adiabatic pulses are that they are more difficult to produce and they take more time to produce the desired flip angle.
The description of the imaging factors used during an imaging acquisition, commonly printed around the border of MR images. These factors may include repetition time, echo time, number of averages, field of view, acquisition matrix size, and slice thickness.
An array processor is a common accessory to the computer system of an MRI machine. It functions to speed up numeric calculations, such as the Fourier transformation used to reconstruct images and spectra.
B1 is the symbol used to represent the radio frequency field of the MRI system. The B1 field is produced by the RF coil at the Larmor frequency.
The bloch equations are used in the classical physics description of the behavior of the macroscopic magnetization vectors.
Bo (B zero) is the symbol used to represent the constant (main) magnetic field of the MRI system. It is usually expressed in units of Tesla (10,000 gauss or about 20,000 times the magnetic field of the earth).
An insulated container for holding liquified gases, i.e., cryogens. May also be called a cryostat.
A musical instrument invented by the aborigines of Australia. It is constructed from a hollowed out log and makes a single tone.
Free induction decay. This is the sinusoidal signal generated by spins in the x-y plane that decays exponentially with time.
An electrical conductor such as a copper mesh or an aluminum sheet that is used to block out electric fields. Most MRI rooms are surrounded by a Faraday shield to keep radio waves from coming into the room, and MR radio waves from leaving the room.
A mathematical procedure used in MR that converts a time-domain signal into a frequency- or spatial-domain signal or image. It is analogous to the way that our ear distinguishes or separates out separate sounds or frequencies from noise we hear. Our eyes do not work this way. If we see a mixture of blue and yellow we see the color green, not the original blue and yellow.
A gradient amplifier supplies power to a set of gradient coils, providing the variation in magnetic field strength required to obtain images and perform localization. MRI systems therefore require three gradient amplifiers, one for each set of gradient coils: x, y, and z. Gradient amplifier may use large amount of power and frequently require cooling with chilled water or forced air flow.
K-space is an imaginary space whose coordinates are in terms of phase and frequency for conventional imaging and in terms of phase in 2 or 3 dimensions for 2-D and 3-D chemical shift imaging. The K-space matrix is to obtain the familiar spatial dimensions.
The Larmor frequency is the frequency or rate of precession of the nuclear magnetic moment (spins) and is proportional to the magnetic field strength as shown in the Larmor equation: f= -gBo/2pi where f is the Larmor frequency in Hertz, g is the gyromagnetic ratio of the nucleus, and Bo is the magnetic field strength.
A phantom is an object of known size and composition (such as a bottle of saline) that is used to test the functioning of an MRI machine.
An abbreviation for "picture element"; the rectangles or squares that make up a digital image in MRI, CT, digital fluoroscopy and radiography.
Unexpected loss of superconductivity in a superconducting magnet that causes heating and very rapid vaporization of the cryogens such as liquid helium. This can cause damage to the magnet and can force the atmosphere out of the scanner room potentially causing anoxic conditions.
The RF transmitter in an MRI scanner is a mini radio station that include an amplifier and tuning circuits that supply radio frequency power to the RF coil inside the magnet. RF transmitters in whole body imagers are commonly rated at about 20kW; comparable in power to an actual radio station.
The density of resonating spins, e.g. protons, in a region of interest. "Proton density" spin echo images come close to imaging the spin density.
A substance, usually a metal alloy, whose electrical resistance abruptly drops to zero at low temperatures. MRI magnets commonly use titanium-niobium wires imbedded in a larger copper wire that is cooled with liquid helium to about 4 degrees absolute. The copper acts to conduct away heat in case a occurs and also acts as an insulator at superconducting temperatures.
A mythical creature that looks like a horse with a single horn on it's forehead.
A vector is a quantity having both magnitude and direction, that is frequently represented with an arrow.
An abbreviation for volume element; a three dimensional rectangular solid contributing signal to the intensity of a in an image.