A tomographic imaging plane bisecting the body into top and bottom parts.
[Chapter
10]
Birdcage Coil
An transmit and receive RF imaging coil which looks like a birdcage. [Chapter
9]
Chemical Shift
A variation in the resonance frequency of a nuclear spin due to the chemical
environment around the nucleus. Chemical shift is reported in ppm. [Chapter
4]
Coil
One or more loops of a conductor used to create a magnetic field. In MRI,
the term refers to the radiofrequency coil. [Chapter
9]
Complex Conjugate
Two complex numbers are complex conjugates of each other if their real parts are equal and their imaginary parts are opposite in sign. [Chapter 2]
Convolution
A mathematical operation between two functions. [Chapter
2]
Contrast
The difference in signal intensity of two tissues in an image. [Chapter
8]
Complex Data
Numerical data with a real and an imaginary component. [Chapter
2]
Continuous Wave (CW)
A form of spectroscopy in which a constant amplitude electromagnetic wave
is applied. [Chapter 3]
Contrast Agent
A chemical substance which is introduced into an organism to change the
contrast between two tissues. [Chapter
12]
Coordinate Transformation
A change in the axes used to represent some spatial quantity. [Chapter
2]
Coronal
A tomographic imaging plane bisecting the body into front and back parts.
[Chapter
10]
Dephasing Gradient
A magnetic field gradient used to dephase transverse magnetization. [Chapter
12]
Doubly balanced mixer
An electrical device, often referred to as a product detector, which is
used in MRI to convert signals from the laboratory frame of reference to
the rotating frame of reference. [Chapter
9]
Echo
A form of magnetic resonance signal from the refocusing of transverse magnetization.
[Chapter 4]
Echo Planar Imaging ( EPI )
An MRI sequence capable of producing images at video rates. [Chapter
12]
Echo Time ( TE )
The time between the 90 degree pulse and the maximum in the echo in a spin-echo
sequence. [Chapter 4]
Fast Spin-Echo
A multiple echo spin-echo sequence which records different regions of k-space
with different echos. [Chapter
12]
Field of View
The distance across an image, typically in centimeters.
The field of view in the frequency and phase encoding directions may be different. [Chapter
7]
Figure-8 Coil
A magnetic field gradient coil shaped like the number eight. [Chapter
9]
Free induction decay ( FID )
A form of magnetic resonance signal from the decay of transverse magnetization.
[Chapter 4]
Fourier transform ( FT )
A mathematical technique capable of converting a time domain signal to
a frequency domain signal and vice versa. [Chapter
5]
Frequency Encoding Gradient (Gf)
A magnetic field gradient applied in an imaging sequence during the acquisition
of a signal which encodes spins with different frequencies dependent on
their position in the direction of this gradient. [Chapter
6]
Functional Imaging
An imaging technique based on echo-planar imaging which is used to determine
brain function. [Chapter
12]
Gradient ( G )
A variation in some quantity with respect to another. In the context of
MRI, a magnetic field gradient is a variation in the magnetic field with
respect to distance. [Chapter
6]
Gradient Echo
A form of magnetic resonance signal from the refocusing of transverse magnetization caused by a the application of a specific magnetic field gradient. [Chapter
8]
Gradient Recalled Echo Sequence
An MRI sequence producing signals called gradient echoes as a result of
the application of a refocusing echo. [Chapter
8]
Gyromagnetic Ratio
The ratio of the resonance frequency to the magnetic field strength for
a given nucleus. [Chapter
3]
Imaginary
The component of a signal perpendicular to the real signal. [Chapter
8]
Imaging Sequence
A specific set of RF pulses and magnetic field gradients used to produce
an image. [Chapter 2]
Inferior
The direction towards the feet in an anatomical coordinate system. [Chapter
10]
Inversion Recovery Sequence
An pulse sequence producing signals which represent the longitudinal magnetization
present after the application of a 180o
inversion RF pulse. [Chapter
4, In imaging: Chapter
8]
Inversion Time ( TI )
The time between the inversion pulse and the sampling pulse(s) in an inversion
recovery sequence. [Chapter
4]
Isocenter
A location in an imaging magnet assigned the coordinates (x,y,z)=0,0,0
and having magnetic field strength Bo and resonance
frequency no.
[Chapter 6]
Isotope
Two atoms are isotopes if they have the same number of protons and electrons, but a different number of neutrons.
K-Space
That image space reprsented by the time and phase raw data. The Fourier
transform of k-space is the magnetic resonance image. [Chapter
5]
Larmor frequency
The resonance frequency of a spin in a magnetic field. The rate of precession
of a spin packet in a magnetic field. The frequency which will cause a
transition between the two spin energy levels of a nucleus. [Chapter
3]
A table (or function) used to relate intensity of a screen pixel to the
data value of that pixel in the image. [Chapter
10]
Lorentzian Lineshape
A function obtained from the Fourier transform of an exponential signal.
[Chapter 5]
Magnitude
The length of a magnetization vector. In MRI the square root of the sum
of the squares of Mx and My components
of transverse magnetization. [Chapter
2]
Magnetic Resonance Angiography (MRA)
An imaging technique which images flowing blood. [Chapter
12]
Magnetic Resonance Imaging (MRI)
An imaging technique based on the principles of NMR. [Chapter
1]
Net Magnetization Vector
A vector representing the sum of the magnetization from a spin system.
[Chapter 3]
Nuclear Magnetic Resonance (NMR)
A spectroscopic technique used by scientists to elucidate chemical structure
and molecular dynamics. [Chapter
1]
Oblique Imaging
An imaging technique which produces images along oblique planes between
the conventional X, Y, and Z axes. [Chapter
8]
Phantom
An anthropogenic object that can be imaged to test the performance of a magnetic resonance imaging system. [Chapter
9]
The direction towards the back in an anatomical coordinate system. [Chapter
10]
Precess
A rotational motion about an axis of a vector whose origin is fixed at
the origin. [Chapter 3]
Proportionality Constant
A constant used to convert one set of units to another. [Chapter
8]
Pulse Sequence
A series of RF pulses and/or magnetic field gradients applied to a spin
system to produce a signal representative of some property of the spin
system. [Chapter 4]
Quadrature Detection
Detection of Mx and My simultaneously
as a function of time. [Chapter
9]
r-Weighted Image
A magnetic resonance image where the contrast is predominantly dependent
on spin density. [Chapter
8]
Radio Frequency
A frequency band in the electromagnetic spectrum with frequencies in the
millons of cycles per second. [Chapter
3]
Raw data
The Mx and My data as a function
of phase and time from an imaging sequence. This is also called k-space
data. [Chapter 10]
Real
The component of a signal perpendicular to the imaginary signal. [Chapter
2]
Relaxometry
The measurement and study of spin-lattice and spin-spin relaxation times.
Repetition Time
The time between repetitions of the basic sequence in an imaging sequence.
[Chapter 4]
Resonance
An exchange of energy between two systems at a specific frequency. [Chapter
3]
RF Pulse
A short burst of RF energy which has a specific shape.
Rotation Matrix
A matrix used to describe the rotation of a vector. [Chapter
3]
Saddle Coil
A coil geometry which has two loops of a conductor wrapped around opposite
sides of a cylinder. [RF: Chapter
9]
Sagittal
A tomographic imaging plane bisecting the body into left and right parts.
[Chapter 10]
Single Turn Solenoid
An transmit and receive RF imaging coil which, in general, has a cylindrical
shape. [Chapter 9]
Specific Absorption Rate (SAR)
The number of Watts of RF energy per kilogram of body weight in an imaging
sequence. [Chapter 9]
Spin
A fundamental property of matter responsible for MRI and NMR. [Chapter
3]
An MRI sequence whose signal is an echo resulting from the refocusing of
magnetization after the application of a 90o and 180o
RF pulses. [Chapter 4.
In Imaging: Chapter 8]
Spin-Lattice Relaxation
The return of the longitudinal magnitization to its equilibrium value along
the +Z axis. [Chapter 3]
Spin-Lattice Relaxation Time ( T1
)
The time to reduce the difference between the longitudinal magnitization
and its equilibrium magnetization by a factor of e. [Chapter
3]
Spin Packet
A group of spins experiencing the same magnetic field. [Chapter
3]
Spin-Spin Relaxation
The return of the transverse magnitization to its equilibrium value, zero.
[Chapter 3]
Spin-Spin Relaxation Time
The time to reduce the transverse magnetization by a factor of e. [Chapter
3]
To have no resistance. A perfect superconductor can carry an electrical
current without losses. [Chapter
10]
Superior
The direction towards the head in an anatomical coordinate system. [Chapter
9]
Surface Coil
An receive only RF imaging coil which, in general, fits against the surface
of the object being imaged. [Chapter
9]
T1-Weighted Image
A magnetic resonance image where the contrast is predominantly dependent
on T1. [Chapter
8]
T2-Weighted Image
A magnetic resonance image where the contrast is predominantly dependent
on T2. [Chapter
8]
T2*
Pronounced T-2-star, is the spin-spin relaxation time composed of contributions
from molecular interactions and inhomogeneities in the magnetic field.
[Chapter 3]
Timing Diagram
A multiaxis plot of some aspects of a pulse sequence as a function of time.
[Chapter 4]