MR glossary Flashcards
_____________ is a term describing the containment of the static magnetic field through the use of secondary coils attached around the MRI scanner.
Active shielding
: ____________ is a term used to describe the adjustment of the current within the shim coils on a per patient or per sequence basis.
Active shimming
3 : __________ are reconstructed from diffusion weighted images with multiple b-values, and corresponds to the spatially distributed diffusion coefficients of the target tissues
ADC images
: ____________ occurs when tissue outside the Field of View is undersampled, causing a misregistration of anatomical location, in the phase direction, but on the opposite side of the anatomical location, also known as wrap-around artifact
Aliasing artifact
The ____________ is part of the computer system that converts the analog acquired MR signal into a digital signal
Analog-to-digital converter (ADC)
: An ________ comprises a multiprocessor that is switched in sequence and in parallel while simultaneously performing a computing task.
Array processor
An _____________ is one that has uneven measurements, with regards to the phase, frequency and slice thickness dimensions.
Anisotropic voxel
____________ are signal misrepresentations that do not correspond to the spatial location of the specific tissue imaged
Artifacts
: _______________ is defined as the range or spectrum of frequencies (minimum to maximum processed frequency)of a pulse sequence acquired by an RF system.
Bandwidth
The ____________ is an integrated part of the magnet design that acts as its own transceiver coil, with large FOV capabilities, but lacking the high SNR of localized coils
Body coil
The __________ is defined as a factor in diffusion weighted imaging; the higher the factor, the stronger the diffusion weighting.
B-value
The ___________ is defined as the static main magnetic field of an MR system.
B0
The __________ is the alternating magnetic field generated by the RF in a transceiver coil
B1
_____________ prevents or reduces motion artifacts in an MR image caused by the beating heart or pulsating blood flow and enables the images to be acquired synchronized to movement
Cardiac triggering
________________ is due to the difference in resonant frequencies between fat and water, causing a phase shift in voxels containing fat and water
Chemical shift artifact
Describing image display, the ________ function scrolls through the entire sequence’s images, giving the appearance of CSF flowing or cardiac movement, from the cycle of the images acquired.
Cine
: __________ can be defined as the signal strength differences between two adjacent tissue types.
Contrast
_______________ utilizes the reduced T1 relaxation time of blood through the use of an intravenously injected Gadolinium contrast agent
CE MRA
: _______________ occurs when slices are positioned too close together, causing signals from adjacent slices to affect one another
Cross talk artifact
_________ occurs after initial RF application, causing phase differences to appear between precessing spins, resulting in decay of transverse magnetization
Dephasing
: ___________ is an effect resulting in a slightly weakened magnetic field when a substance is introduced into it. This material is considered to have a negative magnetic susceptibility.
Diamagnetism
An ________ is the MR signal generated by an RF or a gradient pulse
Echo
: _________ is simply defined as the distance between echoes.
Echo spacing
The time between the excitation pulse of a sequence and the resulting echo used as the MR signal is known as:
Echo time
A technique used to suppress fluids, utilizing a long echo time coupled with a long Inversion time is known as __________.
FLAIR
__________ materials, such as iron, contain unpaired electrons, each with a small magnetic field of its own, that align readily with each other in response to an external magnetic field.
Ferromagnetic
The mathematical process of converting raw data into an image suitable for display is known as _________.
Fourier transform
The angle to which the longitudinal magnetization is tipped into the transverse plane, following the initial RF excitation pulse, is known as ________.
Flip angle
_________ is defined as the number of times that a periodic function or vibration repeats itself in a specified time. It is usually measured in hertz (Hz).
Frequency
The timing the collection of MR data to physiological motion in order to minimize motion artifacts is known as:
Gating
The linear increased or decreased change in the magnetic field of a certain orientation is defined as a _____
Gradient
: ________ is defined as the ratio of the magnetic moment (field strength) of a rotating charged particle, such as an electron, to its angular momentum (frequency).
Gyromagnetic ratio
What is the term for the echo generated by switching a pair of dephasing and rephasing gradients, without the use of a 180° refocusing pulse?
Gradient echo
An MR sequence that begins with 180º RF inverting pulse followed by 90º RF excitation pulse, then 180º RF refocusing pulse is known as
: Inversion recovery
: _________ is known as the specific frequency at which magnetic resonance in a nucleus can be excited and detected, and varies directly with magnetic field strength.
Larmor frequency
_________ is the magnetic and thermal environment through which nuclei exchange energy in longitudinal (T1) relaxation
Lattice
___________ is defined as the Z component of the net magnetization vector in the direction of the static magnetic field
Longitudinal magnetization
MR technique utilized to image flowing blood and specific vasculature structures
Magnetic resonance angiography (MRA)
MR technique which quantitatively assesses the mechanical properties of tissues, based on the propagation of shear waves:
Magnetic resonance elastography (MRE)
MR technique generating a spectrum of metabolites in a specific volume of interest:
Magnetic resonance spectroscopy (MRS)
__________ is defined as the magnitude and direction of the magnetization resulting from the collection of atomic nuclei.
: Net magnetization vector
What is an uncharged neutral particle located in the nucleus of most atoms which serves as a stabilizer?
Neutron
: _________ is defined as a loss of resolution due to excessively large voxels, typically caused by slices that are too thick
Partial volume averaging
An artificial object that can be imaged to test the performance and quality of a magnetic resonance system would be
Phantom
________ is comprised of the components of the magnetization in the imaging object after excitation, sampled from the receiver coil signal and stored as a function of time during the data acquisition of an MR imaging sequence
Raw data
_________ gradient – magnetic field gradient applied during the moment when the echo is formed
Readout
_________ is defined as an event in a superconducting MR system causing a loss of superconductivity, a rapid loss of the magnet cryogens
Quench
Short TI Inversion Recovery: a version of the Inversion Recovery pulse sequence where the inversion time (TI) is set to ______ times the T1 of fat, nulling the signal from fat at the specific field strength in which it’s being acquired
0.69
MRA technique relying on flow related enhancement to distinguish between stationary spins and flowing spins:
Time of flight
_________ is defined as a volume element with 3-Dimensional characteristics
Voxel
