MRI GLOSSARY/TERMINOLOGY Flashcards
any disease producing agent, especially a virus, bacterium or other
microorganism
Pathogen
the cause or origin of a disease
Etiology
refers to the practice, in medicine, of avoiding contact with patients’ bodily fluids, by means of the wearing of nonporous articles such as medical gloves, goggles and face shields, regardless of any known transmittable
diseases.
Universal Precautions
stage of disease when symptoms are not present.
Latent disease phase
Oral, sublingual, or rectal delivery
Enteral
Intravenous (IV), Intramuscular (IM), Subcutaneous (SC);
any route other than by mouth (PO) or rectal
Parenteral
infections acquired during a hospital stay or while
receiving some type of medical treatment.
Nosocomial infections
is an object that carries microorganisms from one person to another via
indirect contact.
A fomite
Diseases, such as malaria, in which microorganisms are transferred via an insect, come under the classification of
Vector borne infections
is a white blood cell.
A leukocyte
occurs when microorganisms enter the body and fluids carrying white blood cells travel to the site to destroy them.
Phagocytosis
The source of infection where pathogens thrive in numbers sufficient to cause a threat is known as a
reservoir
the removing or killing of most microorganisms
Medical asepsis
the removing or killing of all microorganisms completely
Surgical asepsis
“the thing speaks for itself”, or, a doctrine or legal ruling that permits the presumption that a defendant was negligent even without direct evidence of how any defendant behaved.
Res Ipsa Loquitur
“let the master answer” is a legal doctrine which states that, in many circumstances, an employer is responsible for the actions of employees performed within the course of their employment.
Respondeat Superior
“not to pick up something” is a failure to exercise the care that a reasonably prudent person would exercise in like circumstances.
Negligence
professional negligence by act or omission by a health care provider in which the treatment provided falls below the accepted standard of practice in the medical community and causes injury or death to the patient, with most cases involving medical error, simply defined as a failure to render proper services through reprehensible ignorance or negligence
Medical malpractice
in common law jurisdictions, is a wrong that involves a breach of
a civil duty (other than a contractual duty) owed to someone else. It is
differentiated from a crime, which involves a breach of a duty owed to
society in general.
**And may be defined as a personal injury; or as “a civil action other than a breach of contract.”
A Tort
law that pertains to private legal rights and matters
Civil law
law that pertains to crimes and their punishment
Criminal law
a crime that is punishable by a fine and/or up to one year
in jail
Misdemeanor
a crime that is punishable by a fine and prison time that can exceed one year in jail
Felony
a medical or psychological treatment guideline, and can be general or specific.
A standard of care
event or reaction is one caused by a medical professional, whether it be negligence, drug interactions, or even erroneous medical advice.
An iatrogenic
can mean something that is a hindrance or puts an individual
or group at a disadvantage, or something that someone is responsible
for, or something that increases the chance of something occurring.
A liability
In law a person is said to be legally _______ when they are financially and
legally responsible for something
Liable
a controversial form of consent which is not expressly granted by a person, but rather inferred from a person’s actions and the facts and circumstances of a particular situation (or in some cases, by a person’s silence or inaction).
Implied consent
is a phrase often used in law to indicate that the consent a person gives meets certain minimum standards.
Informed consent
is an instrument (or document) that allows a patient to appoint an agent to make health care decisions in the event that the primary individual is incapable of executing such decisions.
A Health Care Proxy
is to only do good and to prevent evil or harm.
Beneficence
a term describing the containment of the static magnetic fringe field through the use of secondary coils attached around the MRI scanner
Active shielding
a term used to describe the adjustment of the current within the shim coils on a per/patient or per/sequence basis, for the purposes of achieving uniform fat suppression or optimal prescan calibrations. A well shimmed FID is the desired end result of a good active shim calibration
Active shimming
are reconstructed from diffusion weighted images with multiple bvalues, and correspond 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
equates to signal height or strength; the larger the amplitude, the
larger the number of protons
Amplitude
being continuous, or having a continuous range of values
Analog
is part of the computer system that converts the analog acquired MR signal into a digital signal
Analog-to-digital converter (ADC)
is a voxel with uneven measurements, with regards to the phase, frequency and slice thickness dimensions
anisotropic voxel
comprises a multiprocessor that is switched in sequence and in
parallel while simultaneously performing a computing task
array processor
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
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
The body coil
is defined as a factor in diffusion weighted imaging; the higher the factor, the stronger the diffusion weighting
The b-value
is defined as the static main magnetic field of an MR system
The B^0
field
is the alternating magnetic field generated by the RF in a transceiver
coil, perpendicular to B0
The B1field
prevents or reduces motion artifacts in the MR image caused by
the heartbeat or pulsating blood flow and enables the images to be acquired
synchronized to cardiac 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
function scrolls through the entire sequence’s images, giving the appearance of CSF flowing or cardiac movement, from the cycling of the images acquired; a “movie” function of scrolling images
the Cine
the physiological reaction to being confined in a small space or location, the fear of being trapped
Claustrophobia
maintaining a constant state of “in-phase” relationships between protons; located at the same phase cycle simultaneously
Coherent –
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 (Contrast-enhanced MR angiography)
Circularly polarized transmission or receiver coil with two orthogonal
transmission and/or receiver channels, also known as a quadrature coil. This yields better signal-to-noise than a linear coil
CP COIL
occurs when slices are positioned too close together, causing signals from adjacent slices to affect one another. This affects T1 contrast, and is remedied by utilizing an interleaved slice profile or by increasing slice gap
Cross-talk artifact
are the liquids that are supercooled (4° Kelvin) in order to maintain the
superconductivity of the magnet coils
Cryogens
Formula for the temporal change of the magnetic field, especially
important with regards to patient safety in relation to gradients. This is due to the electrical field generated in conductive materials, as in human tissue
dB/dt
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
the movement of atoms or molecules from an area of higher
concentration to an area of lower concentration. (Brownian motion)
Diffusion
displays the mobility of water molecules in all three
coordinates
Diffusion tensor
A technique utilizing the differences in resonant frequencies of fat and
water separating the two tissues, acquiring each separately, then adding the two to yield a water-only image (fat suppression), then subtracting the two to yield a fat-only image
DIXON
A spin echo sequence with two echoes, two generated images per
slice location
Double Echo
The time which the gradient system can be run at maximum power
DUTY CYCLE
Basic T1 perfusion imaging (pituitary or prostate dynamic sequences, longer acquisition times/dynamic compared to DSC)
Dynamic Contrast Enhancement – refers to DCE,
better known as T2* gradient echo Perfusion imaging, utilized in Brain Perfusion studies
Dynamic Susceptibility Contrast – refers to DSC
The MR signal generated by an RF or a gradient pulse
ECHO
Very fast MR imaging technique where the complete image is acquired using a single selective excitation pulse, field gradients are periodically switched to generate a series of gradient echoes
Echo Planar Imaging
Distance between two echoes, as in Fast Spin Echo or EPI sequences. The shorter the echo spacing, the more compact the sequence timing and few artifacts result
Echo Spacing
The time between the excitation pulse of a sequence and the resulting echo used as the MR signal
Echo Time (TE)
Multiple echoes in sequence, each obtaining rows of k-space, shortening overall scan time, also reducing SNR with each additional echo train
Echo Train
The electrical currents generated in a conductor by changing
magnetic fields or movement of the conductor within the magnetic field
Eddy Currents
In a pulse sequence, the contrast and overall SNR of an image is determined by the position of the echo when the phase encoding gradient has the smallest amplitude. At this time, the echo signal has the strongest signal and undergoes minimal dephasing.
Effective TE
The time between the initial RF excitation pulse and this time is the effective echo time (TEeff)
referring to prospective cardiac triggering techniques, the patient’s
heart rate controls the TR, or termed the effective or available TR (TReff), according to the beats per minute (BPM) factor
Effective TR
The electrical voltage created in a receiver coil as a result of a temporal change in the magnetic field
Electromagnetic Induction
Number of gradient echoes in an Echo Planar sequence acquired after the initial excitation pulse; equating to the scan time acceleration factor
EPI factor
(an EPI factor of 64 is 64 times faster than a routine gradient echo sequence)
The radiofrequency (RF) pulse used to disturb the equilibrium of the Net Magnetization Vector; the higher the energy of excitation, the greater the flipped angle of magnetization
Excitation pulse
Algorithm for fast reconstruction of raw data into an MR image
Fast Fourier Transformation(FFT)
An image yielding only the signals from fat protons in an image
and suppressing the signal from water; usually a “phase” of the Dixon technique
Fat-only Image
An MR technique used to suppress signal from fat protons, yielding a “water-only” image, utilizing a chemically selective presaturation pulse
Fat Saturation
the process of utilizing specific sequence parameters to null signal from fat in the MR sequence, as in STIR, for example
Fat Suppression
the property of being strongly attracted to either pole of a magnet. Ferromagnetic 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
Ferromagnetism
the base size of the slice to be acquired, measured in dimensions of phase (short axis of anatomy) and frequency (long axis)
Field of View
A technique used to suppress fluids, utilizing a long echo time (TE) coupled with a long Inversion Time (TI)
FLAIR – FLuid Attenuated Inversion Recovery
the angle to which the longitudinal magnetization is tipped into the transverse plane, following the initial RF excitation pulse
Flip Angle
an MR technique used to reduce artifacts from spin phase effects through the use of additional gradient pulses
Flow Compensation/Gradient
Moment Nulling
the invisible lines of force that extend around a magnetic field, with the
greatest strength/force being at the two poles/ends of the magnet
Flux
the mathematical process of converting raw data into an image suitable for display
Fourier Transform
a time-based electrical signal that is detected in a nuclear magnetic resonance spectrometer, that is produced by induction from the motion
of the magnetic moments of nuclei, that decays with time (T2*), that can be
converted to a more conventional frequency-based signal using analysis by Fourier transforms
Free Induction Decay; abbreviated FID
the number of times that a periodic function or vibration repeats itself in a specified time. It is usually measured in hertz (Hz), where 1 Hz = 1 cycle per second
Frequency
the process of locating an MR signal in one dimension by applying a magnetic field gradient along that dimension during the period when
the signal is being received, utilizing differences in frequencies along the same row in order to spatially differentiate one location from another
Frequency Encoding
A non-toxic paramagnetic contrast agent used in MR imaging. The
infusion of❓ based paramagnetic contrast agents (GBCA’s)shortens the T1 (and T2) times of tissue, dependent upon concentration
Gadolinium
timing the collection of MR data to physiological motion in order to
minimize motion artifacts
Gating
unit of magnetic induction in the centimeter-gram-second system of physical units. Old unit for magnetic field strength.
Gauss
Today, the unit Tesla (T) is used (1 Tesla = 10000 Gauss). The 5 Gauss line is currently used as a safety standard for the exclusion of implanted metallic devices
the linear increased or decreased change in the magnetic field of a
certain orientation.
Gradients
Coils used to generate magnetic gradient fields.
Gradient Coils
Echo generated by switching a pair of dephasing and rephasing
gradients, without the use of a 180° refocusing pulse (seen in spin echo sequences)
Gradient Echo
the ratio of the magnetic moment (field strength) of a rotating charged particle, such as an electron, to its angular momentum (frequency).
Gyromagnetic Ratio
The value of the gyromagnetic ratio of hydrogen is 42.57 MHz/Tesla
Uniformity of the main magnetic field; a magnetic field is considered homogenous when it has the same field strength across the entire field
Homogeneity
Due to the symmetry of the matrix to be sampled, a little more than
half of the raw data is necessary to be acquired, reconstructing the remaining data to complete the image, greatly reducing scan time
Half-Fourier
Mathematical computation converting the collected raw data signals into images using Fourier Transform
Image Reconstruction
The ability to differentiate adjacent tissue structures. Higher
image resolution increases detection of smaller pathologies.
Image Resolution
Resolution increases with a smaller FOV, higher matrix, and thinner slices
Lack of homogeneity or uniformity in the main magnetic
field
Inhomogeneity
Also referred to as Time of Flight (TOF) MR angiography
Inflow technique
MR sequence that begins with 180º RF inverting pulse followed by 90º RF excitation pulse, then 180º RF refocusing pulse
Inversion Recovery
The time between the initial 180º RF and the 90º RF excitation pulse in an Inversion Recovery sequence
Inversion time (TI)
Atomic nuclei that contain the same number of protons but differ in the
number of neutrons in the nucleus of the atom
Isotope
A location within the magnet bore assigned coordinates X-0, Y-0, Z-0,
and having magnetic field strength B0 and center frequency relative to field
strength
Isocenter
data acquisition matrix containing raw image data prior to image processing.
k-space
an equation stating that the frequency of precession of nuclear magnetic moment is directly proportional to the product of the magnetic field strength(B0) and the gyromagnetic ratio
Larmor equation
the specific frequency at which magnetic resonance in a nucleus can be excited and detected, and varies directly with magnetic field strength
Larmor frequency
the magnetic and thermal environment through which nuclei exchange
energy in longitudinal (T1) relaxation
Lattice
The Z component of the net magnetization vector in the direction of the static magnetic field. Following RF excitation, this vector returns to its equilibrium value at a rate characterized by the time constant T1
Longitudinal magnetization
Return of longitudinal magnetization to its equilibrium value after RF excitation due to the exchange of energy between the nuclear spins
and the lattice
Longitudinal relaxation
Magnetic lines of force which extend from a north and south pole to form a closed loop around the outside of a magnetic material. A magnetic field
has properties of both magnitude (strength) and direction
Magnetic field
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)
an MR technique using a series of echoes following a single excitation pulse, usually in the form of 180º RF pulses that generate images
Multi-echo imaging
a vector which represents the sum of the magnetization from a spin system; the magnitude and direction of the magnetization resulting from the collection of atomic nuclei
Net magnetization vector (NMV)
an uncharged neutral particle located in the nucleus of most atoms
which serves as a stabilizer
Neutron
how many times each line of k-space data is acquired during the scan, or how many times each slice is repeated to gain signal and reduce noise, improving SNR
NEX – Number of Excitations
NSA – Number of Signals Averaged: see NEX
The core or center part of an atom, which contains protons having a
positive charge and neutrons having no electrical charge, except in hydrogen
where the nucleus is a single proton
Nucleus
An imaging technique which produces images along planes that are not
perpendicular to the X,Y, or Z axes
Oblique
a plane or section that is perpendicular to the X,Y, or Z
axes
Orthogonal
A scan time acceleration technique which requires the use of a
phased array coil to reconstruct an image in less time than conventional imaging
Parallel Imaging
property of magnetism signifying weak magnetic properties due to its unpaired electrons.
Paramagnetic
IV Gadolinium contrast is an example of a paramagnetic substance
a loss of resolution due to excessively large voxels, typically caused by slices that are too thick
Partial volume averaging
Lining the MR room with steel or other ferromagnetic plating, thus reducing the scope and distance of the fringe field
Passive shielding
Shimming the magnetic field with metal pieces either within or on the outer surface of the magnet bore, for the purpose of a more homogenous magnetic field
Passive shimming
A magnet designed with blocks of ferromagnetic materials to generate a magnetic field, typically heavy in construction. No supercooling or additional electrical power required, typically low field
Permanent magnet
An artificial object that can be imaged to test the performance and
quality of a magnetic resonance system
Phantom
An angular relationship describing the degree of synchronism between
sinusoidal waveforms of the same frequency
Phase
a term describing the degree to which precessing nuclear spins are synchronous
Phase coherence
an MRA technique based on the speed of the vessels of interest, utilizing velocity encoding (VENC)
Phase contrast
the process of locating an MR signal along the phase axis, directly correlating spatial resolution and scan time with the number of phase
encodings in an MR image
Phase encoding
Picture element, two-dimensional
Pixel
a rotational motion about an axis of a vector whose origin is fixed at the
origin of the coordinate system
Precess
a technique employing repeated RF excitation of tissues outside the ROI for the purpose of reducing or eliminating their phase effect artifacts
Presaturation
a positively charged particle located in the nucleus of an atom. The # of
protons in the nucleus controls the chemical properties of that element
Proton
an image minimizing T1 and T2 effects, with contrast primarily dependent upon the density of protons in the imaging volume
Proton Density weighting
A set of specifically timed pulses and/or magnetic field gradients producing an image with specific characteristics based on the timing and duration
of the pulses programmed
Pulse Sequence
an event in a superconducting MR system causing a loss of
superconductivity, a rapid loss of the magnet cryogens, potentially creating a
hazard for patients / operators in the magnet room
Quench
A frequency band in the electromagnetic spectrum with frequencies in the millions of cycles per second
Radiofrequency
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
magnetic field gradient applied during the moment when the echo is formed, and is responsible for frequency encoding in the image
Readout gradient
MRI equipment device that detects and amplifies the RF signals picked
up by the receiver coil
Receiver
A coil, or antenna used to detect the NMR signal. Types of receiver coils include solenoid, quadrature and phased array coils
Receiver coil
After excitation the longitudinal magnetization returns toward equilibrium with a time constant T1 and the transverse magnetization decays toward zero with a time constant T2
Relaxation time
the process of returning out-of-phase magnetic moments to phase coherence, instigated by applying a 180º RF pulse (spin echo) or reversing a
magnetic gradient (gradient echo)
Rephasing
the time between successive pulse sequences applied to the same slice, the time between consecutive 90º RF excitation pulses. TR is the controlling factor of T1 contrast, and a factor in MR scan time
Repetition time
TR is the controlling factor of T1 contrast, and a factor in MR scan time
a magnet that can be turned on and off, and uses the principles of electromagnetism to generate a magnetic field
Resistive magnet
the exchange of energy between two systems at aspecific frequency
Resonance
Coils positioned near the main magnetic field that have a small
current, and are used to provide localized magnetic fields improving homogeneity
Shim coils
the conversion of analog signals to digital values through a specific
measurement process
Sampling
The process of improving the homogeneity of the
magnetic field,
Shimming
either through active shimming (use of shim coils) or passive shimming (
Ratio between the amplitude of the received signal and background noise
Signal-to-Noise Ratio (SNR)
is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative
Slew rate
the ability to define adjacent points in an image (detail)
Spatial resolution
The number of Watts of RF energy per kilogram of body weight in an imaging sequence
Specific Absorption Rate (SAR)
An MRI pulse sequence whose signal is an echo resulting from the refocusing of magnetization after the application of 90º and 180º RF pulses
Spin echo
The return of the longitudinal magnetization to its equilibrium value along the Z axis (T1 recovery)
Spin-lattice relaxation
The return of the transverse magnetization to its equilibrium value, zero (T2 decay)
Spin-spin relaxation
A gradient echo sequence in which a non-zero steady state develops for both transverse and longitudinal components of magnetization
Steady-state free precession
Short TI Inversion Recovery: a version of the Inversion Recovery pulse
sequence where the inversion time (TI) is set to 0.69 times the T1 of fat, nulling the signal from fat at the specific field strength in which it’s being acquired
STIR
A magnet whose field is generated by current in wires made of a superconducting material, and is cooled with cryogens. Typically high field systems with horizontal field orientation
Superconducting magnet
spin-lattice or longitudinal relaxation time
T1
Image contrast created with short TR’s and short TE’s whose contrast is determined by the T1 times of tissues
T1 Weighting
spin-spin or transverse relaxation time
T2
Image contrast created with long TR’s and long TE’s whose contrast is determined by the T2 times of tissues
T2 Weighting
The time between the pulses (btwn 90ºRF - 180ºRF and 180ºRF - echo) in
spin echo (also known as 1/2 TE)
Tau
SI unit of magnetic field strength
Tesla
MRA technique relying on flow related enhancement to distinguish between stationary spins and flowing spins
Time of Flight (TOF)
an MRI surface coil that functions as both a transmitter
and a receiver
Transceiver coil
the segment of the MR scanner that produces the RF current and delivers it to the transmitting coil (antenna)
Transmitter
The X-Y component of the net magnetization, at right angles to the main magnetic field
Transverse magnetization
quantity that has both magnitude and direction
Vector
speed in a particular direction
Velocity
MRA technique used for encoding flow velocities
Velocity Encoding (VENC)
volume element with 3-Dimensional characteristics
Voxel
