P3 Flashcards
MRI CONTRAST IS AFFECTED BY THE ____ AND _____
AMPLITUDE, TIMING OF THE RF PULSE
63% RECOVERY
T1 Longitudinal
37% LOSS OF ENERGY
T2 TRANSVERSE
time interval in which signals are measured after RF excitation
TE (echo time)
the time between two excitations is called ____
TR (repetition time)
a short TR (<1000ms) and short TE (<45 ms) scan is ___
T1 WI
Long TR (>2000ms) and long TE (>45ms) scan is ___
T2 WI
Long TR (>2000ms) and short TE (<45ms) scan is ____
proton density image
DARK ON TI
- Edema, tumor, infection, inflammation, hemorrhage (hyperacute,chronic)
- Low proton density, calcification
- Flow void
BRIGHT ON T1
- Fat, subacute hemorrhage, melanin, protein rich fluid.
- Slowly flowing blood
- Paramagnetic substances (gadolinium, copper, manganese)
BRIGHT ON T2
- Edema, tumor, infection, inflammation, subdural collection
- Methemoglobin in late subacute hemorrhage
DARK ON T2
- Low proton density, calcification, fibrous tissue
- Paramagnetic substances (deoxy hemoglobin, methemoglobin (intracellular), ferritin, hemosiderin, melanin.
- Protein rich fluid
- Flow void
The _____ is the simplest type of MRI sequence.
gradient echo pulse sequence
The major purpose behind the gradient technique is a _____.
significant reduction in scan time
allow very short repetition time
thus decreasing the scan time
Small flip angle
The gradient echo is generated by the _____, except that it is used twice in succession and in opposite direction; it is used in reverse at first to ______ of spinning protons and then right after, it is used as a readout gradient to _____ and hence acquired signals.
frequency encode gradient
enforce transverse dephasement
realign the dephased protons
the process of dephasing magnetic
moments with gradients is called ____
gradient spoiling
Gradients that rephase are called
______
rewinders
Gradient that dephase are called
spoilers
The paramagnetic agents are most commonly based on _____
gadolinium, dysprosium, or manganese
The _____ is the result of unpaired electron spins in certain electron orbital shells of transitional metals or lanthanides.
paramagnetic property
_____ are the superparamagnetic agents
used.
Iron oxide particles
Such particles have high magnetic susceptibility and create a relatively large regional gradient magnetic
field.
Iron oxide
_____ is induced within the contrast agent
Magnetization
The most commonly used compounds for contrast enhancement are _____
gadolinium-based
Most clinically used MRI contrast agents work through shortening the _____ of protons located
nearby.
T1 relaxation time
T1 shortens with an increase in rate of ____ from high energy states (spin anti-aligned with the main field) to low energy states (spin aligned).
stimulated emission
_____ administration is well suited to GI tract scans, while _____ administration proves more useful for most other scans.
Oral, intravascular
Contrast agent administration is used extensively to ____
improve tumor localization and characterization
In most cases, the contrast agent is used to ____
increase the signal intensity of the tumor on T1W images.
Contrast agents can enter brain tissue in areas in which the ____ is disturbed, resulting in ____ of many types of brain abnormalities.
BBB, increased visibility
The most serious side effect caused by MRI contrasts are attributed to _____.
gadolinium
The FDA reports that patients with renal failure and kidney diseases cannot
filter the chemical dye quickly enough and it stays in the body. There it causes a serious medical condition called
_____, according to a study conducted by _______ published in ______ in ______
nephrogenic systemic fibrosis, or NSF
Dr. Thomas Grobner
“Nephrology Dialysis Transplantation”
January, 2006
symptoms include hardened skin with red patches and are most commonly found in the limbs.
NSF
This rare illness has no cure, but only affects patients with existing kidney problems injected with gadolinium.
NSF
NSF was first described in the medical literature in ____
2000
The first case of NSF was identified in ____
1997
– MISSILE EFFECT
BIOLOGICAL EFFECTS
– EFFECT ON FERROMAGNETIC IMPLANTS
MECHANICAL EFFECTS
▪ INDUCED CURRENTS (PERIPHERAL NERVOUS SYSTEM)
▪ AUDITORY DAMAGE
GRADIENT FIELD
▪ RF POWER DEPOSITION
▪ BURNS
RF FIELD
- This region includes all areas that are freely accessible to the general public
ZONE 1
- Unscreened MRI patients also may be attenders
also
ZONE 2
- This area is the region in which screened MRI patients and personnel
ZONE 3
- The MRI room where only screened patients are allowed and on a direct supervision of MRI personnel
ZONE 4
- WILL PRODUCE TYPICAL KNOCKING SOUND
AUDITORY DAMAGE
- RESULTS FROM ELECTRO MAGNETIC FIELDS
- RESULTS IN HEATING OF HUMAN BODY
INDUCED CURRENTS (PERIPHERAL NERVOUS SYSTEM)
- DOES NOT QUENCH THE MAGNET THIS TURN OFF MOST ELECTRICAL POWER IN THE SCANNER ROOM AND OPERATOR AREA
EMERGENCY STOPPER BUTTON
- Done in an emergency, to run magnetic field ZERO in order to remove projectile/patient from the scanner in an emergency if these done
cyrogens (helium and nitrogen) BOIL OFF and DEACTIVATE the magnet
QUENCH
• Frequency-encoding direction
• The different resonant frequency of fat & water is transformed into spatial difference.
• Common in vertebral bodies, orbits, solid organs surrounded by fat.
.
CHEMICAL SHIFT ARTIFACT
• Occurs when the field of view (FOV) is smaller than the body part being imaged causing the region beyond to
project on the other side of the image.
Aliasing or “Wrap-around”
• Anatomy outside FOV still provides a signal if it is in close proximity to receiver coil. Data from signal must be
encoded (i.e. allocated a pixel position).
Wrap Around Artifact aka Aliasing
Axis: Phase direction (duplication of phase values)
Appearance: Dark and bright edge on either side of structure where fat & water interface
CHEMICAL SHIFT ARTIFACT
Appearance: Anatomy outside FOV is folded on top of anatomy inside FOV
Wrap Around Artifact aka Aliasing
Axis: Phase direction (duplication of phase values)
▪ An artificially created black line located at fat-water interfaces such as muscle-fat interfaces.
Black Line Artifact
Appearance: Ring of dark signal around organs where fat and water interfaces occur within same voxel
Chemical Misregistration Artifact aka Out-of-Phase, Black Boundary, or India Ink
• Bright or dark lines that are seen parallel & next to borders of abrupt intensity change. May simulate a syrinx
on sagittal image of spinal cord.
• Related to the finite number of encoding steps used by the Fourier transform.
Gibbs or Truncation Artifact
: More encoding steps lessen the intensity and narrows the artifact
Mitigation
Appearance: Rippling artifact a t interfaces of high and low signal
Gibbs or Truncation Artifact
▪ Most are related to hardware or software problems beyond the radiologist control. May occur in either
frequency or phase direction.
Zipper Artifacts
• Bright noise or repeating densities usually oriented in the phase direction.
• Extend across the entire FOV, unlike truncation artifacts that diminish quickly away from the boundary causing them.
Motion Artifacts
• Loss of signal seen in a n image from a multi-angle, multi-slice acquisition.
Slice-overlap (cross-slice) Artifacts
• Result of imperfect slice excitation, i.e. non-rectangular, of adjacent slices causing reduction in signal over entire
Image.
Cross-talk Artifact
Appearance: Adjacent slices have reduced contrast
Cross-talk Artifact
• Seen most frequently in tendons and ligaments that are oriented at a 55° angle to the main magnetic field.
Magic Angle Effects
Axis: Phase and frequency direction
Cause:
• When tightly bound collagen-water molecules lie at 55° from the main magnetic field (Bo) and appear
hyperintense.
Magic Angle Artifact
• Unsaturated spins in blood o r C S F entering t h e initial slices results in greater signal than reduces on subsequent slices.
• May be confused with thrombus.
• Can use spatial saturation to reduce.
• Mechanism for TOF angiography
Entry slice (Inflow) artifact
Shimming, area of interest in near isocenter
Field inhomogeneity
• Causes a nonuniform, washed-out appearance t o a n image.
RF Overflow Artifacts (Clipping)
are an interference pattern most
commonly seen when doing gradient echo images.
Moire fringes
• A focal dot of increased or decreased signal in the center of an image.
Central Point Artifact
• Another amplifier artifact caused by unbalanced gain in the two channels of a quadrature coil. Combining two
signals of different intensity causes some frequencies to become less than zero causing 180 degree “ghost.
Quadrature ghost artifact
• Variations in t h e magnetic field strength that occurs near the interfaces of substance of different magnetic susceptibility such as ferromagnetic foreign bodies.
• Causes dephasing of spins and frequency shifts of the surrounding tissue.
Susceptibility Artifacts
• Band-like, usually oblique stripes.
Zebra Artifacts
• Varying magnetic field from gradients can induce electrical currents in conductors such as the cryostat
causing distortion of the gradient waveforms.
Eddy Current Artifacts
• Change in intensity of blood in large vessel such as aorta from slice to slice when there is synchronization of the
cardiac cycle and the pulse sequence, i.e., repetition rate
= heart rate (TR=1/HR)
Diastolic Pseudogating
• Potentially being mistaken for tendinopathy
Magic Ancgle Artifact
Berlex Laboratories introduced
Magnevist
Other contrast agents approved
for clinical MRI use:
Dotarem
ProHance
Omniscan
• Potentially being mistaken for tendinopathy
Magic Angle Artifact
the first commercial contrast agent was introduced on ____ by
_____ from
Wayne, New Jersey.
1988, Berlex Laboratories
have been used for clinical MRI of the GI Tract.
Kaolin and Bentonite
are administered orally in an aqueous
suspension where they mix with
gastric contents and pass through
the GI System
Kaolin and Bentonite
• Paramagnetic
• Toxic on its own
• LD50 of 1 mM/kg
• Will also remain present in the
body days after administration
• A concentration of 1 mM/kg is
sufficient to cause obvious
neurotoxicity to the brain.
Gadolinium
• This is the process in which a
molecule binds to a metal ion to
form a stable, ring like complex.
Chelation
_____ significantly reduces its
toxicity by forming a stable and
inert complex, which prevents free
Gd ions from interacting with
biologic tissue
Chelation of Gadolinium with
diethylenetriaminepentaacetic
acid
• Highly toxic as they interfere
with calcium dependent biologic
process
• Has a strong affinity for tissues
like the bones, liver and kidneys
leading to toxicity
• Delayed excretion
Free Gadolinium Ions
• Stable, non-reactive complex
• Remains in the blood stream and
is rapidly excreted via the
kidneys, reducing tissue
accumulation
• Highly Water Soluble
• Rapid Excretion
• Maintains paramagnetic
properties of Gd
Chelated Gadolinium
they are considered non-
specific agents in that they are not
taken up by a particular organ,
tissue or lesion type.
Gd-DTPA
Reduces T1 and T2 Relaxation
Times.
Gd-DTPA
shorten T1 and T2, but the principal image contrast results from Shorter T1.
Gadolinium contrast agents
Gd-DTPA reduces T1 Relaxation
time by about ____
30 – 50%
Gd-DTPA reduces T2 Relaxation
Time by about
10 – 30%
has the potential to allow evaluation of regional blood flow, blood volume, and tissue perfusion. These techniques have
already been used to delineate areas
of decreased or absent blood flow in
the brain and heart.
Contrast-enhanced perfusion
sensitive imaging
This allows dynamic studies to be performed that can aid in assessing organ and tissue function.
combining of contrast agent
administration with a very fast image
acquisition.
include patients,
visitors, or facility
staff who have not
undergone formal
safety training (within
the last 12 months) as
designated by the MRI
safety director.
NON-MRI
PERSONNEL
include office staff and
patient aides who have
passed minimal safety
education to ensure their
own safety as they work
within Zone III.
LEVEL 1 Personnel
include MRI
technologists,
radiologists, and nursing
staff who have been
extensively trained in
MRI safety, including
issues relating to
thermal loading, burns,
and neuromuscular
excitation from rapidly
changing gradients.
LEVEL 2 Personnel
In ____ , the American Society
for Testing and Materials
International released the
terminology used to classify the
compatibility of devices within
the MRI Magnetic Field.
2005
items that are nonconducting, nonmetallic, and nonmagnetic items, such as a plastic Petri dish.
MR safe
An item that is known to pose hazards in all MR environments
MR unsafe
An item that has been demonstrated to pose no known hazards in a specified MR environment with specified conditions of use.
MR Conditional
An item that poses no known hazards in all MR imaging environments.
MR Safe
____ refers to the rate at which
radiofrequency (RF) energy is
absorbed by the patient’s tissues
during an MRI scan. It is
measured in _____.
SAR, watts per kilogram (W/kg)
is extremely cold,
and direct contact can cause
severe frostbite and tissue
damage.
Liquid helium
in the MRI room
can lead to suffocation if
ventilation is inadequate.
Oxygen depletion
are used to
detect dangerously low levels
Oxygen monitors
is the sudden loss of superconductivity, causing the magnet to rapudly heat up, releasing helium gas into the MRI room
quench
• Appears as repetitive, displaced
versions of moving anatomy,
seen along the phase-encoding
direction.
Phase Mismapping (Ghosting)
• Caused by motion from
respiration, cardiac pulsation,
swallowing, or CSF flow affects
the phase-encoding gradient.
Phase Mismapping (Ghosting)
• Caused by undersampling in the
phase or frequency direction,
causing misregistration.
Aliasing (Wraparound Artifact)
• Appears as Dark rings at fat-
muscle boundaries, often
around abdominal organs.
Out-of-Phase Signal Cancellation
• Caused by Periodic out-of-phase
behavior of fat and water
protons.
Out-of-Phase Signal Cancellation
Appears as Distorted,
signal void areas around
metallic implants,
hemorrhage, or air
pockets.
Magnetic Susceptibility Artifact
• Caused by Differences in
magnetization between
tissues, leading to local
field inhomogeneities.
Magnetic Susceptibility Artifact
Appears as Alternating bright
and dark bands, often seen at
high-contrast interfaces like the
spinal cord.
Truncation Artifact (Gibbs Ringing)
• Caused by Undersampling in k-
space leading to sharp
transitions in signal intensity.
Truncation Artifact (Gibbs Ringing)
• Appears as A bright or dark line across the image, often in the
frequency-encoding direction.
• Caused by RF interference from external sources (e.g., door leakage,
electronic devices).
Zipper Artifact
• Appears as Uneven signal
intensity, causing some areas to
appear darker than expected.
• Caused by Poor coil loading,
inhomogeneous RF
transmission, or incorrect flip
angles
Shading Artifact
• Appears as Wavy, zebra-like
patterns, seen in gradient-echo
sequences covering a large field
of view.
• Caused by Field inhomogeneity
and aliasing effects.
Moiré Pattern Artifact
• Appears as Signal loss in
adjacent slices in multi-slice
acquisitions.
• Caused by RF pulse bleed-over
between slices due to non-ideal
slice profiles.
Cross-Excitation / Cross-Talk
• Appears as Ghosting, signal loss,
or bright blood flow patterns in
vessels and CSF spaces.
• Motion from pulsatile blood
flow or CSF movement, affecting
phase encoding.
Flow Artifacts
• Appears as High signal intensity in the first slice of a multi-slice sequence
• Caused by Fresh, unsaturated blood entering the imaging plane without previous RF exposure
Entry-Slice Phenomenon
