ARMRIT Flashcards
Artifact and Cardiac
On a T1 weighted image, edema appears dark because
It has a Long T1 relaxation time
Gibbs Truncation
caused by under sampling, corrected by increasing phase matrix or reducing FOV
magnetic susceptibility
artifact caused by metal, to reduce effects use smaller voxels, shorter TE, and increased bandwidth.
How to correct for Metal artifact
Use FSE/SE, the additional 180 pulses help with inhomogeneities, do not use parallel imaging, this requires gradients, use high TSE factors/ Long ETL, wide rBW, thin slices, STIR’s over Fat supressio, good SNR and high NEX
Chemical shift artifact
Occurs because fat and water precess at different frequencies.
how do you correct chemical shift artifact
If you increase the receiver bandwidth you get a shorter sampling time and less time for artifact to enter the slice the sacrifice here is SNR
Flow artifact
Can be corrected by applying Gradient moment nulling or flow comp.
Gradient moment Nulling/flow comp
minimizes phase shift obtained by transverse magnetization of excited nuclei moving along the gradients, (only works for first-order motion such as small vessels CSF)
zipper artifact
a leak in RF shielding, ensure door suction and all doors are closed in scan room to minimize or correct.
Partial volume averaging artifact
occurs when multiple tissue types are contained within a single voxel, generally happens with thicker slices
How to correct for partial volume averaging artifact
best way is to decrease in voxel volume or thinner slices
Moire/Fringe Field artifact
caused by interference of aliased signals at different phases
Magic angle artifact
occurs when a tendon or ligament is positioned at 55 degrees in the direction of the main magnetic field and a short TE is used.
how to correct for magic angle artifact
long TE,
Best method to evaluate cardiac infarction is
Perfusion cardiac imaging
Trigger delay
delay after system detects the R wave before transmitting RF to intended slice
Purpose of trigger delay
To postpone slice acquisition until the heart is diastolic (relaxation period of heart beat)
Trigger window
waiting period before each R wave and is expressed as % of R-R interval
Mitral Valve
bicuspid, Left AV valve
Tricuspid
Right AV valve
Aortic Valve
Located between Left Ventricle and ascending aorta, semilunar valve
pulmonary valve
lies between pulmonary artery and the right ventricle
P wave
atrial muscle contraction (systole)
QRS complex
Ventricular Systole (muscle contraction) some might say this is the R-T interval
T Wave
Ventricular Diastole (muscle relaxation) or T-R interval (
The coils in a magnet from the innermost to the outermost are
bore, rf, gradient, main magnet (revise)
____ discovered that a charged particle such as a proton spinning on its own axis has a magnetic field known as a magnetic momentum
Felix Bloch
____ developed the equation showing precession of nuclear spins being proportional to magnetic field strength
Sir Joseph Larmor
in 1975 _______ introduced 2D NMR using phase and frequency encoding and the fourier transform
Richard Ernst
In the year _____ Scherings _____ IV Gadolinium contrast gets the first approval by FDA
1988, Magnevist
When was function mri developed
1991
_____ and ____ won the 2003 nobel prize in medicine or their work in the 1970’s developing MR imaging techniques and capabilities
Lauterbur and Mansfield
_____ coined the work “electricity” and was the first to realize the earth is a giant magnet
william gilbert
_____developed the mathematical equation to analyze heat transfer between solid bodies, later becoming the basis for the rapid processing of phase and frequency signals in MRI
Joseph Fourier
______discovered that a current flowing through a wire could produce a magnetic field
Hans Christian Oersted
Shielding of the magnet does what to the field
decreases the size of the fringe field and increases the MSG
How does shielding within the magnet housing affect the system spatial gradient
It increases the systems spatial gradient, because it decreases the size of the fringe field forcing lines of flux together
frequency encoding gradient being right to left means this is the ____ gradient
X gradient
when did michael colimbini die
2001
decreasing TE will do what to SNR
increase
partial echo
is a fast imaging technique that only acquires part of the MRI signal during the frequeny encoding process
partial fourier
is a technique used to fill k-space by only recording a portion of all of the phase encoding steps and leveraging the conjugate symmetry of k space
saturation occurs when the __
TR is SHORTER than the T1 of the tissue
passive shielding
the process of using ferromagnetic materials placed in the scanner bore to improve the homogeneity of the main magnetic field
