exam 2 Flashcards
Phase is measured in____________
Radians or Degrees
The 90 degree RF pulse is also called the ______________
flip angle
Using a long TE enhances T2 and T2* contrast.
true/false
true
A long TE gives spins more time to dephase therefor increasing T2 contrast
true/false
true
The definition of weighting is the parameters are selected to make one contrast mechanism dominate or the others.
true/false
true
What is meant by the tumbling rate?
The rate at which a molecule moves. This has a direct effect on T1 and T2 relaxation times of tissues.
Fat has a fast tumbling rate motion due to Lipids tightly packed together.
true/false
false
The T1 time of fat is short
true/false
true
T1 time of water is long
true/false
true
Select all the Extrinsic factors.
TR
TE
Flip Angle
Select all that apply to Intrinsic factors
T2 recovery
T1 recovery
Proton Density
This parameter determines the—Time between the excitation pulse and the middle of the Spin Echo,Measures in ms and determines amount of Transverse or T2 decay
TE
Time between Excitation Pulses determines the amount of Longitudinal or T1Recovery is…..
TR
Select all that apply to T1 weighting.
Bright Fat, Dark Water
Short TR and TE times
TR must be short so that fat and water have time to recover to Bo
Gradients serve many functions in MRI. Select all that apply to them.
Clice selectoin
phase encoding
frequency encoding
The two points along a gradient contain a range of frequencies. This band of frequencies are called?
bandwidth
The range of frequencies the RF pulse sends in to match the band of frequencies along our slope is termed?
transmit bandwidth
When increasing your slice thickness from 3mm to 10mm select the two items needed to achieve this.
Shallow slope of the gradient.
broad transmit bandwidth
Which gradient is turned on during the echo (signal)?
frequency encoding
Frequency encoding typically is along the long axis of the anatomy.
true/false
true
The frequency encoding gradient is also called the?
readout gradient
The steepness of the slope of the read out gradient will determine the Frequency Field of View
true/false
true
A steep phase encoding gradient results in large phase shifts
true/false
true
The amount of time the read out gradient is left on is known as the acquisition window.
true/false
true
The sampling frequency is determined by the Nyquist theorem.
true/false
true
Receive Bandwidth = ________ x Nyquist frequency
2
In FFT if a high amplitude is located within a pixel will this be assigned a Dark or Bright signal?
bright
——Advantages of this pulse sequence is it rephases faster requiring a shorter TE as well as a shorter TR
—Disadvantages- susceptible to magnetic field inhomogeneities. What pulse sequence are these characteristics describing.
gradient echo
Rephase gradients are called__________ ?
rewinders
—This parameter is the time between Excitation Pulses. —Determines the amount of Longitudinal or T1Recovery
TR
—T1 time of water is long.
true/false
true
What type of energy is involved in making MR images
Radio frequency
f = γB0 represents _____________ equation?
larmor
If you had a 1.5 Tesla MRI unit what would the processional frequency of a hydrogen be approximately?
63.86
The time from the initial 90 degree RF pulse to the next RF pulse is termed?
Repetition Time
—T1 recovery(spin lattice relaxation) is the relaxation time for 63% of the Net magnetization of the tissue to recover.
true/false
true
—The T2 relaxation time is the time it takes for tissue to decay in the transverse plane to 37% (or 63% to be lost)
true/false
true
——Advantages of this pulse sequence is it rephases faster requiring a shorter TE as well as a shorter TR
—Disadvantages- susceptible to magnetic field inhomogeneities. What pulse sequence are these characteristics describing.
gradient echo
—The T2 time of water is long.
true/false
true
—The T2 time of fat is short
true/false
true
What best describes Temporal resolution?
Ability to distinguish structural differences over time
If you increase the receive bandwidth what affect will this have on SNR?
decrease
To determine voxel volume you need the pixel dimensions and the slice thickness to determine volume.
true/false
true
One 90 degree Excitation Pulse and one 180 degree refocusing pulse describes what pulse sequence?
spin echo
What is the TI of CSF in a T2 weighted image?
1700-2200ms
This modified TSE/FSE parameter pushes any transverse magnetization into the longitudinal plane, making it available for the beginning of the next TR period.
DRIVE
This type of K space filling will fill the outer lines first and then fill the central lines after contrast injection
key hole
What pulse sequence would be best to show pathology that may be next to CSF?
FLAIR
When gradients are used to dephase and rephase the residual magnetization this is called?
gradient spoiling
RF is transmitted at a certain frequency to exite a slice at a specific phase.
RF spoiling
What type of energy is involved in making MR images
Radio frequency
Hydrogen Nuclei start to Recover back to Bo or the Longitudinal Plane, they are now Out of Phase
true/false
true
________mechanics deals with large objects
classical
Precession Frequency depends on what two factors?
Type of nucleus
Strength of Bo
The F.I.D. can be defined as
Signal after the R.F. pulse is removed
Primary signal
Dephasing Hydrogen ProtonsCorre
All of these
Magnetic susceptability can be defined as
The ease by which an object can become magnetized
When a patient is subjected to a strong magnetic field the patient becomes polarized and has
net magnetization
FerroMagnetism refers to ojects that are
easily infuenced by BO
Hydrogen contains its own large magnetic moment due to the odd number of Protons in the Nucleus
true/false
true
In order for resonance to occur the RF Pulse needs to match the exact precessional Frequency of Hydrogen Atoms
true/false
true
Once a Magnetic Moment is exposed to an external Magnetic Field it will line up with or against the external field.
true/false
true
