ARMRIT Flashcards
Which parameter in a pulse sequence helps prevent “crosstalk” between two adjacent images
Slive Interval
When selecting only one slice at a time during a pulse sequence, which method for providing spatial localization is employed?
2DFT
In spatial localization, which factor most affects slice thickness and position?
Bandwidth and strength of the G’s
Determine Scan Time
TR 550 ms
NEX 4
Matrix 256 x 192
7 minutes
Which is a normally enhancing structure after the administration of gadolinium
Choroid plexus
Inverstion time, in an Inversion pulse sequence, is the time interval between the:
180 and 90 degree pulses
Decreasing slice thickness will
Decrease SNR
A gradient is employed exposing the patients body to a series of increasing or decreasing magnetic field strengths for slice selection, in what relation to the slice is this gradient?
Perpendicular
What year was the first MRI enhancement agent approved for clinical use?
1988
In a pulse sequence employing 2DFT, the time can be calclulated using which formula
TRxNEXxMatrixw
In an Inversion recovery pulse sequence, what TI will produce a STIR fat suppressed pulse sequence?
80 - 120
Residual, undesirable gradient magnetic fields that persist for a variable time duration after the pulse of electricity from the gradient power supply is terminated are known as
Eddy Currents
Tissues that have low (short) relaxation times
Have higher relaxation rates
The two types of enhancement media described by Lauffer, the mechanisms of T1 agents is:
To decrease T1 relaxation time, thus emitting high signal
which parameters describe a PD image
Long TR
Short TE
Scan time
TR 2000
NEX 1
Matrix 256x128
4 Minutes
Combining a metal lon with a ligand reduces their tendency to bind to proteins, enzymes, or membranes. The degree to which they disassociate is a measure of their
Toxicity
In a horizontal Field magnet what is the primary G’s for a sagittal slice
Gx
when matrix goes up
the pixel goes down
In spatial localization, the “logical” slice selection gradient is symbolized
Gz
Information acquired when you increase or decrease the frequency of the RF pulse of the G’s, causing the center of the excited plane to change with the center of the G’s RF pulse is
Slice Position
Decreasing the NEX
Decrease SNR and Resolution
In a horizontal field magnet, what is the primary Gs for a Coronal slice
Gy
In General, parameters for a T1 and T2 weighted images are as follows:
T1
TR 100-1000 ms
TE 20-30 ms
T2
TR 1600-3000 ms
TE 70-100 ms
When selecting a volume of slices, which method for providing spatial encoding is employed
3DFT
Who described the mathematical method for converting a time-varying signal into it’s frequency components, which are used to obtain positional information from the MR signal
Jean Baptiste Joseph Fourier
Decreasing matrix does what to pixel
Increases pixel
The maximum exposure to the head and trunk from the main magnetic field (B0) is:
3T
Patients with a pacemaker are contraindicated for an MRI scan in MR magnets with field strength of:
Any Strength
Maximum exposure to the extremities from the main magnetic field (Bo) is:
5T
Hazzards associated with ferromagnetic objects such as O2 tanks are contraindicated in MR magnets with field strengths of
Any Strength
Passed through a strong magnetic field; aneurysm clips, sutures, and surgical clips can experience the force of:
Torque
Painful peripheral nerve stimulation can be caused by
GMF
Side effects of associated with the main magnetic field (Bo) are
Tissue heating and cataract formation.
Acoustic noise is experienced during an MRI study and is caused by
GMF
SAR is decided by coupling what type of electromagnetic energy employed in MRI to body tissue
RF
an explosive boiling off of liquid helium and/or liquid nitrogen and a sudden loss of superconductivity is known as a
Quench
Guidelines which exclude pregnant individuals from exposures to MRI are mainly to protect the individual from
Radio Frequency
Maximum exposure to RF frequency averaged over the whole body is
no more than 0.4 w/kg
Magnetically sensitive objects such as credit cards etc should be kept behind the ____ Gauss line
5
Maximum exposure to RF in one gram of tissue is
a maximum spatial peak of 8 w/kg
Side effects associated with gradient magnetic fields are
cardiac fibrillation, magnetophosphenes
the factor which determines the calculated SAR average is
the patients weight in kilograms
Conductive material in the MRI environment can be affected by electrical currents from
GMF and/or RF
the safety rate index for MRI Gadollinium enhancement agent is
50
the effects of main magnetic field inhomogeneites on the FID signal are corrected for in a spin-echo sequence by applying a second RF pulse. The flip angle of this RF pulse is
180 degrees
an equation dervied to predict the MR signal intensity of a particular tissue as the result of a spin-echo pulse sequence is the
Bloch equation
a 90 degree RF pulse will alter the NMV, a secondary effect is
the hydrogen protons will have phase coherence.
the main magnetic field of MRI systems in clinical use must meet an acceptable specification of
20-30 PPM
what type of electromagnetic coils correct inhomogeneites in the main magnetic field
shim coils
the larmor frequency of hydrogen protons in a 1.5 Tesla magnetic field is
63.9MHz/Tesla
T1 process is also known as
Spin Lattice
the purpose of a magnetic resonance angiography is to image the
Blood flow
Which type of MRI magnet requires a steady current of electricity in coils of conductor wrapped around an air or iron core?
resistive
Magnetic susceptibility is defined as
tendency of a substance to attract or repel magnetic lines of force which is decided by the magnetic properties of its electrons
in comparison to CT a disadvantage of MRI is that
special and costly site planning and shielding
Fast transition phenomenon and entry phenomenon are theories that explain which of the following tissue characteristics
Velocity effects
which type of electromagnetic coils can be found both inside and outside of the housing of the MRI magnet
RF coils
In the USA, MRI systems in clinical use have main magnetic field strengths that range from
0.06 to 3 Tesla
which type of receiver radio frequency coil is placed close to a patients body for the purpose of imaging superficial anatomic strucures
surface coils
at any one time, human body tissue is made up primarily
50-90% of what tissue
H2O
On a PD image two types of tissue that that contain very low concentrations of hydrogen and appear very hypointense are
cortical bone and lung
the introduction of Gado based contrast enhancement agents by IV injection can involve passing through an abnormal BBB, the tissue compartments involved are
intravascular to interstitial space
Once the NMV has moved away from equillibrium, the following will occur
the transverse component will increase
The transmit radio frequency coil generates a second electromagnetic field to the hydrogen protons. this field is designated
B1
which type of electromagnetic coils produce smaller magnetic field which allow spatial localization to be performed.
gradient coils
the tissue characteristic that depends heavily on the relative content of fat molecules and free water is
T1 effects
T2 process is also known as
Spin Spin
which type of MRI magnet requires a special cooling system to dissipate heat produced by very large currents?
resistive
In MR imaging for a chemical substance to be affected by the main magnetic field and the radio wave it must contain an
odd number of total protons and neutrons
Magnetism can be defined as the ability of certain substances to attract
iron cobalt nicke
a sinewave is a symbol used to measure electromagnetic energy. A sinewaves two components of measurements are
Wavelength and frequency
The component Mz is most associated with
Parallel to Bo, T1 relaxation, longitudinal magnetization
of the following RF flip angles which is the smallest that will produce the maximum signal.
90 degrees
to describe the uniformity of the MRI systems main magnetic field, the term employed is
Homogeneity.
