Data Acquisition and Processing
The time during which the frequency encoding gradient is on:
Increases with a reduction in receiver bandwidth
A disadvantage of TOF MRA is high signal in some background tissues. To minimize signal from background tissues, TE should be selected that enable the signals from fat and water to be:
Out of phase Out of phase TE's minimize signals from background stationary tissues in time of flight MR angiography.
Parallel imaging techniques are also known as all of the following except: a. SENSE b. SMASH c. GRAPPA d. SAT
SAT
What is SENSE in parallel imaging?
SENSitivity Encoding and is related to image domain performed for rapid imaging with high resolution
When using parallel imaging to reduce acquisition times, which of the following is always true?
SNR is reduced and spatial resolution is unaffected
If the TR of a gradient echo pulse sequence is considerably less than the T2 (and T2*), the condition that will exist is known as
Steady State
Having acquired a 3D TOF, when producing an MRA projection image set using the MIP technique, which of the following can appear bright and therefore the same as flow within the vessel?
Tissues or substances with extremely short T1-relaxation times
Blood flow velocities are greatest:
center of the vessel this is the case in what is known as laminar flow
Collecting the low frequency (high amplitude signal) data points in k-space at the start of the scan (in a spiral fashion) is known as
centric
The basic MR principle with regard to MR spectroscopy is : a. Faraday's law b. Chemical Shift c. flow-related enhancement d. the BOLD effect
chemical shift
Reducing the TE yields images with what change in image contrast? A. Increased T1 information B. Decreased T1 information C. Increased T2 information D. Decreased T2 information E. None of the above
d. decreased T2 information
Increasing the receiver bandwidth (wide BW); a. decreases available ETL b.Inverts available ETL c. Increases the available ETL d. had no effect on ETL
d. has no effect on ETL
the technique whereby a portion of the lines of k-space are "sampled" and "filled" and the remaining lines are interpolated is known as all of the following EXCEPT: a. Half Fourier b. Partial Fourier c. Fractional Fourier d. Interleaved acquisition
d. interleaved acquisition interleaved acquisition is acquired to avoid cross-talk artifact
Single-order moment nulling only compensates for
first-order motion, such as flow with constant velocity
The signal intensity on TOF MRA sequence is related to
flow-related enhancement
The effective TE in a fast spin echo pulse sequence determines the:
image contrast
Each "frame" of a cardiac cine sequence displays the heart:
in different phases of the cardiac cycle
Doubling the number of signals averaged (NSA) will:
increase SNR by the square root of 2
In a vessel with a plaque producing a high degree of stenosis, the velocity of the blood flow in the center point of the stenosis is
increased
Increasing the phase matrix does what to scan time?
increases
Increasing the TE:
increases the contrast based on T2-relaxation times of the tissue
What is parallel imaging?
it is an imaging technique that is used to provide fast scans with unchanged spatial resolution at the cost of SNR associated with Rectangular FOV imaging ex: abdominal imaging
Normal blood flow (demonstrated by a parabolic blood flow profile) is known as:
laminar flow
Reducing the flip angle yields images with what change in image contrast?
less T1 information
increasing slice thickness does what to the SNR?
Increases SNR
When doing an MRV of the superior sagittal sinus, a sat band should be placed ____ to the axial slices.
inferior
Using a 3D acquisition, the number of slices allowed when increasing the TR:
is not affected
Using a conventional spin echo multi-slice sequence, the number of slices allowed when increasing the TR:
is not affected
What kind of image characteristics are produced during steady-state?
T2*
Reducing TE does what to SNR?
increases
Does increasing slice thickness affect scan time?
no
number of shots is calculated by
#PEs/ETL
What is BOLD?
(Blood Oxygen Level Dependent) Oxygenated blood has different magnetic properties than deoxygenated blood.
Gradient echo sequences requiring high signal from fluid are known as
-T2* gradient echo -steady state gradient echo -coherent gradient echo
Doubling NSA will increase the SNR by a factor of:
1.41
In a spin echo sequence, the time between the 90 pulse and the 180 pulse is
1/2 TE
The MRA sequence that can be made sensitive to any flow velocity is
3D PC MRA
The MRA sequence that is sensitive to flow direction is
3D PC MRA
The MRA sequence that is least sensitive to slow flow is
3D TOF
The MRA sequence that is most sensitive to smaller vessels is
3D TOF
Reducing the FOV by a factor of 2 will reduce the voxel volume by a factor of:
4
With a fast spin echo sequence utilizing an eight echo train length (ETL), the number of lines of k-space filled during each TR will be:
8
In a 3D acquisition, slices are produced by:
A phase encoding gradient applied in the slice direction. Acquired by volume imaging.
In a 3D acquisition, the slices are produced by
A phase encoding gradient applied in the slice selection direction
In order to produce a high quality reformatted image, the:
Acquisition voxel should be isotropic the 3D volume element is known as "voxel" an isotropic voxel is a cube whereby all sides are equal
What is the most commonly used fMRI sequence?
BOLD
Increasing the matrix does what to SNR?
Decreases SNR
Hemangiomas in the liver are typically benign lesions, and are best visualized with:
Delayed images Hemangiomas in the liver are typically venous-fed, benign lesions, and are best visualized with delayed enhancement images. Liver cancers, on the other hand, are typically arterial-fed and are best seen on first pass dynamic images.
Why is GRE T2*-weighted images utilized in fMRI?
GRE T2*-weighted images take advantage of the fact that deoxygenated hemoglobin is paramagnetic, whereas oxygenated hemoglobin is not. Because of the paramagnetic properties of the deoxyhemoglobin molecule which causes rapid dephasing, T2* signal is retained longer in a region where/when it has more oxygenated blood compared to where/when there is less oxygenated blood.
When acquiring an fMRI series to map out the visual cortex, which of the following pulse sequences would be utilized in order to maximize sensitivity to the BOLD effect?
Gradient Echo EPI
On T1 weighted images of the spine, the CSF (cerebrospinal fluid) appears:
Hypointense to the spinal cord
A major advantage of a 2D TOF sequence over a 3D time of flight sequence is the ability to:
Image a larger area without saturation of the flowing blood
A gradient echo sequence in which any residual transverse magnetization is removed prior to the next excitation pulse is known as:
Incoherent/Spoiled
Presaturation pulses are often used to:
Reduce flow artifacts
When would be an example of using a T1 Spoiled gradient echo sequence?
SPGR Cor Oblique acquisition for a patient with history of seizures for evaluation of hippocampus
If a STIR sequence using a TR of 3000, a TE of 20, and a TI of 140 in a 1.5 T imager, produces an image with dark fat and bright water. The contrast in such an image is primarily based on
T1
TOF MRA techniques are acquired with the use of a 2D or 3D
T1 gradient echo sequence this sequence is acquired with TR and flip angle selections to suppress stationary tissues and allow for the visualization of flowing blood (within the vessels) after image acquisitions; reconstruction techniques are employed
In which of the following sequences would MS plaques appear hyperintense relative to both CSF and normal white matter?
T2 FLAIR
In a spin echo sequence, flowing blood is normally seen as a signal void because the:
TE is too long to image flow 90 pulse and 180 pulse is slice selective Blood that is excited by the 90 pulse will have moved out of the slice by the time the 180 pulse has been applied. In order to produce signal, tissue must receive both the 90 and the 180 pulses. Short TE allows less dephasing
The time between excitation pulses is known as the:
TR
The intrinsic contrast mechanism with regard to fMRI is:
The BOLD effect
A short TI inversion recovery (STIR) sequence can suppress the signal from:
fat and gadolinium-enhancing lesion
Decreasing the receiver bandwidth (utilizing a narrow BW): a. decreases number of slices b.inverts the number of slices c.increases the number of slices d. has no effect on the number of slices
a. decreases the number of slices
Reducing the TR yields images with: A. Increased T1 information B. Decreased T1 information C. Increased T2 information D. Decreased T2 information E. None of the above
a. increased T1 information
Increasing slice thickness from 5 to 10mm (by a factor of 2, i.e 2x thicker), the SNR: a. increases by a factor of 2 b. increases by a factor of 4 c. is not affected d. decreases by a factor of 2
a. increases by a factor of 2
Blood flow at the area of a stenosis (vascular narrowing is known as:
accelerated flow
in order to produce a high quality reformatted image, the:
acquisition voxel should be isotropic the 3D volume element is known as voxel. When voxel is isotropic, any and all reconstructed views will have the same spatial resolution.
the signal intensity on diffusion sequences is related to
amount of diffusion
Changing the b-value alters
amplitude,timing, and/or duration of the diffusion gradients
Fourier Transform is performed in the
array processor
Increasing the TR yields images with: A. Increased T1 information B. Decreased T1 information C. Increased T2 information D. Decreased T2 information E. None of the above
b. decreased T1 information
Increasing the number of phase encodings will produce an image with: a. increased voxel volume b.decreased voxel volume c. an unchanged voxel volume d. higher SNR
b. decreased voxel volume
Gradient echo sequences acquired for high signal from fluid are known as all of the following except: a. coherent gradient echoes b.incoherent gradient echoes c. steady-state gradient echoes d. T2* gradient echoes
b. incoherent gradient echo
Increasing TE yields images with: A. Increased T1 information B. Decreased T1 information C. Increased T2 information D. Decreased T2 information E. None of the above
c. Increased T2 information
In a fast spin echo sequence, the central lines of k-space are associated with the: a. Image's spatial resolution b. TR c. Effective TE d. Scan Time
c. effective TE
When parallel imaging techniques are performed, a low resolution ____ scan is acquired prior to the acquisition
calibration
The evaluation of cardiac function can be provided by any or all of the following EXCEPT: a. Cardiac cine b. multiphase imaging c. perfusion imagin d. short axis single slice, single phase
d. short axis single slice, single phase
The following are important in MRA sequences to minimize loss of signal due to dephasing within a voxel: a. Long TR b. small voxels c. Short TE d. b and c
d. small voxels and short TE with longer TEs, more time is given for intravoxel dephasing, thereby reducing the signal from within the vessel. With larger voxels, inhomogeneities within the voxel are increased, and these also increase intravoxel dephasing and reduce signal intensity
Increasing number of phase encodings will produce an image with
decreased voxel volume
Using a conventional spin-echo multi-slice pulse sequence, increasing the TE from 20 msec. to 40 msec will __ the number of slices allowed:
decreases
Reducing the TR down to or below the T1-relaxation time of the tissue:
decreases signal to noise ratio of the image and increases saturation effects
In a phase contrast technique, it is possible to use the data to determine the:
direction of blood flow
Increasing the number of slices in a 2D acquisition
does not affect scan time
Using a 3D acquisition, the number of slices allowed when increasing the number of slices from 64 to 128:
doubles the scan time
the high frequency (low amplitude) data points in k-space provide:
edge detail (spatial resolution)
The main purpose of producing/calculating an ADC map (image) is to:
eliminate the T2 shine-through
The technique by which signal data is modified from the "time domain" to the "frequency domain" is known as:
fourier transform
The technique by which signal data is transformed from a plot of signal intensity over time to a plot of signal intensity over frequency is known as:
fourier transform
To rephase the signal from moving spins, gradient moment nulling techniques use a:
gradient
Cardiac cine acquisitions typically utilize a / an __________________ pulse sequence.
gradient echo pulse sequence
Increasing the matrix in the frequency direction from 256 to 512 will:
have no effect on scan time
In a fast spin echo sequence, spatial resolution is associated with
high amplitude phase encoding gradients
In a fast spin echo sequence, the effective TE is the echo that is performed with the:
low amplitude phase-encoding gradients
Increasing the flip angle yields images with what change in image contrast?
more T1 information
A major advantage of MRA over conventional angiography is that
multiple views can be produced from a single acquisition
Cardiac analysis performed with a technique using SAT bands to assess wall motion is known as
myocardial tagging
When triggering a scan from the patient's EKG, the TR of the sequence is determined by the
patient's heart rate
A chemical or spectral fat suppression sequence will suppress the signal from fat based on the:
precessional frequency of fat
Phase encoding is performed :
prior to the frequency encoding
When performing a dynamic perfusion exam of the brain utilizing a gadolinium based MR contrast agent, the result of the T2* shortening is
reduced MR signal
Reducing the TE:
reduces contrast based on T2 relaxation times
Reducing the number of lines filled in k-space will produce an image:
reduces number of phase encoding steps, resulting in shorter scan times, increase in SNR, decrease in spatial resolution
What exists at the time of the next excitation pulse in Steady State?
residual transverse magnetization
Single order gradient moment nulling does not compensate for
reverse flow and accelerated flow
In a gradient echo sequence, reducing the flip angle while holding the TR constant reduces:
saturation
In a TOF sequence, tissue is HYPOintense relative to flowing blood because of the:
saturation effects TOF will produce low signal from tissue yet bright signal from flowing blood (in Gre). the rapid repetition of the RF pulse, resulting from the selected TR time, will saturate the tissue
The removal of signal from vessels in an MRA sequence is achieved by
spatial presaturation
When a gradient echo sequence is acquired for dynamic contrast-enhanced imaging of the liver, ____ is performed.
spoiling
What is used to to reduce steady-state (T2*) effect?
spoiling, to allow for fast scans with T1 contrast spoiling is performed for rapid T1 imaging for dynamic enhanced imaging of the organs/MRA
During contrast-enhanced imaging of the abdominal organs, images are acquired without and with gadolinium enhancement. To better visualize contrast enhancement, ___ can be performed.
subtraction
When doing an MRA of the IVC, a saturation band should be placed ___ to the axial slices.
superior
When doing an MRA of the carotid arteries, a saturation band should be placed ____ to the axial slices.
superior
When doing an MRA of the circle of Willis, a sat band should be placed ____ axial slices.
superior
Gradient echo sequences acquired for the evaluation of hemorrhagic lesions rely on:
susceptibility this artifact allows for the determination "blood" within or associated with lesions
For a given tissue with a given T1-relaxation time and TR, the flip angle, which will result in the maximum signal for that tissue, is:
the Ernst Angle
Why does SENSE imaging use a calibration scan?
to provide information about RF signal detection
Fourier transformation converts signal data from the FID into the spectrum true or false
true
Normal flow is known as
turbulent
The signal intensity on PC MRA sequences is related to
velocity induced phase shift
Phase contrast techniques produce images in which the signal intensity within the vessel is dependent on (among other parameters) the:
velocity of the flowing blood
Cine (kinematic) studies are often performed on various joints. The main purpose of such a study is to:
visualize motion and function
A major advantage of 3D TOF techniques over 2D TOF is the ability to:
visualize smaller vessels
A 3D dataset can be reconstructed to display "what appears to be" a 3D image of the anatomy. This technique is known as
volume rendering
The swirling blood flow that occurs just past the area of a stenosis is known as:
vortex flow
In a balanced GRE acquisition, the contrast weighting is
weighted for the ratio of T2/T1
How does Steady State occur?
when multiple RF pulses are applied during GrE acquisitions
