Review Questions for MRI: Data Acquisition and Processing
Collecting the low frequency (high amplitude signal) data points in k-space at the start of the scan (in a rectilinear fashion) is known as:
Centric
In a phase-contrast technique, it is possible to use the data to determine the:
Direction of blood flow
Increasing TE:
Does not affect scan time
Increasing the number of slices in a 2D acquisition:
Does not affect scan time
Increasing the slice thickness:
Does not affect scan time
Increasing the FOV:
Does not afffect scan time
Using a 3D acquisition, 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)
In a fast spin echo sequence, the central lines of k-space are associated with the:
Effective TE
The main purpose of producing/calculating an ADC map (image) is to:
Eliminate the T2 shine-through
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:
Elliptic centric
The SNR will increase in a 3D sequence with an increase in:
FOV and Number of slices
A short T1 inversion recovery (STIR) sequence can suppress the signal from:
Fat and A gadolinium-enhancing lesion
In a time of flight sequence, flowing blood is HYPERintense relative to stationary tissue because of the:
Flow-related enhancement
The signal intensity on TOF MRA sequences is related to:
Flow-related enhancement
STIR sequences can suppress the signal from all of the following EXCEPT:
Fluid (CSF)
Short tau inversion recovery (STIR) sequences are typically used for the evaluation of all of the following EXCEPT:
Fluid (CSF)
In a fast spin echo pulse sequence, if the echo trail length is increased by a factor of four, the scan will be:
Four times as fast
The technique by which signal data is modified from the "time domain" to the "frequency domain" is known as:
Fourier transformation
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 transformation
One direction in k-space represents phase, while the other represents:
Frequency
The "readout" gradient is also known as the:
Frequency
The gradient that is on during the production of the echo is the:
Frequency
The gradient that is on during the production of the echo is called the:
Frequency encoding gradient/readout gradient
Each "frame" of a cardiac ciné sequence displays the heart:
In different phases of the cardiac cycle
Decreasing the receiver bandwidth (narrow BW):
Increases the SNR
Increasing the TE:
Increases the contrast based on T2-relaxation times of the tissues
The time during which the frequency encoding gradient is on:
Increases with a reduction in receiver bandwidth
When doing an MRV of the superior sagittal sinus, a saturation band should be placed ___________________ to the axial slices.
Inferior
To create a projection image in MRA, the technique most commonly employed is:
Maximum intensity pixel
Increasing the flip angle yields images with:
More T1 information
Reducing the TR yields images with:
More T1 information
Increasing the TE yields images with:
More T2 information
In choosing the direction of phase encoding, the technologist usually considers the direction in which the:
Motion artifacts traverse the least tissue or areas of interest
In which of the following EPI sequences would one expect there to be the least susceptibility (distortion) artifacts? A. Single-shot SE-EPI, 256 phase x 256 frequency B. Single-shot GRE-EPI, 512 phase x 192 frequency C. Multi-shot (4-shot) SE-EPI, 256 phase x 256 frequency D. Single-shot SE-EPI, 192 phase x 192 frequency
Multi-shot (4-shot) SE-EPI, 256 phase x 256 frequency
Creating additional images in various planes from a 3D dataset is accomplished by a technique known as:
Multiplanar reformatting
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
In an image acquired with a balanced GRE sequence (Figure C.2), all of the following have high (bright) signal EXCEPT:
Normal myocardium
When triggering a scan from the patient's ECG, the TR of the sequence is determined by the:
Patient's heart rate
T2-weighted fluid attenuated inversion recovery (FLAIR) sequences are typically used for the evaluation of:
Periventricular white matter disease
A chemical or spectral fat suppression sequence will suppress the signal from fat based on the:
Precessional frequency of fat
Parallel imaging techniques are also known as all of the following EXCEPT:
SAT
As the TE increases:
SNR decreases
As the TR increases:
SNR increases up to a point
To keep scan time at a minimum, diffusion imagining is typically performed with:
Single-shot FSE acquisition
The 180° pulse that follows the initial 90° pulse in a spin echo sequence will cause the NMR signal to reappear while correcting for:
Slight magnetic field inhomogeneities, Chemical shift, slight magnetic susceptibility effects (All of the above)
Gradient moment nulling is most effective when correcting for motion-induced signal loss from:
Slow constant flow
When a gradient echo sequence is acquired for dynamic contrast-enhanced imaging of the liver, __________________ is performed.
Spoiling
The following is (are) important in MRA sequences to minimize the loss of signal due to dephasing within a voxel:
Small voxels and Short TE
The removal of signal from vessels in an MRA sequence is achieved by:
Spatial presaturation
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 a vessel?
Tissues or substances with extremely short T1-relaxation times
Gradient echo sequences use flip angles:
To control saturation effects
Fourier transformation converts signal data from the FID into the spectrum.
True
Gradient echo sequences can yield either T1 or T2* characteristics.
True
Normal blood flow is known as:
Turbulent flow
When parallel imaging techniques are performed, a low resolution _________________ scan is acquired prior to the acquisition:
Calibration scan
Decreasing the receiver bandwidth (narrow BW):
Increases readout time
Increasing TR:
Increases scan time
Increasing the NSA:
Increases scan time
Increasing the phase matrix:
Increases scan time
Reducing the ETL:
Increases scan time
A single-shot FSE sequence is acquired when:
#PEs = 256 and ETL = 256
A multi-shot FSE sequence is acquired (with four shots) when:
#PEs = 256 and ETL = 64
The number of shots is calculated by:
#PEs/ETL
Which of the following field strengths would require the shortest (lowest) T1 time to suppress/null the signal from fat when acquiring a STIR sequence in an MR exam of the knee? A. 0.35T B. 1.0T C. 1.5T D. 3.0T
0.35T
Doubling the NSA will increase the SNR by a factor of:
1.41
In order to produce a high-quality reformatted image, the:
Acquisition voxel should be isotropic
An inversion recovery (IR) spin echo sequence begins with a:
180° RF pulse
A typical inversion recovery (IR) spin echo sequence uses pulses:
180°, 90°, 180°
If the pulse sequence shown in Figure C.1, were a fast spin echo sequence, the number of lines of K space filled during each TR period would be:
2
In the multi-echo spin echo sequence shown in Figure C.1, the number of images PER SLICE LOCATION created will be:
2
If a given conventional spin echo pulse sequence takes 12 minutes to acquire, a fast spin echo sequence using an ETL of six, with all other factors that affect scan time remaining the same, will take:
2 minutes
In the multi-echo spin echo sequence shown in Figure C.1, the number of LONG TE images created with a 20-slice sequence will be:
20
In the multi-echo spin echo sequence shown in Figure C.1, the number of SHORT TE images created with a 20-slice sequence will be:
20
If a phase resolution of 256 is desired, then the TR must be repeated (for one NSA):
256 times
The MRA sequence that can be made sensitive to any flow velocity is:
3D phase contrast MRA (PC MRA)
The MRA sequence that is sensitive to flow direction is:
3D phase contrast MRA (PC MRA)
The MRA sequence that is least sensitive to slow flow is:
3D time of flight (TOF)
The MRA sequence that is most sensitive to smaller vessels is:
3D time of flight (TOF)
Reducing the FOV by a factor of 2 will reduce the voxel volume by a factor of:
4
In the multi-echo spin echo sequence shown in Figure C.1, the TOTAL number of images created with a 20-slice sequence will be:
40
If one desires to null the signal from a specific tissue using an inversion recovery sequence, one should select an inversion time that is _____________ of the T1 relaxation time of that tissue.
69%
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
A typical spin echo (SE) sequence uses pulses:
90°, 180°
Which of the following best describes an EPI sequence? A. A 90° pulse followed by a 180° pulse B. A 180° pulse followed by a 90°/180° combination C. A "train" of gradient echoes D. A "train" of spin echoes
A "train" of gradient echoes
Which of the following best describes an FSE sequence? A. A 90° pulse followed by a 180° pulse B. A 180° pulse followed by a 90°/180° combination C. A "train" of gradient echoes D. A "train" of spin echoes
A "train" of spin echoes
Which of the following best describes an IR sequence? A. A 90° pulse followed by a 180° pulse B. A 180° pulse followed by a 90°/180° combination C. A "train" of gradient echoes D. A "train" of spin echoes
A 180° pulse followed by a 90°/180° combination
Which of the following best describes a SE sequence? A. A 90° pulse followed by a 180° pulse B. A 180° pulse followed by a 90°/180° combination C. A "train" of gradient echoes D. A "train" of spin echoes
A 90° pulse followed by a 180° pulse
Cardiac ciné acquisitions typically utilize:
A gradient echo pulse sequence
In a 3d acquisition, the slices are produced by:
A phase-encoding gradient applied in the slice selection direction
Blood flow at the area of a stenosis (vascular narrowing is known as:
Accelerated flow
Single-order gradient moment nulling does not compensate for:
Accelerated flow and Reverse flow
Gradient echo sequences can yield either T1 or T2* characteristics, with influences caused by all of the following EXCEPT:
Aliasing
A typical gradient echo sequence begins with a:
Alpha pulse that varies with desired image contrast
The signal intensity on diffusion sequences is related to:
Amount of diffusion
Changing the b-value alters the:
Amplitude, timing, and/or duration of the diffusion gradients
Fourier transformation is performed in the:
Array processor
A gradient echo sequence in which any residual transverse magnetization is removed prior to the next excitation pulse is known as:
At the center of a vessel
The top portion of k-space is a mirror image of the:
Bottom
A FLAIR sequence is utilized to suppress the signal from:
CSF
All of the techniques below can be utilized to optimally time the start of a contrast-enhanced MRA EXCEPT:
Centric k-space filling
The basic MR principle with regard to MR spectroscopy is:
Chemical shift
To evaluate the circle of Willis (COW), 3D TOF MRA sequences are acquired and displayed as an axial view of all of the vasculature. This image is known as:
Collapsed Image
Reducing NSA will reduce the scan time and:
Decrease the SNR
Increasing the number of phase encodings will produce an image with:
Decreased voxel volume
Increasing the number of phase encodings (matrix) from 128 to 256 (by a factor of 2), the SNR:
Decreases
Using a conventional spin echo multi-slice sequence, the number of slices allowed when increasing the TE from 20 to 40ms:
Decreases
Increasing the matrix:
Decreases SNR
Decreasing the receiver bandwidth (narrow BW):
Decreases the number of slices
Reducing the TR down to or below the T1-relaxation time of the tissue:
Decreases the signal-to-noise ration (SNR) of the image and Reduces the contrast based on T2-relaxation times of the tissues
Decreasing the receiver bandwidth (narrow BW):
Increases susceptibility artifact
Between slices 2D acquisitions generally require:
Gaps
To rephase the signal from moving spins, gradient moment nulling techniques use a:
Gradient
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? A. Spin echo EPI B. Gradient echo EPI C. Fast spin echo with driven equilibrium D. 3D spoiled GRE with MTC
Gradient echo EPI
To produce the echo, a gradient echo pulse sequence uses a:
Gradient magnetic field only and RF pulse only
Acquiring half of the phase views of k-space and then interpolating the data for the other half is a technique known as:
Half Fourier
Increasing the receiver bandwidth (wide BW):
Has no effect on the available ETL
Increasing the matrix in the frequency direction from 256 to 512 will:
Have no effect on the scan time
In a fast spin echo sequence, spatial resolution is associated with the:
High amplitude phase-encoding gradients
A major advantage of a 2D time of flight sequence over a 3D time of flight sequence is the ability to:
Image a larger area without saturation of the flowing blood
The effective TE in a fast spin echo pulse sequence determines the:
Image contrast
Dynamic enhanced MRA sequences of the renal arteries are performed with the use of:
Incoherent gradient echoes
Gradient echo sequences acquired for high signal from fluid are known as all of the following EXCEPT:
Incoherent gradient echoes
A gradient echo sequence in which any residual transverse magnetization is removed prior to the next excitation pulse is known as:
Incoherent/spoiled
Doubling the number of signals averaged (NSA) will:
Increase the 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 slice thickness:
Increases SNR
Reducing the TE:
Increases SNR
Increasing the flip angle:
Increases SNR up to the Ernst angle
Increasing slice thickness from 5 to 10mm (by a factor of 2, i.e. 2 x thicker), the SNR:
Increases by a factor of 2
Using a conventional spin echo multi-slice sequence, the number of slices allowed when increasing the TR:
Increases by a factor of TR/TE
Decreasing the receiver bandwidth (narrow BW):
Increases chemical shift artifact
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:
Interleaved acquisition
Using a 3D acquisition, the number of slices allowed when increasing the TR:
Is not affected
Normal blood flow (demonstrated by a parabolic blood flow profile) is known as:
Laminar flow
Increasing the TR yields images with:
Less T1 information
Reducing the flip angle yields images with:
Less T1 information
Reducing the TE yields images with:
Less T2 information
In a fast spin echo (FSE) sequence, acquired with long effective TE (T2-weighted images), scan time can be reduced by the selection of:
Longer ETL
Complete saturation is a condition where:
Longitudinal magnetization is not allowed to recover between excitations
In a fast spin echo sequence, the effective TE is the echo that is performed with the:
Low amplitude phase-encoding gradients
Phase encoding is performed:
Prior to frequency encoding
The presaturation pulses usually occur:
Prior to the excitation pulse
Presaturation pulses are often used to:
Reduce flow artifacts
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 saturation effects
In order to reconstruct an image acquired using parallel imaging, which of the following may be required? A. Test bolus B. Reference or calibration scan C. Back projection D. Half-Fourier acquisition
Reference or calibration scan
During dynamic enhanced imaging for vasculature or visceral structures, contrast is administered and k-space is filled with __________________ to ensure that the contrast enhancement is well visualized.
Reverse centric
When using parallel imaging to reduce acquisition times, which of the following is always true? A. Scan time is reduced and spatial resolution is increased B. Spatial resolution is reduced the greater the acceleration factor selected C. SNR is not affected unless the acceleration factor is greater than 2 D. SNR is reduced and spatial resolution is unaffected
SNR is reduced and spatial resolution is unaffected
In a gradient echo sequence, reducing the flip angle while holding the TR constant reduces:
Saturation
In a time of flight sequence, the tissue is HYPOintense relative to flowing blood because of the:
Saturation effects
To evaluate the circle of Willis (COW), 3D TOF MRA sequences are acquired and background tissue is "carved out" to provide better visualization of the intracranial vasculature. This step is known as:
Segmenting
The evaluation of cardiac function can be provided by any or all of the following EXCEPT:
Short axis single slice, single phase
In a fast spin echo (FSE) sequence, acquired with short effective TE (T1- or PD-weighted images), blurring can be reduced by the selection of:
Shorter ETL
During contrast-enhanced imaging of the abdominal organs, images are acquired without and with gadolinium (Gd) 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 saturation band should be placed ______________ to the axial slices.
Superior
Gradient echo sequences acquired for the evaluation of hemorrhagic lesions rely on:
Susceptibility
If a STIR sequence using a TR of 3000, a TE of 20, and a TI of 140 produces an image with dark fat and bright water. The contrast in such an image is primarily based on:
T1
In which of the following sequences would MS plaques appear hyperintense relative to both CSF and normal white matter? A. T2 FLAIR B. T1 FLAIR C. T2 FSE D. T2 FSE with RF fat suppression
T2 FLAIR
In the multi-echo spin echo sequence shown in Figure C.1, images will be acquired with varying amounts of:
T2 information
In a conventional spin echo multi-echo sequence, it is possible to create multiple images, each with different amounts of:
T2 weighting
Scan time for 2D GRE pulse sequences can be calculated by:
TR x #PEs x NSA
In a spin echo sequence, flowing blood is normally seen as a signal void because the:
TE is too long to image flow and 90° pulse and 180° pulse are both slice selective
In an inversion recovery pulse sequence, the time between the initializing 180° pulse and the 90° pulse is known as:
TI
The time between excitation pulses is known as the:
TR
In a 2D conventional spin echo multi-slice pulse sequence, scan time is given by the equation:
TR (time to repetition) x number of signals averaged (NSA) x number of phase encodings (#PEs)
With conventional spin echo each "line" of k-space is filled in each:
TR period
Scan time for 2D FSE pulse sequences can be calculated by:
TR x #PEs s NSA/ETL
Scan time for 2D IR pulse sequences can be calculated by:
TR x #PEs x NSA
Scan time for 2D SE pulse sequences can be calculated by:
TR x #PEs x NSA
Scan time for a "volume" acquisition can be calculated by:
TR x #PEs x NSA x #slices
Scan time for EPI pulse sequences can be calculated by:
TR x #shots x NSA
In a volume acquisition, the scan time is:
TR x NSA x number of phase encodings x number of slices
The scan time for a 3D (or volume) acquisition is given by:
TR x NSA x number of phase encodings x number of slices
In an inversion recovery pulse sequence, image contrast is controlled by:
TR, TE, and TI
Another name for TI is:
Tau
The intrinsic contrast mechanism with regard to fMRI is:
The BOLD effect
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
The signal intensity on PC MRA sequences is related to:
Velocity-induced phase shift
Ciné (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 time of flight techniques over 2D time of flight 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 (VR)
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
Which of the following would result in an image with the greatest amount of diffusion-weighting?
b-value 1100
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
In a spin echo sequence, the time between the 90° pulse and the 180° pulse is:
½ TE
