What is the term used to measure the magnetic field strength in the periphery of the MRI scan room?
A. SAR
B. Vector
C. Tesla
D. Gauss
D. Gauss
Gauss is used to measure the magnetic field strength in the periphery of the Maria scan room. Tesla measures magnetic field strength in isocenter.
All of the following are potential risk factors for SAR thermal absorption during an MR pulse sequence EXCEPT:
A. Obesity
B. Hypotension
C. Elderly population
D. Diabetes
B. Hypotension
Hypotension (low blood pressure) is not typically considered a primary risk factor for thermal absorption.
A FID crushing artifact can be eliminated with the use of?
A. Flow compensation technique
B. No phase wrap/anti-aliasing
C. Increase NEX
D. A and C
A and C
Increasing NEX helps by averaging out the inconsistent signal, flow compensation (GMN) specifically corrects for phase errors from flowing protons, leading to a more stable signal
____ occurs when tissue outside the FOV is under sampled, causing a misregistration of anatomical location, in the phase direction, but on the opposite side of the anatomical location, also known as wrap-around artifact?
A. Aliasing artifact
B. Chemical shift
C. Zipper
D. Gibbs truncation
A. Aliasing Wrap
To reduce an RF zipper artifact:
A. Increase FOV
B. Oversample phase encoding steps
C. Enable flow compensation
D. Close the scan room door and ensure adequate door suction
D. Close the scan room door and ensure adequate door suction
Which artifact mimics a syrinx in the spine?
A. Zipper
B. FID artifact
C. Truncation
D. Aliasing
C. Truncation
Truncation (Gibbs) causes ringing at high- contrast interfaces. In the spine, this can appear as parallel lines within the spinal cord on a sagittal view, which can be mistaken for syrinx. Increasing the matrix size can reduce this.
Motion is seen as a smearing across the image in the:
A. Phase encoding direction
B. Frequency encoding direction
C. Slice select direction
D. Z axis direction
A. Phase encoding direction
The phase encoding direction takes much longer to complete than the frequency encoding direction. Because of this, patient motion during the scan is smeared or ghosted across this axis.
To reduce the appearance of a Gibbs truncation artifact, the:
A. Number of phase encodings must be increased
B. Number of phase encodings must be decreased
C. NEX must be increased
D. NEX must be decreased
A. Number of phase encodings must be increased
A decrease in the voxel volume yields:
A. Aliasing
B. An increase in partial volume averaging
C. A decrease in partial volume averaging
D. An increase in overall signal to noise
C. A decrease in partial volume averaging
Partial volume averaging occurs when different tissue types are averaged together within a large voxel, obscuring detail. Decreasing the voxel volume reduces this effect, leading to sharper images
A _____ artifact occurs when a tendon or ligament is positioned approximately 55 degrees to the direction of the main magnetic field, and a short TE value pulse sequence is utilized
A. Magic angle
B. Dielectric
C. Aliasing
D. Annefact
E. Parallel imaging
A. Magic angle
A magic angle artifact occurs when a tendon or ligament is positioned approximately 55 degrees to the direction of the main magnetic field, and short TE value pulse sequence is utilized
What causes motion artifact?
Voluntary or involuntary patient movement (breathing, swallowing, cardiac pulsation)
How does motion artifact appear?
Ghosting or blurring in the phase-encoding direction.
How to reduce motion artifact?
Use faster sequences, breath-hold, gating, or immobilization.
What causes chemical shift artifact?
Difference in precessional frequency between fat and water protons.
How does chemical shift artifact appear?
Bright and dark bands at fat-water interfaces.
How to reduce chemical shift artifact?
Use higher bandwidth, lower field strength, or fat-suppression techniques.
What causes susceptibility artifact?
Magnetic field distortions from metal, air, or blood (iron).
What causes Gibbs (Truncation) artifact?
Insufficient data sampling / low matrix size.
How to reduce Gibbs artifact?
Increase matrix size or number of phase-encoding steps.
What causes aliasing artifact?
FOV smaller than body part → signals outside FOV wrap into image.
How to reduce aliasing?
Increase FOV or use anti-aliasing / oversampling techniques.
What causes zipper artifact?
RF interference from outside sources (door not sealed, equipment leakage).
What is magic angle artifact?
Signal increase in tendons oriented ~55° to the main magnetic field (B₀).
How to reduce magic angle artifact?
Use longer TE or reposition the anatomy.
