30 Questions
Which of the following is a cause of phase mismapping artifact?
Anatomy moving along the phase-encoding gradient
What type of motion can cause phase mismapping?
All of the above
What is the effect of distance from the source of motion on ghosting artifact?
Ghosting becomes less obvious
What does the physical separation between each ghost depend on?
The amplitude of the phase-encoding gradient
What is the result of repetitive motion during the scan?
Periodic perturbations of the data collected in k-space
What is the term used to describe the incorrect spatial locations of moving anatomy in the image?
Phase mismapping
Which gradient is applied at a different amplitude every TR?
Phase-encoding gradient
Which direction does ghosting artifact occur along the phase encoding axis of the image?
Anterior to posterior
What is the purpose of swapping phase and frequency in imaging?
To change the direction of ghosting artifact
Which technique can be used to reduce or eliminate motion artifact from respiration in chest and abdominal imaging?
Respiratory compensation
What factors affect the separation between ghosts in an image?
TR, phase matrix, and NSA
What is the purpose of presaturation pulses in imaging?
To null signal from specified areas
Which type of respiratory sensor tracks the position of the diaphragm using a navigator echo?
Software-based strategy
What is the purpose of reordering the lines of k-space in respiratory compensation techniques?
To reflect the periodic motion of breathing throughout the scan
Which technique utilizes signal collected by the transducer or navigator echoes to select a threshold (gate) that only allows data through when a certain condition is met?
Respiratory gating
What is the main drawback of respiratory triggering?
The periodicity of the patient's respiratory cycle becomes the TR and determines the image contrast.
What trade-off is associated with respiratory gating?
Up to 60% of the data may be rejected, increasing the acquisition time.
What is the purpose of increasing the NSA (number of signal averages) in MRI?
To reduce motion artifact
What is the trade-off associated with increasing the NSA in MRI?
Scan time is increased by an entire acquisition period for every additional signal average.
What is the purpose of cardiac triggering in MRI?
To monitor cardiac motion
Which form of triggering uses electrodes and lead wires attached to the patient's chest to produce an EKG for determining the timing of each RF excitation pulse?
Electrocardiogram (ECG, EKG) gating
Which type of triggering is more accurate for imaging the heart itself?
EKG triggering
Peripheral triggering is effective at reducing phase mismapping when imaging which structures?
Small vessels
What does gradient moment rephasing help reduce?
Ghosting caused by flowing nuclei
Which type of triggering is used to acquire each slice at the same phase of the cardiac cycle?
Pulsation triggering
When is peripheral triggering not very useful for imaging the heart itself?
When imaging the heart itself
What is the purpose of pulsation triggering?
To acquire each slice at the same phase of the cardiac cycle
What is the main advantage of EKG triggering over peripheral triggering?
Being more accurate for imaging the heart itself
When is peripheral triggering effective at reducing phase mismapping?
When imaging small vessels
What is the main purpose of gradient moment rephasing?
To reduce ghosting caused by flowing nuclei
Test your knowledge on respiratory signal processing and k-space reordering in this quiz. Explore the concepts behind tracking diaphragm position, measuring amplitude, and eliminating breathing motion artifacts in k-space data.
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