MRI - MIDTERM L2 Flashcards
These are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore of an MR scanner
Gradients
The gradient field slightly distorts the main magnetic field in a _______ pattern
Predictable
The primary purpose of gradient system in MRI is to _________
Create SPATIAL VARIATIONS in the MAGNETIC FIELD
What are the three (3) types of Gradients ?
- X- Gradient (Slice Selection)
- Y-Gradient (Frequency Encoding)
- Z-Gradient (Phase Encoding)
It is a critical component of the MRI system that plays a key role in generating the RF pulses used to excite the protons in the body
Radiofrequency Coils / Transmitter
It is a specific type of coil typically placed directly or near the region of the body being imaged to capture the RF signals emitted by the protons
Surface Coil
It is the process of reducing magnetic field inhomogeneities
Magnetic Shimming
The magnetic field generated by the main magnet in MRI system needs to be ______ as possible to ensure high-quality images
Uniform
What are the Main Types of Shimming ?
- Active Shimming
- Passive Shimming
This uses shim coils which have electronic electronic currents directed through them to generate their own magnetic field, cancelling the remaining field gradients in the main magnetic field
Active Shimming
This uses ferromagnetic pellets or pieces of sheet metal attached to the MRI scanner bore
Passive Shimming
These are used to cool the superconducting magnets that generate the strong magnetic fields necessary for MRI imaging
Cryogens
TRUE OR FALSE
Superconducting Magnets are less efficient than traditional magnets but require extremely high temperatures to maintain their superconducting state.
FALSE
Superconducting Magnets are MORE EFFICIENT than traditional magnets but require extremely LOW TEMPERATURES to maintain their superconducting state.
It is the most commonly used cryogen in MRI systems particularly for cooling the superconducting magnets
Liquid Helium (He-4)
Liquid Helium has a boiling point of __________ which is low enough to keep superconducting magnets at the temperatures required for them to operate
4.2 K (-452.0 °F / -268.9 °C)
It is used as a secondary cooling agent, typically or pre-cooling the magnet before the liquid helium is introduced
Liquid Nitrogen (N2)
The boiling point for Liquid Nitrogen is _______
77 K (-195.8°F / -196.2 °C)
This is used to control the computer
Console
It initiates the appropriate radio-wave transmissions and then receives and analyzes data
Computer
This may be used to perform the same function as those of the operator’s console depending on system configuration
Independent Diagnostic Workstation
It houses the electronics necessary for transmitting the radio-wave pulse sequences and for receiving and analyzing the MRI signal
Computer Room
It represents the strength of the information coming from the tissues being imaged
Signal
These are random variations in the signal that are not related to the tissue properties but come from various sources, including thermal noise in the MRI equipment, electronic noise, or even patient movement.
Noise
It is the _____ of the desired signal to the background noise which influences the quality and clarity of the resulting images
Signal-to-Noise Ratio (SNR)
It is one of the most important factors that affect SNR wherein stronger magnetic fields produce stronger signals and lower magnetic fields produce lower signals
Magnetic Field Strength (B0)
This affects the SNR that when it increases, it collects more signals and thus increases SNR too; smaller quantities of these yield higher resolution images and decrease SNR
Voxel Size and Resolution
This can increase SNR because more signal is accumulated over time while random noise tends to cancel out as more data is collected
Longer Acquisition Time
This results in lower SNR as less signal is accumulated and noise becomes more prominent
Shorter Acquisition Time
These tend to have higher SNR, especially in T1 and T2 Weighted Imaging, because they offer more consistent signal generation
Spin Echo Sequences
It is the time between the middle of the first RF pulse and the peak of the spin echo
Echo Time (ET)
These generally provide faster imaging but can suffer from lower SNR due to factors like susceptibility artifacts and the use of gradient fields.
Gradient Echo Sequences
TRUE OR FALSE
GRE images are typically faster than Spin Echo Sequences
TRUE
It is a conventional spin echo (SE) sequence preceded by a 180° inverting pulse
Inversion Recovery Pulse Sequences
If an SE sequence is denoted by a 90° - 180°-echo, the IR sequence can be written as
180°— (90°- 180°- echo)
The time between the 180° inverting pulse and the 90° pulse
Inversion Time
Their function is to flip the initial longitudinal magnetization (Mo) of all tissues in the image slice or volume
Repetition Time (TR) and Echo Time (TE)
It is an inversion recovery pulse sequence variant where CSF is suppressed to better visualize lesions in the brain
Fluid Attenuated Inversion Recovery (FLAIR)
It is a rapid GRE or SE technique where an entire 2D planar image is acquired in a single or small number of excitations
Echo Planar Imaging (EPI)
It is the FASTEST ACQUISITION method in MRI with 100ms/slice
Echo Planar Imaging (EPI)
It measures the diffusion of water molecules in tissue, particularly useful in detecting early changes in stroke or cancer
Diffusion-Weighted Imaging (DWI) Sequence
It is determined by the random microscopic motion water protons, which measures the motion of spins, specifically in water.
Image Contrast
ADC stands for
Apparent Diffusion Coefficient
It increases SNR because it allows more time for signal acquisition at each frequency, capturing a stronger signal.
Narrower Bandwidth
It decreases SNR, as the signal is spread over a broader frequency range, and thus the signal strength per unit frequency decreases
Wider Bandwidth
This can influence SNR because they may contribute to the magnetic field inhomogeneities
Body Size and Position
This may cause blurring and artifacts that can help improve SNR
Movement
Use of these can enhance the signal in certain tissues, thus improving the SNR in areas of interest
MRI Contrast Agents
What are the five (5) types of Pulse Sequences:
- Spin Echo Sequences
- Gradient Echo Sequences
- Inversion Recovery Pulse Sequences
- Echo Planar Imaging
- Diffusion-Weighted Imaging Sequence
Enumerate the factors affecting SNR (6):
- Magnetic Field Strength
- Voxel Size and Resolution
- Acquisition Time
- Pulse Sequence
- Receiver Bandwidth
- Patient-related Factors
From LARGEST TO SMALLEST, arrange the components of an MR scanner.
A. Magnet, Gradient Coils, RF Coils
B. Magnet, RF Coils, Gradient Coils
C. RF Coils, Gradient Coils, Magnet
D. Gradient Coils, Magnet, RF Coils
A. Magnet, Gradient Coils, RF Coils
