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Questions and Answers
Signal-to-noise ratio (SNR) decreases when voxel volume increases.
Signal-to-noise ratio (SNR) decreases when voxel volume increases.
False
Contrast to noise ratio (CNR) is defined as the difference in SNR between two adjacent areas.
Contrast to noise ratio (CNR) is defined as the difference in SNR between two adjacent areas.
True
Small voxels result in low spatial resolution.
Small voxels result in low spatial resolution.
False
Long scan times can lead to better image quality by reducing patient movement.
Long scan times can lead to better image quality by reducing patient movement.
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Spatial resolution is independent of voxel size.
Spatial resolution is independent of voxel size.
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A large magnet is one of the main hardware components in an MRI system.
A large magnet is one of the main hardware components in an MRI system.
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The static magnetic field in MRI systems can only be created using permanent magnets.
The static magnetic field in MRI systems can only be created using permanent magnets.
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Low signal intensity in an MRI image is represented by the color white.
Low signal intensity in an MRI image is represented by the color white.
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The term 'isointense' refers to regions that are darker than the comparison area.
The term 'isointense' refers to regions that are darker than the comparison area.
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Good contrast-to-noise ratio (CNR) is one of the four characteristics that define an effective MRI protocol.
Good contrast-to-noise ratio (CNR) is one of the four characteristics that define an effective MRI protocol.
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An MRI protocol includes parameters that can affect image quality and characteristics.
An MRI protocol includes parameters that can affect image quality and characteristics.
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When comparing two areas in an MRI, hyperintense refers to the area that is darker than the other.
When comparing two areas in an MRI, hyperintense refers to the area that is darker than the other.
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Achieving high spatial resolution in every MRI image is typically feasible due to the constraints in imaging technology.
Achieving high spatial resolution in every MRI image is typically feasible due to the constraints in imaging technology.
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Areas of high proton density have low signal and low SNR.
Areas of high proton density have low signal and low SNR.
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Larger coils receive less noise relative to signal compared to smaller coils.
Larger coils receive less noise relative to signal compared to smaller coils.
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Phased array coils can increase SNR by combining data from multiple coils.
Phased array coils can increase SNR by combining data from multiple coils.
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The position of the coil has no effect on maximizing SNR.
The position of the coil has no effect on maximizing SNR.
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A long TR increases the SNR by allowing full recovery of longitudinal magnetization.
A long TR increases the SNR by allowing full recovery of longitudinal magnetization.
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A flip angle of 90° creates maximum signal amplitude when the TR is long.
A flip angle of 90° creates maximum signal amplitude when the TR is long.
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Angling the coil can result in an increase of SNR.
Angling the coil can result in an increase of SNR.
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The flip angle can only vary between 0° and 90°.
The flip angle can only vary between 0° and 90°.
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Increasing the magnetic field strength always leads to a decrease in signal-to-noise ratio (SNR).
Increasing the magnetic field strength always leads to a decrease in signal-to-noise ratio (SNR).
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Noise in the context of MRI is predictable and occurs at specific frequencies.
Noise in the context of MRI is predictable and occurs at specific frequencies.
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Signal-to-noise ratio (SNR) is solely dependent on the noise component in the imaging system.
Signal-to-noise ratio (SNR) is solely dependent on the noise component in the imaging system.
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The proton density of the area under examination influences the amplitude of the received signal.
The proton density of the area under examination influences the amplitude of the received signal.
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Coil type and position do not affect the signal-to-noise ratio (SNR).
Coil type and position do not affect the signal-to-noise ratio (SNR).
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Optimizing SNR requires increasing the contribution from noise rather than the signal.
Optimizing SNR requires increasing the contribution from noise rather than the signal.
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The use of a low-field MRI system may compromise the signal-to-noise ratio (SNR).
The use of a low-field MRI system may compromise the signal-to-noise ratio (SNR).
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The number of signal averages (NSA) is one of the factors that can affect the signal amplitude and, thus, the SNR.
The number of signal averages (NSA) is one of the factors that can affect the signal amplitude and, thus, the SNR.
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An increase in the echo time (TE) leads to a higher signal-to-noise ratio (SNR).
An increase in the echo time (TE) leads to a higher signal-to-noise ratio (SNR).
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The number of excitations (NEX) can significantly improve the signal-to-noise ratio (SNR) of an MR image.
The number of excitations (NEX) can significantly improve the signal-to-noise ratio (SNR) of an MR image.
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Reducing the receive bandwidth (BW) by half will increase the SNR by 40%.
Reducing the receive bandwidth (BW) by half will increase the SNR by 40%.
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Large voxels in MRI contain fewer spins than small voxels and thus have a lower SNR.
Large voxels in MRI contain fewer spins than small voxels and thus have a lower SNR.
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The signal-to-noise ratio (SNR) is unaffected by the number of signal averages (NSA) during data collection.
The signal-to-noise ratio (SNR) is unaffected by the number of signal averages (NSA) during data collection.
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A short echo time (TE) allows more coherent transverse magnetization to contribute to the echo.
A short echo time (TE) allows more coherent transverse magnetization to contribute to the echo.
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The typical range for the number of excitations (NEX) in MR imaging is between 1 and 10.
The typical range for the number of excitations (NEX) in MR imaging is between 1 and 10.
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The pixel in an MRI image represents a unit volume of patient tissue known as a voxel.
The pixel in an MRI image represents a unit volume of patient tissue known as a voxel.
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Study Notes
MRI Concepts
- MRI scanners come in various types. Key hardware components include a large magnet to create the magnetic field, shim coils to homogenize the magnetic field, radiofrequency (RF) coils to transmit and receive radio signals into and from the body part being imaged.
MRI Components
- The most important hardware of an MRI system is a large magnet for generating a magnetic field. The static magnetic field can be created via permanent magnets or electromagnets.
- Shim coils are used to make the magnetic field homogeneous.
- RF coils transmit radio signals into the body part being scanned.
- Receiver coils detect returning radio signals.
MRI Image Concepts
- MRI images have contrast if areas of high signal (white) and low signal (dark) exist.
- Intensity: When describing MRI sequences, specific terms describe shades of gray, including high signal intensity (white), intermediate (grey), and low (black).
- Relative terms also describe image appearance, like hyperintense (brighter), isointense (same brightness), and hypointense (darker).
Technical Factors Influencing MRI Image Contrast and Quality
- MRI protocols are sets of rules, parameters selected on the imaging console.
- Protocols are assessed by their ability to highlight anatomy and pathology, with a focus on four characteristics: high signal-to-noise ratio (SNR), good contrast-to-noise ratio (CNR), high spatial resolution, short scan time.
- Optimizing one parameter may require compromising another. This necessitates informed decision-making based on specific patient needs and pathology, using understanding of underlying physics.
Signal-to-Noise Ratio (SNR)
- SNR is the ratio of signal amplitude to background noise amplitude.
- Signal is predictable, occurring at specific frequencies (Larmor frequency) and times (TE).
- Noise is unpredictable, random in time and space, primarily coming from thermal motion in the patient and electrical noise in the system. Maximizing SNR means making the signal contribution greater than the noise.
- Factors affecting SNR include magnetic field strength, proton density of the region, coil type/position, TR (repetition time), TE (echo time), flip angle, number of signal averages (NSA), receive bandwidth, and voxel volume.
Contrast-to-Noise Ratio (CNR)
- CNR is the difference in SNR between adjacent areas.
- It's crucial for distinguishing areas of high and low signal.
- CNR is influenced by the same factors as SNR.
Spatial Resolution
- Spatial resolution is the ability to distinguish two separate points.
- Small voxel size leads to high spatial resolution, enabling differentiation of small structures.
- Large voxel size leads to lower resolution, where small structures are not distinct.
Scan Time
- Scan time is the duration of data acquisition or filling k-space.
- Short scan times are preferable to minimize motion artifacts. Optimization of scan time is crucial considering patient motion during the scan affecting image quality.
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Description
This quiz covers the essential concepts and components of MRI technology. Understand the critical hardware, including magnets, shim coils, and RF coils, and how they function together to produce high-quality images. Test your knowledge on the principles behind MRI image formation and signal intensity.
