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Questions and Answers
What is the primary factor that affects the spatial resolution in MRI?
What happens to the image resolution when the field of view is decreased?
What is the purpose of increasing the image matrix size in MRI?
What is the relationship between the field of view and the image resolution?
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What is the effect of increasing the slice thickness on the spatial resolution?
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What is the primary advantage of using a higher image matrix size?
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How does the repetition time affect the scan time?
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What is the effect of reducing the field of view on the image quality?
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What is the trade-off when increasing the spatial resolution of an image?
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What is the effect of decreasing the field of view (FOV) on the resolution and SNR?
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What is the effect of increasing the matrix size on the resolution and acquisition time?
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How does doubling the signal impact the signal to noise ratio (SNR)?
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What is the effect of increasing the number of averages on the signal to noise ratio (SNR)?
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What is the primary cost of phase encoding in MRI?
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What is the effect of increasing the field strength on the signal to noise ratio (SNR)?
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What is the effect of decreasing the bandwidth on the acquisition time?
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What is the effect of reducing the number of sequences on the acquisition time?
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What is the trade-off when optimizing coils to improve the signal to noise ratio (SNR)?
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What is the effect of increasing the matrix size on the voxel size and signal reception?
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How does increasing the Field of View (FOV) affect the Signal-to-Noise Ratio (SNR)?
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What is the effect of increasing the matrix size in the phase encoding direction on scan time?
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How does the Repetition Time (TR) affect scan time?
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What is the purpose of increasing the number of excitation (NEX) or averages?
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How does increasing the number of excitation (NEX) or averages affect scan time?
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What is the relationship between signal and scan time?
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What is the limitation on the Repetition Time (TR)?
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Study Notes
MRI Image Quality
- Evaluating image quality involves four main characteristics: spatial resolution, contrast, signal-to-noise ratio (SNR), and scan time.
Spatial Resolution
- Spatial resolution measures the size of the smallest detail that can be differentiated in an image.
- It depends on the image matrix, field of view (FOV), and slice thickness.
- A smaller FOV can increase spatial resolution, but may lead to phase wrap artifacts if the FOV is smaller than the area of interest.
- Increasing the matrix size can also improve spatial resolution, but may increase acquisition time and decrease SNR.
Field of View (FOV)
- FOV refers to the distance over which an MR image is acquired or displayed.
- A smaller FOV can increase spatial resolution by forcing pixels to get smaller to fit the smaller FOV.
- A larger FOV can decrease spatial resolution by forcing pixels to expand to fit the larger FOV.
Image Matrix
- The usual MRI 2D matrix size is 128 x 128 or 256 x 256.
- A larger image matrix (e.g. 320 x 320 or 512 x 512) can improve spatial resolution.
Signal-to-Noise Ratio (SNR)
- SNR is the ratio of the signal to the noise in an image.
- Increasing the signal or decreasing the noise can improve SNR.
- Strategies to improve SNR include: • Increasing the voxel size by decreasing the matrix or increasing the slice thickness. • Increasing the spin density. • Optimizing coils. • Increasing the number of averages (but this will increase acquisition time). • Increasing the field strength (e.g. from 1.5T to 3T). • Decreasing the bandwidth.
Scan Time
- Scan time is affected by the repetition time (TR), number of phase-encoding steps, and number of excitations (NEX).
- Increasing the matrix size in the phase-encoding direction can increase resolution, but also increases scan time.
- Increasing the number of excitations (NEX) or averages can increase signal and quality, but also increases scan time.
- Repetition time (TR) is a factor that directly controls scan time and measures the time from one excitation pulse to the next in milliseconds.
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Description
Evaluate MRI image quality based on spatial resolution, contrast, signal-to-noise ratio, and scan time. Understand the concept of spatial resolution, pixel vs voxel, and more.
