Podcast
Questions and Answers
T1 recovery time in brain tissue at 1 T is long relative to fat.
T1 recovery time in brain tissue at 1 T is long relative to fat.
False (B)
T2 decay occurs via spin–spin relaxation.
T2 decay occurs via spin–spin relaxation.
True (A)
The molecular motion of fat molecules is relatively fast compared to water molecules.
The molecular motion of fat molecules is relatively fast compared to water molecules.
False (B)
Hydrogen atoms in water molecules are arranged with one oxygen atom.
Hydrogen atoms in water molecules are arranged with one oxygen atom.
Both T1 recovery and T2 decay are exponential processes.
Both T1 recovery and T2 decay are exponential processes.
Fat has low inherent energy and easily absorbs energy into its lattice.
Fat has low inherent energy and easily absorbs energy into its lattice.
T1 recovery time is defined as the time taken for 50% of longitudinal magnetization to recover.
T1 recovery time is defined as the time taken for 50% of longitudinal magnetization to recover.
Water has a lower molecular mobility than fat.
Water has a lower molecular mobility than fat.
T2 decay occurs because the magnetic fields of hydrogen nuclei do not interact with each other.
T2 decay occurs because the magnetic fields of hydrogen nuclei do not interact with each other.
The T2 decay time of water is longer than that of fat due to the less efficient spin-spin interactions.
The T2 decay time of water is longer than that of fat due to the less efficient spin-spin interactions.
Molecular tumbling in fat matches the Larmor frequency, allowing for efficient energy exchange from hydrogen.
Molecular tumbling in fat matches the Larmor frequency, allowing for efficient energy exchange from hydrogen.
T1 recovery is more efficient in water compared to fat.
T1 recovery is more efficient in water compared to fat.
The apparent diffusion coefficient (ADC) is an intrinsic parameter affecting image contrast.
The apparent diffusion coefficient (ADC) is an intrinsic parameter affecting image contrast.
T2 decay takes longer in fat than in water.
T2 decay takes longer in fat than in water.
The efficient T2 decay in fat is a result of closely packed hydrogen nuclei increasing spin-spin interactions.
The efficient T2 decay in fat is a result of closely packed hydrogen nuclei increasing spin-spin interactions.
Extrinsic contrast parameters include T1 recovery time and proton density.
Extrinsic contrast parameters include T1 recovery time and proton density.
Tissue with a large transverse magnetization at time TE results in a dark area on the image.
Tissue with a large transverse magnetization at time TE results in a dark area on the image.
Water has a high signal and appears hyperintense on a T1 contrast image.
Water has a high signal and appears hyperintense on a T1 contrast image.
The TR must be shorter than the T1 times of both fat and water to achieve proper T1 contrast.
The TR must be shorter than the T1 times of both fat and water to achieve proper T1 contrast.
Fat appears hyperintense and has a high signal on a T2 contrast image.
Fat appears hyperintense and has a high signal on a T2 contrast image.
A long TE provides sufficient time for both fat and water to dephase.
A long TE provides sufficient time for both fat and water to dephase.
If TR is too long, both fat and water will return to B0 and fully recover their longitudinal magnetization.
If TR is too long, both fat and water will return to B0 and fully recover their longitudinal magnetization.
The signal amplitude received by the coil is small for tissues with small components of in-phase magnetization.
The signal amplitude received by the coil is small for tissues with small components of in-phase magnetization.
T1 time of fat is longer than that of water.
T1 time of fat is longer than that of water.
Flashcards
Contrast mechanisms
Contrast mechanisms
The difference in signal intensity between tissues due to varying relaxation times.
T2 relaxation time
T2 relaxation time
The time it takes for the transverse magnetization to decay to 37% of its original value.
T1 relaxation time
T1 relaxation time
The time it takes for the longitudinal magnetization to recover to 63% of its original value.
T1 weighting
T1 weighting
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T2 weighting
T2 weighting
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TE (Time to Echo)
TE (Time to Echo)
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TR (Repetition time)
TR (Repetition time)
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T1-weighted sequence
T1-weighted sequence
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T1 recovery time
T1 recovery time
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T1 recovery in fat
T1 recovery in fat
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T1 recovery in water
T1 recovery in water
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T2 decay
T2 decay
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Spin-spin relaxation
Spin-spin relaxation
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T2 decay in water
T2 decay in water
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T2 decay time
T2 decay time
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T2 decay in fat
T2 decay in fat
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T2* decay time
T2* decay time
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Image contrast
Image contrast
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Image Contrast Factors
Image Contrast Factors
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Repetition Time (TR)
Repetition Time (TR)
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Echo Time (TE)
Echo Time (TE)
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Proton Density (PD)
Proton Density (PD)
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Study Notes
Image Weighting and Contrast
- Image weighting and contrast are crucial in diagnostic imaging.
- This presentation outlines T1 recovery, T2 decay, tissue relaxation, image contrast, and contrast mechanisms.
- T1 recovery is the time (63%) for longitudinal magnetization to recover in a tissue due to spin-lattice energy transfer.
- T2 decay is the time (63%) for transverse magnetization to decay due to dephasing.
- T1 recovery and T2 decay are exponential processes governed by time constants.
- T1 recovery times vary between tissues, impacting contrast.
- Water has a long T1 recovery time.
- Fat has a short T1 recovery time.
- T2 decay times also differ between tissues (fat versus water) and affect contrast.
- Fat has a short T2 decay time.
- Water has a long T2 decay time.
Image Contrast
- Contrast in diagnostic imaging has two main categories: intrinsic and extrinsic.
- Intrinsic contrast arises from tissue properties (T1 recovery, T2 decay, proton density, flow, and ADC).
- Extrinsic contrast is affected by parameters in MRI (TR, TE, flip angle, TI, turbo factor, echo train length, and B value).
- Larger transverse magnetization components at TE time result in brighter images on the coil.
- Smaller transverse magnetization components lead to darker areas on the coil image.
T1 Contrast
- T1 contrast is affected by the time taken to recover longitudinal magnetization components.
- A shorter TR value results in a higher signal from fat, appearing brighter on a T1-weighted image.
- Water has a longer T1 recovery time, resulting in a lower signal compared to fat.
- Water appears darker in a T1-weighted image.
- A longer TR value allows both fat and water to fully recover, eliminating a contrast difference in both tissues.
T2 Contrast
- T2 contrast depends on the time taken for transverse magnetization components to decay.
- A long TE, allows both fat and water sufficient time to fully dephase.
- Longer T2 times cause a lower signal than those with shorter T2 decay times.
- Fat appears brighter because they dephase faster than water following the RF pulse.
- To highlight differences, a longer TE time is required and this results in hypointense fat tissue with a brighter water tissue.
Relaxation in Different Tissues (Fat and Water)
- Fat molecules have hydrogen atoms closely packed with relatively slow molecular motion.
- Water molecules have hydrogen atoms spaced apart with relatively fast molecular motion.
- These differences in molecular motion affect relaxation times (T1 and T2).
- Fat's faster relaxation rate leads to a shorter T1 and T2 time when compared to water.
Image Contrast Definitions
- T1 recovery and time: The recovery of longitudinal magnetization due to spin-lattice.
- T1 contrast: Fat is hyperintense and water is relatively hypointense due to shorter T1 time.
- T1 weighting: An imaging technique used to highlight differences in T1 recovery times between tissues.
- T2 decay and time: Decay of coherent transverse magnetization due to spin-spin relaxation.
- T2 contrast: Fat is hypointense and water is relatively hyperintense due to longer T2 time.
- T2 weighting: An imaging technique used to highlight differences in T2 relaxation times between tissues.
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