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Questions and Answers
How does increasing the external magnetic field strength typically affect the T1 relaxation time of a tissue?
How does increasing the external magnetic field strength typically affect the T1 relaxation time of a tissue?
- It shortens the T1 relaxation time.
- It lengthens the T1 relaxation time. (correct)
- It initially shortens and then lengthens the T1 relaxation time.
- It does not affect the T1 relaxation time.
What percentage of its maximum value does the transverse magnetization (TM) reduce to during T2 relaxation?
What percentage of its maximum value does the transverse magnetization (TM) reduce to during T2 relaxation?
- Approximately 13%
- Approximately 37% (correct)
- Approximately 50%
- Approximately 63%
What is the primary factor that T2 relaxation depends on within tissues?
What is the primary factor that T2 relaxation depends on within tissues?
- Strength of the applied radiofrequency pulse.
- Inhomogeneity of local magnetic fields. (correct)
- Temperature of the tissue.
- Homogeneity of external magnetic fields.
Why do water molecules typically exhibit a longer T2 relaxation time compared to tissues with larger molecules?
Why do water molecules typically exhibit a longer T2 relaxation time compared to tissues with larger molecules?
What characteristic of impure liquids or tissues with larger molecules leads to a shorter T2 relaxation time?
What characteristic of impure liquids or tissues with larger molecules leads to a shorter T2 relaxation time?
Which of the following statements accurately describes the T2* (T2 star) relaxation time?
Which of the following statements accurately describes the T2* (T2 star) relaxation time?
How does the motion of molecules within a tissue affect T2 relaxation?
How does the motion of molecules within a tissue affect T2 relaxation?
A researcher observes that a particular tissue sample exhibits a short T2 relaxation time. Which of the following could explain this observation?
A researcher observes that a particular tissue sample exhibits a short T2 relaxation time. Which of the following could explain this observation?
In gradient echo sequences, why is T2* relaxation time typically shorter than T2 relaxation time?
In gradient echo sequences, why is T2* relaxation time typically shorter than T2 relaxation time?
If a tissue has a high degree of local magnetic field homogeneity, how will this affect its T2 relaxation time?
If a tissue has a high degree of local magnetic field homogeneity, how will this affect its T2 relaxation time?
Flashcards
What is T2 relaxation time?
What is T2 relaxation time?
Time taken for transverse magnetization (TM) to disappear or decay to 37% of its maximum value.
What causes T2 relaxation?
What causes T2 relaxation?
Caused by the inhomogeneity of local magnetic fields within tissues.
Why does water have a long T2?
Why does water have a long T2?
Water molecules move fast, their magnetic fields fluctuate rapidly, canceling each other out, leading to a longer T2.
Why do impure liquids have short T2?
Why do impure liquids have short T2?
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Does fat have shorter or longer T2?
Does fat have shorter or longer T2?
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What is T2* (T2 star) relaxation?
What is T2* (T2 star) relaxation?
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How is T1 relaxation affected by magnetic field strength?
How is T1 relaxation affected by magnetic field strength?
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Study Notes
- Impure liquids or tissues with larger molecules move at a slow rate and have short T2
- Fat has shorter T2
- Liquids maintain homogeneity
- Protons stay in phase for a long time resulting in long T2
T1 and T2 Curves
- T1 increases with the strength of the external magnetic field
- T1 at 3T is longer than T1 of the same tissue at 1.5T
T2
- T2 is the time taken by transverse magnetization (TM) to disappear
- Similar to T1, it is considered a 'constant' but not an exact time
- T2 is the time taken for TM to reduce to 37% of its maximum value.
- The T2 curve shows the decrease in magnitude (decay) of the TM plotted against time
- 1/T2 is the transverse relaxation rate
- T2 depends on the inhomogeneity of local magnetic fields within the tissues
- Water molecules move very fast, and their magnetic fields fluctuate fast canceling the magnetic fields
- Due to lack of inhomogeneity, protons stay in phase resulting in long T2 for water
- Impure liquid or tissue with larger molecules move slower, maintaining inhomogeneity; protons go out of phase fast, with short T2
T2* (T2 star)
- T2* is relevant in Gradient Recalled Echo (GRE) sequences
- T2* is less than T2
- In addition to magnetic field inhomogeneity intrinsic to tissues causing spin-spin relaxation, inhomogeneity of the external magnetic field (B0) also causes decay of transverse magnetization (TM).
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