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Questions and Answers
What is T1 recovery primarily caused by?
What is T1 recovery primarily caused by?
- Spin lattice energy transfer (correct)
- Dephasing of nuclei
- Spin–spin energy transfer
- External magnetic field inhomogeneity
Which statement about T2 decay is correct?
Which statement about T2 decay is correct?
- T2 decay is faster than T1 recovery in all tissues.
- T2 decay involves the loss of phase coherence. (correct)
- T2 decay is caused by interactions with surrounding tissue Gs.
- The T2 time is invariant across different types of tissues.
How does T1 recovery differ between fat and water?
How does T1 recovery differ between fat and water?
- Both have the same T1 recovery time.
- Water absorbs energy rapidly compared to fat.
- Fat recovers energy more quickly than water, resulting in a shorter T1 time. (correct)
- Fat has a longer T1 time than water.
What happens to the NMV during saturation?
What happens to the NMV during saturation?
Which factor determines how much T1 recovery occurs in a particular tissue?
Which factor determines how much T1 recovery occurs in a particular tissue?
Which sequence describes the relationship between T2* and T2?
Which sequence describes the relationship between T2* and T2?
What is the time taken for 63% of the longitudinal magnetization to recover known as?
What is the time taken for 63% of the longitudinal magnetization to recover known as?
Which process primarily contributes to T2 decay?
Which process primarily contributes to T2 decay?
What predominantly influences the contrast in T1 weighted images?
What predominantly influences the contrast in T1 weighted images?
What is the typical TR range for T1 weighted imaging?
What is the typical TR range for T1 weighted imaging?
How do short TEs affect the appearance of fat and water in T2 weighted imaging?
How do short TEs affect the appearance of fat and water in T2 weighted imaging?
In T2 weighted images, which tissue exhibits a high signal due to its long T2 decay time?
In T2 weighted images, which tissue exhibits a high signal due to its long T2 decay time?
What are the typical TE parameters for T2 weighted imaging?
What are the typical TE parameters for T2 weighted imaging?
What does proton density weighting emphasize in MR imaging?
What does proton density weighting emphasize in MR imaging?
Which tissue type is always dark on MR images because of low proton density?
Which tissue type is always dark on MR images because of low proton density?
What is a key characteristic of T2 weighted images regarding tissue with short T2 decay times?
What is a key characteristic of T2 weighted images regarding tissue with short T2 decay times?
What is the main component that determines the contrast in MR images?
What is the main component that determines the contrast in MR images?
Which intrinsic contrast mechanism is characterized by the return of longitudinal magnetization?
Which intrinsic contrast mechanism is characterized by the return of longitudinal magnetization?
Which parameter is NOT an extrinsic contrast parameter in MR imaging?
Which parameter is NOT an extrinsic contrast parameter in MR imaging?
How do fat and water differ in terms of molecular motion and energy absorption?
How do fat and water differ in terms of molecular motion and energy absorption?
What effect does faster molecular motion have on energy release?
What effect does faster molecular motion have on energy release?
What does the term 'Free Induction Decay (FID)' refer to in MR imaging?
What does the term 'Free Induction Decay (FID)' refer to in MR imaging?
Which component is most affected by relaxation processes in MR imaging?
Which component is most affected by relaxation processes in MR imaging?
How do intrinsic contrast mechanisms influence MR imaging?
How do intrinsic contrast mechanisms influence MR imaging?
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Study Notes
Image Contrast Mechanisms
- High signal areas (large transverse magnetization) appear white in images.
- Low signal areas (small transverse magnetization) appear dark in images.
- Intermediate signal areas are displayed as shades of gray.
Contrast in MR vs. CT
- MR contrast is influenced by two types of parameters: extrinsic (operator-controlled) and intrinsic (not operator-controlled).
Extrinsic Contrast Parameters
- Repetition Time (TR): Time interval between RF pulse applications.
- Echo Time (TE): Duration from RF pulse to signal collection.
- Flip Angle: Angle of the NMV movement due to an RF pulse.
- Turbo-Factor (ETL/TF): Influences echo train length.
- Time from Inversion (TI): Time elapsed following an inversion pulse.
Intrinsic Contrast Mechanisms
- T1 Recovery: Time for longitudinal magnetization recovery.
- T2 Decay: Time for loss of transverse magnetization.
- Proton Density: Variation based on number of hydrogen protons.
- Flow: Movement contributing to signal changes.
- Apparent Diffusion Coefficient (ADC): Reflects tissue diffusion properties.
Molecular Motion
- Molecules exhibit rotational and translational motion.
- Faster motion complicates energy release to surroundings.
Composition of Fat and Water
- Fat:
- Large molecules, slow molecular motion, low energy absorption efficiency.
- Water:
- Small molecules, high molecular motion, high energy absorption inefficiency.
Relaxation Processes
- RF pulse induces resonance, followed by signal decay upon pulse removal (free induction decay, FID).
- Differences in relaxation rates among tissues create contrast during imaging.
T1 Recovery
- T1 recovery involves energy transfer (spin-lattice) as NMV returns to alignment with B0.
- Recovery is exponential and varies by tissue type.
- Short TRs result in incomplete recovery for both fat and water.
T2 Decay
- T2 decay represents the time for 63% of transverse magnetization loss due to dephasing.
- Caused by spin-spin energy transfer and results in signal decay.
- T2 time varies among different tissues.
Imaging Techniques
- T1 Weighted Images:
- Short TR, short TE; highlights anatomical detail.
- Fat appears bright; water appears dark (high contrast).
- T2 Weighted Images:
- Long TR, long TE; emphasizes pathology.
- Fat appears dark; water appears bright.
- Proton Density (PD) Weighted Images:
- Long TR, short TE; highlights differences in hydrogen proton density.
- Low PD areas are dark; high PD areas are bright.
Contrast Examples in T1 and T2 Weighting
- T1: Bright high signals from fat compared to water.
- T2: Dark appearance of fat against bright water background, emphasizing pathology.
Key Parameters for Imaging
- T1 Weighted: TR 300-600 ms, TE 10-30 ms.
- T2 Weighted: TR 2000 ms+, TE 70 ms+.
- PD Weighted: Long TR and short TE to reduce T1 and T2 effects.
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