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Questions and Answers
Which parameter is associated with intrinsic contrast?
Which parameter is associated with intrinsic contrast?
- Flip angle
- B value
- T2 decay time (correct)
- Turbo factor
What results in high signal in terms of intrinsic contrast?
What results in high signal in terms of intrinsic contrast?
- Large signal amplitude received by the coil (correct)
- Small transverse magnetization components
- Low proton density
- Long $T1$ recovery times
Which parameter is NOT a part of extrinsic contrast mechanisms?
Which parameter is NOT a part of extrinsic contrast mechanisms?
- Apparent diffusion coefficient (ADC)
- T1 recovery time (correct)
- Time of echo (TE)
- Flow
What is the relationship between fat and water regarding T1 contrast?
What is the relationship between fat and water regarding T1 contrast?
What ultimately leads to the appearance of a bright area on an image in T1 contrast?
What ultimately leads to the appearance of a bright area on an image in T1 contrast?
What happens if the TR is set too long when imaging fat and water?
What happens if the TR is set too long when imaging fat and water?
Which signal characteristic is true for fat on a T1 contrast image?
Which signal characteristic is true for fat on a T1 contrast image?
In terms of T2 weighting, which statement accurately describes water?
In terms of T2 weighting, which statement accurately describes water?
What is necessary regarding TE to ensure proper imaging of fat and water?
What is necessary regarding TE to ensure proper imaging of fat and water?
How does the T2 times of fat compare to that of water?
How does the T2 times of fat compare to that of water?
What is the term for the time it takes for 63% of longitudinal magnetization to recover in a tissue?
What is the term for the time it takes for 63% of longitudinal magnetization to recover in a tissue?
What causes T1 recovery in tissues?
What causes T1 recovery in tissues?
Which tissue type has a short T1 recovery time?
Which tissue type has a short T1 recovery time?
The primary contrast in MRI is due to differences in which two substances?
The primary contrast in MRI is due to differences in which two substances?
Which of the following correctly describes the molecular tumbling rate of water compared to fat?
Which of the following correctly describes the molecular tumbling rate of water compared to fat?
What is the difference in energy absorption between fat and water during T1 recovery?
What is the difference in energy absorption between fat and water during T1 recovery?
In the context of T1 recovery and T2 decay, what do the terms 'exponential processes' refer to?
In the context of T1 recovery and T2 decay, what do the terms 'exponential processes' refer to?
How is T2 decay primarily characterized?
How is T2 decay primarily characterized?
What is the main reason for less efficient T1 recovery in fat?
What is the main reason for less efficient T1 recovery in fat?
How does T2 decay time differ between fat and water?
How does T2 decay time differ between fat and water?
What is primarily responsible for efficient T2 decay in fat?
What is primarily responsible for efficient T2 decay in fat?
What accounts for the rapid loss of coherent transverse magnetization in fat?
What accounts for the rapid loss of coherent transverse magnetization in fat?
What is the result of magnetic moments of hydrogen nuclei dephasing quickly in fat?
What is the result of magnetic moments of hydrogen nuclei dephasing quickly in fat?
Which statement regarding the efficiency of T2 decay in water is accurate?
Which statement regarding the efficiency of T2 decay in water is accurate?
What primarily affects the image contrast in diagnostic imaging?
What primarily affects the image contrast in diagnostic imaging?
Which of the following accurately describes T2* decay?
Which of the following accurately describes T2* decay?
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Study Notes
T1 Recovery
- T1 recovery is the time it takes for 63% of longitudinal magnetization to recover in a tissue.
- It occurs because hydrogen nuclei give up their energy to the surrounding environment, or molecular lattice.
- T1 recovery is an exponential process, with the T1 recovery time representing the time it takes for 63% of the magnetization to recover in the longitudinal plane.
T2 Decay
- T2 decay is the time it takes for 63% of the transverse magnetization to decay due to dephasing.
- T2 decay occurs because of interactions (magnetic fields and spin-spin interactions) between the magnetic moments of hydrogen nuclei.
- T2 decay is an exponential process, with the T2 decay time representing the time it takes for 63% of the magnetization to be lost in the transverse plane.
Relaxation in different tissues
- Fat and water have significantly different T1 and T2 relaxation times.
- Fat molecules are closely packed together, with slow molecular tumbling rates.
- Water molecules are spaced apart, with faster molecular tumbling rates.
Fat
- Fat has a short T1 recovery time, which means it recovers longitudinal magnetization more quickly compared to water.
- This is because fat has a lower inherent energy and easily absorbs energy from hydrogen nuclei.
- Fat also has a short T2 decay time, due to the close proximity of molecules and spin-spin interactions.
Water
- Water has a long T1 recovery time, as it has a higher inherent energy and does not easily absorb energy from hydrogen nuclei.
- Water also has a long T2 decay time due to its molecular spacing, resulting in less frequent spin-spin interactions.
Image Contrast
- Image contrast in Magnetic Resonance Imaging (MRI) is affected by intrinsic parameters (T1, T2, proton density) and extrinsic parameters (TR, TE, flip angle, TI).
- Tissues with a large transverse component of magnetization at time TE will have a high signal, appearing bright, and vice versa.
T1 Contrast
- T1 contrast is achieved by using a short TR (shorter than both T1 times of fat and water).
- This results in fat having a high signal, appearing hyperintense, while water appears hypointense.
T2 Contrast
- T2 contrast is achieved by using a long TE (longer than both T2 times of fat and water).
- This results in water having a high signal, appearing hyperintense, while fat appears hypointense.
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