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Questions and Answers
What is the difference in resonant frequency between fat and water protons at 1.5 T?
What is the difference in resonant frequency between fat and water protons at 1.5 T?
What is the most common cause of chemical shift artifacts?
What is the most common cause of chemical shift artifacts?
What is the purpose of gradients coils in MRI?
What is the purpose of gradients coils in MRI?
What is the most common way for T2 relaxation to occur?
What is the most common way for T2 relaxation to occur?
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What type of energy loss occurs when the spin system is in a pure state of rotation?
What type of energy loss occurs when the spin system is in a pure state of rotation?
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What is the most effective way to reduce truncation errors in the Fourier representation of images?
What is the most effective way to reduce truncation errors in the Fourier representation of images?
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What type of energy loss occurs when the spin system is in a spin-up state and energy is transferred into nearby nuclei, atoms, and molecules?
What type of energy loss occurs when the spin system is in a spin-up state and energy is transferred into nearby nuclei, atoms, and molecules?
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How is the FID signal generated?
How is the FID signal generated?
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How is the z-gradient produced?
How is the z-gradient produced?
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How does Philips define receiver bandwidth?
How does Philips define receiver bandwidth?
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What type of noise levels can cause permanent threshold shifts (PTS)?
What type of noise levels can cause permanent threshold shifts (PTS)?
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What is the partial volume effect?
What is the partial volume effect?
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What is the relationship between SAR and RF frequency?
What is the relationship between SAR and RF frequency?
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What is the peak of the echo caused by?
What is the peak of the echo caused by?
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What is the effect of making TE short compared to T2?
What is the effect of making TE short compared to T2?
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What is the purpose of reducing the height of the readout gradient but increasing its width?
What is the purpose of reducing the height of the readout gradient but increasing its width?
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How does SAR affect tissue temperature?
How does SAR affect tissue temperature?
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What is the most common artifact seen around water-containing structures?
What is the most common artifact seen around water-containing structures?
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What type of protection is mandatory for all patients undergoing MRI?
What type of protection is mandatory for all patients undergoing MRI?
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What is the time between the 180° inverting pulse and the 90°-pulse in an inversion recovery (IR) sequence?
What is the time between the 180° inverting pulse and the 90°-pulse in an inversion recovery (IR) sequence?
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What type of MRI is used to image the body in different parts of the body?
What type of MRI is used to image the body in different parts of the body?
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What is the most effective way to reduce artifacts caused by physiologic motions?
What is the most effective way to reduce artifacts caused by physiologic motions?
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What is the unit of measurement for receiver bandwidth?
What is the unit of measurement for receiver bandwidth?
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What is the effect of certain medications on thermoregulatory responses?
What is the effect of certain medications on thermoregulatory responses?
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What is the main purpose of an inversion recovery (IR) sequence?
What is the main purpose of an inversion recovery (IR) sequence?
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What is the relationship between the signal intensity (S) of a SE sequence and [H]?
What is the relationship between the signal intensity (S) of a SE sequence and [H]?
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What does Ampère's Law describe?
What does Ampère's Law describe?
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What type of MRI is used to image the body in different parts of the body, depending on the level of stimulus that is being used?
What type of MRI is used to image the body in different parts of the body, depending on the level of stimulus that is being used?
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What type of images are produced by different methods and have different properties?
What type of images are produced by different methods and have different properties?
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What technique may be used to reduce truncation artifacts while still maintaining image quality?
What technique may be used to reduce truncation artifacts while still maintaining image quality?
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What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied?
What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied?
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What does FOV stand for?
What does FOV stand for?
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What direction are artifacts most prominent in?
What direction are artifacts most prominent in?
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What is the relationship between SAR and RF-flip angle?
What is the relationship between SAR and RF-flip angle?
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What is the purpose of a RF-pulse?
What is the purpose of a RF-pulse?
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What is the effect of making TE long compared to T2?
What is the effect of making TE long compared to T2?
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What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place?
What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place?
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How are MR images produced?
How are MR images produced?
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What is the effect of body size on SAR?
What is the effect of body size on SAR?
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What is the most common artifact seen around fat?
What is the most common artifact seen around fat?
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What is the right-hand rule used for?
What is the right-hand rule used for?
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What is the purpose of T1 relaxation?
What is the purpose of T1 relaxation?
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What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place, and the type of magnetic field that is being used?
What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place, and the type of magnetic field that is being used?
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What is the relationship between FOV and the spacing between samples in k-space?
What is the relationship between FOV and the spacing between samples in k-space?
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What is the most effective way to reduce artifacts propagated in the phase?
What is the most effective way to reduce artifacts propagated in the phase?
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What is the purpose of the dephase lobe?
What is the purpose of the dephase lobe?
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What is the effect of regional perfusion on tissue temperature?
What is the effect of regional perfusion on tissue temperature?
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What is the most effective way to minimize truncation errors?
What is the most effective way to minimize truncation errors?
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What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place, and the type of magnetic field that is being used, and the type of person that is being scanned?
What type of MRI is used to image the body in different parts of the body, depending on the type of stimulus that is being used and the time that the stimulus is being applied, and the type of relaxation that is taking place, and the type of magnetic field that is being used, and the type of person that is being scanned?
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When was the use of fast spin echo (FSE) signal generation introduced?
When was the use of fast spin echo (FSE) signal generation introduced?
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Study Notes
- Gradients coils are used to encode the MR signal in space.
- Gradients are created by sending current in opposite directions through coils, and they produce a gradient field that slightly distorts the main magnetic field.
- The direction and magnitude of gradient fields can be appreciated by using Ampère's Law and the right-hand rule.
- The z-gradient is produced using two coils carrying current in opposite directions, and this is known as a Maxwell coil configuration.
- When added to the constant (Bo) field, the result is a gradually increasing field along the z-axis.
- SAR is a measure of the amount of power deposited by a radiofrequency field in a certain mass of tissue.
- SAR increases significantly with body size.
- SAR is proportional to the square of the RF frequency.
- SAR is proportional to the square of the RF-flip angle.
- SAR is a measure of the intensity of RF radiation.
- SAR is only one factor that determines tissue temperature.
- Certain factors, like regional perfusion, baseline patient body temperature, and the patient's thermoregulatory capacity, can also affect tissue temperature.
- Overheating is a risk for patients with reduced thermoregulatory capacities, like infants, pregnant women, the elderly, obese, diabetics, febrile patients, and those with cardiac decompensation.
- Certain medications, like beta-blockers, diuretics, calcium-channel blockers, amphetamines, and sedatives, can also impair thermoregulatory responses.
- These factors should always be considered when scanning a susceptible patient, even if predicted SAR values seem to be within safe limits.
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