Questions and Answers
What is the fundamental equation in MR imaging known as?
What is the frequency at which resonance of the nuclei is excited?
Larmor frequency
What is the image phenomenon where darks become bright and brights become dark called?
Contrast reversal
What is the measurement of the decay of Mxy and T2 interactions known as?
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What is the time required for a system to return to its equilibrium state called?
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What is the time taken for 63% of the longitudinal magnetization to recover called?
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What is the time taken for 63% of the transverse magnetization to decay known as?
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A ______ process must occur in order to eliminate effects of field inhomogeneity.
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A rephrasing process must occur in order to eliminate the effects of field inhomogeneity, this process allows one to measure the ______.
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What defines the level of detail of an image in MR imaging?
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The strength of the signal in an MRI read depends on the proton density and on the (2) ______.
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What describes the net magnetization vector being moved from the Z-axis to the transverse plane?
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What is the component of the bulk magnetization in the XY plane called?
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What pulse is followed by a 90-degree RF pulse in an inversion recovery sequence?
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What is the time in milliseconds between the application of the 90° pulse and the peak of the echo signal called?
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What defines the repetition time in pulse sequences?
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What allows information from many different slices of the patient to be obtained during the waiting periods of the pulse sequence?
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What describes the sum total of all precessing in phase photons in the same direction?
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What describes the quantity of resonating spins in a tissue expressed as a percentage of proton density of water?
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What refers to the type of coil design used in MRI?
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What determines a slice in MR imaging?
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What refers to the process of removing small inhomogeneities present in the magnetic field?
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What is the science that deals with the absorption or emission of energy from matter called?
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What phenomenon involves a small but specific displacement of the resonance frequency of a particular nucleus in different chemical environments?
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What is created by moving charged particles in a magnetic field?
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Why is hydrogen primarily used in MR imaging?
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What occurs when the RF pulse is discontinued and the nuclei return to their preexcited state?
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What refers to the ability to distinguish separate points of information in an image?
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What describes a vibration of large amplitude caused by a relatively small periodic stimulus?
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What signal results after an RF pulse has excited the nuclear spin system to resonance?
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What indicates a change of the individual components of a vector quantity along a given spatial coordinate?
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What is the minimum signal intensity between two structures that distinguishes them as separate?
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What depends upon the manner of nuclei perturbations and the intervening relaxation process in MR imaging?
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What occurs if gradient linearity is poor in MR imaging?
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What allows signals to be pinpointed within the body for spatial location?
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What converts the received signal into amplitude information?
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What affects slice thickness in MRI?
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What describes geometric distortion, inhomogeneous signal intensity, and spurious signals?
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Study Notes
Larmor Equation and Frequency
- Larmor equation defines the relationship between Larmor frequency, gyromagnetic ratio, and magnetic field strength: W = B0 × Y.
- Larmor frequency is the resonance frequency at which nuclei are excited, measured in radians/second or Hz.
Relaxation Times
- T1 relaxation time represents the time needed for 63% of longitudinal magnetization to recover, aligning with the z-axis.
- T2 relaxation time indicates the decay time for 63% of transverse magnetization in a uniform magnetic field, associated with out-of-phase spins.
- Relaxation time is crucial for a system to return to equilibrium after excitation.
Imaging Phenomena and Quality
- Contrast reversal occurs when dark areas become bright and vice versa, prominent in sequences with extended repetition time (TR).
- Resolution denotes the level of detail in an image, directly linked to image quality.
- Partial saturation involves shifting net magnetization vector to the transverse plane using a sequence of RF pulses.
- Contrast discrimination is the minimum signal intensity difference between structures, defining their separation.
Signal Processing and Pulse Sequences
- Inversion recovery employs a 180-degree RF pulse followed by a 90-degree pulse to enhance specific imaging contrasts.
- Spin echo involves a 90-degree pulse, followed by a 180-degree pulse to refocus spins, enhancing image clarity.
- Echo time (TE) is the interval from the 90-degree pulse to peak echo signal, while repetition time (TR) denotes the cycle duration of RF pulses.
Magnetic Properties and Environment
- Magnetic field gradients are essential for determining imaging slices, affecting spatial resolution.
- Chemical shift refers to frequency displacement of resonance for nuclei in varying chemical environments.
- Magnetic shimming addresses inhomogeneities that can degrade image quality.
Structural Aspects and Techniques
- Spin density is a measurement of nuclei concentration in a material, expressed as a percentage relative to water's proton density.
- Saddle coil design is commonly used in MRI for effective signal reception.
- Free induction decay denotes the signal post-RF pulse excitation, indicating signal decay due to transverse relaxation.
Advanced Concepts
- Free precession occurs when RF pulse ends, allowing nuclei to revert to their pre-excitation state while generating a signal.
- Gradient linearity is necessary for homogeneous image quality; poor linearity may introduce distortions.
- Fourier transform is a mathematical technique that converts received signals into amplitude information for imaging.
Artifacts and Image Quality
- Artifacts in MRI imaging encompass geometric distortions, inhomogeneous signal intensity, and spurious signals that degrade image quality.
- The intervening relaxation process contributes to the gray scale of MR images, influenced by the nuclei's perturbations and relaxation times.
Studying That Suits You
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Description
Test your knowledge on key concepts in MRI with these flashcards. Covering terms like the Larmor equation and frequency, this quiz helps reinforce your understanding of magnetic resonance imaging fundamentals. Perfect for students preparing for an MRI exam.
