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?
Signup and view all the answers
What is the time required for a system to return to its equilibrium state called?
Signup and view all the answers
What is the time taken for 63% of the longitudinal magnetization to recover called?
Signup and view all the answers
What is the time taken for 63% of the transverse magnetization to decay known as?
Signup and view all the answers
A ______ process must occur in order to eliminate effects of field inhomogeneity.
Signup and view all the answers
A rephrasing process must occur in order to eliminate the effects of field inhomogeneity, this process allows one to measure the ______.
Signup and view all the answers
What defines the level of detail of an image in MR imaging?
Signup and view all the answers
The strength of the signal in an MRI read depends on the proton density and on the (2) ______.
Signup and view all the answers
What describes the net magnetization vector being moved from the Z-axis to the transverse plane?
Signup and view all the answers
What is the component of the bulk magnetization in the XY plane called?
Signup and view all the answers
What pulse is followed by a 90-degree RF pulse in an inversion recovery sequence?
Signup and view all the answers
What is the time in milliseconds between the application of the 90° pulse and the peak of the echo signal called?
Signup and view all the answers
What defines the repetition time in pulse sequences?
Signup and view all the answers
What allows information from many different slices of the patient to be obtained during the waiting periods of the pulse sequence?
Signup and view all the answers
What describes the sum total of all precessing in phase photons in the same direction?
Signup and view all the answers
What describes the quantity of resonating spins in a tissue expressed as a percentage of proton density of water?
Signup and view all the answers
What refers to the type of coil design used in MRI?
Signup and view all the answers
What determines a slice in MR imaging?
Signup and view all the answers
What refers to the process of removing small inhomogeneities present in the magnetic field?
Signup and view all the answers
What is the science that deals with the absorption or emission of energy from matter called?
Signup and view all the answers
What phenomenon involves a small but specific displacement of the resonance frequency of a particular nucleus in different chemical environments?
Signup and view all the answers
What is created by moving charged particles in a magnetic field?
Signup and view all the answers
Why is hydrogen primarily used in MR imaging?
Signup and view all the answers
What occurs when the RF pulse is discontinued and the nuclei return to their preexcited state?
Signup and view all the answers
What refers to the ability to distinguish separate points of information in an image?
Signup and view all the answers
What describes a vibration of large amplitude caused by a relatively small periodic stimulus?
Signup and view all the answers
What signal results after an RF pulse has excited the nuclear spin system to resonance?
Signup and view all the answers
What indicates a change of the individual components of a vector quantity along a given spatial coordinate?
Signup and view all the answers
What is the minimum signal intensity between two structures that distinguishes them as separate?
Signup and view all the answers
What depends upon the manner of nuclei perturbations and the intervening relaxation process in MR imaging?
Signup and view all the answers
What occurs if gradient linearity is poor in MR imaging?
Signup and view all the answers
What allows signals to be pinpointed within the body for spatial location?
Signup and view all the answers
What converts the received signal into amplitude information?
Signup and view all the answers
What affects slice thickness in MRI?
Signup and view all the answers
What describes geometric distortion, inhomogeneous signal intensity, and spurious signals?
Signup and view all the answers
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
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
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.