page 52-55 Flashcards
What is the range of magnetic field strength (measured in Tesla) for clinical use in MRI scanners?
The magnetic field strength for clinical use in MRI scanners may range from 1.5 to 4 Tesla.
What is the purpose of radiofrequency pulses in MRI?
Radiofrequency pulses are sent to interfere, causing protons to absorb energy depending on frequency.
What detects the resonance frequency of absorbed energy in MRI?
The resonance frequency of absorbed energy is detected by radiofrequency coils.
What are the different types of coils used in MRI systems?
There are various types of coils, including head coil, neck coil, body coil, extremity coil, flat spine coil, and breast coil.
What distinguishes surface coils from volume coils in MRI?
Surface coils allow precise imaging of a small portion, while volume coils allow imaging of the whole specimen with the same resolution.
What is required for conducting a fMRI study besides the MRI machine?
Specific software is required for designing tasks and stimuli, controlling stimulus presentation, and monitoring responses in fMRI studies.
Why is it essential to screen participants before an MRI scan?
Screening is necessary to avoid inserting ferromagnetic material and to assess any contraindications for the MRI.
What are potential MRI accidents involving metal objects?
MRI accidents can include pacemaker malfunctions, blinding from metal movement in the eye, dislodgement of aneurysm clips, and projectile trauma from various objects.
What chronic risks are associated with MRI for operators?
There isn’t sufficient data to draw conclusions about chronic risks, and there doesn’t seem to be an increase in cancer risk for chronic exposure.
What are the subjective experiences associated with acute risks of MRI?
Acute risks may include sensory effects like nausea, vertigo, metallic taste, and magneto-phosphenes.
What does the Specific Absorption Rate (SAR) measure in MRI?
SAR measures the rate at which energy is absorbed by the human body when exposed to RF electromagnetic fields in MRI.
How can burns be a risk during an MRI scan?
Looping wires can act as RF antennas, focusing energy in a small area, posing a risk for burns, especially with certain items like metallic clothing or jewelry.
What potential risk is associated with gradient field changes in MRI?
Gradient field changes may cause peripheral nerve stimulation, ranging from distracting to painful, especially with conductive loops.
How is claustrophobia addressed during MRI scans?
Claustrophobia can be ameliorated with comfort measures such as talking with the subject, providing air flow, and using a panic button.
What is the potential danger associated with quenching in MRI?
Quenching involves a rapid decrease in magnetic field strength and may be initiated voluntarily in serious emergencies, leading to various dangers like loud noise, loss of visibility, and potential physical damage.
What are the principles of neuroimaging using MRI?
Neuroimaging principles involve subjecting the subject to a strong magnetic field, transmitting radio waves into the subject, receiving re-transmitted radio waves, and reconstructing images based on nuclear magnetic resonance (NMR) properties.
Why is hydrogen (H) the major atom of interest in MRI?
Hydrogen is the most abundant atom in the human body, and its protons are sensitive to MRI, making it the primary species of interest.
What is the gyromagnetic ratio, and why is it important in MRI?
The gyromagnetic ratio (γ) is a constant for a given nucleus, crucial for targeting specific atoms to reconstruct images in MRI.
How does the process of nuclear magnetic resonance (NMR) work in MRI?
Nuclei with NMR properties spin, act like tiny magnets when subjected to an external magnetic field, and emit radiofrequency signals when perturbed, allowing imaging of atomic nuclei.
What are the three types of magnetic fields involved in MRI?
The three types of magnetic fields are static magnetic fields (B0), radiofrequency fields, and gradient magnetic fields.
What is the process of RF excitation in the MRI sequence?
RF excitation involves sending electromagnetic energy to a sample at its resonant frequency, tipping the magnetization away from equilibrium.
What is net magnetization in the context of MRI?
Net magnetization is the sum of magnetic moments of all spins within a spin system, providing a macroscopic measure of many spins in MRI.
Why is the echo time (TE) important in MRI?
Echo time is the period necessary for the energy emitted by the sample to be received, and it can be selected to receive a specific type of signal in MRI.
What are the steps involved in the MRI sequence?
The MRI sequence involves Equilibrium, RF excitation, precession producing signals, readout signal reception, and returning to equilibrium while reapplying RF excitation.
What is the role of static magnetic fields in MRI?
Static magnetic fields (B0) in MRI do not change and provide the main field that is static and nearly homogeneous.
How do radiofrequency fields contribute to MRI?
Radiofrequency fields in MRI are electromagnetic fields that oscillate at radio frequencies, used to manipulate the magnetization of specific types of atoms.
What is the purpose of gradient magnetic fields in MRI?
Gradient magnetic fields in MRI change gradually over space and quickly over time, contributing to spatial information in the imaging process.
What is the importance of the gyromagnetic ratio (γ) in MRI?
The gyromagnetic ratio (γ) is constant for a given nucleus and is crucial for targeting specific atoms to reconstruct images in MRI.
How does the precession of spinning nuclei contribute to MRI?
Spinning nuclei in MRI undergo precession, a gyroscopic motion, causing alignment changes in the magnetic field, leading to the generation of signals.
What does the net magnetization measure in MRI?
Net magnetization in MRI is the sum of magnetic moments of all spins within a spin system, providing a macroscopic measure of many spins.
What determines the Larmor frequency in MRI?
The Larmor frequency in MRI is determined by the product of the gyromagnetic ratio (γ) and the magnetic field strength (B0).
Why is hydrogen (H) the primary atom of interest in MRI?
Hydrogen is the most abundant atom in the human body, and its protons are sensitive to MRI, making it the primary species of interest.
What are the potential physiological effects of MRI on red blood cells?
In MRI, red blood cells, especially sickled ones, may alter shape in a magnetic field, making sickle-cell anemia a contraindication.
How is tissue heating measured in MRI?
Tissue heating in MRI is measured through the Specific Absorption Rate (SAR), indicating the rate at which energy is absorbed by the human body when exposed to RF electromagnetic fields.
What are potential risks associated with looped wires during MRI?
Looping wires in MRI can act as RF antennas, focusing energy in a small area and posing a risk for burns, especially with items like metallic clothing or jewelry.
What is the potential risk associated with projectile effects in MRI?
Ferromagnetic objects present in the MRI chamber may be attracted to the magnet, emphasizing the importance of removing them before turning on the MRI.
