MRI Flashcards
(30 cards)
What is the first step in the process of image formation?
Excitation
This step involves determining the Larmor frequency and sending an RF pulse.
What is the role of the RF pulse in the excitation process?
Creates resonance and flips the net magnetization vector to the transverse direction
This allows for the generation of an image from the patient’s tissues.
What occurs during the relaxation phase of image formation?
Energy absorbed by protons during excitation is given off
This is essential for the return of protons to their equilibrium state.
Name the two types of relaxation processes.
- Longitudinal/Spin-lattice (T1 relaxation)
- Transverse/Spin-spin (T2 relaxation)
These processes describe how protons return to their equilibrium states after excitation.
What is T1 relaxation?
Re-growth of net magnetization along the Z axis, also known as spin lattice relaxation
It specifically pertains to protons that experienced the excitation pulse.
What does T1 represent in the context of relaxation?
The time constant describing how MZ returns to its equilibrium value
It indicates the duration for the longitudinal magnetization to recover.
How does the rate of T1 relaxation differ among tissues?
Different for different tissues; T1 relaxation in fat is faster than in water
This difference is due to the binding of hydrogen atoms in fat tissue compared to water.
Fill in the blank: The process of image formation includes ______, Relaxation, Acquisition, and Computing and Display.
Excitation
True or False: T1 relaxation occurs in protons that did not experience the excitation pulse.
False
T1 relaxation specifically occurs in protons that have experienced the excitation pulse.
What does T1 represent in the T1 relaxation curve?
T1 is the time constant representing the regrowth of 63% of longitudinal magnetization.
The formula is Mz(t) = M0(1 - e^(-t/T1)).
What is the equation for Mz when t = T1?
Mz = 0.63 M0.
This represents 63% of the maximum longitudinal magnetization.
What does T2 relaxation describe?
T2 relaxation describes the behavior in the X-Y plane right after the excitation pulse.
It involves the loss of phase coherence due to spin-spin interaction.
What happens to the magnetization vector immediately after the excitation pulse?
The magnetization vector flips in the X-Y plane and the protons spin in phase.
This is referred to as transverse magnetization.
What is the T2 relaxation rate dependent on?
The T2 relaxation rate is different for various tissues.
Factors include tissue characteristics and spin-spin interaction.
What is the T2 relaxation equation?
Mxy(t) = M0 e^(-t/T2).
When t = T2, Mxy = 0.37 M0.
List T1 and T2 relaxation times for Fat at 1.5T.
T1: 260 ms, T2: 80 ms.
What factors affect T1 relaxation?
Factors include:
* Molecular size and motion
* Magnetic field strength.
What factors affect T2 relaxation?
Factors include:
* Tissue characteristics
* Magnetic field effects
* Field inhomogeneities
* Magnetic susceptibilities.
What is Free Induction Decay (FID)?
FID is the signal received during T2 relaxation, which quickly becomes weaker.
It lasts approximately 40 ms.
What is the role of Gradient Coils in MRI?
Gradient coils create additional magnetic fields superimposed on the main magnetic field B0.
They enable spatial localization of signals.
What are the three functions of Gradient Coils?
Functions include:
* Slice encoding
* Phase encoding
* Frequency encoding.
What is slice selection in MRI?
Slice selection is performed with all protons having the same frequency and phase.
It uses frequency encoding.
