Chapter 1-Fundamentals Flashcards
MRI is
A. Non-Ionizing
B. Ionizing imaging
A. Non-Ionizing
Explain the process in which we transmit an imaging with MRI.
The patients molecules receive an external low-level electromagnetic stimulation and they respond by creating their own signal
MRI uses what type of atom in the body and why?
hydrogen due to the abundance of it in our bodies
How many protons does a hydrogen atom have?
1 proton which are positively charged and spin on on their own axis.
How come protons are needed to generate a magnetic field??
It is due to the positively charged proton that they have. They spin on their own axis. Any charged particle that’s moving can generate a magnetic field
What are the 3 requirements for MRI to work?
1) strong magnetic field (aka the magnet
2) external RF energy (the tissue must be stimulated)
3) ODD number of protons (aka like hydrogen which only has one)
The magnetic field is often called the “B O” field.
True or False
True.. the BO field is the same as magnetic field
What is the difference in “parallen and anti-parellel” when talking about the protons aligning themselves during MRI?
Parallel = “ground -state” aka low energy, they are relaxed
ANTI-parallel- “EXCITED, high energy
What is the “net magnetic moment”
the result of the protons aligning is called the net magnetic moment = equilibrium
What occurs when we “TILT” the net magnetization, thus wobbling occurs?
that is called precession.
When all the protons are aligned, there is a ______ signal.
A. No signal
B. Strong Signal
C. Weak signal
A. when everything is aligned there is no signal, thus why we need to disturb them to create an image.
The precessional frequency is often called the _____ frequency.
RESONANT
the precessional frequency/resonant frequency is measured by
the strength of the magnetic field and the rate of precessional/wobble
What is the gyromagnetic ratio?
it is how the resonant/precessional frequency is affected by the magnetic field strength
What is the gyromagnetic ratio?
it is how the resonant/precessional frequency is affected by the magnetic field strength
the ____ the magnetic field the ____ the resonant frequency
the HIGHER the magnetic field, the HIGHER the resonant frequency.
What is the gyromagnetic ratio for hydrogen?
42.6
Therefore a 1 Tesla strength magnet would be 42.6 million rotations per second
What is the precessional frequency for a 0.5 Tesla magnet?
0.5 Tesla = 21.3 MHZ
The math is 42.6 x 0.5 = 21.3
what is the resonant frequency of a 1 Tesla strength magnet?
1 Tesla = 42.6 MHZ
The math is 42.6 x 1 = 42.6
What is the resonant frequency of a 1.5 Tesla Magnet?
1.5 Tesla = 63.9 MHZ
The math is 42.6 x 1.5 = 63.9
what is the resonant frequency of a 2.0 Tesla Magnet?
2 Tesla = 85.2 MHZ
The math is 42.6 x 2.0 = 85.2
What is the resonant frequency of a 3.0 Tesla magnet?
3 Tesla = 127.8 MHZ
The math is 42.6 x 3.0 = 127.8
When we “disturb” the protons equilibrium, this creates an image. When we “relax, they move back to equilibrium, What causes this disturbance?
the RF pulse
True or False
The transfer of energy only happens if the frequency of the energy source is the same as the system
True
What is the direction of the main magnetic field?
transverse or longitudinal?
longitudinal
True or False
The STRONGER the RF pulse, the LONGER it is applied, and the more it will “WOBBLE”
True
What is the flip angle?
the angle at which the net magnetization is tilted AWAY from the magnetic field
When the flip angle is 90 degrees, this is considered a spin echo
True or False
True
When the flip angle is less than 90 degrees, this is considered a gradient echo
True or False
True
How is the flip angle determined?
it is determined by the RF duration and the amplitude
What is the process of “relaxation”?
once the RF pulse is turned off, the nuclei returns to the equilibrium, losing the energy to the surrounding environment.
T1 Relaxation is also called Spin- _____
A. Spin- Spin
B. Spin-Lattice
T1=Spin- Lattice
The relaxation sends the energy into the lattice (enviroment)
T1- is often called ______
Transverse or longitundinal?
longitudinal
T1 is the time for net magnetization to grow to ___ %
63
T1 is controlled by ___
TR or TE?
TR = T1
Explain what the white matter, gray matter and CSF will look like in a T1 image
White matter= bright (short t1)
Gray matter= slightly bright (long t1)
CSF = DARK (realllllly long t1)
T2 is often called spin- _____.
spin spin or spin lattice?
Spin- Spin = T2
T2 is controlled by
TE or TR?
TE=T2
T2 is the amount of time it takes to decay ____ %.
37
When does dephasing occur?
When the relaxation occurs and the protons start canceling eachother out.
True or False
DEPHASING causes a DROP in net magnetization
True
Why is T2 called spin-spin?
Because instead of spin and leaving the energy to the lattice like t1, the energy goes from one proton to another.
What is free induction decay?
the signal decay due to dephasing process
What will happen to the image if the protons COMPLETELY cancel each other out?
There will be no signal
What good does the 180 pulse do?
By using the 180 pulse, we REPHASE the protons back to “in-phase”
T2 is also known as transverse magnetization. True or False
True
