What are the two phenomenons that occur when protons are placed in Bo?
align with Bo and precession
What is precession?
spinning or rotation around an external magnet and depends on type of nucleus and intensity of the magnet.
Define equilibrium in relation to MRI.
It is the highest state that net magnetization can have. It is when a patient is placed in a strong external magnet, the protons start aligning with Bo, more are aligning than not and start precessing out of phase.(they align with Bo because it is a lower energy state). the ones that align antiparallel are a higher energy state.
What is the abbreviation used for equilibrium?
Mo, Mxy=zero at equilibrium
Why can M not be detected along the Bo?
It is too weak and cannot electromagneticlly induce.
what is an angle in which protons can be flipped/rotated from the z-axis because the RF is energized and as long as its energized will continue to rotate?
flip angle
What pulse is strong, but short?
Hard pulse
What is a weak, but long pulse?
soft pulse
What pulse has a rotation angle less than 90 degree?
Alpha Pulse
What is described as a when Mz is smaller than Mo and Mxy is no longer zero, it is at equilibrium?
Partial saturation. (nuclear spin is partial saturated)
A decrease in Mxy is called ____, whereas an increase in Mxy is called ____.
transverse relaxation, longitudinal relaxation.
What is symbolized by RFt and RFs?
RFt is an RF pulse transmitted to a patient. RFS is a RF pulse that is received from the patient.
What determines the amplitude of the FID?
same parameters that influence Mo, the number of spins involved (proton density), Bo, and y.
What is Hydrogen's gyromagnetic ratio?
42.6 MHz/T
What is hydrogen's frequency of precession in a 1.5 T magnet?
63.9 MHz/T
Ensemble of spins are hard to measure because signals represent each individual nucleus. Therefore the Net Magnetization is used, which is abbreviated by what letter?
M
Net magnetization is the sum of the ___?
individual nuclear magnetic moments
List factors that are related to the amount of signal available for MRI.
The temperature of the material under investigation, the strength of the external magnetic field, the gyromagnetic ratio and the number of nuclei available in the volum of interest.
Explain why a signal can not be received from Mz.
The net magnetization along the Z-axis, Mz, is invisible. From the quantum mechanical view, directly measuring this magnetization is impossible form the classical point of view, the magnetization is so small relative to Bo that it cannot be measured.
What is the purpose of an RF in MRI?
The us of RF pulses in MRI produces an XY component to the net magnetization. When the net magnetization vector is roated, the Mz shrinks and Mxy grows. The net magetization in the XY plane is the only magnetization that can be detected.
Why are vector diagrams useful in MRI?
They are important becasue they show us direction and magnitude and allow us to follow the net magnetization.
What are electric currents measured in?
amperes
What is the difference in A/C current and D/C current?
In DC current the current is flowing in one direction. If the switch is open the current stops and when its closed it resumes going in the same direction again. In AC current if the switch is open current does not flow, but once its is closed it flows in one direction and then reverses to flow in the opp. direction.
Household current is generated and transmitted as what type of phase?
three phase
The unit for electrical power is what?
watt
the smallest unit of charge is a____?
electron
Why is the proton used in MRI instead of an electron?
Protons are used because they are in a fixed location in the nucleus and because tehy are larger than an electron.
What are three means of electrification?
contact, friction, induction
Know the four principles of electrostatic laws
:)Chp. 2
unlike verses like charges
Coulomb's law
Charge Distribution
Charge Concentration
What is the smallest region of magnetism?
magnetic domain
A magnet has two poles called what?
Dipoles
The magnetic field leaves the ____ pole and enters the ____pole of the magnet.
North, South
The magnetic field lines are called what?
magnetic lines of induction
The father of MRI is who?
Felix Bloch
Despite controversy, who recevied the Nobel Peace Prize for developing MRI?
Lauterbur
What is the ability to image differences amoung low-contrast tissues?
Contrast resolution
What is the ability to identify an object as separate and distinct from one another?
Spatial Resolution
Lis the four advantages of MRI over all other imaging modalities.
Contrast Resolution, Direct Mult. Planar Imaging, Spectroscopy, and No Ionizing radiation.
What are the two essential characteristics of the MRI computer system?
It has to be able to store a large amount of info. and it has to be fast.
What is an atom and what part of the atome is used fror MRI imaging?
Atoms ake up the body and include electrons, protons, and neutrons. Protons are used for MRI.
State the correct abbreviations for the following:
Static Magnetic Field
Net Magnetization
Net Magnetization along the Z axis
Net Magnetization along the XY axis
Net Magnetization at equilibrium
Bo
M
Mz
Mxy
Mo
What is the interaction between the spinning mass of the gyroscope and the mass of the earth that is manifest through the gravitational field, or more simple term, wobble?
precession
What is the Larmor Equation and its parts?
f=yBo and it identifies the frequency of precession.
-f=precessional frequency
-y=gyromagnetic ratio
-Bo=Static Magnetic Field Strength
What is a quantity that has magnitude and direction?
vector
What is when a patient is placed in the presence of a strong external magnetic field, some of the individual nuclear magnetic moment align with the external magnetic field?
Net Magnetization
What is a magnet when it has both a north and south pole present?
Dipoles
Why is Hydrogen useful in MRI?
because it is the most abundant in our body due to the majority of our body is made up of water.
T/F Bo is measured in Tesla
True
what is equilibrium?
the state of tissue that is fully magnetized by static magnetic field
why is it so important to use 180
compenstate for the dephasing that occurs with 90 pulse
T1
longitudinal
T2
transverse (faster)
Columbs law?
force of attraction or pulse between electrostatic charges
magnetisim
dia,para,ferro
vector
quantity that has magnitude and direction
parts of the machine
gantry, computer operator, console
primary signal
fid
which plane must you use to get a signal
transverse
unit of elelectrification
amperes
unit of power
watts
what is special about larmour equation?
we use this to tune into protons
after 90 what happens during spin echo?
the reason to absorb energy precess and flip into transverse then it shuts off and goes to fid then start to dephasing
characteristic that make a good atom
high gyromagnetic ratio and 1/2 filled outer shell
what are the components of the Rf pulse
Tr,Te
stronger the Mr
the larger the Mo
a grouping of one or more pulses is said to be what?
a pulse sequence
The application of RF pulses at certain repetition times and the receiving of signals at predefined echo times produce what in MRI images?
contrast
Application of the next RF pulse for each slice is what?
TR
The time from the appliction of RF pulse to the peak of the signal induced into the coil is?
TE
The time from 180 degree inverting pulse to the 90 degree excitation pulse is?
TI
What type of pulse sequence utilizes flip angles that are variable?
