mri final

In the presence of a strong magnetic field, what does a proton do

precess

which is not a component of an mri scanner

collimator

nuclei in a lowery energy state can be raised to a higher state with the application of…

RF pulse

electrodynamics deals primarily with

moving electric fields

what are the two important basic properties of a nucleus for mri signal

nuclear magnetic moment and spin

what is the advantage of mri over other modalities

soft tissue contrast

what causes heating in electromagnetic type mri scanner

resistance

what unit is used to measure electric charge

coulomb (C)

the energy and length of the rf pulse determines..

the flip angle

at equilibrium, what is true about the net magnetization

Mz= Mo; Mx=My=0

the application of an rf pulse at equilibrium results in..

a reduction in Mz and reduction in Mxy

when subjected to an external magnetic field, 1H nuclei….

align parallel or antiparallel to the magnetic field

A vector has…

magnitude and direction

the frequency of the rf pulse determines…

which nuclei are excited

the Tesla (T) is a…

measurement of magnetic field strength

a fourier transformation of an FID from an mri scanner has units of…

intensity vs. frequency

which type of current is used in households

alternating current (AC)

all electromagnetic radiation travels at what speed

speed of light

what is the primary mri signal

free induction decay (FID)

what is the smallest region of magnetism called

magnetic domain

we use the variable M as…

a vector quantity that refers to the magnetization

spins are saturated with the application of…

90 degree RF pulse

copper and aluminum are types of

conductors

mri machines operate with the use of large..

magnetic fields

which law related to electricity describe the forces of attraction between electric charges?

colombs’s law

which law quantifies the force between two charged particles

coulomb’s law

longitudinal relaxation refers to

regrowth in the Z direction

what % of the human body is made of hydrogens

80%

in the absence of a magnetic field, the spin states of the same atoms have…

the same energy

after an rf excitation pulse, the Mz vector ___ and the Mxy vector ___

starts to regrow; starts to decay

what term describes the ability of an imaging system to precisely identify the nature of differences in anatomy?

specificity

relative to ct, the ionizing radiation dose from an mri scan is..

zero

example of vector

magnetic fields strength and direction

what equation is used to find the frequency of precession of a particular proton?

f0= yB0

example of ferromagnetic material

iron

fundamental unit of electrical charge

coulomb

free induction decay recorded from an mri scanner has units of

intensity vs. time

rubber, glass and plastic are

insulators

what happens after RF excitation

the net magnetization wants to realign with the external magnetic field

electrostatics deals with

stationary electric fields

what does larmor equation tell us

precessional frequency

how many spin states does 1H atom have

2

as magnetization returns to equilibrium, it ___ in the XY plane and __ in the Z direction

decays; grows

mri operates in the same electromagnetic energy range as

radio waves

in a pulse sequence diagram, the rf pulse is usually shown as

several ovals

who discovered that tumor tissues respond differently to magnetic excitation and relaxation compared to healthy tissues

raymond damadian

at equilibrium, there are slightly more 1H atoms in the ____ than in the ___ during exposure to external magnetic field

lower energy state; higher energy state

an rf pulse transmitted into the body at the proper frequency will do what

change the net magnetization of the protons

what is the orientation of magnetization of hydrogen protons in the human body when it is placed in strong magnetic field (B0)

aligned with B0

unit of measurement for electric current

ampere

describes how well an imaging system can detect subtle differences in anatomy

sensitivity

to get an mri signal, we measure..

net magentzaion in the XY plane

gyromagnetic ratio of hydrogen

42.6 MHz/T

rf pulses are used to

manipulate the magnitude and direction of the net magentzion vector

what happens to the net magnetization vector at equilibrium

points along the z axis direction (direction of B0)

which nuclei has the highest gyromagnetic ratio

1H

net magnetization is induced by

spinning photons

T2 relaxation

transverse relaxation

if the south pole of two magnets were facing each other and brought together, the two would ___ but if a north pole and south pole were facing each other they would _

repel; attract

magnetic field in mri by convention is in which axis

z axis

at equilibrium, which of the following is true

Mz= M0 ; My= Mx=0

electromagnetic radiation associated with mri has frequencies of approximately..

10—200 MHz

what happens to net magnetization vector at equilibrium

points along z axis (direction of B0)

at equilibrium….

magnetization only exits the z direction

what is the orientation of the magnetization of hydrogen protons under normal conditions in the human body

random

paramagnetic material

gadolinium

spin quantum number of 1H

1/2

diamagnetic material

mercury

frequency of precession depends on

type of nucleus and intensity of magnetic field

what rate does a 1H atom process when it is subjected to a magnetic field of 3T

127.8 MHz

gyromagnetic ratio of 1H

42.6 MHz/T

what is not related to mri

kvp

who received a noble prize related to development of mri

james hutchinson

FID signal allows us to observe…

the decay of Mxy

when energy or mass is transferred between 2 objects without physical contact between the two objects, this is known as

induction

equation used to calculate the exact frequency of precession in a nucleus

f= yB0

gyromagnetic ration (y) represents

ratio of magnetic moment to angular momentum

principal advantage of mri

contrast resolution

the large arrow denoted by MZ symbolizes..

net magnetization of the protons

b0 refers to

the main magnetic field

what is true about soft and hard rf pulses

hard pulses are strong and soft

transverse relaxation refers to

decay in the XY plane

what happens to nuclei when they are subjected to a strong external magnetic field

they process about an axis

what is the spin quantum number for a spin up electron

+1/2

An echo in a spin echo sequence will form at what time after a 180 pulse

TE/2

to maximize PD contrast in spin echo imaging, TR time must be ___ and TE must be __

long; short

contrast agents in MRI typically work by doing what?

shortening T1 time

in T1 weighted imaging, what combination of TR and TE is generally used

short TR and short TE

MRI signal intensity is proportional to

proton density

what is used to produce the final MRI image from the raw data

inverse fourier transform

example of material that contains a lot of tightly bound H atoms

Bone

which is NOT a typical application of T2 weighted imaging

differentiating between gray and white matter in brain tissue

an example of when a spin echo sequence has an imaginary component in the FT

when there is motion

3 principle MRI tissue parameters

proton density, T1 relaxation time, T2 relaxation time

which parameter does not control image contrast

bandwidth

the time between 180 pulse and a 90 pulse in an inversion recovery scan is the

t1 time

in gradient echo images, what parameters primarily control t1 weighting

flip angle and TR time

what does T1 relaxation time represent

the time it takes for Mz to regrow by 63%

the FT intensity versus time is __

intensity vs frequency

what causes spins to rephase and form a spin echo

a 180 pulse