Dmi 65 MRI Quiz
what does an electrical current induce?
why do protons have electric current?
because they have a positive charge and spin
a moving electric charge = an electrical current
what happens to protons when put into an external magnetic field?
align themselves in the external magnetic field
how many ways do protons align themselves in an external magnetic field?
in the direction of the field, parallel to it
in the completely opposite direction or anti-parallel
which type of alignment is preferred?
the one that takes less energy which is parallel to the external magnetic field
what is a precession?
when objects wobble about an axis
what is precession frequency?
how many times the protons precess per second
what happens to the precession frequency when the external magnetic field is stronger?
what is the larmor equation?
w0 = yB0
precession frequency (Hz) = gyromagnetic ratio x strength of magnetic field (tesla)
what is an RF pulse?
radio frequency pulse that is sent to the patient to disturb the protons which are peacefully precessing in alignment with the external magnetic field.
does every RF pulse disturb the alignment of the protons?
how can an RF pulse disturb the peaceful precessing of a proton?
when the RF is in the same frequency as the proton
what is resonance?
when the protons pick up somne energy from having the same frequency as the RF pulse that was sent
what kind of magnetization does an RF pulse create?
what two effects are created when an RF pulse that has the same frequency as the precession frequency of the protons are sent?
some protons pick up energy and decreases the amount of longtidunal magnetization
protons get in synch, start to precess in phase. Their vectors now also add up in a direction transverse to the external magnetic field thus a transversal magnetization is established
what are two the types of MRI antennas used?
the magnetic property associated with a spinning proton, neturon, or some nuclei is referred to as a magnetic what?
what is the symbol for magnetic moment?
when do nuclei possess magnetic properties?
when they are composed of an odd number of neutrons or protons
which element is the most commonly used or intereacted with in MRI?
the electromagnetic waves used in MRI are in which portion of the electromagnetic spectrum?
a radiowave that is transmitted just long enough to flip spinning nuclei away from alignment with the z axis and into precession in the xy plane is called?
90 degree pulse
a T-1 weighted scan is good for showing what?
a T-2 weighted scan is good for showing what?
how does air appear in a t-1 and t-2 scan?
how does fluid appear in a t-1 and t-2 scan?
t-1 = dark
t-2 = bright
how does bone appear in a t-1 and t-2 scan?
how does fat appear in a t-1 and t-2 scan?
t-1 = bright
t-2 = bright or dark
what is the TR (repitition time) range of a t-1 scan?
what is the TE (echo time) range of a t-1 scan?
what is the proton density of a t-1 scan?
what is the TR (repitition time) range of a t-2 scan?
what is the TE (echo time) range of a t-2 scan?
+ or - 100
what is the proton density of a t-2 scan?
Dmi 65 MRI Quiz