The flashcards below were created by user
swtjo3joe
on FreezingBlue Flashcards.
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what does an electrical current induce?
magnetic field
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why do protons have electric current?
- because they have a positive charge and spin
- a moving electric charge = an electrical current
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what happens to protons when put into an external magnetic field?
align themselves in the external magnetic field
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how many ways do protons align themselves in an external magnetic field?
- 2
- in the direction of the field, parallel to it
- in the completely opposite direction or anti-parallel
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which type of alignment is preferred?
the one that takes less energy which is parallel to the external magnetic field
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what is a precession?
when objects wobble about an axis
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what is precession frequency?
how many times the protons precess per second
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what happens to the precession frequency when the external magnetic field is stronger?
increases
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what is the larmor equation?
w0 = yB0
precession frequency (Hz) = gyromagnetic ratio x strength of magnetic field (tesla)
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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.
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does every RF pulse disturb the alignment of the protons?
no
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how can an RF pulse disturb the peaceful precessing of a proton?
when the RF is in the same frequency as the proton
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what is resonance?
when the protons pick up somne energy from having the same frequency as the RF pulse that was sent
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what kind of magnetization does an RF pulse create?
transversal magnetization
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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
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what are two the types of MRI antennas used?
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the magnetic property associated with a spinning proton, neturon, or some nuclei is referred to as a magnetic what?
moment
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what is the symbol for magnetic moment?
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when do nuclei possess magnetic properties?
when they are composed of an odd number of neutrons or protons
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which element is the most commonly used or intereacted with in MRI?
hydrogen
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the electromagnetic waves used in MRI are in which portion of the electromagnetic spectrum?
radio
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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
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a T-1 weighted scan is good for showing what?
anatomy
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a T-2 weighted scan is good for showing what?
pathology
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how does air appear in a t-1 and t-2 scan?
both dark
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how does fluid appear in a t-1 and t-2 scan?
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how does bone appear in a t-1 and t-2 scan?
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how does fat appear in a t-1 and t-2 scan?
- t-1 = bright
- t-2 = bright or dark
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what is the TR (repitition time) range of a t-1 scan?
400-750
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what is the TE (echo time) range of a t-1 scan?
5-20
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what is the proton density of a t-1 scan?
1000
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what is the TR (repitition time) range of a t-2 scan?
300-8000
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what is the TE (echo time) range of a t-2 scan?
+ or - 100
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what is the proton density of a t-2 scan?
30
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