MRI Interpretation Flashcards
What is the physical property used in CT?
x-ray absorption
what is the physical property used in ultrasound?
reflected sound
what is the physical property used in MRI?
net magnetization
*it does NOT use ionizing radiation
what is the term given to the H2 nuclei that align themselves parallel to the magnetic field?
B0 (B-knot)
what is the term given for the cumulative magnetic force of H2 nuclei?
M vector
As H2 nuclei return to their original energy state, what 2 things happen?
- they release energy
2. the wobbling in phase becomes more random
what happens to the longitudinal magnetization when the energy of protons are released?
long. mag. increases until it reaches its equilibrium value
what happens to transverse magnetization as there is a loss of phase coherence?
transverse mag. decays to its equilibrium value of zero
What is T1?
“longitudinal relaxation”-how fast a tissue loses its energy and returns to B0
what is T2?
“transverse relaxation”- how slow/fast a tissue maintains its transverse magnetization
What are the properties of the tissue type and CANNOT be changed by the operator of the MRI unit?
T1, T2, and density
what properties can the operator manipulate on the MRI unit?
TR (repetition time)
TE (echo time)
what is TR?
(repetition time)- the amt of time in ms allowed to elapse btwn successive 90 degree RF pulses
what is TE?
(echo time)- is the time interval that elapses btwn a 90 degree RF pulse and measurement of the first spin echo signal
what is spin-echo pulse sequence?
a single 90 degree pulse followed by one or more 180 degree pulses
How are T1 images produced?
short TR - these are tissues (like fat) that return to B0 the fastest and gives off the most energy and appears bright (white) on T1 images
which is the fat image? which is the water image?
T1- fat
T2- water
In a T1 image, what color does fat appear?
fat = white *water = black
how are T2 images produced?
long TE - those tissues that hold their transverse magnetization longest give off the strongest signal and appear bright
T1 images give off energy faster. T2 images hold onto energy longer.
true
what should you dial in on the MRI to select for a T1 image?
short TR- <30 ms
what should you dial in on MRI to select for T2 image?
long TR- >2000 ms
long TE- >60 ms
which image is referred to as pathology image? which is anatomical image?
T1= anatomical image T2= pathology image
Describe the properties of tissues with high intensity signal.
- short T1
- long T2
- high proton density
DEscribe the properties of tissues with low intensity signal.
- long T1
- short T2
- low proton density
what is STIR imaging good for?
(short tau inversion recovery)- when you want the fat suppressed and want a max. highlighting of fluid
what is gradient echo used for?
uses only one RF excitation pulse, at less than 90 degrees, when you need to cut down on T2 imaging time
*good for ligaments and articular cartilage
what disease is gradient echo good to diagnose?
pigmetned villonodular synovitis
what can be used to identify fluid filled lesions?
(contrast gadolinium)- produces a rim sign surrounding the lesion
the shorter the T1 of tissue, the brighter the image. what tissues does this apply to?
fat, methemoglobin, mucus
the longer the T2 of the tissue, the brighter the image. what tissues does this apply to?
water, CSF
what substances are always black (void of signal) on images produced by any pulse sequence?
calcium
air
flowing blood
hemosiderin
what structures always appear black because fo their relatively low water content?
tendons ligaments cartilage cortical bone *skeletal muscle- appears gray
what color does marrow appear on T1 and T2?
T1- bright
T2-dark
(marrow has high content of fat)
what are the contraindications for MRI?
patients with cardiac pacemakers, defibrillators, or cochlear implants
- demagnetizing implants (dental implants, sphincters, stoma plugs, ocular implants)
- bone growth stimulators
- implantable electronic drug infusion pumps
is MRI contraindicated in pregnancy?
no
are orthopedic implants contraindicatd in pregnancy?
no
intraocular metallic foreign bodies, pellets, and bullets from foreign countries, and shrapnel is contraindicated for use of MRI though
true
in what order should you read T1 and T2 images?
read T2 before T1
in what order should you read films based on the axis they are cut?
coronal/frontal, followed by transverse, followed by sagittal
in what order should you view the different films?
coronal : proximal to distal
transverse: inferior to superior
sagittal: lateral to medial
