Week 3.1 MRI Flashcards
an MRI magnetic field is _____x stronger then Earth’s magnetic field
90,000x
what does the MRI magnetic field do
align the atoms in the body, and the magnetic moment (or spin) aligns with the field (tissue specific based on hydrogen)
the file is lined up based on the tissue specificity which is due to
hydrogen and other molecular content
TF: MRI uses radiation
false
what is the radio-frequency (RF) pulse
emitted at 90 degree angles to the magnetic field. and deflects the spin of hydrogen atoms in the transverse plane
what happens when the RF is turned off
detection of rotated spins
what happens when the signal decays due to relaxation
subdivided into T1 and T2 phases.
T1 recovery (____)
(Longitudinal)
time it takes for spins to realign with original magnetic field (how long to resting state)
T2 decay (_____)
(Transverse)
time it takes for the spin to lose energy in the transverse plane
which is longer, T1 or T2
T1 is longer, because T2 is like a snap shot
what is TE
echo time, this is after the original pulse. A spin echo is created by applying a refocusing RF that flips the spin 180 degrees, and the spin realigns and produces a signal peak at TE.
what is TR
repetition time, or the time between successive 90 degree angle RF pulses.
TF: T1 and T2 have the same TE and TR values
false, they have different values
RF pulses are repeated ___ of times during a study
100s
what creates different types of images
varying of pulse timing creates different TE and TR, which produces different types of images
T1 has ___ TR and TE times
short
T1 is created at ___ energy levels which means
high energy levels, which means good anatomic detail, and the tissues with lower relaxation times
what kind of signal intensity do you get in fat with a T1 view
high signal intensity
T2 has ___ TR and TE times
long
T2 is created at ___ energy levels which means
low, which means tissues with longer relaxation times, and grainer and less spatial resolution compared to T1.
T2 images have high signal intensity in ___, making it valuable when looking for ____
water, inflammation
Difference between T1 and T2
T1 is detailed, and more anatomic detail, and T2 is grainy, but shows bright white where there is inflammation
What is a saying to remember T2 and MRI
world war 2: white water type 2
H2O (water is white in Type 2)
what has a high intensity in a T1 image
fat/yellow marrow
acute hemorrhage
what has a high intensity in a T2 image
fluid, CSF, synovial fluid inflammation soft tissue tumors acute and stress fractures early and late AVN
T1 looks at ____ and T2 looks at _____
anatomy
pathology (T2)
how does fat look on a T1 vs T2
T1 white
T2 grey
how does water look on a T1 vs T2
T1 grey
T2 white
how does marrow look on a T1 vs T2
T1 bright
T2 grey
how does cortex look on a T1 vs T2
T1 and T2 dark
MRI sequences: SE
spin-echo pulse sequences, that gets T1 and T2
GRE
gradient recalled echo sequences
STIR
short T1 inversion recovery which suppresses fat
FLAIR
fluid attenuation inversion recovery, which suppresses water, so it is good for imaging of the brain and CNS
TIRM
turbo inversion recovery magnitude, used to assess osteomyelitis in the bone and head and neck tumors.
MRI contrast uses…
gadolinium, which is an IV injection, that decreases the signal on T2 weighted image, and increases the signal of T1 weighted images.
how does implanted hardware or foreign bodies affect an MRI
most ortho hardware is not magnetized, so you can still get an MRI, even after TKA/THA, but you will get artifact locally
can you get an MRI if you have pedicle screws in your Low back
no
if you suspect things that will interfere or be bad in an MRI, what can you do
pre-MRI x-ray, especially if you suspect shrapnel or metal
TF: pacemakers are not affected by an MRI
false, they are affected
how long does an MRI take
30-60 minutes
who may not like MRI
claustrophobic, pain, obese people
how many Newtons of pull does an MRI machine have
200-600 N pull
what are some MRI types
open and seated
what are indications to do an MRI
soft tissues ligaments, tendon, muscle, cartilage, vascular demyelinating diseases neoplasm, infection, inflammation and seizure post acute CVA, TIA, dementia
what are indications for a CT
cortical bone, chest, abdomen or pelvis
fracture, lose bodies,
bony stenosis
occult fractures in patients with osteoporosis
initial eval of CVA, trauma or hemorrhage
