MRI Imaging for the PA Flashcards
What does an MRI use to create its image?
molecular composition of tissues and a strong magnetic field to manipulate electrical activity of HYDROGEN atoms in the body
When a patient enters an MRI machine, what direction does the protons current flow?
protons current will line up parallel to the main superconducting magnet of the MRI
What are the coils of the magnet in the MRI responsible for?
Transmitting RF pulses
Receiving the signal or echo
What happens when the RF pulse is transmitted by the transmitter coil?
protons are displaced from their original alignment
Why is the superconduction magnet kept really cold?
to reduce the heat from the friction of the protons
What do transmitter coils send?
a short magnetic pulse = RF pulse
What happens when the RF pulse is turned off?
the protons realign in a parallel state to magnet and energy in the form of RF signals are released
When the protons realign in a parallel state to the magnet after the RF pulse is turned off, what is this called?
recovery
What is T1 relaxation?
Recovery; time it takes for the tissue to recover to parallel state
What is the length of time for recovery and the echo called?
T1 and T2
What is TE?
echo time
What is TR?
repetition time
What weighting does T1 have?
short TE of 10-20 s
short TR of 300-700 ms
What appears white in T1 image?
Fat
Gadolinium
Proteinaceous Fluid
Melanin
What is T2 relaxation?
Decay; time it takes for tissue to return to perpendicular to magnetic field
What weighting does T2 have?
Short TE of 20 ms
LONG TR of 2000ms
What is the mnemonic to for T2?
WWII - water white in 2
What typically appears white in T2?
water fat edema inflammation infection cyst hemorrhage
What vascular structures are enhanced with Gadolinium?
Tumors
Areas of inflammation
What is the effect of Gadolinium?
shorten the T1 relaxation time of hydrogen nuclei to create a brighter signal
How is Gadolinium excreted?
by the kidney
What are some advantages of MRIs?
capable of high-resolution images in multiple planes
can provide detailed soft tissue characteristics
non-invasive
No known harmful effects
What are some disadvantages of MRIs?
More expensive than xray or CT
Long scan time (30-45 min.)
Limited by multiple things
What limits the use of an MRI?
patients body habitus patient anxiety or pain ferrous implants Implanted pumps/electronic devices contrast issues (allergy)
What is the magnetic field strength of most MRIs?
0.5 to 3 Tesla
What is Earth’s magnetic field strength?
50 microT
Which type of MRI machine gives a better quality image?
closed
What is the magnetic field strength of open MRI machines?
0.1 to 1 T
What procedures require the patient to be placed head first in to machine?
Head and Neck Chest Cervical Thoracic and Whole Spine Abdomen Shoulders and Upper Limb
What procedures require the patient to be placed feet first in to machine?
Pelvis
Hips
Lower Limbs
What are CT scans used for?
trauma to identify and characterize injury patterns and severity
What is CT better than xray for diagnosing?
identifies subtle fractures
Visualizes articular extension of fracture
Assesses for the presence of articular step-off/gap
What is MRI most used for?
PRIMARILY EVALUATION OF SOFT TISSUE
diagnosing occult fractures
concern for associated ligament or articular cartilage injury
What is MRI the modality of choice for?
Disc Herniation
To assess “internal derangement” of joints
What type of MRI images are occult fractures best visualized on?
T2 images in which the light up as edema of bone marrow
Where do bone bruises appear on an MRI image?
In T2 weighted images as hyperintense signal
What is an MRI standard for assessing of the spine?
spinal cord anatomy, tumors, or trauma
PreOp eval. of pts. with spondylosis or disk herniation = MOC
What does Gadolinium help with when used in MRI?
differentiates tissues receiving higher blood flow; infection, tumor, postsurgical scar
