MRI Flashcards
what is a scout film
displays an image of the studied body region on which is superimposed a sequentially numbered parallel lines or “slices” example IM 3/38
What do the abbreviations THK and FOV stand for
THK- thickness of the slices
FOV - field of view (3x3 cm, 4x4cm etc)
how can the sequence number help you sort through the different types of imaging studies (T1, T2, etc)
Often times one type of image is given the even numbers while its corresponding image is given even numbers (T1s even T2s odd so you can compare the same image with different weighting side by side)
Describe the image orientation of axial, sagittal plane, and frontal plane images
axial- you are looking up fro the patients feel
sagittal -
coronal - patient facing toward the viewer
what does the MRI measure
contrast between tissues based on relative relaxation times of hydrogen protons after radio frequency perturbation from their relaxed precessional axis
T1 (Brief RF) and T2 are the different types of perturbation
What tissues do T1 images emphasize?
T1 (Brief RF) - tissues with protons that quickly recover and yield a short RF recording time (shot TE and TR time)
- fat emphasis due to the faster proton recovery relative to muscle
- fat is bright white due to higher single intensity
- bone cortex is dark
- good for anatomy not pathology
What tissues do the T2 images emphasize
T2 (longer duration RF) - tissues that recover more slowly are emphasized (long TE and TR)
- muscle is emphasized on these images as bright white
- fat is gray
- better than T2 for viewing pathology
- cortex dark
what image type will bone, fibrotic and inflamed tissues show up on best?
- fibrotic - less water and tend to have longer recovery times therefore are best visualized on T2
- inflammatory - increased water content creating longer recovery times and better visualization on T2 images
- bone will have low signal intensity in T1
what is magic angle phenomenon
image artifact created by misleading changes in signal intensity associated with collagen based tissues orientation. signals can cancel or amplify
How are MRI findings described (what is the nomenclature)
Relative signal intensity (normal, increased, decreased, etc)
How are T1 and T2 images different
T1 weighted - fat is white, water is gray, marrow is bright, cortex is dark, good for anatomy
T2 weighted - fat is gray, water is white, marrow is gray, cortex is dark, good for pathology because lesion are usually water based
Hydrogen is most present in what type of tissues
water based tissues
What structure is the MRI actually measuring
it is imaging protons
what is precess
the tendency of protons in the presence of a magnetic field to spine around an axis
the loud noise of the MRI is the magnetic field pulse. what does this accomplish for the MRI image
- organized alignment of the axis of proton spin/precess
2. gradient of frequencies decreasing with distance from the magnetic coils
what is flip angle and what is its value in the MRI
angle to which a proton will shift its spin axis when perturbed by the MRI
- the time it takes for the proton to return to its normal angle is measured via a RF signal released by the proton as its normal angle is restored
what do T1 and T2 images measures
Both are measures simultaneously, but pick up different parts of the signal
- T1 measures the longitudinal vector of the RF signal
- T2 measures the transverse vector of the signal
What advantages does MRI have over radiating images such as CT and X-ray
- multiple plane image angles
- good contrast with water dense tissue
- no know health hazards
- good for soft tissue imaging
- good for neurology
What disadvantages does MRI have over radiating images such as CT and X-ray
- more expensive
- trouble with claustrophobia and motion artifact
- limited availability
- bone trauma poorly demonstrated
what are the three basic acquisition techniques for MRI
- PD (spin) - proton density
- T1
- T2
what does the PD image emphasize
- high signal intensity with water based tissues (synovial fluid and effusion)
- low signal intensity with bone or air filled spaces
- good for orthopedic trauma
- long TR (repetition of pulse) and short TE (peak echo time)
What tissue you can help you differentiate T1 from T2
Look at the fat (world war II - water is white on T2)
- T1 fat is bright white and water is gray
- T2 Fat is gray and water is bright white
What color will water appear in CT, T1 and T2 images
CT/x-ray - gray
T1 - dark
t2 - bright
What color will air appear in CT, T1 and T2 images
CT/x-ray - black
T1 - dark
t2 - dark
What color will fat appear in CT, T1 and T2 images
CT/x-ray - black
T1 - white
t2 - gray
What color will bone cortex appear in CT, T1 and T2 images
CT/x-ray - white
T1 - gray-black
t2 - dark gray
What color will bone cortex appear in CT, T1 and T2 images
CT/x-ray - gray
T1 - bright
t2 - gray
hybrid MRI sequence translation tips
- Look to the relative T1 and T2 weighting
- “look to the fat” for signal intensity to help identify signal type
What are some examples of MRI enhancement techniques
FSE
FS
GAD
STIR
What is a bankart fracture
avulsion of the superior glenoid
What is a bouchard nodes
the large boney out growths of the joint
- hallmark of OA
What is the FBI sign
Fat, Blood, intra-articular
- escape of fat and blood from the bone marrow space into the int capsule
AKA - lipohaemarthrosis
