Imaging: CT scan Flashcards
How do CT scans produce cross-sectional images?
x-ray attenuation
How are CT images read?
transverse images read from bottom looking up
Advantages of CT?
- eliminates superimposition of tissues
- good resolution
- sensitive and specific for fracture
- all views obtained in one patient position
Disadvantages of CT?
- more radiation exposure (100-1000x)
- may have reaction to contrast agents if used
- soft tissue not well visualized
- high cost
How do magnetic resonance imaging produce images?
pulses of radio frequency and strong external magnet to create electromagnetic field
Advantages of MRI?
good for soft tissue
no radiation exposure
see in all planes
great contrast
Disadvantages of MRI?
loss of bony detail
long, expensive
can’t do if metal implants or exposure (pacemaker, welders)
T1 images are also called
longitudinal magnetization
T1 images are based on how long it takes protons to _______ back to resting state after RF pulse
relax
T2 images are also called
transverse magnetization
T2 images are based on how long resonating protons remain ______ following a RF pulse
in phase
T1 are ____ repetition and echo times
short
T2 are ____ repetition and echo times
long
Fat, marrow of bone of T1 images are what?
bright
areas of high water concentration in T1 images are what?
dark
Fat, calcification of T2 images are what?
dark
areas of high water content in T2 images are what?
bright
T2 images are ideal for what injury?
acute trauma
Functional MRI is based on what?
increased blood flow in the brain
How does a DEXA scan work?
high and low energy x-ray are directed at bone. the difference in absorption b/t beams used to find bone density
Nuclear medicine examples are
SPECT, PET, (with CT), Radionuclide scintigraphy (Bone scan)
what is the radioactive tracer for radionuclide scintigraphy?
methylene
scan 2-3 hours after injection
Radionuclide Scintigraphy good choice for what?
detecting stress fractures and follow up of metastatic bone disease
Advantages of radionuclide scintigraphy?
highly sensitive
fast
not $$
Disadvantages of radionuclide scintigraphy?
easily influenced by osteoblastic activity
poor specificity
