Intro to Imaging Flashcards
axial plane
top (cranial/superior) vs bottom (caudal/inferior)
Nuclear medicine
Radioactive agents allow for physiologic imaging (PET uses glucose analog taken up by metabolically active cells)
ultrasound pros/cons
pros: non-invasive, no ioninzing radation, can be used to evaluate bloodflow or guide procedures, portable
cons: dependent on operator skill, cannot penetrate air or bone
mri pros/cons
pros: no ionizing radiation, detail of soft tissues and blood vessels
cons: expensive, slower, no pt with pacemakers
ALARA
“as low as reasonably achievable” - need to always weigh risks and benefits of imaging
Physics of X-ray
Electromagnetic radiation: electrons emitted from cathode interact with metal (W or Mb) target/anode, generating x-rays
coronal plane
front (anterior/ventral) vs back (posterior/dorsal)
MRI physics
- Energy from an oscillating magnetic field aligns the spin of the protons in the water molecules in the body
- Radiofrequency current applied to change magnetic field
- Protons absorb energy and spins flip
- Field is turned off and protons “precess” back to normal, generating a radio signal
CT
3D radiograph generated by rotating source/detector
ionizing radiation
Particle or wave with sufficient energy to remove an electron from an atom (shorter wavelength and higher frequency than UV)
Imaging modalities that do (and do not) use ionizing radiation
ionizing radiation:
- radiography (mammography, angiography)
- CT
- nuclear imaging/PET
no ionizing radiation:
- ultrasound
- MRI
MRI image description
“intensity”
hyperintense = white
hypointense = black
X-ray image description
“density”
air (black) => fat => soft tissue => calcium/bone => metal/contrast (white)
sagittal plane
left vs right
Ultrasound physics
Transducer sends sound waves into the body and receives echoing waves with different speeds and wavelengths
Ultrasound image description
“echogenicity”
anechoic (black - fluid, air) => hypoechoic (gray - soft tissue) => hyperechoic (whiter - bone, fat)
**cannot penetrate bone or air
radiation dose from:
chest x-ray
cheast CT
average annual background radiation
annual occupation exposure limit
chest x-ray = 0.1 mSv
chest CT = 5-8 mSv (~50-100x more than x-ray)
average background = 3.5 mSv
occupational limit = 50 mSv (~500 chest x-rays/yr)
pros/cons of radiography
pros: widely available, cheap, fast, bony detail
cons: ioninzing radation, 2D, lower tissue detail
