(2) Fundamental Principles of Imaging Modalities

ionizing radiation exposure

what is an R&F room?

radiography and fluoroscopy room

• rooms for diagnostic imaging made form still x-ray images and real time moving images (fluoroscopy)

how does an xray tube work?

hot cathode (-) emits electrons that are attracted to tungsten anode (+)

• cathode : generates electrons

• anode : stops electrons

when fast moving electrons hit the metal target (anode) what happens to kinetic energy

99% → heat

1% → exits as electron beam (goes to target or is scattered)

what is the primary function of the envelope?

• provide support and electrical insulation for anode and cathode

• maintain vacuum in the tube

what do x rays penetrate?

less dense matter

• skin

• body tissue

NOT BONE

how does bone appear on xray?

bone is dense and blocks xrays

• appears white

how does soft tissue appear on xray?

grey

how does air filled areas appear on xray?

black

how do metallic objects appear on xray?

stark white → high contrast

how does blood appear on xray?

grey

where does scatted from xray come from?

1% backscatter from walls

3% leaks from tube

96% from patient

what is a film badge dosimeter?

used for monitoring cumulative radiation dose due to ionizing radiation

• photographic film

• holder

should be work in front of body (between shoulders and waist)

what is primary radiation? remnant? scatter? attenuation?

primary : beam of photons before it interacts with patient

remnant : resulting beam that is able to exit from patient

scatter : radiation that interacts with matter and continues in a different direction

attenuation : primary radiation that is partially absorbed as it travels through the pt

scatter reduces

contrast

which patient transmits more radiation? thinner or thicker

which patient absorbs more radiation? thinner of thicker

transmits : thinner

absorbs : thicker

what determines the quality/contrast of the beam?

kVp = energy of xrays

• more kVp improves image quality but reduced contrast

what is contrast?

difference in densiy of adjacent structures on the image

• high contrast & low kVp : more B&W

  • this is because lower energy photons are more easily absorbed by denser tissue rather than just passing through them

  • creates greater difference in attenuation

• low contrast & high kVp: more greys

what is Mas?

milliampere-seconds

• quantity of xray produced

  • tube current (mA) x exposure time (s)

*directly controls number of xray photons → determines image brightness

in what position of xray source/film would increased organ size be seen?

xray source is closer to the organ than xray film

*OID (object to image receptor distance)

know

what is distortion?

misrepresentation of anatomical part by size/shape

• occurs when x ray beam is not perpendicular to cassette/film

• shape, size, elongation,foreshortening

blunted angles → pleural effusion

collapsed lung

opacities indicate

fluid

infectious infiltrate

aspiration

blood

what is this

endotrachial tube can be used to treat collapsed lung