Introduction to medical imaging
X-ray (plain radiograph)
Useful for visualising the skeletal system and some disease processes in soft tissue.
o Tend to be digital rather than x-ray films nowadays
A heterogeneous beam of x-rays
o based on the density and composition of the structure a proportion of the x-
ray is absorbed
o the x-rays that pass through are detected as black and less dense tissues
(white/shade of grey)
o Grey/white areas are denser tissues that have absorbed more x-rays
Most common
Denser
o more rays absorbed-less pass through
Basically a shadow of the parts of the patient that absorb or block the x-rays
o -photographic negative
o -radio- opaque-white=areas that block the x-ray (denser)
o -radio- lucent-black=areas that did not stop the x-rays (less dense)
Abnormalities
o say what you can see.
Advantages:
Cheap
Readily available & portable- move round wards and to surgery
Disadvantages:
Uses ionising radiation- not a big deal unless have it every week all over.
o We all have background radiation
o Cornwall: radon gas
But damage can be caused to fast replicating cells
o Testes, ovaries
Limited range of densities
o -air
black
o -fat
lighter grey than air
o -soft tissue/fluid
shades of grey
o -calcium & impregnated tissue=most dense naturally occurring tissue,
white
o -metal
white
2D representation of a 3D object
o parts of body hidden by more dense body part
o e.g vertebral column covers heart therefore can only see outline.
o limited range of being able to differentiate between body parts
o cannot make out chambers of hear
, Only calcified tissue shows up clearly
o (soft tissue does not show up very well)
o Not very sensitive
(you have to lose 30% of bone mass before it shows up on x-ray-
very bad)
Things in front can obscure structures behind
Processes taking place inside the bone cannot be seen
o Outer bone too dense
o (avascular necrosis, osteomyelitis etc)
Chest X-rays
Which direction you take an
x-ray may alter what you see.
AP-creates enlarged image of the heart
PA-heart not as enlarged more normal,
o chest x-rays not spread out as far
x-ray taken this way as less distortion.
PA view- usual view
1. Clavicle in lung field
2. Ribs slanted
3. Scapula outwards from lung field
4. Heart shadow smaller
5. Usual view for chest
1. AP view-
1. Clavicle remains at top of lung field
2. Ribs lie more horizontal
3. Scapula comes in the lung field
4. Heart shadow looks larger
5. Usually bedridden and infants
X-ray (plain radiograph)
Useful for visualising the skeletal system and some disease processes in soft tissue.
o Tend to be digital rather than x-ray films nowadays
A heterogeneous beam of x-rays
o based on the density and composition of the structure a proportion of the x-
ray is absorbed
o the x-rays that pass through are detected as black and less dense tissues
(white/shade of grey)
o Grey/white areas are denser tissues that have absorbed more x-rays
Most common
Denser
o more rays absorbed-less pass through
Basically a shadow of the parts of the patient that absorb or block the x-rays
o -photographic negative
o -radio- opaque-white=areas that block the x-ray (denser)
o -radio- lucent-black=areas that did not stop the x-rays (less dense)
Abnormalities
o say what you can see.
Advantages:
Cheap
Readily available & portable- move round wards and to surgery
Disadvantages:
Uses ionising radiation- not a big deal unless have it every week all over.
o We all have background radiation
o Cornwall: radon gas
But damage can be caused to fast replicating cells
o Testes, ovaries
Limited range of densities
o -air
black
o -fat
lighter grey than air
o -soft tissue/fluid
shades of grey
o -calcium & impregnated tissue=most dense naturally occurring tissue,
white
o -metal
white
2D representation of a 3D object
o parts of body hidden by more dense body part
o e.g vertebral column covers heart therefore can only see outline.
o limited range of being able to differentiate between body parts
o cannot make out chambers of hear
, Only calcified tissue shows up clearly
o (soft tissue does not show up very well)
o Not very sensitive
(you have to lose 30% of bone mass before it shows up on x-ray-
very bad)
Things in front can obscure structures behind
Processes taking place inside the bone cannot be seen
o Outer bone too dense
o (avascular necrosis, osteomyelitis etc)
Chest X-rays
Which direction you take an
x-ray may alter what you see.
AP-creates enlarged image of the heart
PA-heart not as enlarged more normal,
o chest x-rays not spread out as far
x-ray taken this way as less distortion.
PA view- usual view
1. Clavicle in lung field
2. Ribs slanted
3. Scapula outwards from lung field
4. Heart shadow smaller
5. Usual view for chest
1. AP view-
1. Clavicle remains at top of lung field
2. Ribs lie more horizontal
3. Scapula comes in the lung field
4. Heart shadow looks larger
5. Usually bedridden and infants
