2a. Skull Bones Views and Positioning Flashcards
How many views are there for the skull
name them
3 views
AP or PA/FO or OF 20-25
Townes/FO30/30Half axial/AP axial
Lateral (HR)
what is the patients position for the FO/AP projection
in terms of patient sitting/lying down, chin position, MSP
patient seated erect/supine
chin raised to bring RBL to 20-25*
MSP perpindicular to IR
what is the central ray and centering point for the FO/AP view
CR perpindicular to IR and centered in the midline to the nasion
what are the exposure factors for the FO/AP view
mAs and kVp
70kVp and 16mAs
what is the SID for the FO/AP view
110cm
what do you want the petrous ridges position for the FO/AP view
petrous ridge in lower 1/3 of orbit
how will you position patient when their OMBL is at 90, how will you get the baseline to be 20-25
raise head up so baseline is at 20-25*
this pulls the petrous ridge down
what does it mean if the petrous ridge is too low/below the orbit
youve tilted head too far back/raised head too much
what is the image criteria for the FO/AP view in terms of rotation
Want to measure lateral border of orbit to the lateral border of skull/equidistant = no rotation
what is the image criteria for the FO/AP view in terms of structure superimposition
petrous ridge superimpose infraorbital margin and should not be sitting higher than lower 1/3 of orbit
what is the image criteria for the FO/AP view in terms of area of interest
entire cranial vault visualised
what is the image criteria for the FO/AP view in terms of exposure
sufficient exposure to visualise frontal bone without overexposing the perimeter regions of the skull
for the FO/AP view how do you adjust/detect the OMBL/RBL alignment
for superimposition of the petrous ridge and lower orbital margin:
increase OMBL by 5*
approx 5 degrees for every 1cm
for the FO/AP view how do you adjust/detect the OMBL/RBL alignment in terms of correcting the tilt
for superimposition of the petrous ridge and lower orbital margin:
increase OMBL by 10*
approx 5* for every 1cm
what is the townes projection also named as
2 names
30* Half-axial or AP axial
what 3 bones and landmarks are of import in the FO projection
frontal sinus
supraorbital rim
petrous ridge
what 4 bones and landmarks are of import in the townes projection
occipital bone
foramen magnum
petrous ridge
mastoid air cells on lateral borders
what info about the skull does the townes view give
info about the back of the skull
what is the patients position for the townes projection
in terms of patient sitting/lying down, chin position, MSP, distance between IR and ___
patient erect/supine
chin tucked down so OMBL/RBL is perp to IR
MSP perpind to IR
Equal distance between EAM and IR
what is the central ray for the townes view
CR angled 30* caudally
what are the exposure factors for the townes view
mAs and kVp
77kV, 25mAs
what is the SID for the townes view
110cm
what is the image criteria for the townes view in terms of rotation
cranium demonstrated without rotation
check rotation by distance from foramen magnum to either outer side of skull, make sure its equidistant
what is the image criteria for the townes view in terms of structural superimposition
dorsum sellae centered within the foramen magnum
what is the image criteria for the townes view in terms of structural distortion
foramen magnum is not foreshortened or elongated
what is the centering point for the townes view
midline 5cms above nasion
what is the patients position for the lateral skull projection
in terms of patient sitting/lying down, what is perp to IR, sponge use
patient supine
interpupillary line perp to IR
place head on sponge pad to ensure back of skull is not cut off
what is the central ray for the lateral skull view
horizontal ray
what is the centering point for the lateral skull view
5cm above EAM
what are the exposure factors for the lateral skull view
mAs and kVp
70kVp
12mAs
what is the SID for the lateral skull view
110cm
what is the image criteria for the lateral skull view in terms of area of interest
entire skull visualized
what is the image criteria for the lateral skull view in terms of rotation
head in neutral position, without rotation or tilt (chin in neutral)
Check for rotation by using anterior skull line to check superimposition and use Pituitary fossa to make sure clinoid processes are symmetrical
why is the lateral skull view done supine
to see air fluid levels
also easier to check whether patient is straight or not
If patient cant do supine lateral skull view what else can you do
patient standing erect and side on to IR
what is the OMBL baseline, where is it and what is it used for
orbito-meatal baseline
From EAM to lateral canthus of eye
baseline position OMBL is perpendicular to the IR and for other views we will move patients head from this baseline position
what is the IOML
infraorbital meatal line
line that runs between infraorbital margin and EAM
what is the interpupillary line
where is it and what is it used for
horizontal line between centre of pupils of eyes
used to make sure patient isnt rotated
is the lateral skull xray view a angled view
what is structure is shown in profile
what should be superimposed
non angled view
sella turcica in profile
TMJ superimposed
what structures are the caldwell skull view used to visualise (2things)
frontal and paranasal sinuses
what is the townes skull view used to evaluate (2things)
what structures is it good for visualising (3 structures)
evaluate skull fractures and neoplasia
petrous temporal bone, dorsum sella, laboid suture
is the AP skull xray view a angled view
when is this view useful
non angled
when you cant get the pateint in a PA position
is the PA skull xray view a angled view
what is structures should overlap
non angled view
petrous ridge will overlap lower 1/3 of orbits
what is PA view better than AP skull view 2 reasons
lower dosage to eyes
crisper facial stuctures as closer to detectors so less magnification
AP skull view ends up with which part being more blurry
orbit more blurry as further away from detector
