Extra Oral Radiography Flashcards
what is the radiographic baseline?
- Radiographic baseline - line from outer canthus of eye to EAM. represents base of skull
what is scatter radiation?
when xrays pass through tissues - some are scattered = compton effect
skull radiography - increase in field of beam - more scatter produced
adds to background fog
greyer film - lack of contrast
what is an anti scatter grid?
stop photons scattered in patient reaching the film
avoids degrading image and reducing contrast
narrow strips of lead alterating with plastic
fixed/stationary or moving/oscillating
what is a postero - anterior mandible used for?
fractures - medio lateral displacement
cusps/malignancy causing medio lateral expansion or bone destruction
what does a PA give good visualisation of?
limited visualisation of?
posterior body and ramus
head/neck of condyle
in a PA what can the spine obstruct?
the midline
advantages of PA?
reduced magnification of facial structures
reduced dose to eyes
positioning for a PA?
patient faces film - nose/forehead touching holder
radiographic baseline = horizontal
centre of beam to midline of patient at height of mid ramus
what are reverse townes used for?
improve visualisation oh head/neck of condyle
trauma or pathology
positioning for reverse townes?
xray beam angled 30 degrees up
centre of beam aimed to midline of pt and through condyle
indications for taking a lateral oblique of the jaw?
fractures of body,ramus,condyle
pathology - cysts
assess wisdom teeth
dental assessment of special needs patients
caries in children - bitewings not tolerated
positioning for lateral oblique jaw?
isocentric positioning with a skull unit
dental tube + vertical angulation
dental tube + horizontal angulation
what is isocentric positioning?
patient supine - position for area to be imaged
rotate machine into horizontal plane
angle 25 degrees towards head
tilt top of pt’s head towards film
what is vertical angulation?
pt holds cassette against and parallel to area under exam
tubehead positioned underneath lower body of mandible - not under exam
aim tube towards teeth under investigation
tubehead angled slightly upwards
what does vertical angulation allow?
will project opposing body of mandible up and away from area of interest
disadvantages of vertical angulation?
angulation can cause vertical distortion of teeth
maxillary teeth not always shown clearly
horizontal angulation?
pt holds cassette against/parallel to area under exam
tubehead aimed along occlusal plane below ear towards max/mandib teeth to be examined
aims through radiographic keyhole = triangular space between back of ramus and cervical spine
disadvantages of horizontal angulation?
xray beam may not pass directly between the contact points of teeth = overlapped on film
what are ceph radiographs used for?
ortho assesment
pre ortho surgery
what is used during a ceph to standardise the image and make the image reproducible?
patient positioned with ear rods
what must a ceph have?
must have means of calculating amount of magnification
must be able to visualise hard and soft tissue
means of calculating magnification/calibrating digital image
positioning for a lateral ceph?
mid saggital plane parallel to film/receptor
frankfurt plane horizontal
centre of xray beam aimed at EAM
teeth in occlusion
how to keep maginification to a minimum?
long focus to patient distance
short patient to film distance
distance from xray to patient?
1.5-2m distance
what are aluminium filters used for?
positioned over anterior part of face
attenuate beam in anterior facial region
allows visualisation of bone and soft tissue on one film despite high exposure factors for facial bones
if digital - soft tissue made up by software
reducing the beam size reduces what?
dose
other type of ceph?
postero anterior ceph
what is a lateral skull used for?
trauma - fractures
pathology - pagets, myeloma
used primarily to visualise vault of skull
difference of a lateral ceph compared to lateral skull?
lateral ceph uses cephalostat, has an aluminium filter, large focus to patient distance, patient must be in occlusion
what is an occipito mental used for?
facial bone fractures - zygoma, le fort and orbital blowout
pathology - occasionally used in sinus disease
different angulations give views of different areas
positioning for occipito mental?
patient faces film holder nose/chin touching the holder radiographic baseline 45 degrees to film centre of xray bea,m to midline of pt through base of nose beam 10-30 degrees to feet
increased angulation causes what>?
projects dense bones of skull base down away from facial structures = improved view of zygomatic arch = diff perspective - useful for evaluation of bony displacement
what is the frankfurt plane?
Frankfurt plane - inferior orbital border IOB to upper border represents anthropological base line
what is the maxillary occlusal plane?
Maxillary occlusal plane - ala of nose to tragus of ear
