4th year Flashcards
what do MF views show?
facial bones/skull from either a lateral or AP or basal perspective
which type of MF view is rarely indicated now?
basal
collimation
the control of the size and shape of the xray beam
- use smallest field of view compatible with diagnostic requirements
where does collimation occur?
at the tube head
what feature ensures correct collimation?
light beam shows area on patient which will be exposed to primary beam
cross shows where central ray will strike receptor
EO views equipment
xray tube head
collimator
cassette with film or digital
intensifying screen
min speed 400
have phosphor layer which gives out light when xrays interact with it
- film sensitive to that light
grid
thin lead strips adjacent to cassette which attenuate obliquely travelling photons before they reach the film
but for the same number of photons to reach film dose must be increased, otherwise insufficient blackening
lead v good absorber of xrays
OM line
ST line
central part of EAM to outer canthus of eye
much more easily visualised
OM vs FP
differs by approx 10 degrees
what is OM line used for?
radiographic baseline for skull radiographs
- supposed to mimic angle of the skull base
- helps get pt in right positioning
FP
orbitale to porion
most inferior IO rim to superior EAM
skeletal - select overlying ST
lateral skull
similar to a lat ceph - but free positioning and no ST images
shows lat view of whole skull as well as facial bones and upper cervical spine
no cephalostat/wedge for ST profile
indications for lat skull
*but increasingly replaced by CT (also detects intra-cranial abnormalities)
facial fractures to show vertical and AP displacement (but both sides superimposed on each other so not widely used)
fractures of skull/skull base
skull pathology (e.g. Pagets, myeloma - see discrete radiolucencies)
pituitary fossa enlargement, sphenoid sinus enlargement
what does an OM show?
orbit frontal sinus - often asymmetric MS zygoma, zygomatic arch nasal septum coronoid process odontoid peg/dens of C2
taking OM
OM line at 45 degrees to IR - nose-chin position
mid-sagittal plane perpendicular to IR
inter pupillary line parallel to floor
xray beam perpendicular to IR
centred in midline, level with region of interest
what does AP/PA refer to?
direction of beam and position of tube and image receptor relative to pt
PA
tube posterior, IR anterior
AP
tube anterior, IR posterior
what are MF views usually - PA or AP?
PA
when might you do an AP MF view?
if eg. can’t put traumatised tissues against IR
- but image less clear
why PA direction?
reduced magnification
- objects closer to film are magnified less than more distant objects
- structures we want to see as close to IR as possible
dose reduction
- low energy photons entering back of head are attenuated before they reach radiosensitive tissues e.g. lens
- salivary glands also radiosensitive but can’t do much as in field of view
alterations to standard 0 degree OM projection
changing angulation of xray beam alters projection of bones onto radiograph
gives better view of some areas e.g. zygomatic arch
gives different view of displacement e.g. displacement at IO rim in zygomatic complex fractures
what imaging types are indicated for sinus disease?
MRI or CT
why is xray not indicated for sinus disease?
acute sinusitis can be diagnosed and treated clinically
signs on xray are non-specific and are encountered in asymptomatic people
if persists beyond 10days of tx, CT is recommended when the results could alter management
what does a PA mandible show?
posterior body, angle, ramus of mandible
superimpositions
- cervical spine - obscures anterior mandible
- mastoid process and zygomatic arch - obscures condyle
taking a PA mandible
OM line perpendicular to IR
- forehead-nose position
mid-sagittal plane perpendicular to floor and IR
interpupillary line parallel to floor
xray beam perpendicular to IR centred between angles of mandible
what does a SMV show?
base of skull inc foramina sphenoid sinus MS plain view of mandible inc condyle zygomatic arches*
taking SMV
ensure no history of neck injury/disease extend H and N as far as possible OM line parallel to IR mid-sagittal plane perpendicular to IR and floor vertex of head contacts IR beam centred between angles of mandible
OM indications
(sinus disease - no longer indicated - maxillary, frontal, ethmoid)
middle 1/3 facial fractures - zygoma, le fort
coronoid process fracture
imaging for middle 1/3 facial injury
XR of facial bones indicated
CT (inc CBCT) specialised investigation
imaging for mandibular trauma
OPG/XR indicated for uncomplicated fracture
CT (inc CBCT) specialised investigation
MRI - only in specific circumstances
PA mandible indications
fractures of angle, posterior body and ramus of mandible - medial and lateral displacement (wouldn't use for condylar heads - CBCT) cysts/tumours (same areas of mandible) - medial and lateral expansion/destruction - use CBCT if available as more detailed info facial deformity (often then taken in a cephalostat - PA cephalometric)
indications for SMV
fracture of zygomatic arch
expansion of more posterior mandible (anteriorly true occlusal as not so good anteriorly)
cranial base pathology (now replaced by CT)
- lots of superimposition so infrequently done unless 3D imaging not available
SMV to show zygomatic arches
can make show if need to but don’t normally see as such thin bones
- would need separate exposure
arch very thin so normal beam too penetrating, energy and quantity need to be reduced
exposure factors (kV and time) reduced cf those to show skull
therefore skull underexposed so appearing white
Reverse Townes
beam from occiput to forehead
good for condylar heads
which legislation means you need to do a CE report?
IRMER17
why should you do a radiographic report?
IRMER17 medicolegal best practice records audit
CE report
list views and justification grade images dentition (FDI) Rxs RRs/associated pathology RCTs caries supporting bone (indicates) periradicular changes anything else
symmetry
margins
bone consistency
what shape is most concerning?
irregular
sclerosing osteitis
bone becomes more radiodense due to an infection
more radiolucent
loss of previously opaque material e.g. bone, teeth
more radiopaque
increased density e.g. cortical bone increased thickness e.g. overlaps alteration e.g. ST calcification ST within an air space - replacing air with anything - appears radiopaque sclerosing osteitis
what margin is worrying?
ill-defined
what does a corticated margin indicate?
has to keep remodelling, slow growth
wouldn’t have if aggressive
effect on other structures
none
displacement (usually indicates slow-growing)
expansion (reasonably slow growing)
resorption (more aggressive)
why can well-defined lesions lose their corticated margins?
if they become infected e.g. abscess
can mimic malignancy
radiological sieve
normal developmental traumatic inflammatory cystic (typically radiolucent) neoplastic (benign/malignant) osteodystrophy metabolic/systemic idiopathic iatrogenic foreign body artefact
CT
multiple axial slices across long axis of pt
can also look at coronal and sagittal images
v high xray dose exam
thin fan shaped beam and line detector
CBCT
xray beam is a cone
bigger flat panel detector
typically only goes round pt once - single location
hard tissues as not great ST differentiation, whereas CT is both
- don’t do CBCT if need STs
lower radiation dose
Justification
by practitioner
specific objectives
total diagnostic/therapeutic benefits to individual and society
individual detriment exposure may cause
efficacy, benefits and risks of available alternatives
history and exam only acceptable means of determining which views required
clinical indications for CBCT
implant planning impacted teeth (normal and supernumeraries) - location - relations e.g. IDC - ? related other teeth e.g. RR pathology - cystic lesions, infections, benign tumours orthognathic surgery hypodontia - implant planning cleft palate - bone defects dental anomalies - dilaceration, double teeth endo problems - ECR autotransplantation
Sedentexct
safety and efficiency of new and emerging dental xray modality and CT
EADMFR basic principles on use of CBCT
use only when Q can’t be answered adequately with lower dose method
if evaluation of STs required - medical CT/MRI
use smallest vol compatible with clinical situation
choose resolution compatible with HPA
