radiology Flashcards
justification
all exposure must benefit pt and/or provide new infor to aid management/dx that cannot be obtained otherwise
optimisation
ALARP
as
low
as
reasonably
practicable
dose limitation
for radiation workers and members of public
3 key principles of radiation exposure
justification
optimisation
dose limitation
methods of dose reduction
collimation (rectangular)
fast film speed (E speed or faster)
long FSD (20cm)
60-70keV
beam diameter no greater than 60mm
radiation protection supervisor
ensure regulation and trainig are followed
radiation protection advisor
advises n risk, regulations, training, quality etc
employer
IRMER 2017
legal protection, safety, make sure equipment in line with IRR17 and staff following regulations
referrer
check pt demographics and clinical justification of radiograph, trained
practitioner
justifies exposure
Benefit Vs Risk
check no recent relevant radiographs
operator
ALARP, takes exposure, processes and reports
IRMER2017
ionising radiation medical exposures regulation 2017
IRR2017
ionising radiation regulations
paralleling Vs bisecting angle
Paralleling → No contact but object and receptor are parallel and beam perpendicular to receptor.
Bisecting angle → In contact but not parallel and beam perpendicular to receptor.
why should you report radiographs
medico legal - IRMER 2017
records
audit
6 safety features
- controlled area
- warning sign for controlled area
- sign lights up when equipment on and during exposure
- exposure when continous pressure only
- exposure stops automatically
- emergency stop button
characteristics of ghost image
higher
opposite side
larger/wider
comptom scatter effect on image
fogs and decreases image quality due to x-ray hitter outer electroms and losing direction and energy
photoelectric effect on image
complete absorption giving a white imahge as does not reach film
normal
metal in X-ray tube head
lead - absrobs x-rays
copper
tungsten
aluminium
erros in OPT
anteriors distorted
pt not in focal plane
errors in OPT
blurry image
pt moved during exposure
errors in OPT
image too wide
canine guide set in front of canines
how can positioning erros in OPT be limited
use guides - chin rests, bite block, hand rests, guide lights for frankfort plane (paralell to floor) and canines line
ask pt to stay still and tongue to roof of mouth
developmental bone pathology
2
tori
fibrous dysplasia
inflammatory bone pathology
2
dry socket
osteomyelitis
neoplasam bone pathology
2
osteoma
osteosarcoma
metabolic bone diseases
osteoporosis
osteomalacia
Paget’s
giant cell lesion?
high risk radiograph frequency
6months
moderate risk radiograph frequency
12 months
low risk radiograph frequency
18-24months
radiographic image defintion
Pictorial representation of body part. Record of the pattern of attenuation of x-ray beam after it has passed through matter
binding energy
Additional energy required to exceed electrostatic force. Energy required to remove electrons from a shell
xray beam intensity
Quantity of photon energy passing through cross-sectional area of beam per unit time
how are xrays produced
Deceleration of fast moving electrons (electrons fired at atoms at high speeds, collide and decelerate)
components of xray tube head
Filament,
transformer,
target,
target surround,
evacuated glass envelope,
shielding (lead),
filtration (aluminium),
collimator (lead),
spacer cone
attenutaion
Reduction in number of photons within the beam
- No attenuation (black image) - photons pass through object unaltered and all photons reach the film
- Partial attenuation (grey image) - photons change direction, losing energy (scatter and absorption)
- Complete attenuation (white image) - photon stopped, losing all energy within tissue (absorption)
difference between low and high tube pf (kVp) and what we use
Low tube pd - increases photoelectric interactions, contrast and absorbed dose (better image, but more dose to pt)
High tube pd - decreases photoelectric interactions, contrast and absorbed dose (poorer image but less dose to pt)
60-70kVp - for diagnostic quality but compromise in not too much radiation to pt
characteristic spectrum
electron collides with inner shell electron, target electron displaced to outer shell/completely lost from atom, orbiting electrons re-arrange to fill vacant orbital slot
continuous specturm
electron passes close to nucleus of atom and is decelerated and deflected, amount of deceleration and deflection proportional to energy loss
photoelectric effect
Complete absorption/attenuation. X-ray photon interacts with inner shell electron, photon energy just greater than binding energy. Photon disappears, as energy used to overcome electron binding energy. Electron ejected and difference in energy emitted as light/heat, outer void filled by free electron. Complete absorption of photon energy
inc by
* Thicker object,
* lower photon energy,
* object has high atomic number
photoelectric effect
Complete absorption/attenuation. X-ray photon interacts with inner shell electron, photon energy just greater than binding energy. Photon disappears, as energy used to overcome electron binding energy. Electron ejected and difference in energy emitted as light/heat, outer void filled by free electron. Complete absorption of photon energy
inc by
* Thicker object,
* lower photon energy,
* object has high atomic number
compton scatter
X-ray photon interacts with loosely bound outer shell electron. Photon energy»_space; binding energy, electron ejected and colliding photon has lower energy (deflected and scattered) and can continuing interacting. Atom stabilised through free electron capture
Scattered photons produced before image scattered backwards; scattered photons produced after image scattered backwards and darken/fog image
* prevented by Lead film packets, collimation
blue film holder
ant PA
yellow film holder
posterior PA
red film holder
bitewings
green film holder
endo
true occlusal
90 degrees to mandible (paralleling technique)
bony pathology
oblique occlusal
indications
pathology too large for PA/ or not possible
trauma
localisation using parallax
centring points for oblique occlusal
maxilla - 1cm above ala-tragal line
mandible - through lower border
indications for OPT
orthodontics - developing dentition
developmental and acquired anomalies
caries, pulpal and perio disease
pathological jaw lension
surgery
trauma (mandible fractures)
limitations of OPT
width of layer in focus
horizontal distortion
long exposure time
big shoulders
positioning difficulties (severe malocclulion, extremes of age, obese)
key planes for OPT
mid-saggital plane - perpendicular to floor
frankfrot plane - horizontal to floor
canine lines - go through upper canine
focal trough
layer in the pt containing structures of interest that are demonstrated with sufficient resolution to make them recognisable
structures at other depths are not clearly seen
lateral cephalometry
standardised and reproducible radiographic forms of the skull and facial bones
gives a lateral view of facial bones, base of skull and upper C spine
soft tissue profiles are alwso seen
enables measures of dental and skeletal relationships
mandible # view
OPT and PA mandible
middle third face fractures
views
occipitomental
zygomatic arch fractures
views
submentovertex
best view for facial fractures (supersedes rest)
CBCT
benefit of CBCT
3D representation of structures of interest
can be views in different planes
CBCT vs CT
faster and reduced dose
CT is line detector where CBCT is flat panel
indications for CBCT
jaw/face fracturees
implant planning
pathology - cysts, tumours
impacted teeth
orthognathic surgery
clefts
parallax
apparent change in position of an object caused by a real change in the position of the observer
rule for parallax
SLOB - same lingual opposite buccal
my PAL moves with me
object being localised moves in same direct as the tube shift then object is lingual/palatal to fixed reference point
stages in chemical processing
5
Development,
rinse,
fixation,
washing,
drying
components of xray
Outer plastic cover,
black/white paper,
film,
patterned lead foil,
raised dot
digital
pros
cons
pros
* image enhancement
* dose reduction
* immediate image
* no wet processing/chemicals
* constant image quality - if equip maintained
cons
* cost
* large size
differences between differeing digital IO sensors
CCD - direct link to computer. Sensor thick and not very flexible, not sensitive to light
PSP - latent image stored after exposure, laser scanning causes light emission, conversion to electronic signal. Variable room light sensitivity, handling similar to film, plate relatively flexible
ultrasoud
no ionising radiation.
indications
* Salivary gland pathology,
* USgFNA/USgFNB,
* cervical lymphadenopathy
sialography
indications
obstruction, stricture of ducts
MRI
indications
soft tissue analysis, perineurial spread, bone invasion, marrow changes
CT
indications
bony substances, bony changes, joints, jaw fractures
PET-CT indication
18-FDG injected and attracted to metabolically active tissues. Tumours of unknown origin/primary
