16. Radiology Flashcards
1
Q
Principles
- 3 key principles and definitions
- 4 method of dose reduction
- 4 key personnel and responsibilities according to IRMER 2017
- Radiograph frequency for high, moderate and low risk individuals
A
- Justification - all exposure must benefit patient and/or provide new info to aid management/diagnosis
Optimisation - ALARP
Dose limitation - for radiation workers and members of public - Collimation (rectangular), fast film speed (E-speed or faster)< long fad (>200mm), digital film, rare-earth screens, 60-70keV
- Employer
Referrer - justification, authorisation, optimisation
Practitioner - justification, authorisation, optimisation
Operator - dose limitation - High risk - 6mths
Moderate risk - 12mths
Low risk - 18-24mths
2
Q
Physics
- Definition of radiographic image
- Definition of binding energy
- Definition of x-ray beam intensity
- Summary of how x-rays are produced
A
- Pictorial representation of body part. Record of the pattern of attenuation of x-ray beam after it has passed through matter
- Additional energy required to exceed electrostatic force. Energy required to remove electrons from a shell
- Quantity of photon energy passing through cross-sectional area of beam per unit time
- Deceleration of fast moving electrons (electrons fired at atoms at high speeds, collide and decelerate)
3
Q
Imaging
- 6 components of X-ray tube head
- Definition of attenuation
- Types of attenuation
- Difference between low and high tube pd (kVp) and what the compromise is
- Categories of radiographic grading, definitions and expended levels of occurrence
A
- Filament, transformer, target, target surround, evacuated glass envelope, shielding (lead), filtration (aluminium), collimator (lead), spacer cone
- Reduction in number of photons within the beam
3. 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)
- Low tube pd - increases photoelectric interactions, contrast and absorbed dose
High tube pd - decreases photoelectric interactions, contrast and absorbed dose
60-70kVp - Grade 1 - excellent; no errors of patient prep, exposure, positioning or film handling (>70%)
Grade 2 - diagnostically acceptable; some errors of patient prep, exposure, positioning or film handling, but errors do not detract from diagnostic utility of radiograph (<20%)
Grade 3 - unacceptable; errors of patient prep, exposure, positioning or film handling make the radiograph diagnostically unacceptable and must be retaken (<10%)
4
Q
Target-spectra interactions
- Mechanism of characteristic spectrum
- Mechanism of continuous spectrum
A
- 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
- Electron passes close to nucleus of atom and is decelerated and deflected, amount of deceleration and deflection proportional to energy loss
5
Q
Effects
- Mechanism of photoelectric effect
- 3 factors increasing likelihood of photoelectric effect
- Mechanism of Compton scatter
- Effect of Compton scatter
- 2 prevention methods for Compton scatter
A
- 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
- Thicker object, lower photon energy, object has high atomic number
- 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
- Lead film packets, collimation
6
Q
IO Views
- Colours of IO film holders
- 3 indications for PA
- 3 indications for BW
- Name 2 IO techniques and describe them
A
- Blue - ant PA; yellow - post PA; red - BW; green - endo
- PAP, perio bone levels, RCT success
- Caries detection, restoration quality, perio bone levels
- Paralleling technique - image receptor and object (tooth) are parallel but not in contact. Problems include magnification due to divergent x-ray beam (can be overcome by using long fsd)
Bisecting angle technique - image receptor and object partly in contact but not parallel. Image receptor and object (tooth) are close together at the crowns but further apart at the apices. Can be performed without image receptor holders. Vertical angle selection is key - x-ray beam 90d to bisecting line of the angle between the long axis of the object (tooth) and the long axis of the image receptor plane
7
Q
Occlusal radiography
- 2 types of occlusal views and 3 indications for one
- Key centring points for oblique occlusals
A
- True occlusal - 90d to mandible (paralleling technique) - bony pathology
Oblique occlusal - pathology too large for PA, trauma, localisation using parallax, PA indicated but not possible - Maxilla 1cm above ala-tragus line; mandible through lower border
8
Q
OPT
- 2 other names for OPT
- What OPT shows
- 4 indications
- 4 limitations
- 3 key lines for OPT and how they should be positioned
- Reason for horizontally stretched image and how to correct
- Reason for horizontally compressed image and how to correct
- Reason for anterior teeth distorted
A
- Panoramic, DPT, DPR
- Full image of dentition and peri-oral anatomy (including condyles, maxillary sinuses, C-spine)
- Orthodontics (developing dentition), developmental and acquired anomalies, caries, pulpal and perio disease, pathological jaw lesions, surgery, trauma (mandible fractures)
- Width of layer in focus, horizontal distortion, long exposure time, big shoulders, positioning difficulties (class II/1, III, extremes of age, obese patients)
- Mid-sagittal plane (perpendicular), FP (horizontal), vertical canine line (shine on upper canine)
- Canines too far back (guide in front of canines)
- Canines too far forward (guide behind canines)
- Anteriors not in focal plane
9
Q
OPT 2
- Definition and 3 features of ghost image
- Definition of focal trough/image layer
- Vertical beam angulation of OPT
A
- Radiopacity on opposite side of image
Due to earrings, metal restoration, soft tissue calcifications, etc
Always high (8d), always horizontally magnified, usually more anterior, can interfere with diagnosis - Focal trough/image layer is the layer in the patient, containing structures of interest that are demonstrated with sufficient resolution to make them recognisable, whilst structures at other depths are not clearly seen
- 8d upward from lingual to buccal
10
Q
Lateral ceph
- Definition
- How to position patient
- 3 indications/uses
A
- Standardised and reproducible radiographic forms of the skull and facial bones. Give a lateral view of facial bones, base of skull and upper C-spine. Soft tissue profiles are also seen. Enables measurement of dental and skeletal relationships
- FP horizontal, MSP vertical and parallel to cassette and the correct distance from cassette (5ft - 152.4cm)
- Orthodontics, orthographic surgery, vertical/AP skeletal discrepancies, implant planning where CBCT unavailable
11
Q
Maxillofacial views
- 3 types of views and 1 indication for each
- What has superseded these generally
A
- PA mandible (mandible #), occipitomental (middle third facial fractures), SMV view (zygomatic arch fractures)
- CBCT
12
Q
CBCT
- Main benefit of CBCT
- Differences between CT and CBCT
- 4 CBCT indications
A
- 3D reproduction of structures of interest. Can be viewed in different planes
- CBCT - flat panel detector, CT line detector. CBCT is faster and reduced dose
- Jaw/facial fractures, implant planning, impacted teeth, pathology (cysts, tumours), orthographic surgery, clefts
13
Q
Localisation
- Definition
- How to perform
- 3 indications
- Definition of parallax
- Key rule of parallax
A
- Identifies location of a structure/pathological lesion in relation to other structures
- Two views required (OPT and PA/oblique occlusal or PA and BW/oblique occlusal)
- Position of unerupted teeth, location of roots/root canals, relationship of pathological lesions, trauma, soft tissue swellings
- Apparent change in the position of an object caused by a real change in the position of the observer
- SLOB - same lingual opposite buccal. If object being localised moves in same direction as the tube shift, then object is lingual to reference point
14
Q
Films and Processing
- 3 components of x-ray film
- Ideal film speed and why
- Function of intensifying screens
- Dimensions of film sizes
- Stages in chemical processing
- How to perform safelight testing
A
- Outer plastic cover, black/white paper, film, patterned lead foil, raised dot
- E-speed or faster (E-speed is twice as fast as D - half the exposure time and dose)
- Dose reduction
- 0 - 21x34mm (ant PA); 1 - 24x40mm; 2 - 30x40mm (post PA, BW); 4 - 57x75mm (occlusal)
- Development, rinse, fixation, washing, drying
- In dark, coins are placed at measured, equal intervals on an EO film. Film covered completely with card. Safelights turned on, each coin uncovered at intervals of 10-30s, leaving last coin uncovered. Film processed and analysed
15
Q
Digital vs Analogue
- 3 benefits of digital
- 2 cons of digital
- Differences between 2 types of digital IO sensors
A
- Image enhancement, dose reduction, immediate image (real time), no wet processing, no chemicals, constant image quality
- Cost, reduced flexibility, large size
- CCD - direct link to computer. Sensory 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
