Radiology Flashcards
How can X-rays on a graph be systematically shown?
As a sine wave
What is the speed of light?
3x10(8)ms-1
What is the name of the innermost electron shell?
The K shell
What is the name of the energy that must be exceeded in order to remove an electron from its shell
The binding energy must be exceeded
Which electron shell has the highest binding energy
The closer the electron is to the nucleas the higher the binding energy - K has the highest binding energy
How can you work out the specific amount of energy required to move an electron to an outer shell
The energy required to move an electron to an outer shell is the difference in the binding energey of the shells
What kind of current does X-ray production require?
X-ray production requires a unidirectional current
X-ray production requires a uni-directional current but xray units are powered by alternating current. The units have a generator to modify this so that it mimics a direct current.
What is this change called?
Refraction
Does divergence decrease or increase with distance from the xray source?
Divergence decreases with the distance from the xray source
What is the inverse square law
Intensity beam is inversely proportional to the square of the distance between the xray source and the point of measurement
Therefore if you DOUBLE the distance you will quarter the dose
What is the purpose of the glass envelope in the xray tube
The glass component acts as a vacuum to ensure the electrons are not hindered by gas molecules
Why does the metal sheielding tend to be made of lead
This absorbs the X-rays
What sis the purpose of the aluminium filtration?
This removes the lower energy, non diagnostic X-rays from the Bea,
What is the purpose of the oil in the xray tube head
This dissipates the heat produced by the xray tube by thermal convection
The spacer cone provides the ‘focus to skin distance’’ what is this distance?
200mm
What is the purpose of the collimator
This is a lead diaphragm attached to the end of the spacer cone and this acts too reduce the patient dose
What is the benefit of rectangular collimation
It can potentially reduce surface area irradiated by almost 50%
It can also improve image contrast by reducing scatter
What is the penumbra affect and why one’s it happen?
This is blurring of the radiogrpahic image due to the focal spot not being a single point but rather a small area
How can the penumbra affect be reduced
This can be minimised by shrinking the focal spot
What are the three fates of X-ray photons emitted from the focal spot.
- Attenuated by the lead sheilding
- Attenuated by the aluminium filtration
- Exit tube-head to form the x-ray beam
Describe continuous radiation
Bombarding electrons interacts with the nucleas of the target atom, causing the electrons to be rapidly decelerated and deflected - kinetic energy released as xray photons.
Produces a continuous range of xray photon energies
Describe characteristic radiation
Bombarding electrons interact with inner electron shells target atom, photon energies depend on the binding energies of the electron shells
Produces specific energies of xray photon, characteristic to the element used for that target
What does it mean if an electron has been ionised
It has been displaced entirely
What does it mean if an electron has become excited
It has moved to an upper shell
Scattered and absorbed electrons cause reduction in the intensity of the ray beam, what is the term for this?
Attenuation
What are the three ways photons in a diagnostic xray can interact with matter
Transmission - pass though unaltered
Absorption - stopped by the matter - so fully deposited into the tissues
Scatter - changes direction
Attenuation indirectly leads to the radiographic image because diffferent tissues have varying degrees of attenuation, what level of attenuation do the three colours represent;
Black, grey and white
Black - minimal attentution
Grey - partial attenuation
White - complete attenuation
What is the photoelectric effect
Photon in xray beam interacts with the INNER SHELL electron in subject, resulting in absorption of the photon and creation of photoelectron.
When does the photoelectric affect occur
This occurs when the energy of the incoming photon is equal to ( or just greater than) the binding energy of the inner shell electron
With what kind of electrons does the photoelectric effect predominate with
Lower energy photons
Since human tissues have relatively low binding energies
What is the Compton effect
Photon in xray beam interacts with OUTER SHELL electrons,resulting in partial absorption and scatter of the photon and creates a recoil electron
When does the Compton effect occur?
Occurs when energy of the incoming photon is MUCH greater than the binding energy of electron
What kind of electrons predominate in the Compton effect
Much higher energy photons and shell electrons which are loosely boud
What direction do lower energy photons tend to scatter in and does this affect the image
Lower energy photons tend to ‘backward scatter’ and they do not affect the image
Higher energy photons tend to undergo forward scatter these may still reach the receptor, what are the issues with this?
Can cause darkening of the images in the wrong places
Results in ‘fogging’ of image - reduces image contrast/ quality
What kind of scatter is mainly found on an xray tube operating at 70kV
Forward scatter, forward scatter is the reason the control area need too completely surround the patient
How can we reduce scatter?
Collimation; reducing the size and shape of the beam
What is the problem with lowering Kv on the xray unit
This increases the dose absorbed by the patient
What is the effect of raising kV on xray unit
It results in reduced contrast between the tissues with different Z so resulting in rubbish images
What is the differences; name 3; between ( continuous radiation and characteristic radiation interaction) and ( photo electric and components effect)
Continuous and characteristic radiation
- occur in xray tube
- electrons interacting with tungsten atoms
- leads to production of xray photons
Photoelectric and Compton
- occurs in patient/receptor/sheilding
- xray photos interact with atoms
- leads to attenuation of xray beam
Each ionisation process will deposit a certain amount of energy locally, what approximate amount?
35eV`
What is the most significant effect of ionising radiation
Damage to DNA
What damage can happen to the DNA when exposed to Ionsing radiation?
Faulty repair of chromosome breaks
Describe the direct effect of radiation on DNA
Radiation interacts with the atoms of a DNA molecule or another important part of the cell
What is the indirect effect of radiation on DNA
Radiation interacts with water in the cell, producing freee radials which can cause damage
Free radicals are unstable, highly reactive molecules
What type of break in DNA can usually be repaired
Single strand break can usually be repaired
Double stranded breaks are usually more diffult to repair, what kind of radiation usually causes these?
Alpha radiation
What is the problem with double stranded DNA breaks
If their repair is faulty this can lead to mutations which can affect cell function e.g. if they are mis-rejoined
What two factors is tissue radio-sensitivity dependant on?
The function of the cellls that make up the tissues
If the cells are actively dividing
The more rapidly the cell is dividing, the greater the sensitivity to radiation.
Name 3 highly radio- senstive cells
Bone marrow, lymphoid tissue, gastrointestinal tissue
What is absorbed dose
The energy deposited by the radiation
What is equivalent dose
Equivalent dose is the absorbed dose multipled by a radiation weighting factor
What is effective dose
Equivalent dose to each organ, multipled by the tissue weighting factor
What does the LNT model do?
Estimates the long term biological damage from radiation
There are two biological effects that radiation can have.
Name both;
Deterministic effects
Stochastic effect
What is the deterministic effect of radiation
Tissue reactions.
They only occur above a certain dose
The severity of the effect is related to the dose recieved
What is the stochastic effect of radiation
This is the basis of the LNT model
The probability of the occurrence is related to the dose recived
What are the two categories of stochastic effects
Somatic - results in a disease of disorder e..g cance
Genetics - abnormalities in descendants
Does pregnancy need to be taken into account when taking a dental X-ray, explain your answer
Pregnancy des not need to be taken into account for dental X-rays because the dose to the foetus is so low.
The foetus should not be irradiated inadvertently nor should the X-ray bema be directed at the patients abdomen
What is the estimated annual background radiation dose
2,2mSv
What does comes form an intra-oral X-ray
0.005mSv
Who does the IRMER17 guidance apply to.
Patients
IRR17 guidance applies to who
Staff and the public
How far should be control area extend from the X-ray tube and patient?
At least 1.5m
Radiation protection philosophy is
Justification
Optimisation
Dose limitation
What do these mean
Justification - practices must have sufficient benefit to individuals or society in order to offset detriment
Optimisation - indictable doses and the number of people exposed should be kept as low as reasonably practicable, taking into account economic and social factors
Dose limitation - system of individual dose limits so that the risks to Individuals are acceptable
What does ALARP mean and what does this refer to
As low as reasonably practicable
This refers to the protection of patients dose - dose optimisation
What are diagnostic reference levels and what are they used for?
Legislation requires employers to have established dose levels for typical examinations for standard size patients.
They are compared to national reference levels and enables identification of units giving a high r dose
What is the plate and sensor used in digital radiography?
Phosphor plate and solid state sensor
There are three types of phosphor plate sizes, 0 2 and 4. Name what kind of radiograph each is usually for.
0 - anteior periapicals
2- bitewings and posterior peripapicals
4- occlusal radiographs
What effect does having more pixels on a radiographic image have
More pixels=better detail= higher resolution
Radiographs are typically processed in how many bits and how may gray shades are available
8 bits
256 gray shades
What is the international standard format for handling digital medical image called
DICOM
Digital imaging and communications in medicine
PACS is a medical imaging technology which provides storage and access to images
What does PACS stand for
Picture archiving and communication system
What are the two types of digital intra-oral receptor?
Solid state sensor
Phosphor plate
How is the final image created in a phosphor plate
This plate is not connected to the computer, after it has been exposed to the x-rays it must be put into a scanner and read to create the final image
How is the image produced from the phosphor plates in the scanner
The receptor is scanned by a laser and the laser energy causes the excited phosphor crystals to emit visible light.
This light is dectected and creates the digital image `
Solis state sensors are connected to the computer and the final image is created virtually and instantly. Why are these not as commonly used
They are more bulky and more expensive
What is the purpose of the identification dot on the receptor
To aid orientation of the image
Name 3 advantages of phosphor plates versus solid state sensors
Thinner lighter and usually flexible
They are wireless
More comfortable for the patient
What is the purpose of silver halide crystal n film radiography
They are embedded in the gelatin binder and they effectively become the ‘pixels’ in the final image
They become sensitised upon interaction with x-ray photons and then during processing they sensitised crystals are converted to particles of black metallic silver which are the dark parts of the image.
Non sensitised crystals are removed - lighter parts of the image
If a film radiograph had been taken are there was an embossed pattern showing upp on the image, what has happened here?
This is the lead foil showing and the receptor has been placed the wrong way round
If you increase the film speed will that cause an increase or decrease in the amount of radiation required to achieve an image?
Reduction
Film speed is affected by the number and size of silver halide crystals.
If you have larger crystals what will this result in?
Larger crystals will result in a faster film but a poorer image quality
In regards to film speed receptor E is twice as fast as receptor D, what does this mean in terms of radiation dose and exposure time with E compared to D
E needs half the exposure time and half the radiation dose
What percentage is the reduction dose when you change from E receptor to F
20
Intensifying screens are used along indirect action fil for extra-oral radiographs, they reduce radiation dose but what is the consequence of them?
They Also reduce detail
What are the 5 steps in film processing?
- Developing
- Washing
3.fixing
4.washing - Drying
Why is the manual cycle done in a red light room
Because the red light doesn’t interact with the radiogrpahic emulsion
Name 2 advantages and 2 disadvantages of self developing films
Advantages
- no darkroom or processing facilitates required
- faster
Disadvantages
- poorer image quality
- image deteriorates more rapidly over time
What three things can the developing process of film radiographs be affected by
Time, temperature and solution concentration
What are three developing issues which could cause the radiograph to come out pael
Film removed from the solution too early
Solution too cold
Solution too. Old/dilute
Radiographic image looks greenish and becomes brown over time, what has gone wrong here and why
There as been inadequate fixing here and some non sensitise crystals are left behind because of this
Give 4 Advatages of digital radiograph
No need for chemical processing
Easy storage and archive of images
Easy back up of images
Easy transfer/ sharing of images
Give 4 disadvantages of digital radiography
Risk of data/corruption loss
Image enchantment can create misleading images
Requires diagnostic level computer monitors for optimal viewing
Hard copy print outs generally have lower image quality
What are three purposes of extra-oral radiography
- imaging larger sections of the dentition
- alternative when patient is unable to tolerate intra-oral radiography
- imaging non dentoalveolar regions
There are two terms for angulation of the beam, true and oblique what is the difference
True = perpendicular to the head
Oblique = not perperpendicualr to the head
How may degrees difference is there between the Frankfort plane and the orbitomeatal line
10 degrees
What is the cephalogram unit designed to do
Produce a standardised and reproducible radiograph
What is the purpose of the cephalostat
It ensures standardised positioning off equipment and patients head
Avoids discernpanies taken by different members of staff and reduces magnification/distortion of the image
What is the standardised distance from the receptor to the X-ray foal spot to minimise magnification
1.5-1.8 metres
If we wanted to view the facial soft tissues on a cephalogram more clearly how do we solve the problem that exposure settings are optimised for the hard tissues
Place an aluminium wedge filter in the unit to attentuate the specific area of the beam exposing the facial soft tissues
What are we aiming to do with collimating
Reduce the dose as much as possible
The field of view should not be bigger than what is clinically required
What is oblique lateral radiography and why not commonly used
This provides view of posteior jaws without the superimposition of hte contralateral side
This is uncommon nowadays as it is difficult to. Master the technique and it is superseded by panoramic radiographs
How can gutta percha be used to. Aid in radiogrpahic localisation
It can be placed into a sinus opening to see where it is drawing
What is the definition of parallax
An apparent change in the position of an object, caused by a real change in the position of the observer
What is the mnemonic to aid in working out parallax
SLOB - Same lingual opposite buccal
PAL - my pal goes with me
What are the equivalent views for horizontal tube shift in the parallax technique
2 periapicals
2 bitewings
2 oblique occlusals ( with different central points)
What are the two different views for vertical tube shift in the parallax technique
Panoramic and oblique occlusal
Panoramic and lower periapical
If the radiographic image has white areas around the edges what do you suspect has happened there?
Delamination
Separation of the phosphor layer from the base plate
Mishandling or getting wet and dry ing up
Y does damage on film imaging often appear has black marks?
Due to the sensitisation of the radiogrpahic emulsion
What is a step wedge
It is a type of object used to check image quality/contrast, it has overlapping layers of lead foil
What are the 3 parts of quality assurance
1.image quality rating
2. Image quality analysis
3. Reject analysis
What is cone cutting and what are some reasons it may happen
This is a collimation error
- there is incorrect assembly of receptor holder
- incorrect alignment between X-ray tube and receptor holder
- incorrect orientation of rectangular colliation
In lateral cephalograms the X-ray beam is perpendicular to the receptor and what facial plane
The mid saggital plane
What group of people does IRR17 deal with
Deals with occupational exposures of the GENERAL PUBLIC
IRMER17 deals with what
Medical exposures of patients
Who is IRR17 enforced by
Health and safety executive
Who is IRMER17 informed by
Health improvement Scotland
In relation to radiation exposure what is a ‘ carer and comfortor’’
Individuals who ‘ knowing and willingly’ exposure to ionising radiation through support and comfort of those undergoing the exposure
IRMER17 requires that all exposures are ALARP, whose responsibility is this?
The practioner and the operator
