OCSE revision notes

Question 1

What is Exposure Index and range for uni x-ray tube?

Answer 1

Range of interest indicated by a green square surrounding the image
* Linear scale - proportional to exposure
* Normal EI range usually 250-350 (may vary depending on manufacturer)

Question 2

Possible reasons for changes in Exposure Index?

Answer 2

Exposure field recognition error – doesn’t recognise area you have
exposed
* Unexpected material in field
* Collimation margins not detected
* Scatter

Question 3

If EI is out of range:
what should you do

Answer 3

Look where green square is
* Look for distortion
* Look what DAP says
- If DAP is within range but EI is not, likely to be a processing error.
- If DAP not within range, could be an equipment fault. Note down
exposure factors used, DAP and EI, report to senior radiographer or RPS,
perform QA, take room out of action until issue resolved.

Question 4

Radiographic Brightness
High density = low brightness, low density = high brightness.

Answer 4

Are you able to see trabecular patterns within the bone?
* Need to say how you would rectify it if the image is too bright or not
bright enough (e.g. windowing, repeats)

Question 5

What affects Exposure

Answer 5

• Increasing kV and reducing mAs decreases absorbed dose, but not
  always DAP (DAP measures the amount of radiation exiting the tube)
• There are less x-ray photons so less of the photons produced are
  absorbed by the patient
• As we increase kV, the contrast decreases – algorithm has to work
  harder to produce a diagnostic image, will lead to changes in EI
• Both collimation and mAs have a proportional effect on DAP (as long as
  no other changes are applied):
• Double mAs = double DAP
• Half area of collimation = half DAP

Question 6

How do you manage absorbed dose?

Answer 6

To maintain image quality, but managed absorbed dose, the following Rule of
10 should be used:
For every 10kVp increased, the mAs should be halved – gives the same overall
exposure and image quality, EI should stay the same, but DAP may change

Question 7

How does AEC work

Answer 7

• The AEC determines the mAs of the exposure to produce an image with
  optimal density.
• mAs is pre-set but kV needs to be set.
• Time is the variable factor – determined by the exposure of an ionisation
  chamber

Question 8

Impact of changes with AECs

Answer 8

• Inaccurate centring – area over the detector may not have the same
  density as correct anatomy/pathology
• Incorrect detector – incorrect anatomy or pathology will be over the
  detector, may not have the same density as the correct AOI
• kVp too high/low – time will be changed as mAs will change accordingly
  When increasing SID from 100cm to 180cm – double the exposure (add 10kV
  and double your mAs)

Question 9

Grids

Answer 9

• Stops scatter from reaching the IR (attenuates some of the primary
  beam) but does not stop scatter from reaching the patient.
• Consider using a grid for any area over 15cm in depth.
• Justify use of a grid every time – grids increase dose to the patient as
  more mAs is needed with a grid than without.
• Increase contrast due to less scatter on the IR.
  Grid factor is usually 4. Assume this or ask your examiner, but state out loud
  that you are assuming this.

Question 10

Describing “normal”

Answer 10

Just stating ‘no bony injury’ without further detail is not enough for this exam
(possibly is in practice). You need to base your answer on the clinical history.
Some examples of descriptions of “normal”:
* No bony injury. The glenohumeral joint is congruent. The
acromioclavicular joint remains undisrupted.
* No bony injury. Normal bone, soft tissue and joint appearances.
* Normal appearances of heart, mediastinum and lungs. No evidence of
pneumothorax. normal bony anatomy (clinical history: stabbed in right
side of chest)
* Normal appearances of bone and soft tissue. No breaks in bony cortex or
abnormal lucent/opaque areas. Joints aligned normally

Question 11

Adapted technique scenarios- Wider collimation than normal

Answer 11

say what the normal collimation should
be, say where the obvious deformity appears to be, increasing the AOI will
ensure that the fracture is fully demonstrated on the first image, hopefully
preventing need for repeats

Question 12

Adapted technique scenarios- Addition (or removal) of a grid

Answer 12

larger volume of tissue being imaged,
increased amount of scatter produced, will adversely affect the resultant
image if a grid is not used

Question 13

Adapted technique scenarios- angling of the tube

Answer 13

ensure perpendicular relationship between affected
body part and IR

Question 14

Adapted technique scenarios- Larger SID

Answer 14

if IR cannot be placed in contact with the body part being
imaged, need to increase SID to account for increased magnification.
Standard SID for CXR is 180cm because the heart naturally has space
between it and the IR so need to reduce magnification.

Question 15

Adapted technique scenarios- Placing affected body part on radiolucent pad

Answer 15

raises affected body part
enabling posterior/anterior aspect to be visualised on the IR

Question 16

Explaining differences in DAP

Answer 16

if exposure factors used are the same then the only thing changed is collimation.

if one projection has a smaller field of view (e.g AP lumbar spine compared to AP pelvis), reduced are exposed so reduces DAP and therefore reduced DRL will be lower.

DAP measures the beam leaving the tube, not the patient dose
DAP also does not take SID into account - remains the same.

Question 17

What is exposure index and what are possible reasons for change in EI

Answer 17

-Range of interest indicated by a green square surrounding the image
* Linear scale - proportional to exposure
* Normal EI range usually 250-350 (may vary depending on manufacturer)

• Exposure field recognition error – doesn’t recognise area you have
  exposed
• Unexpected material in field
• Collimation margins not detected
• Scatter

Question 18

if EI is out of range, what do you do?

Answer 18

• Look where green square is
• Look for distortion
• Look what DAP says
• If DAP is within range but EI is not, likely to be a processing error.
• If DAP not within range, could be an equipment fault. Note down
  exposure factors used, DAP and EI, report to senior radiographer or RPS,
  perform QA, take room out of action until issue resolved.

Question 19

pregnancy pelvis x-ray exposure factors

Answer 19

high kV technique is needed to reduce dose to foetus
increase kV and reduce mAs to get kV over 100
overall image quality and brightness maintained even though contrast is affected but still ALARP

Question 20

What do you do if there is half the volume of tissue?

Answer 20

half the volume of tissue requires half the exposure (e.g child’s ankle compared to adults ankle)

To halve an exposure - minus 10 kV and 1/2 the mAs

(very low kV gives very good contrast)

Question 21

What do you do if there is double the volume of tissue?

Answer 21

double the volume of tissue requires double the exposure
add 10KV and double the mAs

Question 22

For x-raying COPD how will you change the exposure from the standard exposure 85kV 2.5mAs

Answer 22

Lungs will be very low density, reduce the exposure because of effects of cumulative dose 75kV 1.5mAs

Question 23

For x-raying pleural effusion how will you change the exposure from the standard exposure 85kV 2.5mAs

Answer 23

same exposure, will allow comparison with previous imaging without increasing patient dose. 85kV 2.5mAs

Question 24

For x-raying surgical emphysema- how will you change the exposure from the standard exposure 85kV 2.5mAs

Answer 24

For x-raying surgical emphysema- reduce kV due to air in soft tissues, requires less penetrating. Keep mAs same, same number of photons to maintain image quality. 75kV 2.5mAs

Question 25

Grid portrait or landscape?

Answer 25

-look at which direction the grid lines are running
-if anything the tube cranially, placing IR portrait ensures that primary beam will pass through the grid slots rather than being attenuated by them (would lead to grid cut-off)

Question 26

What do you need to mention for safeguarding scenarios?

Answer 26

Recommended steps
- listen to the patient and show understanding and support
- remain calm and try not to show shock or disbelief
- assess person’s capacity and establish their wishes/views about the safeguarding issue and procedure
- inform the person that you are required to share this information, explaining what will be shared, who with and why
- make a written record of what the person has told you exactly, what you seen and your actions (dont paraphrase)
-follow local safeguarding procedures and incident reporting procedures
-ensure the patient’s privacy and dignity are maintained and that they are safe.

Question 27

what is pneumocephalus?

Answer 27

air within the cranial vault, may be due to surgery or fractures of the skull

Question 28

What would a hyperdense middle cerebral artery mean (MCA) mean?

Answer 28

may be noted in strokes and indicates the presence of a large thrombus within the vessel

Question 29

What is oedema?

Answer 29

build up of fluid causing swelling

Question 30

Confidentiality notes for situations

Calmly explain that I cant discuss patient’s information and ask the person to wait in an appropriate area while I discuss with the team. (this means not breaching patient confidentiality)

Speak to the referring clinician and confirm the relationship of the visitor with the patient. (this maintains confidentiality)

Explaining that any doses of radiation will be minimum and kept ALARP. (may provide reassurance and a duty to explain this as the radiographer, not disclosing any patient information)

Ensure consent is discussed with medical team and that the examination is in the best interest of the patient. (medical team will give consent for the examination whilst patient is incapacitated. Next of kin legally cannot withhold consent)

Fully document in CRIS or patient notes including your rationale for your decision (meet medico-legal documents and patient can be aware of actions taken whilst they could not give consent)

Answer 30

Confidentiality notes for situations

Calmly explain that I cant discuss patient’s information and ask the person to wait in an appropriate area while I discuss with the team. (this means not breaching patient confidentiality)

Speak to the referring clinician and confirm the relationship of the visitor with the patient. (this maintains confidentiality)

Explaining that any doses of radiation will be minimum and kept ALARP. (may provide reassurance and a duty to explain this as the radiographer, not disclosing any patient information)

Ensure consent is discussed with medical team and that the examination is in the best interest of the patient. (medical team will give consent for the examination whilst patient is incapacitated. Next of kin legally cannot withhold consent)

Fully document in CRIS or patient notes including your rationale for your decision (meet medico-legal documents and patient can be aware of actions taken whilst they could not give consent)

Question 31

Solving complex clinical scenarios
1) features required of an x-ray room for undertaking these examinations

points to consider

Answer 31

-Close to emergency equipment/A&E

-Lots of space to move around the trolley

-Equipment to image on a trolley e.g free detector, to use a grid?, sponge pads, leg supports

-ceiling suspended tube with sufficient track to move around the trolley- obtain required projections

-any other reasonable answers

Question 32

Solving complex clinical scenarios
2) How to apply ALARP principles to the examination

points to consider

Answer 32

-ID patient

-Justify examination

-Careful technique to avoid repeats

-accurate collimation

-optimisation of exposure factors - adjust for the patient and techniques used

Question 33

Solving complex clinical scenarios
3) Patient is fully conscious- how do you obtain informed consent?

points to consider

Answer 33

-explain what you are going to do and how many x-rays you need to take

• ensure they have understood this- give opportunity to ask questions

-confirm with the patient that they are happy for you to carry on

Question 34

How do you improve the quality of an image already taken without increasing patient dose?

Answer 34

-post-processing/windowing

• to improve brightness and contrast