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BDS3 Dental Radiology > Panoramic radiography > Flashcards

Panoramic radiography Flashcards

1
Q

What is a plane radiograph?

A
  • Seeing everything that is between the source of the x-rays and the image receptor in the image
  • Everything is static when its taken
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2
Q

What is a panoramic x-ray?

A
  • It is a wide angle view

- See much more

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3
Q

What is the definition of panorama?

A
  • Complete survey of a subject
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4
Q

What is the definition of radiography?

A
  • Obtain a picture by use of x-rays
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5
Q

What is the definition of tomography?

A
  • Method of radiography displaying details of a selected plane (layer/slice) within the body
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6
Q

What are different names to call panoramic radiography? (2)

A
  • Dental panoramic tomography

- Dental panoramic radiography

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7
Q

What is an image layer or focal through?

A
  • A layer in the patient that contains structures of interest that are demonstrated with sufficient resolution to make them recognisable, whilst structures at other depths (both superficial and deeper) are not clearly seen
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8
Q

With a panoramic what are we trying to see?

A
  • An image layer (definition in other FC)
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9
Q

What is the principle of layer formation with linear tomography?

A
  • X-ray source moves from L to R
  • Receptor moves from R to L
  • Objects not in focal plane projected to continually changing points on film
  • Object in focal plane projected to same point on film
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10
Q

Explain this picture and how it produces layer formation?

A
  • How to produce a layer
  • Stars = something that we particularly want to see
  • X = x-ray source (x would move continuously across)
  • The image receptor is going to move in the opposite direction
  • When draw lines through star, B and L , will see that the only thing which stays in the same place is the star
  • At middle point all 3 are superimposed on one another but at the other points will see that B and L have swapped ends
  • This means that as this is moving the beam is going to be in a slightly different place at each point, meeting at the half way point and then keeping going to the other side
  • Any one point will be creating a very faint image of it but so faint that we cant distinguish it
  • Whereas the only thing where the radiation is going through and putting it onto the same point again and again and again is the star landing in the middle every time
  • That build up of the amount of radiation that makes the star show and makes what is represented by B and L not show
  • Still problem that jaws are on circle so need something a bit different for that to work
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11
Q

What are we trying to achieve in the focal trough/image layer in panoramic radiographs? (5)

A
  • Contains all teeth
  • Structures above and below the teeth
  • Structures superficial and deep to the teeth provided they are close
  • Distant structures not clear
  • Importance of rotation centre, and distance from the teeth
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12
Q

Explain how the stars represent the rotation centre?

A
  • Rotation centre signified by star on tooth
  • X-ray beam is going to go through these teeth by moving through them
  • This rotation centre would be the rotation centre when we are looking at the posterior teeth on the opposite side
  • Our x-rays are the lines going from the rotation centre
  • In reality the rotation centre is not a fixed static rotation centre, it continually changes
  • Other star is the rotation centre for the anterior teeth, this is closer to the teeth than the posterior one is for the posterior teeth - this is important for position the patient
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13
Q

What makes layer formation happen? (2)

A

Project of:
- Movement of the x-ray source, and therefore the x-ray beam through the desired objects - the teeth

  • Movement of the x-ray image receptor (film or digital receptor) through the X-ray beam at the CORRECT SPEED so that desirable objects (teeth etc) will be recorded as clear images
  • Objects outside the desired image layer will be portrayed as either distorted unsharp images, or be imperceptible
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14
Q

What will objects outside the desired image layer be like?

A
  • Will be portrayed as either distorted unsharp images, or be imperceptible
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15
Q

Explain the clock analogy?

A
  • Clock and pocket watch
  • Both designed to tell the time
  • Both tell the same time
  • But if think about the second hand moving around the clock the distance that it has to move each second is greater because it is a bigger circle so it takes the same time but it is a larger distance so along that perimeter edge of the circle it is moving faster
  • So we can think of that as meaning if you’ve got something further from the rotation centre the passage of the x-ray beam through the structure is going to be faster than when you have structures close to their rotation centre
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16
Q

What speed does the x-ray beam need to be going at for posterior teeth that are further from their rotation centre? (2)

A
  • Faster beam passage through teeth

- Image receptor movement also fast to match

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17
Q

What speed does the x-ray beam need to be going at for anterior teeth closer to the rotation centre? (2)

A
  • Slower beam passage through teeth

- Image receptor movement becomes slower to match and prevent distortion (if the speeds don’t match we get distortion)

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18
Q

The rotation centre changes continuously. Where does the x-ray beam go from and to?

A
  • Beam goes from lingual to buccal
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19
Q

What does the distance from the rotation centre to teeth affect? (3)

A
  • Width of ‘layer in focus/focal through’
  • Horizontal distortion if patient in incorrect position, relative to machine focal through
  • Ghost images (see those mostly in the posterior part of the image)
20
Q

What is the width of layer (in focus) or focal through dependent on? (2)

A
  • Width of x-ray beam - same throughout
  • Distance of rotation centre:
  • Closer to rotation centre (anterior teeth) = narrow layer
  • Further away (posterior teeth) = wider layer
21
Q

Give a summary of the formation of a panoramic image? (7)

A
  • Patient positioned within gantry containing x-ray source and image receptor; standing or seated (any metal objects removed prior to this)
  • Frankfort plane horizontal (lower border orbit to upper border external auditory meatus)
  • Patient remains stationary; gantry moves throughout exposure
  • Vertical narrow beam of x-rays passes through patient from lingual to buccal, x-ray tubehead rotates around back of patient
  • X-ray beam angled upwards at around -8 degrees (due to the curve of monsoon)
  • Image receptor rotates around the front of the patient, and passes through x-ray beam
  • Speed of beam through the teeth and image receptor through the beam must be synchronised to produce an accurate image (Formation of correct image layer) - dependent on correct patient position and machine adjustments
22
Q

If a patient has something e.g. a piece of jewellery that they cannot or will not take out when they are meant to be getting a panoramic x-ray what must we do?

A
  • Need to record this (very important)
23
Q

What must we ask the patient to do prior to getting a panoramic radiograph?

A
  • Ask them to remove spectacles, necklaces, ear/nose/lip/tongue jewellery, dentures, appliances in their mouth, metal hair accessories - provide containers
24
Q

Where must the Frankfort plane be when taking a panoramic radiograph?

A
  • Frankfort plane horizontal (lower border orbit to upper border external auditory meatus)
25
Q

Where should the vertical canine line be when taking a panoramic radiograph?

A
  • Vertical canine line should shine on the upper canine; if not then compensate using the appropriate adjustment button
26
Q

Panoramic radiography is not possible for everybody. What are the limitations? (5)

A
  • Patient’s occlusion
  • Long exposure time
  • Big shoulders
  • If you can’t see it, it does not mean its not there - width of layer in focus
  • Horizontal distortion
27
Q

Why might the patients occlusion be a problem that means we cannot take a panoramic radiograph?

A
  • Because patient has to bring upper and lower teeth together and bite into a peg
  • If patient can’t do this then a panoramic radiograph cannot be done
28
Q

What classes of occlusion would make it difficult to position teeth for a panoramic radiograph ?

A
  • Class II Div 1

- Class III

29
Q

Who might we find it difficult to position for a panoramic radiograph? (4)

A
  • Very young children, elderly, obese

- Nervous or other special needs patients

30
Q

When taking panoramic radiographs there is a long exposure time (up to 16 secs). Who might this be a problem for so limiting them from being able to get one taken?

A
  • Nervous or other special needs patients
31
Q

One limitation of panoramic radiography is that there is a narrow width in focus anteriorly. What can this cause?

A
  • Structures not shown are not necessarily not present
32
Q

Why can movement during the process of panoramic radiography be a problem?

A
  • Movement can happen at any time
  • If happens at the beginning and its obvious that it is not going to be any good then the radiographer may stop the exposure
  • But sometimes they will keep it going because the child might stop and might still get something useful out of it
  • Typical thing we see is wavy lower border or the mandible
33
Q

What are possible positioning faults anterio-posterior that can occur when taking a panoramic radiograph? (3)

A
  • Speed of beam through the teeth AND image receptor through the beam must be synchronised to produce an accurate image
  • Patient’s canine behind canine guide line (closer to x-ray source than machine expects) - speed of beam slower through teeth as closer to rotation centre (patient is further back, beam is slower because rotation centre is further away) - if not compensated, image receptor too fast and image magnification horizontally
  • PAtient’s canine in front of canine guide line (further from x-ray source than machine expects) - Speed of beam faster through teeth as further from rotation centre - if not compensated, image receptor too slow and image of teeth reduced in width horizontally
34
Q

One possible fault when taking a panoramic radiograph is the anterior teeth being distorted when not correctly in focal through. How can this happen?

A
  • Too far from receptor - beam slower through teeth but receptor too fast - wider (button showing light in front of canine has not been selected)
  • Too close to receptor - beam faster through teeth but receptor speed too slow - narrowed (button showing light behind canine has not been selected)
  • Height not greatly affected
35
Q

What is a ghost image?

A
  • It is essentially a second image of something which is definitely in the wrong place
  • Primarily made by metal things
  • There are some things that always happen: always higher up due to negative beam angle
36
Q

What are common objects that can cause ghost images? (4)

A
  • Earrings
  • Metal restorations
  • Anatomical features - especially opposite side of the mandible
  • Soft tissue calcifications e.g. lymph nodes, salivary calcification
37
Q

What are general points to remember about ghost images? (4)

A
  • Always higher due to -ve vertical beam angulation (around -8 degrees)
  • Always horizontally magnified
  • Change in antero-posterior position (usually further forward)
  • Can interfere with diagnosis - but not always
38
Q

Explain the process of formation of a ghost image? (4)

A
  • X-ray tube start position directs beam posteriorly towards opposite TMJ region
  • Tube moves round behind patient’s head
  • When image of premolar region is created beam is coming from a more posterior point in opposite side
  • Ghost images usually more anterior than real image
  • Look at the formation of ghost images slide for an explanation of the picture
39
Q

Why might ghost images of metal restorations and the mandible occur?

A
  • Patient positioned anterior to guide line (narrow front teeth)
  • Increased image of spine
  • Ghost image from lower right molar restorations and mandible
40
Q

What are uses of panoramic radiographs in dentistry? (6)

A
  • Development of the dentition (often in relation to orthodontics)
  • Developmental and acquired abnormalities
  • Caries, pulpal and periodontal disease
  • Pathological jaw lesions
  • Surgery - evaluation and review
  • Trauma - fractures of the mandible
41
Q

How can we do dose reduction in extra-oral radiographs? (3)

A
  • Collimation: panoramic programme selection
  • Rare-earth screens: system speed 400 or greater
  • Digital
42
Q

How can we do dose reduction in extra-oral radiographs? (4)

A
  • 60-70kV
  • Rectangular collimation
  • E or F - speed film (fast speed)
  • Digital
43
Q

What kind of image is panoramic radiography?

A
  • A sectional image
44
Q

What is crucial for a clear image in panoramic radiography?

A
  • Patient positioning
45
Q

You are great?

A

I know you can do it!

BDS3 Dental Radiology (13 decks)

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