Panoramic Radiography

Question 1

What is tomography

Answer 1

method of radiography displaying details of a selected plane (layer/slice) within the body

Question 2

Wha tis the image layer/focal trough

Answer 2

layer in the patient that contains the structures of interest that are demonstrated with sufficient resolution to make them recognisable

Question 3

How are structures at other depths to image layer seen

Answer 3

not clear

Question 4

What happens in linear tomography

Answer 4

the X-ray tube is moved in a straight line in one direction while the film moves in the opposite direction

Question 5

Where are objects that are not in the focal plane projected in linear tomography

Answer 5

to continually changing points on the film

Question 6

Where are objects that are in the focal plane projected in linear tomography

Answer 6

Objects in the focal plane are projected to the same point of film

Question 7

Describe the focal trough in panoramic radiographs

Answer 7

• Contains all teeth
  
  • Structures above and below the teeth
  • Structures superficial and deep to the teeth provided they are close
  • Distant structures are not clear

Question 8

Is the rotation centre fixed

Answer 8

no

it continually changes

Question 9

What is layer formation a product of

Answer 9

○ Movement of the X-ray source and therefore 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 will be recorded as clear images

Question 10

What will objects outside the desired image layer be portrayed as

Answer 10

either distorted unsharp images or be imperceptible

Question 11

What is the impact of different size perimeters

Answer 11

• Aka the distance from the rotation centre

the further from the rotation centre, the faster the beam passage around the circumference has to be

Question 12

What does it mean for speed that the posterior teeth are further from the rotation centre

Answer 12

○ This means there is faster beam passage through teeth

○ The image receptor must also move fast to match

Question 13

What does it mean for speed that the anterior teeth are closer to the rotation centre

Answer 13

○ This means there is slower beam passage through the teeth

○ Image receptor movement becomes slower to match and prevents distortion

Question 14

What is the beam direction

Answer 14

lingual to buccal

Question 15

What does the distance from the rotation centre to the teeth affect

Answer 15

The width of ‘layer in focus/focal trough’
Horizontal distortion if patient in incorrect position
Ghost images

Question 16

What is the width of the layer dependent on

Answer 16

Width of the X-ray beam (same throughout so not really a variable)
Distance to rotation centre

Question 17

What is the effect on the width of the layer if it is closer to the rotation centre (ant teeth)

Answer 17

narrower layer

Question 18

What is the effect on the width of the layer if it is further from the rotation centre (post teeth)

Answer 18

Further away (posterior teeth) = wider layer

Question 19

How is patient positioned

Answer 19

• 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 auditoary meatus)
    Patient remains stationery and the gantry moves

Question 20

How is the X-ray beam angled

Answer 20

upwards - 8 degrees (due to curve of Monson)

Question 21

Why must the speed of beam through teeth and image receptor through the beam be synchronized

Answer 21

to produce an accurate image (formation of correct image layer) dependent on correct patient position and machine adjustments

Question 22

What should px be asked to remove

Answer 22

• Ask them to remove glasses, necklaces, jewellery, dentures, appliances in their mouth, metal hair accessories and provide them with containers

Question 23

Where should the vertical canine be

Answer 23

should shine on the upper canine: if not compensate using the appropriate adjustment button

Question 24

What are limitations of DPT

Answer 24

positioning difficulties
long exposure time
narrow width in focus anteriorly
horizontal distortion

Question 25

Which patients occlusion result in position difficulties

Answer 25

§ Class II Div 1

§ Class III

Question 26

How does class II Div 1 result in positioning difficulties

Answer 26

□ Means that the upper incisors are significantly infront of the lower, it may not be possible to get the teeth into the required grooves

Question 27

How does classIII result in positioning difficulties

Answer 27

□ Lower infront of upper

□ Not possible to get teeth into required position as they cannot move their jaw further back

Question 28

How does long exposure time create difficulties

Answer 28

hard staying still

Question 29

What does the narrow width in focus anteriorly cause limitations

Answer 29

Structures not shown are not necessarily not present

Question 30

What can movement during exposure result in

Answer 30

Can sometimes see a wavy border of the mandible, showing there has clearly been movement

Question 31

If the patient’s canine is behind the canine guide line what does this result in

Answer 31

they are closer to x-ray source than machine expects

speed of beam is slower through teeth as they are closer to rotation centre

if not compensated will mean
that image receptor is too fast and the image is magnified horizontally

Question 32

If the patient’s canine is in front of the canine guide line what does this result in

Answer 32

they are closer to the x-ray source than the machine expects

speed of beam is faster as they are further form rotation centre

if not compensated then image receptor is too slow and image of teeth is reduced in width horizontally

Question 33

What are common objects that cause ghost images

Answer 33

○ Earrings
○ Metal restorations
○ Anatomical features - especially opposite side of the mandible e.g ramus
○ Soft tissue calcifications, e.g lymph nodes, salivary calcification

Question 34

What are general points about ghost images

Answer 34

○ Always higher due to negative vertical beam (-8 degrees) e.g if it is an earring then will be reflected higher up
○ Always horizontally magnified
○ Change in antero-posterior position (usually further forward)
Can interfere with diagnosis but not always

Question 35

How are ghost images formed

Answer 35

○ The X-ray tube start position directs beam posteriorly towards opposite TMJ region
○ The tube moves round behind the patient’s head
○ When the image of premolar region is created, beam is coming from posterior point on opposite side
Ghost images are usually more anterior than real image

Question 36

What are applications of DPT in dentistry

Answer 36

• Development of dentition (ortho)
  
  • Developmental and acquired anomalies
  • Caries, pulpal and perio disease (some limitations for caries due to overlap of teeth but if not able to take bitewings this is an alternative)
  • Pathological jaw lesions
  • Trauma - fractures of mandible

Question 37

How is dose reduced in DPT extra orally

Answer 37

• Extra oral
  ○ Collimation (panoramic programme selection)
  ○ Rare-earth screens: system speed 400 or greater
  ○ Digital
  -

Question 38

How is dose reduced in DPT intra orally

Answer 38

Intra-orals
		○ 60-70kV 
		○ Rectangular collimation
		○ E or F-speed film
Digital and if not then fast speed film

Question 39

Summarise DPT

Answer 39

• panoramic radiography is a sectional image
  
  • patient positioning is crucial for clear images
  • recognition of ghost images is important
  • the anatomical features are determined by the “view” of the patient (explained in lecture on radiographic anatomy)