Intro to Radiology

Radiograph:

  • An image produced by transmission of X-rays through an object
  • X-rays pass through the body to reach the image detector and cause blackening in the image
  • Image created by different absorption of X-ray photons by different tissues
  • Two-dimensional image of a 3D object.

X-Rays:

• High energy electromagnetic radiation • Travel as wave packets called ‘photons’

• Invisible to the naked eye \n • Attenuated by matter- this means the rays are either absorbed by the material or scattered in diff directions \n • Ionizing radiation which can damage tissue, therefore:

– All radiographs must be “justified” i.e. the potential benefit must outweigh the risk.

The Radiographic Image

• Radiopaque areas – White

– Represent dense structures which have attenuated(absorbed or scattered) the X- ray beam

• Radiolucent areas – Black

– Areas where the X-ray beam has passed through the object(minimal attenuation).

• Grey shadows represent areas where the X-ray beam has been stopped to a varying degree.

Radiographic Appearance

• Density affected by

  • –  Type of material
  • –  Thickness of material
  • –  Shape of the object
  • –  Intensity of the X-ray

  beam

  • –  Position of object

  relative to the X-ray

  beam and receptor

  • –  Sensitivity and type of the image receptor.

 

objects a-d are all cylinders, the bottom row are x rays

a- metallic- very high density- x ray Is radiopaque

b- air in the centre but metal around the outside-hence white line around cylinder on X-ray

c-dense centrally and low density around oursite- x ray is white block with peripheral area greyish(low density)

d-wood-thinner at the edges than it is centrally- edges attenuate fewer x rays hence radiograph will be lighter centrally and darker around the edges

metal(attenuates the most x rays) >wood>air(in terms of density hence white, then grey, then black)

Limitations of Viewing a 2D Image of 3D Object

• Appreciating overall shape of the object

– Must be viewed from several different positions/angles.

e.g

 importance of different angles:by taking 90 degree x rays of objects its clearer what they are: TOP LEFT IS A PENCIL(dense lead surround by less dense wood), BOTTOMLEFT IS A THUMB TACK(with the pin facing you the metal of the pin is more dense/thick compared to that of the periphery), the other two are a stapler and paperclip (at a sideways angle the X-ray has to go through multiple layers of metal in some regions at once, hence they appear more white)

 top right(left on image) has a displaced tooth in the antrum, doesn't look like it at a first glance but the occlusal surface is facing us

Limitations of Viewing a 2D Image of 3D Object

• Superimposition

  • –  Overlapping shadows of

  different parts of an object or a separate object can obscure view

  • –  Causes limitation of information on location and shape of the object.

 gentleman can't see beyond dense pillar

 x ray of key and paperclip \n

 x ray of what seems to be only key image that was x rayed- key too dense to see paper clip

 orthodontic appliances are very dense and obscure view of crowns, and potentially caries which is radiolucent

Limitations of Viewing a 2D Image of 3D Object

  • No depth information: Is the object at position 1 or 2?

Object 3 overlaps object 4 but on the image you might not be able to tell(esp if object 4 is more dense)

 top of triangle is where image is taken from

 can't tell which object is on top of which hence need another x ray at 90 deg looking end at the staple

 central incisor not erupted- looking at the tooth you can see a shadow- this indicates a supernumerary(additional) tooth which is preventing central incisor form erupting. supernumerary tooth needs extracting, but from one x ray alone, you can't tell whether its on the labial end of the central incisor or the palatal end- this info is needed as it influences surgical procedure

With X rays, its like you’re looking at patient- hence your left is their right and vice versa

• Radiography

– The techniques involved in producing radiographic images

• Radiology \n – The interpretation of medical imaging

• Radiation Protection

– The protection of patients and staff from the harmful effects of ionising radiation

DENTAL ANATOMY

Dentine is of a lower density than enamel

Teeth sit in the alveolar bone, are separated from the bone by pdl

 

Lower right(mandible) quadrant- molars

High density enamel- radiopaque and white around the outside

Slightly lower density dentine-smooth grey

Root canal- soft tissue compared to enamel- doesn’t attenuate x rays as much- hence radiolucent(black) appearance

Black outline around tooth is the pdl space and next to it is a white line which is the bone. This is cortical bone, which is more dense than the cancellous bone seen between the teeth

 

 

Lower right quadrant- two molars each with two roots, and two premolars, crown not as wide as molar and have a single tapering root

 

Maxillary central incisors- enamel is thinner on incisors compared to molars, broader canal and a single conical root

for mandibular teeth, apex/ root points upwards and crown points downwards- mandibular teeth are opposite rotation

Intraoral Radiographs

Periapical -lets you see crowns and roots

 page5image15863040

Bitewing- lots of crowns of both arches at the same time page5image15861792

 

Right bitewing will have the molars on LHS and premolars on RHS

Left bitewing has molars on RHS and premolars LHS

Its like looking at patient head on, their molars are further back in their head(towards outside of image)

 Upper-65 deg angle

Lower-90 deg angree

Taking x rays like this allow with localisation of teeth(i.e lingual, palatal etc)

On the lower occlusal image you can see a submandibular stone- in salivary glands preventing saliva production- had this been a panoramic or periapical image, you wouldn’t be able to tell the stone is lingual to the bone

 

Image detector(and x ray beam) placed outside patients mouth- for intramural its placed inside

DPT- show full mandible and maxilla, roots, crowns can give good assessment of dentition

useful for patients with a large lesion in the bone as it can show a large area at once

 

Lateral cephalograms- v useful in orthodontics as you can see relationship of mandible to maxilla to skull base(bone position and angles)

Charting - Palmer Notation

  • Mouth divided into four quadrants
  • Teeth are numbered 1-8 from central incisor to third molar
  • ‘Letters and numbers system’

  – Modification of Palmer

  – LR3 to represent lower right canine.

 

standard approach is to start in upper right quadrant-ul-lower l-lower right