Radiology

50mSv and 100 mSv in 5 yr cumulative

**Stochastic = probability of occurrence of the change, rather than severity, is dose dependent

• 150mSV to lens of eye
• 500 mSv to skin and extremities

** Deterministic = severity of response is proportional to dose

1mSv and, if higher, not to exceed 1mSv annual average in 5 yrs

• **Stochastic = probability of occurrence of the change, rather than
• severity, is dose dependent

• 15 mSV to lens of eye
• 50 mSv to skin and extremities**
• Deterministic = severity of response is proportional to dose

• sagittal view of the lateral aspects of the condyle and temporal component
• ** Taken in open and closed mouth positions **

sagittal view of medial pole of condyle

• view entire mediolateral dimension of articular eminence, condylar head and neck
• *especially good for condylar neck fractures

multiple slices make it superior to the transcranial for depicting condylar position and osseous changes

• indicated when information is needed about 3D sharp and internal structure of osseous components
• **cannot produce accurate images of disk

• Indirect image of disk obtained by injecting radiopaque contrast agent into one or both joint spaces.
• ** Used to determine disk position, function, morphology in integrity

• Best technique to see TMJ soft tissues, especially good for articular disk
• -- Does not have morbidity associated with arthrograms

• Used to examine skull for disease, trauma, and developmental abnormalities.
• Provides good view of frontal and ethmoid sinuses, nasal fossae, and orbits
• -- Frankfort horizontal is parallel to floor, pt is facing film

• Used to evaluate Maxillary sinuses
• Shows frontal and ethmoid sinuses, orbits, zygomaticofrontal suture, nasal cavity, and coronoid process

• Used to examine suspected fracture of condylar neck
• also shows posterolateral wall of maxillary antrum
• Especially good for revealing a medially displaced condyle
• 

Used to demonstrate base of skull, condylar position and orientation, sphenoid sinus, curvature of mandible, lateral wall of maxillary sinuses, & displacement of fractured zygomatic arch

• Used to demonstrate the premolar-molar region and inferior border of the mandible.
• Oblique ramus projection - cassette places over ramus and condyles - shows ramus from the angle to the condyle (useful for 3rd molars)

• Used to survey the skull and facial bones for evidence of disease, trauma, and developmental abnormalities.
• Used by orthodontist to assess growth and treatment effects

• 5 feet
• -- this minimized magnification due to different patient-to-film distances

• 15 cm
• -- To minimize variation in magnification from patient to patient and to obtain consistent measurement on the same patient over time

• The patient's right side is closest to the X-ray source
• The patient's left side is closest to the film
• Thus, when evaluating bilateral structures below and ahead of the ear rods, the right side structures will be further below and further ahead of their left side counterparts

• 2 X distance = 1/4 Intensity (less exposure)
• -- Inverse square law

• Increase mA
• Increase kVP
• Increase time
• Decrease filtration
• Decrease distance

• Increase energy per photon
• Increase penetration
• Decrease tissue absorption
• Decrease wavelength

Increase photons and exposure time

• Increase sensitivity of the film (decrease dose) for extraoral films
• -- decrease exposure by 50%

Using E speed vs D speed decreases exposure by 50%

• Only affects density, has no effect on contrast
• Doubling mA will allow exposure time to be halved

• -- The higher the kVp, the greater the film density and the lower the visual contrast (many shades of gray)
• -- The lower the kVP, the higher the contrast (mostly distinct blacks and whites)
• To penetrate bony structures of the skull, settings below 70kVp should not be used

• Increase object distance
• Decrease film distance
• Faster film

• Concentrates the beam
• Decreases volume of the irradiated tissues
• Decreases scatter
• Increases film quality

• Uses rare earth filters
• --reduces exposure and improves contrast

• Scattered radiation
• Any x-ray photon whose initial direction or path is scattered while exiting the source tubehead or is deflected by the patient's hard and soft tissues creates noise or radiographic scatter in the x-ray image

To reduce the amount of scattered radiation that reaches the film

An x-ray grid consists of lead strips either parallel to each other or in a converging pattern with radiolucent spacers in between. The grid is placed between the patient and the film cassette, as close as possible to the film cassette. X-ray photons not traveling in the same direction as the primary beam strike the lead strips and are absorbed

• A Focused Grid -- the strips are at increasing angles toward the source of the x-ray beam from the center of the beam outward
• -- Parallel grids are undesirable because they absorb greater proportions of energy in the outer regions of the beam, producing a film with gradually decreasing density from the center of the film outwards

• the ratio of the length of the strips to the size of the space between the grid.
• The higher the ratio, the greater the amount of scatter absorbed, resulting in image contrast

8 - with 80-100 line-pairs or spaces per inch

• 1. A faint radiopaque pattern of the grid on the film image
• 2. Increased exposure settings (exposure enrgy must be doubled or tripled to produce a radiograph with the same density as one made without the grid)

• 1. Convential or blue emitting - coated with calcium tungstate, film speed 200
• 2. Rare earth screens - coated with gadolinium and lanthanum, emit green light, only require 1/2 the xray energy - therefore film speed 400