RADT W5L1 Ch 6, 8 - Dental Xray Image Characteristics, Digital Imaging

Define Radiolucent

Radiolucent structures appear black or dark on a radiograph because it permits passage of xray beam with little resistance.

• ex. tissues, air spaces, dental pulp, periodontal ligament space = radiolucent

Define Radiopaque

Radiopaque structures appear white or light on a radiograph because it absorbs or resists the passage of the xray beam.

• ex. enamel, dentin, bone, hard or thick tissues, maxillary sinus

Fill in the Blanks:

1. if mA is increased, the image will appear ___.

2. If kVp decreases, the image will appear ___.

3. If exposure time decreases, the film density will ____ resulting in a ____ image

4. If a client has increased amount of dense tissue/dense bone, fewer xrays will reach the film, therefore, the radiograph will have less density and appear____.

1. darker

2. lighter

3. decrease, brighter image

4. brighter/lighter

Define Short-Scale Contrast

Short-scale contrast only shows 2 densities = black and white.

• low kVp (less than 70kvp) = short-scale contrast=higher contrast

Define Long-scale contrast

Long-scaled contrast shows many densities = many shades of grey on radiograph = lower contrast

• high kvp (greater than 90kvp) = long scale = low contrast

• not enough radiopaque on film

Define Film contrast

Characteristics of a film that influences contrast

• ex. film processing and quality of the film

Define Subject contrast

Characteristics of the subject that influecne contrast

• ex. thickness, density of the subject

• this can be altered by adjusting kVp[

• if kVp is too high for the subject = little contrast (too dark)

What is the fx of a Stepwedge?

• Used to demonstrate short-scale and long-scale contrast

• Monitor the quality of film and film processing

What is penumbra?

when the xray image appears fuzzy (not sharp)

The sharpness of a radiograph is influenced by…? (3)

1. focal spot size → smaller focal spot = sharper image

2. film composition → faster films with larger crystals = less sharp

   • large crystals do not produce object outlines well

3. movement

How is magnification created in radiographs?

Created from the divergent paths of the xray beam

• affected by the target-receptor distance and the object-receptor distance

• Longer PID = less image mag

• Shorter PID = more image mag

Correcting Vertical Angulation

• Maxillary arch: Increase the positive vertical angulation. Imagine the PID (position indicating device) as if it's pointing slightly downwards towards the floor. 

• Mandibular arch: Increase the negative vertical angulation. The PID would be angled slightly upwards. 

How does Digital Radiography compare to conventional radiography?

• Requires less x-radiation b/c the sensory is more sensitive to xrays

• 50-90% shorter exposure time than conventional radiography

• pt’s exposure to radiation is significantly reduced

Digital xray unit allows exposures of 1/100th of a second. The xray unit can also…

be used for conventional radiography

What is the most common image receptor used for digital dental imaging?

Charged-couple device (CCD)

• also used in fax machines, cameras, microscopes, telescopes

• has a solid-state detector with a silicone chip/electric circuit sensitive to xrays

What are pixels?

Small boxes or “wells” where electrons produced by xrays are deposited. They are arranged in order and a image is projected.

Why is a complementary metal oxide semiconductor (CMOS) better than a CCD?

CMOS aka active pixel sensor has 25% greater resolution, lower cost of production and greater durability than CCD (charged-couple device)

Compare and contrast Direct and Indirect Digital Imaging

Direct Digital Imaging:

• Components: xray, intraoral sensor with fiber optic cable, computer monitor

• captures radiographic image and transmits image to computer

• software used to store radiograph

Indirect Digital Imaging:

• Components: CCD camera, and computer

• once film/sensor has been exposed, radiograph is digitized using CCD camera

What is storage phosphor imaging?

Aka Photo-stimuable phosphor imaging

A type of wireless indirect digital imaging where a reusable imaging plate coated with phosphorus is used instead of a sensor w cable.

• Used similarly to intraoral films

• Phosphorus coated plate resembles an intensifying screen used in extraoral xrays

• ** we use this in Rad lab

What are some disadvantages to digital imaging in comparison to film-based imaging?

Disadvantages:

• Initial set-up costs

• Image quality not as good as conventional

• Sensory size/thickness

• Infection control

• Wear and tear

• legal issues