Lecture 6 Digital Imaging

What produces an analog image?

conventional film

What produces a digital image?

computers + electronic x-ray sensors

What is a digital image composed of?

Pixels (small boxes holding electrons) 

What defines each pixel?

bits of information 

How many shades are possible in the digital gray scale?

up to 256 shades

• greater bit depth = greater gray scale

A digital x-ray covers

less surface area than analog

How many shades of gray in analog film?

16-25 shades

What is direct digital imaging?

X-ray → sensor → image on monitor (instant) 

What equipment is needed for direct digital?

• X-ray machine

• Intraoral sensor

• Computer + software

What is indirect digital imaging?

Film or PSP scanned into digital images 

What happens to PSP plates after scanning?

Image erased → plate reused 

What replaces the film as the image receptor?

sensors 

• wired or wireless

Three main types of digital sensors?

• CCD (Charged Coupled Device) 

• CMOS (Complementary Metal Oxide Semiconductor)

• PSP (Photo Stimulable Phosphor Plates)

CCD sensor

• Most used 

• Requires internal circuit card to be installed in computer 

CMOS sensor

• Less expensive

• Uses standard laptop hardware

• Fewer companies offer

PSP sensor 

• Wireless 

• Scanned to produce image 

How much less exposure time do digital sensors need?

50-90% less than film

Why do sensors need less radiation?

They are more sensitive to x-radiation

Why must digital sensors be covered with barriers?

They cannot be sterilized 

What exposure method is preferred for digital?

Paralleling technique

• film holders with rings stabilize the sensor 

What are some software enhancements?

• Magnification

• Endo measurement

• Digital subtraction

• Gray scale

• Adjust sharpness/colorization

What is magnification?

Enlarging image 

What is endo measurement?

Can be used to measure root canal

What is digital substraction?

Reversing gray scale

• Radiolucent images (normally black) = appear white

• Radiopaque images (normally white) = appear black

What does gray scale do?

Adjust brightness and contrast 

What are some advantages of digital imaging?

• Reduced exposure to radiation

• Immediate viewing

• Eliminates film and processing expense

• Eco-friendly

• Enhancement of diagnostic imaging

• Effective patient education tool

• Electronic sending of images

• Superior and enhanced gray-scale resolution

What are some disadvantages of digital imaging?

• Costs of initial set up

• Image quality

• Sensor size

• Infection control

• Legal issues