digital imaging foundations #1

imaging in dentistry steps

1. determine if x-rays are necessary

2. postition the patient

3. place sensor in the patient's mouth

4. line up the x-ray machine

5. push button

6. generate x-radation

7. radiation goes through the patient

8. radiation hits the sensor

9. image generated

10. interpret the image

4 types of interactions

1. no interactions

2. photoelectric absorption

3. coherent scattering

4. compton scattering

what color is enamel in xray

white

what color is dentin in xray

light gray

what color is pulp in xray

dark gray

radioopaque

dense and resist the passage of x ray beams

Radiolucency

less dense region where radiation is passed through the tissue

analog

data has an infinite set of possible values

digital

data must have a defined set of possible values (expressed in discrete units)

types of analog radiology

film imaging

types of digital imaging

sensor and phosphor plates

phosphor plates

similar fashion to traditional x-ray film whereby the plate (housed in a special cassette) is positioned into in an x-ray film holder and placed in the patient's mouth ready for them to bite down on

who discovered xrays

Wilhelm Röntgen

cons of film xrays

cannot be exposed to light

what is used to process film xrays

chemical processing

layers of film

1. protective layer

2. emulsion

3. adhesive

4. base

5. adhesive

6. emulsion

7. protective layer

inner paper purpose

protect the film from light

lead foil backing purpose

on the back of film to protect patient (absorbed into the lead)

when processing, the film is ____ of package wrapping

pulled out

what is in the emulsion layer

silver crystals

silver crystals in emulsion layer are exposed to radiation or light, the crystals undergo what kind of change

photochemical change

developer solution changes the exposed crystals to

dark (metallic black)

fixer solution removes all the crystals

not exposed to light

in film imaging, resolution depends on ___ of crystals

size

smaller the crystals, the ___ radiation is needed

more

the smaller the crystals, the resolution is ____

increased

pixel (shorten word for)

picture element

each pixel can only have one what

color

pixel matrix

set of rows and columns

the larger the matrix, the ____ the pixel size

smaller

pixels are always going to be what shape

squares

why has digital imaging gotten better overtime

smaller pixels (bigger matrices)

larger matrix = able to _____ more images

enlarge

larger matrix = ____ file size

larger

shades of grey in xray are important for

differentiate structures with different densities

binary digits (BIT) = 0

no electric current

binary digits (BIT) = 1

presence of electric current

bit depth

number of bits used to represent the color or grayscale value of a single pixel

how to determine the number of available shades of gray

2^bit depth

when determining the whitest number, make sure to what

subtract 1 from the equation (you are including 0 in the numbers)

a number closer to 1 is

more white

a number closer to 0 is

more black

sampling

process of measuring the intensity of an analog signal at regular intervals in space

quantization

takes the measured intensity at each sample point and rounds it to the nearest available digital level

increased sampling = _____representation of analog signal

better

direct digital imaging

solid state sensor

indirect digital imaging

photostimulable phosphor technology

Sampling determines how many "dots" make up the picture like

sharpness

chat explanation:

Low Sampling: You use 10 giant tiles. The result is blocky; you can’t tell if that’s a sun or just a big yellow square.

High Sampling: You use 1,000 tiny tiles. Now you can see the curve of the sun and the wisps of the clouds.

Quantization determines how many ___ each dot can be

shades

chat explanation:

Low Quantization (Small Crayon Box): You only have a 4-pack of crayons (Red, Blue, Yellow, Black). The sunset looks harsh

High Quantization (Big Crayon Box): You have the 128-count box with every possible shade of orange and pink. The transition from sky to sun looks perfectly smooth.

solid sensors characteritics

1. silicon crystal chips

2. rigid

3. thick

4. connected directly to your computer

5. active area

active area

region of the sensor that is capable of capturing an image

what size sensor has a larger active area

size 2

the active area is ____ than overall size of the sensor

smaller

how are xray sensors similar to cameras sensors

using light to make images

layers of solid sensor

1. scintilator

2. optical fiber

3. sensor

4. electronic circuits

CCD stands for

charge-coupled device

CMOS stands for

complementary metal oxide semiconductor

both CCD and CMOS image sensors covert light into

electrons

the sensor then reads the ____ of each pixel in the image

accumulated charge (value)

new technologies are now able to use

direct conversion silicon

direct conversion silicon bypass the need for a

scintillator layer (convert directly into electronic signal)

cons of CCDs

1. more expensive

2. uses more power

pro of CCDs

less digital noise

pros of CMOS

1. less expensive

2. uses less power

cons of CMOS

more noise

direct acquisition methods

1. USB

2. WIFI

3. Bluetooth

4. wireless

indirect acquisition method

photostimulable phosphor (PSP) technology

steps of photostimulable phosphor technology

1. absorption and storage of the energy of xrays

2. plate reading

PSP characteristics

1. flexible (pro)

2. thickness (thin) (pro)

3. different sizes (pro)

4. active area is the same as plate size (pro)

5. relatively fragile (con)

Is PSP reusable or disposable?

reusable

how to clear the PSP plate

active face exposed to bright light

big con of PSP

infection control

contrast resolution (aka bit depth)

ability to distinguish different densities

human visual ability

50-150 different shades of grey (in an ideal situation)

spatial resolution

ability to accurately distinguish details

the smaller the pixel size, the ____ the spatial resolution of the image

better

PPI

pixels per inch

line pairs/mm (lp/mm)

1. how many distinguishable line pairs fit within a millimeter (black, white)

2. more lines= sharper image

3. less lines = blurry

what is considered a line pair

one white and one black line

dynamic scale

describes the spectrum of X-ray intensities a detector can accurately capture in a single exposure

(PSP > CCD = CMOS > conventional film)

what type of sensor has the best dynamic scale

PSP (can be used to get an accurate image at many exposures)

sensitivity

ability to absorb the radiation

increased sensitivity ___ dose of radiation

lower

what type of sensor has the best sensitivity

CCD and CMOS

resources are

tools designed to faciliate the diganotic process

What resources can you adjust to help see the image more clearly?

1. brightness

2. contrast

3. magnification

4. filters

5. positive-negative inversion

6. colorize

recommendation 11 states that

radiographic examinations shall be performed when patient history and physical examination, prior images, or laboratory finding indicate a reasonable expectation of health benefit to the patient

recommendation 12 states that

for each new or referred patient, the denist shall make a good faith attempt to obtain previous, pertinent images prior to acquiring new patient images

what does DICOM stand for

digital imaging and communications in medicine

what are the types of image printing

1. thermal printing

2. regular color printer (photographic paper)

what is a legal aspects of xrays that needs to be consistered

making sure the image is not edited in any way

advantages of digital radiography

1. lower radiation dose

2. easier image acquisition

3. eliminates chemical processing

4. possibility of using resources

5. easier coping and sharing

6. easier to store

disadvantages of digital radiography

1. Initial cost is higher

2. rapid evolution of digital technologies (could lead to obsolete system faster)