Image Receptors and Quality

History of X ray film

• Kolls invented first films by using film that was cut into small pieces and wrapped in black paper

• kodak was first film compant to develop prewrapped dental film in 1913

• 1920 kodak developed machine made film packets

Components of Film:

• how many films does it have?

• What feature? Why?

• What protects film from light?

1 or two

• raised dot

  • in mouth faces x ray tube, helps in mounting indicate where image goes in template

• protective black paper

What is placed behind the film? Why? What is after that?

• lead foil

• protects film from receiving any seondary scatter radiation

• (prevents fog)

• Outer package wrapping that protects film from saliva and light

Secondary scatter radiation

radiation that spreads in diff directions from beam when that beam interacts with any substance, like body tisue

Definitions: name that component

1. Serves to attach emilsion to base

2. Attached to both sides of film by adhesive layer

   1. Whats it made of and what do they do?

3. Provides strength and support

4. Protects emulsion from mishandling and processing damage

• adhesive layer

• Emulsion

  • gelatin and silver halide crystals: absorb radiation during exposures and stores energy in crystals

  • Creates the latent (invisible) image on exposed film

• Film base

• Protective layer

film processing

Converts latent image to visible image

• preserves visible image so it says permanent

What are the requirements for film processing (4)

• Darkroom

• Chemicals

  • Developer solution

  • water

  • fixing solution

Films can be ___ processed or developed through?

manually (by hand), automatic

Darkroom requirements for film processing

• correct lighting-safelight and white light

• temp (70 degrees ideal) and humidity control (30-50%)

  • Increased temp = fog

  • Increased humidity = film doesnt dry

  • Decreased humidity: static electricity and film artifact

Film processing: requirments or film processing

Chemicals: developer solution

• converst latent image to visible

• reduces exposed crystals to black metallic silver

• Softens emulsion during processing

Film processing: requirments or film processing

Chemicals: water

• removes developer from film

• Stops developing process

• step is used when manually processing films

Film processing: requirments or film processing

Chemicals: fixing solution

• removes unexposed silver halide crystals from emulsion

• hardens emulsion

• developed black metallic silver is fixed and preserved

Film fog”

darkening of images by sources other than radiation of primary beam to which film was exposed

• grayness

• destroys quality

• Not caused by primary radiation

Causes of film fog (7)

• visible light

• improper safelight

• outdated film

• high developer temp

• scatter/secondary radiation

• improper storage (humidity + temp)

• chemicals in processing

What to consider when acquiring digital systems (6)

• Source of radiation (x ray unit itself)

• Imaging receptors: either psp or sensors

• software program

• PSP plate readers (optimes at mUSOD)

• Scanners and printers if you need to incorporate outside x rays

• back up system

Two ways to obtain Digital X rays

Digital imaging receptors

• indirect dental: photostimuable phosphor plates (PSP)

• Direct digital: sensors

Indirect digital system

• PSP plates

• require the use of a laser to process latent image before converted back to visible image

• middle step for processing = indirect

• Two sided

  • Blue side = phosphor side: x rays hit these crystals to move to higher energy level capturing latent image

  • Back side: backing to reinforce strength

Direct digital system

Sensors:

• immediate image:

• white side = active and side of x ray on

• Other side: cord that directly plugs into computer

What is the silver circle on PSP plate?

• magnet

• When you enter plate into processing machine: magnet first

How is the PSP image created?

• Radiation to the PSP plate which writes latent image

• visible wavelength laser reads image from PSP

• creating and image requires illuminating the plate twice

creating an image requires the plate to be illuminated ?

twice

• First illuminiation is emitting radiation to PSP which creates invisible latent image

• When psp is put thru processor, a red light (second illumuniation source) reads the plate: displayed on computer monitor

  • indirect digital imaging due to middle or second processing step

What traps the x ray energy in the crystals?

How is this stored energy released?

How erased?

Photostimuable phosphor

• stim by red laser and colleced in PSP reader and converted into digital image

• X ray image is erased from plate by intense light source, returning all eelcctrons to orignal state and making plate ready for reuse

Direct digital: two types of sensors?

• charge couple device CCD

• Complementary MEtal Oxide semiconductors (CMOS)

CCD vs CMOS

• CCD:

  • charge is transported across sillicon chip and read at one corner

  • tend to have higher quality and low noise due to more pixels

• CMOS

  • each pixel can be read indivuadually due to multiple transitors

  • lower power

  • cheaper

1. x ray beams reach scintillator

2. Scintillator absorbs charged particle radiation

3. Convert most x rays into visible light\

4. Light ineracts with silicone crystals and electrical charge created and formed in image matrix

5. stored charges removed electronically

6. conputer converts analog to digital to produce image

• X rays have a wide range of?

• at each pixel, the absorption of x rays produces a small?

• energies and wavelength

• voltage (electrical charge) which can flucuate (analog)

ADC

analog to diigital converter: converts analog voltage to digitral number proportional to magnitude of voltage

image matrix

rows and columns of squares known as pixels

Digital images have no ? What do they have?

physical form, exist as numbers on file

What is a pixel?

• single picture element

• Each pixel can only display limited number of ?

• Number of gray levels depends on?

• __ bits/pixel, or 65,536 gray levels

• More pixels, = ?

• HUman eye cannot distinguish more than ? under ideal

• colors/grey levels

• bit depth

• 16bits/pixel

• better resolution and apperance

• 50 grey levesl

size of pixels will determine ?

spatial resolution of image:

• smaller pixel, = more pixels needed for better quality

What allows us to see fine detail of image? what are units?

• spatial resolution: line pair per mm

the smaller the pixels

the better visibility of smaller structures and bettter recored detail

Detector latitude

ability of imaging receptor to capture a range of x ray exposures

are sensors or PSP more sensitive?

Sensorys

for PSP plates, you have a larger range to ?

over or underexpose, high detector latitiude, but still want to use setting to avoid too light or dark

is there a point to going to higher side of green range

• wont produce more detail and uncessary exposure

one basic property that affects radiographic quality

Photographic properties

Photographic properties

• denstiy: amount of darkening of radiograph

• Contrast: difference bween adjacent densities: black, white, grays on film

overerall, contribute to visual appearance of anatomy on radiograph

Radiographic density: controlling factors?

Controlling factors: MAS and distance

• MA/time:"

  • milliamperes * seconds

  • determins quantity of x rays

  • longer = darker

  • dont mess with MAS - mess with time instead

2x the mas? density?

2x density as quantity is directly proportional to MAS

bite wings are used o assess

bone height and interproximal space

optimal density for eval of interprox space and bone height measurement

.32

To correct under or over exposure

30% rule: change of 30 is needed in mAs to demonstrate visible diff in density

along with mAs, the other controlling factor for density is?

distance

Intensity of radiation is inversely proportional to? (inverse square law)

square of the density

• as you increase distance, you decrease density (beam divergence)

what helps maintain quality by standarizing distance between source and image receptor?

cone

Radiographic contrast is defined as ?

• controlled by?

• directly affected by?

difference between adjacent densities

• kV

• much tissues involved attenuate the beam as it enters the body

Fat and caries are ___

radiolucent

contrast is the __, controls the ?

standard for best image?

quality: force of emerging stream of x rays

60-70 kVp

15% rule

kV does influence density as secondary factor: increase kV by 15% = double mAS

a high kv image demonstrates

long scale contrast (more shades of gray)

edges exposed = fogged white border ( light error)

light exposure; go one by one

part way stuck in optime: exposed to light

Quantum mottling: increase time of exposure

quantum mottling

if magnet doesnt impede anatomy when flipped backwards, do you still have to redo?

no

backwards placement of PSP

PSP plate put in processor on angle

dirt on PSP plate

patient glasses:

motion

motion

patient holding film

done on size 1 psp plate

what do you want to see in premolar pa

distal of canine, root apices of 1st, 2nd, premolar, 1st molar, 2-3 mm surrounding tissue

psp processing error

processing error

cardboard cover in wrapping PSP plates gets pulled into optiime processpr

double exposure (same PSP plate twice)

cone cut

cone cut

cone cut

cone cut error

cone not lined up to receptor: happens most common with bisecting angle technique as there is no ring for visual aid

thyroid collar

how?

overlapping: incorrect horizontal angle

elongation: insufficent vertical tube angle: more common in biscecting angle

foreshortening: excessive vertical tube angle: decrease angle to fix

replace sensor

red triangle: series has not been approevs: additional images may still be added

international standard to transmit, store, retrieve, print, process, display medical imaging info

DICOM

dicom header

• background: all image data

• patinet ID and never be seperate

• would contain data if image was altered

images have been saved and sent to DICOM server: yellow barrel

fidelity with which anatomic structure being examined is imaged

radio qualityq

how often testing x ray: how accurate, how much filtration?

how much digital?

3-4 years: visual charts, accuracy must be within 10%, 2 mm, 40-100 mR

D; 200, E: 150, FL 120

way to assure consistnt qualiuty: small graduated increase in thickness

stepwedge

PSP plates should be checked for scratches on a __ basis

monthly

CLEANED WITH cavi wipes

psp plates sould be cleaned with?

denatuerd alcohol

what side is active of sensor XDR

white: direct x ray towards

radiation safety plan submitted to state for what?

pans and CBCT

X

CRACKLING

test digital sensors and monitor __ for image degradation

annually: digital phantom

lowest exposure in which max line pair and number of holes can be cisualized

baseline quality assurance exposure : compare next year

what test pattern to use fo rcontrast and brightness setting of monitor?

• SMPTE: society of motion picture and televesion engineers test pattern

• also limitations in spactial resolution and aliasing display

  • in each corner; differentiate all lines of squares horizontally and vertically

• 5% at both ends visible = adequate

limitations of rectangualr colliamation (5)

• revert to round when:

• endodontic procedures

• long roots

• severe gag refkex

• intraoral around dental dam

  • bisecting angle technique

target receptor distance of __

16”