Radiology - Week 2

Front 1

Radiographic density

Back 1

The degree of blackness on a radiograph.

Dark areas made p of black metallic silver on finished radiograph

Can be increased by raising mA or exposure time or even kVp by increasing the penetrating power of the x-ray beam

Front 2

Radiographic Contrast - What is it? Long scale vs short scale?

Back 2

Differences in radiographic density between adjacent areas on radiograph.

Radiographic contrast depends on:

-Subject density
-kVp level (Higher kVp, the longer the scale of contrast)
-Film contrast (The ability of film to produce long/short scale contrast)
-Film fogging

Long scale contrast - Few black and white shades with many shades of gray.

Short scale contrast - Black and white shades with only a few shades of gray in between

Front 3

Subject density

Back 3

The ability of the different tissue densities to absorb x-rays. Penetrate depending on the differences in atomic number and thickness

From least dense to more dense....

-Air
-Water
-Fat or muscle
-Bone
-Metal

Front 4

Radiographic detail

Back 4

Sharp tissue and organ inteerfaces. Most common factors affecting detail are patient motion or penumbra effect

Front 5

Penumbra Effect (Penumbra)

Back 5

Excessive penumbra causing blurring around edges or shadows cast by x-ray exposure. GREATEST ON CATHODE SIDE OF IMAGE BECAUSE THE EFFECTIVE FOCAL SPOT IS NOT CONSTANT ACROSS THE RADIORAPH (Larger at the cathode)

Changes to three main ffactors that affect the amount of penumbra are:

-Size of focal spot (smaller, less distortion)
-Focal film distance (increased, penumbra/distortion decreased)
-Object film distance (increased, penumbra/distortion increased)

Front 6

Quantum mottle

Back 6

Density variation caused by incomplete exposure of film.

Usually result of low mA

Increasing quantum mottle decreases detail

Front 7

x-ray production process

Back 7

-Thermionic emission (Boiling off of electrons from the filament on cathode side. As filament current increases the filament becomes hotter and more electrons are relased)
-Application of high voltage (at the anode)
-Acceleration of electrons to the anode
-Sudden slowing/stopping of electrons (causes heat and x-rays to be generated)

Front 8

Milliamperage

Back 8

AKA Tube current - Measurement of the number of electrons traveling from cathode to anode during the exposure

Front 9

Time

Back 9

measurement of how long the x-rays are produced - the length of exposure

Directly proportional to the number of electrons crossing the tube and is therefore directly proportional to the number of x-rays created

Front 10

mAs calculations

Back 10

-mA x seconds = mAs

-mAs / seconds = mA

-mAs / mA = seconds

Front 11

Factors affecting Radiographic/Optical Density (OD)

Back 11

-mAs
-kVp
-FFD
-Intensifying screens
-Grids
-Structure
-Generator type
-Beam restrictions
-Anode heel effect
-Processing

Front 12

Kilovoltage

Back 12

AKA Object Density

Measure of the maximum electrical potential across an x-ray tube

Controls penetrability (The thicker the part, the higher the kVp)

Front 13

How does kVp affect the tube current?

Back 13

increase causes an acceleratin of electrons:
-Increases electron kinetic energgy
-Increases photon energy
-Increase acceleration (more peneratrability)
-Increase in scatter radiation

Higher kVp allows you to use less mAs, decreasing tube load and tube heat

Front 14

How does kVp affect CONTRAST

Back 14

Contrast decreases with increased kVp because it increases x-ray energy,increases penetration, and increases scatter radiatin.

-Low kVp (bone) - High contrast, less penetration, more absorption with SHORT GRAY SCALE

-High kVp (abdomen) - Low contrast, more penetration, less absorption. LONG GRAY SCALE

Front 15

How does kVp affect density?

Back 15

Increases with increased kVp due to x-ray energy
-increased penetration, increased scatter radiatino.

More photons reach the film> density increased

Increasing by 20% = double radiographic density

Decrease by 16% = Halve the radiographic density

Front 16

How does kVp affect exposure latitude?

Back 16

High contrast (Black and white) - is narrow latitude, at lower kVp, an error of a few kVp can make a very noticeable diffference

Low contrast (more gray) - wide latitude, difference of a few kVp will make little, if any difference

Front 17

Scatter radiation

Back 17

Produced when x-ray photons from the primary beam redirected after interaction in/on the patient or table.

-longer wavelength, low energy x-ray photon
-Not useful to image
-Decreases contrast
-Degrades visiblity or detail
-Likely to be absorbed by next object it strikes

Front 18

The grid

Back 18

Device used to improve the contrast of the radiographic image by cleaning up scatter radiation before it reaches the image.

-W/O a grid, scatter contributes to 50 - 90% of the image exposure.

Reccomended for parts about 10 cm in thickness or greater and when using kVp at or above 60

-MOST COMMON ONE USED IN VETERINARY MEDICINE IS 8:1

Front 19

Air gap

Back 19

Has same effect as grid by controlling scatter because the scatter photon diverges beyond the borders of the film. Equivalent to a 5:1 grid

Front 20

Completely clear image vs black image

Back 20

Completely clear = Wasn't exposed
Black = was exposed to light, overexposed

Front 21

Distortion

Back 21

Incorrect positioning;

-Elongation: Lengthens lenth of subject
-Foreshortening: shortens length of subject (bring parallell to cassette)
-Magnification: Subject appears larger (shorten OFD)
-False narrowing of vertebrae (make parallel to cassette and pad under neck and between stifles)

Front 22

Intensiffying screen construction

Back 22

Base - Plastic cardboard backingg and flexible

Reflecive layer - Made of titanium dioxide, reflects light back towards the film

Phosphor layer - Light emitting crystals made of either calcium tungstate or rare earth phosphors. Increases ability to conver x-ray to light

Front 23

Screen speeds

Back 23

Slow (detail or fine) - high defenition, better detail

Par (Medium) - Good resolution, minimum exposure

High (regular) - Fast speed, used where more exposure is requred for thick tissue. Can reduce patient exposure, but is grainy.

SCREEN SPEED IS INVERSLY PROPORTIONAL (THE OPPOSITE OF) THE EXPOSURE TIME

Front 24

Large and small crystals

Back 24

Larger crystals - Faster but decrease detail

Smaller crystals = Slower but better detail

Front 25

What is Film made up of?

Back 25

Made up of a polyester base, ligght sensitive emulsion (gelatin) on both sides, AND Silver Halide microcrystals imbedded in the gel (Silver bromide and silver iodine crystals)

Front 26

Latent image

Back 26

The image of film before developing

Front 27

Screen types

Back 27

Blue senstive (ultraviolet) - Blue light emitting phosphors from the screen (Calcium tungstate and some rare-earth phosphors)

Green Sensitive - Green light emitting posphors from sscreen (rare earth phosphors, fast and use less mAs and kVp)

Non screen film (Direct exposure) - Dental x-rays (exposure through direct action of x-ray and have great detail. Plastic or paper inlight proof packet)

Front 28

System speed

Back 28

Screen speed combined with film speed

100 = Slow speed (high detail)
200 = par medium speed
400 - 800 = high speed (less detail)

400 most commonly used in veterinary medicine

Front 29

Film speed

Back 29

higher the number the faster the film.

SLow speed 100 - Smaller SH crystals, longer exposure time, great definition, greatest latitude in exposure and processing

Medium (par) speed 200 - Compromise between time and exposure

High speed 400 - 800 - larger SH crystals, grainier. Shorter exposure time with more latitude in exposure and developing

Front 30

Developer solution

Back 30

Convert silver halide crystals into black metalic silver. Contains a solvent, reducing agent, restrainer an activator and a preservative

Front 31

Fixer solution

Back 31

Removes unchanged halide crystals leaving black metalic silver on the film along with hardeningg it to reduce scrates. Contains a fixer agent, solvent, hardener, acidifier, and preservative

Front 32

FFD

Back 32

Focal film distance = Increase of this increases detail, penumbra decreases, and an increase of it causes less distortion

Front 33

OFD

Back 33

Object film distance = Increase of this , detail is decreased, and penumbra is increased. If it's decreased, there is less distortion