RADT 151 - Density factors UNIT 2

overall darkness of radiogrpahic is called

Density

when looking at a radiograph we have to evaluate

the amount of density

when evaluating density what to you have to look at

1. through out image ( look at the entire image)

2. within the areas of interest

3. background

desnity can also be define as

The amount of light transmitted through the image

what is the formula of Density

DU = log  ^{incident light}

       ^{transmitted light}

^ex: DU = log            ¹

                           ^{% of light}

What if 30% of the incident light is transmitted through the film, what is the density? ( this is if you are using decimal)

DU = log    1

                   .30

answer: X = .5185  0r .52

What if 50% of the incident light is transmitted through the film, what is the density? ( this is when you are using %)

DU = log    100%

                      50%

X = .301029   or .3

what is the optimal density for Bone

1.0 density unit ( .8-1.2 acceptable range)

What is the optimal density for lung

.5 density units (.4 to .6 acceptable range)

What is the optimal density for abdomen

.6 density units

what are the two factors that affect Density

1. Controlling factors (primary)

2. inflencing facotrs(secondary)

what is the primary control factor in density

mA and time and they are part of photographic

In density the influencing factors control

1. kV

2. SID

3. Processing Tissue (atomic #)

4. film/screen system

5. grid

6. beam restriction

7. generator phase

8. filtration

in the controlling factor(primary) ma(milliampes) controls

quanity of radiation( how much energy or current will be applied to the filament to be boiled off and turn into photon)

in controlling Factors time is the

Duration of exposure

In controlling factors (primary) mAs determines

the amount of radiaiton over a period of time- regulate density

when looking at the radiograph at the image is slightly light and a little more density what would you do

have the increase 30% of mAs is needed to visibly change optical density

when you double the amount of mAs what will you have to do with density

have to double density ( in useful range of density)

when you have to half the mAs what will happen to density

density will also have to be in halves ( in the useful range of density)

what is the realtionship between kV and density

kV=factor Density= image quality

ex: kV increases (penetration increases) the Density with go up

these two are directly porportion

kV is the

penetration of the part

if kV increases the penetration what will happen with remnant ( scatter) radiation

it will increase the amount of scatter radiation on the image and also density increases

if you decrease kV what will happen

you will have less penetration, less amount of radiation that will reach the image receptor and density will go down

kV is not

the optimal choice to change density, you are changing the penetration, and also change the scale of contrast

what does kV effect

Contrast and Resolution

what is the 15% rule show

1. if you increase 15% in kV you would double the the density (same as doubling mAs)

2. if you decrease 15% in kV you will half the density ( also change the scale of contrast)

8% changes in kV is about equal to

30% change in mAs

what you change a radiograph image to 8% what will it produce

produce noticeable/ visible change in density

what does SID follow

the inverse square law

when distance increase without composation what did you change

change distance, less radiation will be received in the image receptor,density will decrease as a result.

less radiation reaches the film due to

absorption of radiation in air as it travels greater distance

In mAs compensation when SID increases

the quantity decreases

what do you have to do in order to maintain density when SID has changed

mAs must be changed to compensate for new distance

what is the formula of mAs compensation

mAs₁    =   D₁²

mAs ₂        D₂²

a question you would see for COMPENSATION NOT ABOUT RELATIONSHIP

What new mAs is needed to maintain the same density at a new distance

chemical processing in film image density has a

direct relationship

if temperature in chemical processing increases (even less than 1 degree)

we are going to see the density off the increase due to temperature

the the temperature increases

the chemical activity of solution increases

what is the ph level for concentration in chemical processing

ph 10-12

the the concentration increases (greater concentration)

the chemistry is going to work faster on the film and make it darker making density go up

what is the immersion time for chemical processing

20-30 sec

Atomic density in tissue density what are you talking about

talks about what it is made out of

Atomic density of the bone is higher than

bone = much higher (much dense)

soft tissue= more air

More radiation is needed to create more

remnant radiation

As tissue density increases what happens to image desnity

Density decreases (without compensation)

Bone has the greater

absorption characteristic

what is the atomic density for air

1

what is the atomic density for fluid

4-6

what is the atomic number for soft tissue

5-7

what is the atomic number for muscle(organ)

8

what is the atomic densities for bone

12

as density increases what will happen with absorption and image density

more absorption will occur and less image density

film speed is the

sensitivity film to the radiographic exposure

as film speed increases the what happens to the sensitivity of the film

¨as film speed increases the sensitivity of the film to radiation exposure increases

what would you need for radiation for film/screen combination

less radiation is needed to produce a     density as film speed increases

what is the normal common film screen

Film speed

50

100

200-slow but not the slowest provides significant amount more of detail

300

400-is the standard used to measure the sensitivity of film to radiation.

800

What is the relationship between film speed and density?

the film screen increases density also increases again without no compensation of change

in order to maintain density what do you ahev to do with film speed and ma

the film speed need to change and mAs must change accordingly

as film speed increases

mAs needs to decrease to maintain density

What type of relationship does mAs have with film density

direct proportion

the formula of film speed/mAs

mAs₁   = FS₂                       

mAs₂      FS₁

for screen speed, if it increases what will happen with the photon

more photon are converted to light photons,therfore less radaition is needed to produce a density as screen speed increases

in order to maintain the same density as screen speed increases what will mAs do

mAs will decrease

What type of relationship does mAs have with screen speed?

inverse

Film type and speed must match

screen type and speed

Conventional film with

¨calcium tungstate screens

Orthochromatic film

with rare earth screens

what is the purpose of a grid

Used to reduce scatter radiation from reaching image receptor

grids are important

for exposure of 70 keV

grid a thin waffer looking plate that has

Aluminum strips with spacing

any photon that is not following the direction of the regular beam what will happen

scattered photons will be absorbed in aluminum strips

Reducing the size of the field reduces the amount of radiation reaching image receptor

Beam restriction

what do the lead shutters do for the collimation

absorb radiation

what is the percentage of collimation for 14 ×17

100%

what is the percentage of collimation for 11× 14

70% ;need to 30 % mAs

what is the percentage of collimation for 10×12

40%, you will have to another 30% (so 60%)

what is the percentage of collimation for 8 ×10

10%; you would have to compensate another 30% ( 60+30=90%)

If you used 8 mAs with a 14 x 17 and now collimated down to a 10 x 12 field size, you would now need to use 12.8 mAs

would now need to use 12.8 mAs

reduces the number of soft photons from the primary beam

Filtration

what are the two types of generator phase (current type)

1. single phase (1 line current)

2. three phase(3 line of current)

more current is applied what happens to density

the more electron are boiled off

need more time to produce X amount of radiation

Single phase

need less time to produce  the same amount of radiation

Three phase

anode heel effect does not have

a direct effect on quanitity and intensity over all or amount of density

annode heel effect create

Uneven density

cathode side has

more radiation

anode side has

less radiation

Discrepancy increases with

increased SID

increase field size

less collimation

what does pathology influences

the amount of density that you will see on radiographic image

what are the two classification of pathology

1. Additive

2. descructive

what does additive disease adds and what does it increase

tissue fluid , material to the body and increases attenuation and greater absorption`