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Imaging II Density


What is density? The degree of blackening on an image.
What determines density on an image? The quantity of radiation absorbed by the film.
What causes absorption of radiation on the film? Black metallic silver is deposited on the emulsion layer of the film after it is radiated by the beam.
What affects the quality of a radiograph? The quality is affected by both photographic and geometric properties.
What beam factors control the density produced on am image? mAs (MilliAmperes x exposure time (seconds) affects the quantity of xray photons produced. kVp
When mAs is increased the quantity of xray photons will Increase. It is a directly proportional relationship.
With an increase in mAs, density produced on the image will Increase.
The mAs reciprocity law shows that any combination of mA and time (s) resulting in an equal mAs will Produce an equal amount of density on an image.
To see a noticeable change in density, mAs will need to be increased by 30%
To cause a visible change in a KUB shot at 40 mAs, the new mas must be increased by 30% what would the new technique be? 40x 0.30= 12 40+12=52
Density rule of thumb, for repeat films with insufficient density, for an overexposure you would cut the mAs in half
Density rule of thumb, for repeat films with insufficient density, for an underexposure you would double the mAs
Some things that influence density are kVp SID Anode-Heel Effect Beam Restriction Filtration Film-Screen Combinations Grids Patient Factors Processing
What is kVp? Electrical tube voltage that controls speed of electrons crossing from cathode to anode
In what way does kVp effect density of film As kVp is increased penetrability is increased and thus, density is increased. As kVp is decreased, density is decreased.
What is the 15% rule? Increaseing or decreasing the kVp by 15% has the same effect as doubling the mAs, or halving it respectively.
How does SID influence density? Divergence of the beam affects intensity or the quantity of photons reaching the IR. The relationship is not exactly quantifiable.
As SID increases density will Decrease due to decreased beam intensity and more divergence. An angled beam is an addition to SID.
As SID decreased density will Increase due to increased beam intensity and less divergence. An untangled beam has less SID than an angled beam.
Anode-Heel Effect will affect density due to the more intense Cathode side of the beam which is capable of more penetration
To utilize the Anode-Heel Effect and create uniform density of an image, the larker thicker part of the anatomy should be positioned under the Cathode side of the tube
For a chest exam the cathode side of the tube should be positioned over what area? Lower Abdomen
For an xray of the humerus what part of the anatomy should be under the cathode? The elbow due to more dense tissue that that of the wrist
What area of anatomy should the cathode be over for an xray of the femur? The hip because of the increased density of the pelvis versus the knee
What area of the anatomy for an xray of the tibia/fibula should the cathode be positioned over? The knee because it is much denser tissue that the ankle joint.
What area of the anatomy for an xray of the Tspine should the cathode be positioned over? The Lower Tspine, or the Abdomen because of increased density of the abdominal tissue.
What effect does collimation have on density? It affects the total number of photons available in the area or field size
An INCREASE field size, due to less collimation, will cause increased scatter and an INCREASE in density evident on the film
A DECREASE in field size, due to increased collimation will cause decreased scatter and a DECREASE in density evident on the film
Filtration by the addition of an aluminum filter is used to reduce exposure to what A patients skin
What does filtration do it absorbs lower-energy photons or "soft" radiation and "hardens" the beam
As filtration is INCREASED and the beam becomes more penetrating but beam quantity is reduced density will DECREASE
As filtration is DECREASED but beam quantity is increased density will INCREASE
Film-Screen combination can affect density because of the variation of screen and film speed combinations
Does screen speed or film speed have a greater effect on density? Screen speed exerts a greater effect on image density that film speed.
Highly photosensitive film & high speed ("fast") screens require LESS exposure
How efficiently screens convert xray photons into light photons, or "Flourescence" is Good for patients but NOT good for recorded detail
Screen speed can be affected by The TYPE of phosphor The SIZE of phosphor THICKNESS of phosphor CONCENTRATION of the phosphor
The most EFFICIENT type of phosphor is RARE EARTH materials such as gadolinium and lanthanum
The LARGER the phosphor size the FASTER it will record the information
The THICKER the phosphor the FASTER it will capture the information
The HIGHER the concentration of phosphors the FASTER it will be
RS or Relative Speed is the number that Represents the overall speed of a film-screen system
A Routine high speed system would have a number of 400RS
An extremely slow system would have a number of 100RS
As RS is INCREASED Density is also INCREASED
As RS is DECREASED Density will also DECREASE
Grids are used to help prevent scatter radiation from reaching the IR and also absorb some primary (remnant) photons
The use of a grid requires MORE patient exposure (Increase in mAs) than non-grid exams
Increased grid RATIO or FREQUENCY results in MORE scatter being absorbed by the grid
As grid RATIO/FREQUENCY is INCREASED, thus the amount of radiation reaching the IR is reduced 12:1 more scatter absorbed Density will DECREASE
As grid RATIO/FREQUENCY is DECREASED, thus more radiation reaches the IR 6:1 grid less scatter absorbed Density will INCREASE
Grid Ratio is determined by the Height if the grid, divided by the interspace width
Grid Frequency is determined by the number of lead strips per inch or centimeter
Patient factors can also determine the density on an image such as The Anatomical Part imaged Pathology Attenuation of Photons (absorbed, scattered, transmitted) The Tissue thickness The type of tissue irradiated
Thicker body parts absorb MORE photons
Thinner body parts absorb LESS photons
As tissue thickness is INCREASED i.e>wrist v.s. knee Density is DECREASED
As tissue thickness is DECREASED i.e.>shoulder v.s. ankle Density is INCREASED
Tissue Density varies and then physical makeup depends on it's ATOMIC number
Gas in the body has an atomic number or 1-2
Fat tissue in the body has an atomic number of 6-7
Soft tissue/Fluid in the body has an atomic number of 7-8
Bone tissue in the body has an atomic number of 14
As tissue density is INCREASED, image density will DECREASE, highly dense body tissue absorbs more photons
As tissue density is DECREASED image density will INCREASE, less dense body tissue absorbs less photons
Casts require an increase in exposure (mAs, and or kVp) due to INCREASED part thickness. Plaster is THICKER than fiberglass.
Destructive diseases may cause a DECREASE in anatomic part density and or thickness
Osteoporosis and Emphysema cause a DECREASE in tissue density and require a REDUCTION in mAs and kVp
Lung Tumor, Pulmonary Edema, and Pleural Effusion cause an INCREASE in tissue density and require an INCREASE in mAs and kVp
Processor solutions must be kept at adequate temperatures, if the chemicals automatic replacement rate is under-replenished the images will result in DECREASED density
If the processing chemicals for the images auto replacement rate is Over-replenished, the resulting films will have INCREASED density
If the temperature of the developer is below the optimal temperature the images will have DECREASED density
If the temperature of the developer is above the optimal temperature, the images will have INCREASED density
Created by: ABIGAILDRAKE1984