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Imaging II Density
EXAM 1 DENSITY
| Question | Answer |
|---|---|
| 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
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