Receptor Exposure (Density) Flashcards

Question

_Effects on Image Appearance_ What makes radiography an art, not an exact science? "\_\_\_\_" for changes in technical factors are guidelines. Sometimes they only apply to a range of \_\_\_.

Answer 1

_Effects on Image Appearance_ Variables make radiography an art, not an exact science "**Rules**" for changes in technical factors are guidelines. Sometimes they only apply to a range of **circumstances**.

Answer 2

_Factors Affecting Density_ *Controlling or Influencing* **mAs** controlling factor * Multitude of **influencing** factors * mAs reciprocity* * Failure * Short exposure times of \< than **0.01** seconds * Long exposures times of \> than a **few** seconds

Answer 3

_MAJOR CONTROLLING FACTOR OF DENSITY_ Major controlling factor of density = mAs Controls = amount of radiation produced by controlling amount of electrons flowing across X-ray tube

Answer 4

_Digital Radiography_ Window Level will control the density level Setting the correct mAs is still critical in determining proper digital image receptor exposure.

Answer 5

_mAs_ * mAs and density are directly proportional * Meaning in order to double the density on the radiographic image, you will double the mAs value * In order to half the density on the radiographic image, you will half the mAs value. Ex) The radiologist wants you to repeat a knee film that is double the darkness it should have been. You used 60 kVp at 6 mAs. What do you do? Film was too dark - how much? **Double dark so cut the mAs in half.** **6 mAs divide by 2 = 3 mAs**

Answer 6

_Minimum change for mAs in order to see a change:_ 30% rule for mAs value to see change in density 50 mAs x .30 = 15 mAs You must add 15 mAs to your mAs value in order to see your film become darker. You must subtract 15 mAs from you mAs value in order to see your film become lighter.

Answer 7

_Influencing Factors:_ Influencing factors influence density. If influencing factors change, density changes

Answer 8

_Kilovoltage_ kVp controls energy (strength and wavelength) of the electrons * **Penetration power** of the beam * Changes in kVp alter **intensity** of the beam * Production of **scatter radiation** is affected by the kVp * Patient's **radiation dose**

Answer 9

_Minimum Change in Density using kVp_ In order to see a minimum changes in density you must change your kVp by 10%. 50 kVp at 5 mAs and the film was a little light. 50 x .10 = 5 You must use 55 kVp in order to make the film a little darker.

Answer 10

_Double or Half the Density using kVp_ In order to double or half the density, you must change kVp by 15% 60 kVp at 12 mAs film was double dark. 60 x .15 = 9 kVp 60 -9 ---New kVp=51 kVp

Answer 11

_Why not use kVp to change density?_ Because it also changes * Wavelength * Penetration power of the beam * Patient radiation dosage * Scale of contrast

Answer 12

_Anode Heel Effect_ **Intensity** varies along the **long axis** of the **beam** The anode heel effect **alters the intensity of the beam across the cathode/anode axis** Density up to **45**% greater at the **cathode** side of the beam Anode side = **less** intense Cathode side = **more** intense Where do we want thicker body parts? **Cathode end**

Answer 13

_Source-Image-Distance (SID)_ Inverse square law states that the intensity of the beam varies with the distance from the source of radiation. Exposure is inversely proportion to the square of the distance Shorter SID = **darker** film AND Longer SID = **lighter** film (if same technique is used)

Answer 14

_Inverse Square Law vs New Mas Formula_ *Inverse Square Formula:* * _Old Intensity = New Distance²_ * New Intensity = Old Distance² *To Maintain Density: New mAs Formula* * _Old mAs x New Distance_² * Old Distance²

Answer 15

_Rules for SID Changes:_ * Look for **doubles** * If SID doubles = **4** x mAs * If SID is cut in half = ÷ mAs by **4** * Rule of Thumb: * 40” to 72” = **4** x mAs * 72” to 40” = ÷ mAs by **4**

Answer 16

_Object to Image Receptor Distance OID_ Air gap grid = the air space between the part and IR acts as a grid so: Shorter OID = **darker** film AND Longer OID = **lighter** film (if same technical factors are used)

Answer 17

_Filtration_ Filtration removes longer wavelengths so that less radiation leaves the tube Increase filtration = **lighter** film AND Decrease filtration = **darker** film (if same technical factors are used)

Answer 18

_Beam Restriction "Collimation"_ What do you cut off when you cone down? Primary radiation field smaller field side = **lighter** film VS larger field size = **darker** film (if same technical factors are used)

Answer 19

_Anatomical Parts_ Attenuation is the **decrease** in the number of **photons** as they travel through the body **thickness**. smaller body parts = **darker** film VS larger body parts = **lighter** film (if same technical factors are used)

Answer 20

_Grids_ Grids remove scatter radiation from striking film (less radiation reaching film) Grid = **lighter** film VS Nongrid = **darker** film (if same technical factors are used) Rule of Thumb: * Non-Grid to Grid = **4** x mAs (too light) * Grid to Non-Grid = ÷ mAs by **4** (too dark)

Answer 21

_Film/Screen Combinations_ You will need to remember the **size, thickness,** and **speed** of thefilm/screen. faster the system = **darker** film VS slower the system = **lighter** film (if same technical factors are used)

Answer 22

_Film Processing_ You must process the film using the requirement of the **manufacturer**. If you change the **temperature** of the developer or length of the **time** you will notice a change in the **density**. * Hotter Temp= **Darker** Film VS Cooler Temp = **lighter** film * Longer Time=**Darker** Film VS Shorter Time = **lighter** film

Answer 23

_Quick Tip:_ If less radiation is produced or less radiation is reaching the IR, the overall brightness/density will **decrease**. If more radiation is produced or more radiation is reaching the IR, the overall brightness/density will **increase**.