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Imaging Ch.6
Scatter Control
| Question | Answer |
|---|---|
| How is scatter radiation most easily controlled? | Collimation and grids |
| What is not a way to reduce the production of scatter radiation? | Increasing grid ratio |
| What influences the amount of scatter radiation striking the IR but not the production of scatter radiation? | Increasing the grid ratio |
| What is the best beam limiting decivce for limiting unsharpness surrounding the radiographic image? | Variable aperture collimator |
| What purpose does positive beam limitation serve? | To reduce pt exposure to limiting the exposure field to the same size as the image recepor in the bucky tray |
| What occurs when scatter radiation strikes the film? | Radiographic contrast decreases |
| The height of the lead strips relative to the distance b/t the lead strips is the measure of the | Grid ratio |
| T/F A grid decreases scatter production | F |
| T/F A high ratio grid removes little scatter | F |
| If the height of the lead strip DECREASES and the spcae between the grid strips INCREASES the grid will be MORE effective at removing scatter radiation T/F | F |
| T/F If the height of the lead strips INCREASES and the space between the grid strips DECREASES the grid will be MORE effective at scatter removal | T |
| The # of lead strips per inch in a grid is a meause of the | grid frequency |
| What would be the most difficult grid to use | Cross hatched grid |
| A radiograph that has a goffed appearance has most likley been exposed to what? | Scatter radiation |
| Which beam restriction device can be cut to the size needed? | An aperture diaphragm |
| What is the result of imaging a thicker part or patient? | More compton interactions |
| As grid ratio ____ the removal of scatter ____ | Increases, increases |
| The amount of MAS required with a grid divided by the amount of mas needed w/o a grid is the calucation that determines the | Grid conversion factor and bucky factor |
| Which grid design is manufactured to match the divergence of the xray beam? | The focused grid |
| What occurs when the xray beam is not properly aligned with the grid strips? | grid cut off |
| In genergal, when should a grid be used | When part thickness exceeds 10cm |
| When a grid is needed but not available what may be used for certain exams? | Air grap technique |
| What type of grid error is seen as acceptable density in the middle of the film and with decreasing density bilaterally as you move away from the center? | upside down focused grid |
| What type of grid error is seen as a loss of density at the periphery of the image? | off focus |
| why does the air gap technique work? | the scatter photons are more likley to miss the IR |
| The results of the collimator alignment QC test should demonstrate that the alignment is withing 5% of the SID used T/F | False |
| Also called lateral decentering the ___ grid error results when the CR is not aligned to the middle of a focused grid | off center |
| Changing from an 8:1 grid to a 12:1 grid along with making the appropriate adjustments, will result in: | Decreased Pt dose and an image with a shorter scale of contrast |
Created by:
rachelbeatty4
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