Fundamentals 171 C. 12 Essentials

61. Has lead lines that are angled, or canted, to approximately match the angle of divergence of the primary beam

focused grid

6.Increasing collimation reduces what 3 things?

the volume of anatomic tissue irradiated, reduces scatter production, and reduces patient exposure.

69. Refers to the linear pattern of the lead lines of a grid.

grid pattern

70. The ratio of the height of the lead strips to the distance between them.

grid ratio

71. Radiolucent strips between the lead lines of a grid, generally made of aluminum.

interspace material

30. Describe the purpose of a radiographic grid.

it is intended to absorbs scatter emitted from the patient

72. Changes the shape and size of the projected x-ray field; similar to an aperture diaphragm.

lead mask

2. The effect of scatter radiation can be reduced by ____ and by ___

limiting the amount produced absorbing the scatter before it reaches the IR

73. Has lead lines that run in one direction only

linear grid

8. List 5 types of grid designs

linear parallel, focused parallel, crossed, long dimension short dimension,

67. The orientation of a grid's lead lines to one another.

grid focus

68. Expresses the number of lead lines per unit length in inches, centimeters, or both.

grid frequency

13. Scatter control is of the ____, importance in digital imaging because of

same, or greater the IR's increased sensitivity to low-energy radiation.

10. Grid errors that produce grid cutoff include _____ and errors caused by 3 types of misalignment

- using a focused grid upside down -off-level -off-center -off-focus

1. Scatter radiation, the result of ____, is ______ to radiographic image quality. Excessive scatter results in _____ to the IR and ____

-Compton interactions -detrimental -additional unwanted x-ray exposure (fog) -reduced contrast.

17. flange of Cones and cylinders -length -shape -increasing length?

-can vary -cone or cylinder -can be telescoping

19. Cones and Cylinder -ease of use -location

-easy to use -They slide onto the tube directly below the window.

18. Aperture Diaphragm -ease of use? -location -Is the projected field size adjustable -how common is it?

-easy to use -below the x-ray tube window -no -not as common as other types of beam restricting devices

3.The amount of scatter exiting the patient ______ as the volume of irradiated tissue increases

-increases

32. List the 2 types of grid patterns

-linear -crossed or cross-hatched

33. List the 2 types of grid focus

-parallel grid or non focused grid -focused grid

35. List the 3 types of stationary grids

-the wafer or slip-on grid -grid cassette - grid cap

27. Collimators are equipped with a _____ source and a ____ to project a light field onto the patient. This light is intended to accurately indicate .

-white light -mirror where the primary x-ray beam will be projected during exposure

46. Method for limiting the scatter reaching the image receptor. Scatter will miss the image receptor if there is increased distance between the patient and the image receptor (increased object-to-image receptor distance).

Air Gap technique

41. Recognize how the use of grids affect patient radiation exposure

As grid ratio increases, patient dose increases; as grid ratio decreases, patient dose decreases. The use of grids requires an increase in mAs to maintain exposure to the image receptor. As a result, patient radiation exposure is increased when using grids. The higher the grid ratio, the greater the mAs needed to maintain exposure to the image receptor, increasing patient radiation exposure

20. _____ limit unsharpness surrounding the radiographic image more than ____ do, with _____ accomplishing this task slightly better than ____

Cones and cylinders aperture diaphragms cylinders cones

36. describe the function and purpose of a moving grid.

Grid motion is controlled electrically by the x-ray exposure switch. The grid moves slightly back and forth in a lateral direction over the IR during the entire exposure. These grids typically have dimensions of 17 × 17 inches (43 × 43 cm), so that a 14-by-17-inch (35 × 43 cm) IR can be positioned under the grid either lengthwise or crosswise, depending on the examination requirements.

34. How do you calculate grid ration

Grid ratio=h/D in which h is the height of the lead strips and D is the distance between them

42. Recognize how beam restriction affect spatient radiation exposure

Limiting the size of the x-ray field to the anatomic area of interest will decrease scatter production and reduce patient exposure. Although the mAs may be increased to compensate for decreasing the size of the x-ray field, the tissues located closest to the lateral edge or outside of the collimated x-ray beam will receive the least amount of radiation exposure. Those tissues that lie inside the collimated edge of the x-ray beam will receive the greatest amount of radiation exposure. Collimating to the anatomic area of interest is an important radiation safety practice that should be routinely performed

39. What is the grid error? A loss of exposure at the periphery of the IR

Off-focus error: Using an SID outside of the focal range

38. What is the grid error? Decrease in radiation exposure to the IR (2 options)

Off-level error: Angling the x-ray tube across the grid lines or angling the grid itself during exposure Off-center error: The center of the x-ray beam is not aligned from side to side with the center of a focused grid

37. What is the grid error Significant underexposure to the lateral edges of the IR

Upside-down focused grid: Placing a focused grid upside down on the IR

45. • Describe the use of shielding accessories to absorb scatter radiation.

Placing a lead shield on the x-ray table close to the collimated edge of the area of interest absorbs scatter exiting the patient that could degrade image quality. The lateral lumbar spine projection and the lateral spot are projections in which a significant amount of scatter exits the patient. Placing a lead shield behind the patient's lower back absorbs the scatter and reduces the amount striking the IR (Fig. 12.28). Accurate placement of the lead shield is important so it does not affect the processing of the digital image. Placing a lead shield on the table to limit the scatter radiation reaching the IR does not reduce the exposure to the patient.

7. ______ are devices placed between the patient and IR to absorb scatter radiation. They consist of a series of ____ and _____, They allow transmitted radiation to ____ while scatter radiation is ____.

Radiographic grids lead strips radiolucent interspaces pass through absorbed

5. a.Beam restriction limits what 3 things? b. List 4 types of beam restrictors.

a. the area exposed to radiation, the patient dose, and the amount of scatter produced in the patient. b. -Aperture diaphragms, -cones -cylinders, -collimators

12.The ____ technique is another method, although seldom used, for reducing the amount of scatter reaching the IR.

air gap

47. The simplest type of beam-restricting device, constructed of a flat piece of lead that has a hole in it.

aperture diaphragm

14. The simplest type of beam-restricting device, constructed of a flat piece of lead that has a hole in it.

apeture diaphragm

48. Automatically limits the size and shape of the primary beam to the size and shape of the image receptor. Also called a positive beam-limiting device.

automatic collimator

28. Automatically limits the size and shape of the primary beam to the size and shape of the image receptor. Also called a

automatic collimator positive beam-limiting device

43. Explain the air gap technique and describe its use

based on the simple concept that much of the scatter will miss the IR if there is increased distance between the patient and IR (increased object-to-image receptor distance [OID]) (Fig. 12.27). The greater the gap, the greater the reduction in scatter reaching the IR. Similar to a grid, contrast is increased, the number of photons reaching the IR is reduced because less scatter reaches the IR, and the mAs must be increased to compensate.

49. Changes the shape and size of the primary beam; located just below the x-ray tube housing.

beam restricting device

50. Refers to a decrease in the size of the projected radiation field, also known as collimation

beam restriction

51. The Potter-Bucky diaphragm located directly below the radiographic tabletop, which contains the grid and holds the image receptor.

bucky

52. Can be used to determine the adjustment in milliampere/second needed when changing from using a grid to nongrid (or vice versa) or for changing to grids with different grid ratios; also called the grid-conversion factor.

bucky factor

23. Cones and cylinders are almost always made to produce a _____ projected filed

circular

53. Can be used to determine the adjustment in milliampere/second needed when changing from using a grid to nongrid (or vice versa) or for changing to grids with different grid ratios; also called the grid-conversion factor.

collimation

24. Located immediately below the tube window where the entrance shutters limit the x-ray beam field size.

collimator

25. which beam restriction device is considered the best

collimator

54. Located immediately below the tube window where the entrance shutters limit the x-ray beam field size.

collimator

55. Essentially an aperture diaphragm that has an extended flange attached.

cone

15. essentially an aperture diaphragm that has an extended flange attached to it. The flange can vary in length

cone and cylinder

22. Cones v Cylinders ____ have a disadvantage compared to ____ explain which one is more useful

cones cylinders If the angle of the flange of the cone is greater than the angle of divergence of the primary beam, the base plate or aperture diaphragm of the cone is the only metal restricting the primary beam cylinders

56. An imaginary line if points were connected along the length of a linear focused grid.

convergent line

57. An imaginary point, if imaginary lines were drawn from each of the lead lines in a linear focused grid

convergent point

58 Has lead lines that run at a right angle to one another.

cross-hatched grid

59. Has lead lines that run at a right angle to one another.

crossed grid

16. Essentially an aperture diaphragm that has an extended flange attached to it.

cylinder

60. Essentially an aperture diaphragm that has an extended flange attached to it.

cylinder

9.The use of a grid in a radiographic examination results in ____ reaching the IR. The ______ is used to calculate the increase in exposure needed when grids are used.

fewer x-ray photons grid conversion or Bucky factor

62. A device that has very thin lead strips with radiolucent interspaces; intended to absorb scatter radiation emitted from the patient before it strikes the image receptor

grid

63. Contains a permanently mounted grid and allows the image receptor to slide in behind it.

grid cap

64. An image receptor that has a grid permanently mounted to its front surface.

grid cassedt

65. Can be used to determine the adjustment in milliampere/second needed when changing from using a grid to nongrid (or vice versa) or for changing to grids with different grid ratios; also called the Bucky factor.

grid conversion factor (GCF)

66. A decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid.

grid cutoff

4. A _____kVp increases the energy of scatter radiation exiting the patient.

higher

11. Adding a grid will require an ____ in mAs to maintain exposure to the image receptor and, therefore, ____ the radiation exposure to the patient.

increase increase

29. State the purpose of automatic collimators or positive beam-limiting devices.

mechanically adjust the primary beam size and shape to that of the IR when the IR is placed in the Bucky tray, just below the tabletop. Automatic collimation makes it difficult for the radiographer to increase the size of the primary beam to a field larger than the IR, which would result in increasing the patient's radiation exposure. good for protection against over exposure

74. A zebra pattern artifact that can occur during computed radiography imaging if the grid frequency is similar to the laser scanning frequency or if a grid cassette is placed in a Bucky

moire effect

75 Has lead lines that run parallel to one another; also called a parallel grid.

nonfocused grid

76. Has lead lines that run parallel to one another; also called a nonfocused grid

parallel grid

77. Automatically limits the size and shape of the primary beam to the size and shape of the image receptor. Also called an automatic collimator.

positive beam-limiting (PBL) device

26. The field shape produced by a collimator is always _____ unless using a lead mask, cone, or cylinder placed below the collimator.

rectangular or square

44. Why is the air gap technique limited in its usefulness? How is this problem overcome? Is this feasible? What is the effect on patient dose compared to using a grid? Why?

the necessary OID results in decreased sharpness. To overcome this decrease in sharpness, an increase in SID is required, which may not always be feasible The air gap technique results in patient dose that is the same as, or slightly less than, using a comparable grid. Exposure may be slightly less because a grid absorbs some of the transmitted photons (grid cutoff) whereas the air gap technique does not.

21. what are some drawbacks of both cones and cylinders?

they are limited in terms of the sizes that are available, and they are not necessarily interchangeable among tube housings.

40. Identify the factors to be considered in using a grid.

thickness of the part, the kVp, patient dose, contrast improvement, the likelihood of grid errors

31. Describe the construction of grids

thin lead strips or lines that have a precise height, thickness, and space between them. Radiolucent interspace material separates the lead lines. Interspace material typically is made of aluminum. An aluminum front and back panel cover the lead lines and interspace material of the grid.

78. A stationary grid placed on top of the image receptor.

wafer grid