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Imaging Applications and Quality > Lab 2 > Flashcards

Lab 2 Flashcards

1
Q

What is the purpose of a grid?

A

To absorb scatter radiation that has been produced in the patients body before it reaches the IR

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2
Q

T/F

Dose to the patient always increases when there is grid cut off

A

False

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3
Q

What are the 4 causes of grid cut off?

A
  1. Lateral descentering w/wo grid
  2. Upside down focused grid
  3. Off focus grid cut off
  4. Combination of all or some of the above
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4
Q

What is the most common type of grid cut off?

A

Lateral descentering

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5
Q

What is laterally descentering a result of?

A

Not being in detent laterally

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6
Q

Where is an upside down focused grid most common in?

A

Portable x ray or CR plates

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7
Q

What is off focus grid cut off?

A

Using the wrong SID for the grid

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8
Q

What is the result on the image from an upside down focused grid error?

A

-Dark band of central exposure
-Severe cut off (whiteness) on the edges

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9
Q

What is the result on the image from lateral descentering without tilt?

A

-Uniform loss of primary beam across the image resulting ina uniformly light radiograph

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10
Q

What is the hardest grid cut off error to detect?

A

Lateral decentering without tilt

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11
Q

What does OD stand for in regards to grid cut off?

A

Optical density

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12
Q

What is optical density?

A

Amount of darkness in the image

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13
Q

What is the result on the image from lateral decentering with tilt?

A

-All incident rays will be angled across entire image, resulting in lower optical density

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14
Q

What will be the result on the image for an off focus grid cut off error?

A

-Fairly even exposure with lack of OD
-Cut off more towards the edges of the image

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15
Q

What is the result on the image for an off centered and off focused grid error?

A

-An uneven exposure with a gradient of dark to light

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16
Q

What is the objective of grid alignment testing?

A

To test the alignment of the radiographic grid in the bucky mechanism with respect to the central ray of the x ray tube

17
Q

What equipment is needed for a grid alignment test?

A

-Grid alignment test tool
-Lead strips
-Densitometer

18
Q

What tool is this?

A

A grid alignment test tool

19
Q

If the grid is aligned correctly, how should the holes in the test tool appear?

A

Center hole will have the highest OD, The OD should fall off symmetrically on either side of the center hole.

20
Q

Based on the results from the grid alignment test, is the grid misaligned towards the window or the door of Room 2?

A

Grid misaaligned twards the window in room 2

21
Q

According to SC35, what is the frequency of grid alignment testing?

A

Annually

22
Q

What are the 3 factors that may cause beam-grid misalignment in a moving grid?

A
  1. Improper centering of the x-ray beam to the bucky.
  2. Misalignment of the grid within the bucky mechanism.
  3. Malfunction in the reciprocating action of the grid - delay between initiation of grid motion and beginning of x-ray exposure may be out of sync.
23
Q

Define the following term

Grid lattitude

A

The margin of error in centering the x ray beam to the center of the grid before significant grid cut off appears in the resulting image

24
Q

What is the beam grid alignment specified by the manufacturer?

A

+or- 1 inch

25
Q

Where is the grid lattitude measurement listed?

A

Either on the front of the grid or with the literature supplied by the manufacturer

26
Q

What would the histogram for this mammography image look like?

A

-2 spikes for the the super white and black areas

27
Q

What would the histogram for this mammography image look like?

A

No major spikes

28
Q

What is the purpose of timer accuracy testing?

A

To ensure accurate exposure time

29
Q

What materials are needed for a timer accuracy test?

A

Digital exposure timer

30
Q

According to S.C. 35, the actual time of exposure should be within how many seconds of the time selected by the operator.

A

Plus or minus 10% + 1ms

31
Q

According to the HARP Act, the actual time of exposure should be within how many seconds of the time selected by the operator?

A

10%

32
Q

As per S.C. 35, the irradiation time meter accuracy test should be performed how often to ensure that it is working within limits?

A

Annually

Imaging Applications and Quality (16 decks)

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