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SPRING 2024: Principles II > UNIT 1: Technical Conversions and Exposure Systems > Flashcards

UNIT 1: Technical Conversions and Exposure Systems Flashcards

1
Q

What is the purpose of exposure systems?

A

Provides a consistent method of image production
• Holds most variable constant while changing only one
• Provides consistent subject contrast and exposure from study to study
• Allows radiologists to see patterns in pathology easier
• Provides lower patient doses by reducing repeats

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2
Q

What is Anatomically Programmed Radiography (APR)?

A

Preprogrammed technique based on anatomical region (body part)

-A type of technique chart in which the user selects a body part and projection from a menu on the console, and the kVp and mAs are automatically present for the exposure

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3
Q

What is the device used to measure patient thickness?

A

Caliper

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4
Q

What are the 4 types of technique charts?

A
  • Fixed kVp
  • Variable kVp
  • Pediatric
  • High kVp
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5
Q

When are high kVp charts used?

A

For chest images and Barium studies

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6
Q

What is included in a technique chart?

A

-AEC cells to activate
-kVp
-mAs
-Grid use
-Patient size
-FSS

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7
Q

What are the characteristics of Variable kVp charts?

A

Variable kVp (Fixed mAs)

• Finer adjustments made per patient thickness
• Shorter scale of contrast
• Increased patient dose
• Increased tube wear

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8
Q

What are the characteristics of a Fixed kVp chart?

A

Fixed kVp (Variable mAs)

• Decreased patient dose
• Longer exposure latitude( means more room for error)
• Longer contrast scale (Optimum kVp)
• More scatter
• Reduced x-ray tube wear
• Decreased time settings - reduce motion

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9
Q

Which type of technique chart uses optimum kVp?

A

Fixed kVp chart

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10
Q

What is optimum kVp?

A

Maximum kVp that will produce images with appropriate subject contrast

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11
Q

What are the benefits of using the optimum kVp?

A
  • Minimizes Skin Dose (ESE)
  • Allows for reduced mAs
  • Facilitates Long Scale Subject Contrast
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12
Q

What is Exposure Latitude? How does this affect Radiographer practices?

A

-The range of technical parameters that produce a diagnostic image
-More room for error

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13
Q

Steps of creating a technique chart

A

1. Measure thickness of phantom using caliper
2. Produce 5-7 test images on phantom
3. Reject analysis
4. Extrapolate technique chart
5. Clinical trials
6. Clinical fine tuning
7. Ongoing fine tuning

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14
Q

Extrapolating Fixed kVp chart

A

mAs doubles and halves for every 5cm

Ex:

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15
Q

Variable kVp technique chart equation to find kVp

A

2 kVp x part thickness + 40cm

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16
Q

Extrapolating Variable kVp chart

A

For every 1cm of patient thickness, kVp increases or decreases 2

EX:

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17
Q

Two classifications of image quality

A

Photographic and Geometric

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18
Q

Photographic quality factors are

A

the factors that can either enhance or degrade the anatomic details visible on the image

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19
Q

What factors affect photographic quality

A

-Contrast
-IR exposure/density

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20
Q

Contrast is

A

the ability to distinguish different shades of gray

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21
Q

Is contrast controlled by kVp in digital or film screen systems?

A

Film screen systems

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22
Q

Long scale and Short scale contrast: High kVp vs Low kVp

A

-High kVp = more uniform penetration of the body = Long Scale Contrast
-Low kVp = more photons absorbed = Short Scale Contrast

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23
Q

How does contrast work in digital systems?

A

The computer uses various mathematical functions to process the data received from the digital IR and then displays that data with the appropriate contrast range for that specific body part

24
Q

Density is

A

the degree of blackening on the radiograph in film screen systems

25
Q

For digital system, the term we use in place of density is

A

IR exposure

26
Q

IR exposure is

A

the amount or intensity of photons that reach the IR

27
Q

IR exposure does or does not directly correspond to the brightness level on the computer monitor

A

does NOT

28
Q

The contrast and brightness can be manipulated by using

A

Post processing functions

29
Q

Window width vs Window level

A

-Window width: a user can define the number of gray shades (gray scale) to be displayed. Changes the displayed CONTRAST (the number of shades of gray displayed) on the viewing monitor
-Window level: the center gray shade of the scale to be displayed. Changes the level of BRIGHTNESS (center shade of gray) displayed on the viewing monitor

30
Q

What are the Geometric Quality Factors?

A

-Detail
-Distortion

31
Q

The controlling factor for detail is

A

focal spot size

32
Q

Penumbra

A

Influencing the spread of photons at the edge of the object’s projected shadow. Image blur, unsharpness.

33
Q

Distortion is

A

the misrepresentation of the size or shape of an object

34
Q

Distortion is controlled by

A

patient positioning

35
Q

Magnification is

A

A distortion of size

36
Q

Shape distortion is due to

A

Part angulation

37
Q

What are the 2 types of part distortion?

A

-Elongation: is a type of shape distortion that occurs from angulation of the central ray, tube and IR are not aligned
-Foreshortening is caused by angulation of the body part, part and IR are not aligned

38
Q

The controlling factor for shape distortion

A

is patient positioning

39
Q

What patient factors affect image quality?

A

-Anatomic part thickness
-Body composition
-Underlying pathology

40
Q

For Anatomic part thickness, with other variables held constant, thicker parts need more

A

-kVp to penetrate the part
-mAs to provide the number of photons needed to transverse the patient and reach the IR

41
Q

For Body Composition: Sthetnic, Hypersthenic, Hyposthenic, Asthenic

A

-Sthenic to Hypersthenic patient tend to have higher ratios of muscle and tend to be thicker in measurement
-Hyposthenic and Asthenic patients tend to be thinner and have less muscle/ fat

42
Q

Photons will be attenuated more in the following order:

A
  1. Bone
  2. Muscle
  3. Fat
  4. Lung / air
43
Q

A pathologic process that increases subject density is called an

A

Additive Condition

44
Q

An additive condition results in

A

radiopacity (the “white” area on a conventional radiograph)

45
Q

Radiopacity vs Radiolucent

A

-Radiopacity: will result in a lighter or white area on the radiography
-Radiolucent: (blacker) compared to surrounding tissues

46
Q

A destructive condition results in

A

radiolucency (shows up black on radiograph)

47
Q

List of the some of the factors that may be found on a technique chart:

A

• kVp
• mA
• Exposure time (s)
• SID
• Grids
• Screens
• Speed class
• Focal-spot size
• Filtration
• Image Receptor
• AEC cells

48
Q

Phantoms are

A

used to develop technique charts before a chart is tested in the clinical (on patients) environment

49
Q

Caliper

A

a measuring device used to measure the thickness of the anatomic area under examination

50
Q

The caliper must be placed at the location of the central ray entrance to the exit point at the thickest or thinnest part?

A

Thickest

51
Q

Steps for establishing a technique chart:

A
  1. Measure thickness of phantom using a caliper
  2. Produce 5-7 test images using phantom body part
  3. Radiologist performs reject analysis
    4.Extrapolate Technique chart using Baseline image selected by Reject analysis
  4. Perform Clinical trials
  5. Perform clinical fine tuning
  6. Perform ongoing fine tuning and maintenance of the chart
52
Q

Two main types of technique charts:

A

Fixed kVp and Variable kVp

53
Q

Variable kVp Charts

A

• Vary kVp by body part thickness, mAs remains constant
• Produces higher contrast images = perceived increase in resolution
• Tends to increase patient dose
• Allows smaller adiustments based on part thickness

54
Q

Fixed kVp Charts

A

-mAs varies
-Optimal kVp= maximum level that produces images with contrast within acceptance levels

Advantages:
• Ensures sufficient penetration of the body part.
• Sufficient penetration permits visualization through the area of interest
• Produces lower contrast and patient dose
• Uses lower mA and time - reducing x-ray tube wear
• Lengthened exposure latitude

55
Q

Automatic Exposure Control (AEC)

A

• Uses ionizing chamber or solid-state detectors to terminate exposure time when a preset intensity has been reached.
• Eliminates the need to set exposure TIME only - mA and kVp must still be set manually.
• Location of ionization chamber is most important - therefore accurate positioning is critical when using AEC.
• A Technique chart using AEC should contain all factors except for time and addition of cell locations.

56
Q

What is dose creep

A

Dose creep is when a radiographer uses higher exposure than what is actually needed so that they can avoid image noise and having to do repeats

57
Q

Fixed kVp vs Variable kVp

A

-Fixed kVp chart: reduces patient dose, has a longer scale contrast, increased latitude, higher overall kVp, longer tube life
-Variable kVp chart: reduces scatter production, has a shorter scale contrast, improved visibility of detail, consistent image quality

SPRING 2024: Principles II (13 decks)

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