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SPRING 2024: RADIATION PROTECTION Class Notes Flashcards > UNIT 3: Equipment Design > Flashcards

UNIT 3: Equipment Design Flashcards

1
Q

Primary/ useful beam

A

those x-rays emitted through the x-ray port, or tube window

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2
Q

Scattered radiation

A

all the non-useful-image-forming radiation that arises from the interaction of an x-ray beam with the atoms of a patient or any other object in the path of the beam

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3
Q

Off focus radiation

A

X-rays emitted from parts of the x-ray tube other than the focal spot. Also called stem radiation

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4
Q

PBL

A

(Positive beam limitation) A feature of radiographic collimators that automatically adjusts them so that the radiation field size matches the size of the image receptor. Also known as automatic collimation

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5
Q

Filtration

A

Elements that are part of or added to the x-ray tube to reduce exposure to the patient’s skin and superficial tissue by absorbing most of the lower energy photons from the produced heterogeneous beam and thereby increasing the mean energy, or quality, of the x-ray beam

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6
Q

Total filtration

A

inherent filtration and added filtration jointly combine to equal the required amount necessary to filter the useful beam adequately (2.5 mm AI/Eq)

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7
Q

HVL

A

(Half-value layer) The thickness of a designated absorber (customarily a metal such as aluminum) required to decrease the intensity of the primary x-ray beam by 50% of its initial value

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8
Q

Exposure Reproducibility

A

Consistency in output in radiation intensity for identical generator settings from one individual exposure to subsequent exposures. This means that the x-ray unit must have the ability to duplicate certain radiographic exposures for any given combination of peak kilovolts (kVp), milliamperes (mA), and time. A variance of 5% or less is acceptable.

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9
Q

Exposure Linearity

A

Consistency in output radiation intensity at any selected kVp when x-ray generator settings are changed from one milliamperage and time combination to another. Mathematically, it is the ratio of the difference in mR/mAs values between two successive x-ray unit generator stations to the sum of those mR/mAs values. It must be less than 0.1. When changing from one mA station to a neighboring mA station, the most that linearity can vary is 10%

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10
Q

HLC

A

(High Level Control) An operating mode for state-of-the-art fluoroscopic equipment in which patient entrance exposure rates are substantially higher than normally allowed for routine procedures. The higher exposure rate allows visualization of smaller and lower contrast objects that do not usually appear during standard fluoroscopy. HLCF is also known as “boost” mode

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11
Q

How is the protective tube housing constructed to protect the patient and radiographer?

A

The housing enclosing the x-ray tube must be constructed with lead lining to reduce radiation leakage through any portion of the housing away from the useful beam

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12
Q

What is the maximum allowable leakage from the x-ray tube? (inc. distance)

A

.88 mGy/hour at 1 meter from the source (when operated at highest tube voltage and current)

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13
Q

What radiation protection requirements are related to the console/ control panel?

A

For the radiation safety of the radiographer, it must be located behind a properly shielded barrier that also has a radiation-absorbent window, Fully display the conditions of exposure and provide a positive indication when the x-ray tube is energized, exposure hand control be mechanically affixed to the console such that it cannot be activated while the operator is in an unshielded location.

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14
Q

Identify the optimal characteristics of the radiographic exam table

A

support patients whose weight can be up to 400 pounds, a free-moving tabletop that allows easy movement of the patient during an imaging procedure, thickness of the tabletop must be uniform, for under-table x-ray tubes as used in fluoroscopy, the patient support surface should be as radiolucent as possible, Carbon fiber commonly used.

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15
Q

What is the recommended relationship between collimation and the IR?

A

Tape measure or laser Distance must be accurate within 2% of SID, Light localizer to be within 2% of SID, Centering indicator must be accurate to within 1% of SID. The primary x-ray beam shall be adequately collimated so that it is no larger than the size of the image receptor being used for the examination

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16
Q

Describe the optimal construction characteristics of the collimation system

A

*Two sets of adjustable lead shutters mounted within the device at different levels
*A light source to illuminate the x-ray field and permit it to be centered over the area of clinical interest
*A mirror to deflect the light beam toward the patient to be imaged

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17
Q

How far should the patient’s skin be from the collimator for fixed radiographic equipment?

A

At least 15 cm(6 inches) below the collimator

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18
Q

How far should the patient’s skin be from the collimator for portable or mobile radiographic equipment?

A

at least 30 cm (12 inches)

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19
Q

What is the purpose of the light in the x-ray tube housing? What is the relationship between the light and the primary beam?

A

-to outline the desired margins of the radiographic beam adequately on the patient’s anatomy
-Good coincidence (i.e. very similar physical size and overlapping alignment) between the x-ray beam and the localizing light beam is essential to eliminate collimator cutoff of the body structures that need to be imaged

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20
Q

How would a variance greater than 2% between the beam/ light source affect radiation protection?

A

The beam would be out of Alignment

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21
Q

What would happen if the PBL and IR agreements were not in sync?

A

The positive beam limitation (PBL) is to restrict the size and shape of the x-ray beam so it does not exceed the size of the selected image receptor, if they’re not in sync areas of the patient outside the image receptor would be irritated

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22
Q

What is the relationship between cones, flared metal tubes and straight cylinder?

A

Cones are circular metal tubes that attach to the x-ray tube housing or variable rectangular collimator to limit the x-ray beam to a predetermined size and shape. Cones can be Flared metal tubes or Straight cylinders

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23
Q

What is the purpose of filtration?

A

Reduces exposure to patient’s skin and superficial tissues by absorbing low energy photons (long-wavelength or soft x-rays)

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24
Q

How does filtration impact the characteristics of the primary x-ray beam?

A

Increases quality or mean energy of beam

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25
Q

Describe how filtration reduces absorbed dose (D) to the patient.

A

the absorbed dose to the patient decreases because very low-energy photons would increase the patient’s radiation dose if it weren’t for filtration

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26
Q

Inherent filtration includes:

A

Glass envelope encasing x-ray tube
Insulating oil surrounding x-ray tube
Glass window in tube housing

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27
Q

What is the minimum amount of filtration applied to the x-ray beam as it exits the tube?

A

1.5 millimeters of filtration

28
Q

Added filtration includes:

A

Sheets of aluminum

29
Q

regulatory standard for total filtration

A
30
Q

Identify & describe the characteristics of the most commonly used filtration material.

A

-Aluminum

  • Lightweight
  • Sturdy
  • Relatively inexpensive
  • Readily available
31
Q

What is the relationship between the Radiation Control for Health & Safety Act of 1968, HVL and kVp?

A

In compliance with the Radiation Control for Health and Safety Act of 1968, a diagnostic x-ray beam must always be adequately filtered. This means that a sufficient quantity of low-energy photons has been removed from a beam produced at a given kVp. The half-value layer (HVL) of the beam must be measured to verify this.

32
Q

What is the purpose of using compensating filters?

A

Dose reduction from less exposure and uniform radiographic imaging of body parts that vary considerably in thickness or tissue composition

33
Q

What material are compensating filters made from?

A

*Aluminum
*Lead-acrylic
*Other suitable materials

34
Q

example of a compensating filter

A

wedge filter, trough or bilateral wedge filter

35
Q

Describe the design of a radiographic grid and its function

A

Parallel radiopaque strips separated by low-attenuation strips of:
* Aluminum
* Plastic fiber
* Wood

36
Q

When should a grid be employed?

A

When the thickness of the body part is 10 cm (about 4 inches) or greater

37
Q

Explain how a grid affects patient dose

A

Increase patient dose

38
Q

What is the minimum SSD that should be used with mobile radiography and why?

A

At least 30 cm (12 inches), limits the effects of inverse square falloff of radiation intensity with distance

39
Q

How does the use of a DR system help to reduce repeat rates?

A

image contrast and overall brightness may be manipulated after image acquisition

40
Q

Dose creep

A

Routine practice of overexposing patient to avoid possible repeats, occurs due to the lack of negative impact observed when the patient’s anatomy is overexposed but the display still exhibits quality images

41
Q

How does “dose creep” relate to the ALARA principle?

A

Dose creep goes against ALARA

42
Q

Advantages of DR

A
  • Lower dose
  • Ease of use
  • Immediate imaging results
  • Manipulation of the image
43
Q

Advantages of CR

A
  • Compatible with a wide range of preinstalled traditional systems
  • Multiple cassette sizes allow for greater flexibility
    *The CR PSP imaging plates are subject to mechanical damage and also to chemical oxidation but can be replaced without great expense
  • CR allow user to change the grid to accommodate the imaging task
44
Q

What is the benefit of utilizing a fluoroscopic system as a “remote control facility”?

A

Allows the operator to remain outside the fluoroscopic room

45
Q

Explain how brightness is affected and compensated for during fluoroscopic procedures when different fields of view are applied

A

Brightness is increased during minification of the image

46
Q

How does utilizing the different fields of view during a fluoroscopic procedure impact patient dose?

A

magnification increase patient dose

47
Q

How might implementing the “digital zoom” affect patient dose?

A

No change in patient exposure

48
Q

How does collimation during fluoroscopic procedures reduce patient dose?

A

decrease the volume of irradiated tissue

49
Q

What is the “last image hold” feature, and how does it benefit the patient?

A

allows the fluoroscopist to momentarily halt the radiation and review the most recent image before giving the patient another pulse of radiation

50
Q

Describe the filtration requirements for fluoroscopic units and identify the acceptable HVL of these machines.

A

-A minimum of 2.5 mm total aluminum
-HVL: 3 to 4.5 mm aluminum

51
Q

Describe the characteristics of the cumulative fluoroscopic timer.

A

This resettable device measures the collective x-ray beam-on time and sounds an audible alarm or, in some cases, temporarily interrupts the radiation until it is reset after the fluoroscope has been activated for 5 minutes. It also serves to alert the fluoroscopist to the amount of time the patient has been receiving x-ray exposure.

52
Q

proper SSD for the different fluoroscopic units

A
53
Q

Where should the input phosphor of the II be placed in relation to the patient to reduce entrance skin exposure rate?

A

as close as practically possible to the pt to reduce entrance exposure

54
Q

What is the cumulative time (in fluoroscopy) and how does is support radiation protection?

A

Sound alarms that interrupts the exposure after 5 minutes. This allows for fluoroscope to be active for shorter periods

55
Q

What is the maximum ESE rate for the following fluoro units at the table top when the Image Intensifier is 30 cm (12” above the table top):

A
56
Q

What are the requirements of the fluoroscopic primary protective barrier?

A

-2 mm lead equivalent
-The assembly must be physically joined with the x-ray tube and interlocked so that the fluoroscopic x-ray tube cannot be activated when the II or other detection system is in a parked, unaligned, and unconnected position

57
Q

Identify the requirements & rationale for the fluoroscopic control switch

A

dead-man switch, this ensures the exposure is terminated if the person operating the switch becomes incapacitated

58
Q

What is the risk of using c-arm fluoroscopy?

A

relatively large patient radiation dose

59
Q

What should be employed to reduce occupational exposure during c-arm fluoroscopic procedures?

A

Must have appropriate education and training and wearing of wrap-around lead aprons and thyroid shields

60
Q

Identify the requirements for using a mobile c-arm

A

minimal source-to-end of collimator assembly distance of 30 cm (12 inches)

61
Q

How should the mobile c-arm be placed in relation to the patient and why?

A

With the x-ray tube under the patient so scatter radiation is less intense

62
Q

When would a radiographer encounter HLCF? Explain the purpose of this tool.

A

interventional procedures in which visualization of fine catheters or other not easily seen structures is crucial

63
Q

How can radiation protection be maximized when using HLCF?

A

Using pulsed mode and frequent last image hold

64
Q

What recommendation has the FDA made in regard to HLCF use in interventional procedures?

A

manual continuous positive pressure on a special high-level foot pedal, accompanied by a steady audible signal to remind personnel that the high-level fluoroscopic mode was in use

65
Q

What is the maximum fluoroscopic exposure rate (inc. the distance) for:
● continuous fluoroscopy?
● pulsed mode fluoroscopy?

A

-20 R/min (176 mGya/min entrance dose rate)
-Much higher

66
Q

Identify the elements that should be included in the documentation of fluoroscopic procedures?

A
  • A diagram
  • Annotated photograph
  • Narrative description
67
Q

Identify the roles/ responsibilities of the radiographer during interventional procedures as it pertains to radiation protection

A

call attention if the physician loses track of how long a procedure is taking

SPRING 2024: RADIATION PROTECTION Class Notes Flashcards (13 decks)

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