UNIT 3: Equipment Design

Question 1

Primary/ useful beam

Answer 1

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

Question 2

Scattered radiation

Answer 2

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

Question 3

Off focus radiation

Answer 3

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

Question 4

PBL

Answer 4

(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

Question 5

Filtration

Answer 5

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

Question 6

Total filtration

Answer 6

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

Question 7

HVL

Answer 7

(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

Question 8

Exposure Reproducibility

Answer 8

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.

Question 9

Exposure Linearity

Answer 9

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%

Question 10

HLC

Answer 10

(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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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.

Question 14

Identify the optimal characteristics of the radiographic exam table

Answer 14

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.

Question 15

What is the recommended relationship between collimation and the IR?

Answer 15

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

Question 16

Describe the optimal construction characteristics of the collimation system

Answer 16

*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

Question 17

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

Answer 17

At least 15 cm(6 inches) below the collimator

Question 18

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

Answer 18

at least 30 cm (12 inches)

Question 19

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

Answer 19

-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

Question 20

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

Answer 20

The beam would be out of Alignment

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What is the purpose of filtration?

Answer 23

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

Question 24

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

Answer 24

Increases quality or mean energy of beam

Question 25

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

Answer 25

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

Question 26

Inherent filtration includes:

Answer 26

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

Question 27

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

Answer 27

1.5 millimeters of filtration

Question 28

Added filtration includes:

Answer 28

Sheets of aluminum

Question 29

regulatory standard for total filtration

Answer 29

Question 30

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

Answer 30

-Aluminum * Lightweight * Sturdy * Relatively inexpensive * Readily available

Question 31

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

Answer 31

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.

Question 32

What is the purpose of using compensating filters?

Answer 32

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

Question 33

What material are compensating filters made from?

Answer 33

*Aluminum *Lead-acrylic *Other suitable materials

Question 34

example of a compensating filter

Answer 34

wedge filter, trough or bilateral wedge filter

Question 35

Describe the design of a radiographic grid and its function

Answer 35

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

Question 36

When should a grid be employed?

Answer 36

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

Question 37

Explain how a grid affects patient dose

Answer 37

Increase patient dose

Question 38

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

Answer 38

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

Question 39

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

Answer 39

image contrast and overall brightness may be manipulated after image acquisition

Question 40

Dose creep

Answer 40

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

Question 41

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

Answer 41

Dose creep goes against ALARA

Question 42

Advantages of DR

Answer 42

* Lower dose * Ease of use * Immediate imaging results * Manipulation of the image

Question 43

Advantages of CR

Answer 43

* 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

Question 44

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

Answer 44

Allows the operator to remain outside the fluoroscopic room

Question 45

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

Answer 45

Brightness is increased during minification of the image

Question 46

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

Answer 46

magnification increase patient dose

Question 47

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

Answer 47

No change in patient exposure

Question 48

How does collimation during fluoroscopic procedures reduce patient dose?

Answer 48

decrease the volume of irradiated tissue

Question 49

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

Answer 49

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

Question 50

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

Answer 50

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

Question 51

Describe the characteristics of the cumulative fluoroscopic timer.

Answer 51

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.

Question 52

proper SSD for the different fluoroscopic units

Answer 52

Question 53

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

Answer 53

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

Question 54

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

Answer 54

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

Question 55

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):

Answer 55

Question 56

What are the requirements of the fluoroscopic primary protective barrier?

Answer 56

-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

Question 57

Identify the requirements & rationale for the fluoroscopic control switch

Answer 57

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

Question 58

What is the risk of using c-arm fluoroscopy?

Answer 58

relatively large patient radiation dose

Question 59

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

Answer 59

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

Question 60

Identify the requirements for using a mobile c-arm

Answer 60

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

Question 61

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

Answer 61

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

Question 62

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

Answer 62

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

Question 63

How can radiation protection be maximized when using HLCF?

Answer 63

Using pulsed mode and frequent last image hold

Question 64

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

Answer 64

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

Question 65

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

Answer 65

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

Question 66

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

Answer 66

* A diagram * Annotated photograph * Narrative description

Question 67

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

Answer 67

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