Radiation Protection CHapter 11

Question 1

Box shaped and contains the radiographic beam defining system. this system consist of 2 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 and a mirror to deflect the light beam toward the patient to be radiographed

Answer 1

light-localizing variable aperture rectangular collimator

Question 2

Upper shutters–mounted as close as possible to the tube window to reduce the amount of off-focus radiation (x-rays emitted from parts of the tube other than the focal spot) coming from the primary beam and exiting at various angles from the x-ray tube window

Answer 2

first set shutters

Question 3

Lower Shutters– mounted below the level of the light source and mirror and function to confine further the radiographic beam to the area of clinical interest

Answer 3

second set shutters

Question 4

What does the second set of shutters consist of?

Answer 4

two pairs of lead plates oriented at right angles to each other

Question 5

Refers to the brightness of a surface– specifically it quantifies the intensity of a light source-must be adequate to permit the localizing light beam to outline the margins of the radiographic beam adequately on the patients anatomy

Answer 5

luminance

Question 6

consist of electronic sensors in a cassette holder that sends signals to the collimator housing

Answer 6

positive beam limitation (PBL)

Question 7

simplest of all limitation devices- consist of a flat piece of lead with a hold of designated size and shape cut in the center (can be rectangular, square, or round)

Answer 7

aperture diaphragm

Question 8

To reduce exposure to the patients skin and superficial tissue by absorbing most of the lower energy photons

Answer 8

filtration

Question 9

Includes the glass envelope encasing the x-ray tube, the insulating oil surrounding the tube, and the glass window in the tube housing

Answer 9

inherent filtration

Question 10

What is the aluminum equivalent for inherent filtration?

Answer 10

0.5 mm

Question 11

Consists of sheets of aluminum (or equivalent) of appropriate thickness

Answer 11

added filtration

Question 12

where is added filtration located?

Answer 12

outside the glass window of the tube housing above the collimator shutters

Question 13

the combination of inherent and added filtration (these combine to equal required amount necessary to filter useful beam adequately)

Answer 13

total filtration

Question 14

Total Filtration regulatory standards

Answer 14

2.5 mm aluminum equivalent for fixed x-ray units operating above 70 kVp

Question 15

when the thickness of a designated absorber (such as aluminum) is required to decrease the intensity of the primary beam by 50% of its initial value (laws regulate that so much of the low energy rays must be removed)

Answer 15

half-value layer

Question 16

due to the fact that computerized images can be manipulated after exposure and repeat images are rare, patients receive higher radiation doses than necessary to produce the initial images

Answer 16

dose-creep

Question 17

process that allows the fluoroscopist to see the most recent image without exposing the patient to another pulse of radiation

Answer 17

last-image hold

Question 18

resettable device that times the x-ray beams “on time” and sounds an audible alarm or temporarily interrupts the exposure after the fluoroscope has been activated for 5 minutes

Answer 18

cumulative timer

Question 19

The x-ray tube housing that encloses the x-ray tube must be constructed so that leakage radiation does not reach the patient. At what distance is this measured from the x-ray source and at what dose?

Answer 19

1m (3.3 ft) does not exceed 100 mR/hr when the tube is operated at its highest voltage at the highest current that allows continuous radiation

Question 20

why the x-ray tabletop must be as radiolucent as possible?

Answer 20

so that it will absorb only minimal amounts of radiation, thereby reducing the patients radiation dose (because of lower techniques)

Question 21

know the material that the radiographic table is commonly made of

Answer 21

a carbon fiber material

Question 22

what is the most common x-ray beam limitation device

Answer 22

light-localizing variable aperture rectangular collimator

Question 23

know the types of x-ray beam limitation devices

Answer 23

light localizing variable aperture rectangular collimator, aperture diaphragm, cones, cylinders

Question 24

know what these devices join to do

Answer 24

confine the useful, or primary beam. before it enters the area of clinical interest, thereby limiting the quantity of body tissue radiated

Question 25

why does the luminance of the collimator light have to be adequate?

Answer 25

to permit the localizing light beam to outline the margins of the radiographic beam adequately on the patients anatomy

Question 26

know what happens to the collimator when PBL is activated?

Answer 26

the collimators are automatically adjusted so that the radiation field matches the size of the IR

Question 27

know how the radiographer ensures that the collimation is adequate

Answer 27

by collimating the radiographic beam so that it is no larger than the IR

Question 28

what dimensions of the hole in the aperture diaphragm determine

Answer 28

the size and shape of the radiographic beam

Question 29

know some examples of radiographic exams that would use cones

Answer 29

head projections, sella turcica, paranasal sinuses, vertebral column, and chest

Question 30

know how filtration decreases the overall intensity of radiation

Answer 30

effectively removes low-energy (soft) x-rays from a polyenergetic x-ray beam without severely decreasing the xray beam intensity

Question 31

how much filtration the light localizing variable aperture rectangular collimator adds

Answer 31

1.5 mm aluminum equivalent

Question 32

what is the most commonly used metal for filters in diagnostic radiology

Answer 32

aluminum (z-13)

Question 33

why is this metal used

Answer 33

*(light weight, sturdy, relatively in expensive, and is readily available)*

Question 34

what is the source skin distance in general radiology

Answer 34

12"

Question 35

what does DR mostly eliminate the need for

Answer 35

repeats due to improper technique

Question 36

even with digital radiography, what is still your responsibility as a radiographer

Answer 36

to determine and use technical factors the first time you expose

Question 37

know the 3 benefits of image intensification fluoroscopy

Answer 37

1. increased image brightness 2. saving the radiologist time 3. patient dose reduction

Question 38

what is the significant impact that pulsed or intermittent fluoroscopy has made

Answer 38

significantly decreases patient dose, especially in long procedures and helps extend the life of the tube

Question 39

what is the required and preferred SSD for fluoroscopy

Answer 39

``` required= minimum 12" preferred= 15" ```

Question 40

know the function of a filter in fluoroscopy

Answer 40

reduce patient dose

Question 41

in fluoroscopy what is the total aluminum equivalent filtration that must be permanently installed?

Answer 41

2.5 mm

Question 42

what are the maximum current federal standards that limit entrance skin exposure rates of general purpose intensified fluoroscopic units

Answer 42

10 roentgens/per minute

Question 43

what is the primary protective layer required for an image intensifier

Answer 43

2mm lead equivalent

Question 44

know how to reduce patient entrance dose for c-arm procedures

Answer 44

the patient to image intensifier distance should be as short as possible

Question 45

know whos responsibility it is to monitor and document fluoroscopic procedure times

Answer 45

radiographer