Chapter 15 Notes

Question 1

principal factors that affect amount of scatter produced are

Answer 1

kilovoltage and the irradiated material

Question 2

as kilovoltage increases

Answer 2

scatter increases

Question 3

as volume of irradiated tissue increases

Answer 3

scatter increases

Question 4

volume will increase as

Answer 4

the field size increases or as the patient thickness increases

Question 5

higher Z# materials have

Answer 5

more electrons and a greater chance of absorbing photons

Question 6

what is the most commonly employed beam restrictor in radiography

Answer 6

the collimator

Question 7

the collimator permits

Answer 7

an infinite number of field sizes

Question 8

the exposure field should never

Answer 8

exceed the size of the image receptor

Question 9

kVp affects

Answer 9

the penetrability of beam

Question 10

increasing kVp will

Answer 10

decrease photoelectric absorption, increase Compton scatter, and decrease dose

Question 11

decreasing kVp will

Answer 11

increase photoelectric absorption, decrease Compton scatter, and increase dose

Question 12

decreasing field size without mAs compensation can

Answer 12

increase image noise

Question 13

thicker and denser body parts will

Answer 13

produce more scatter

Question 14

the collimator’s bottom shutters will

Answer 14

reduce penumbra

Question 15

define pneumbra

Answer 15

geometric unsharpness around periphery of image (also known as edge sharpness)

Question 16

off-focus radiation occurs from

Answer 16

areas of x-ray tube other than focal spot area

Question 17

the collimator’s upper shutters will

Answer 17

reduce off-focus radiation reaching IR

Question 18

the light field needs to be accurate within what percent of SID

Answer 18

+-2%

Question 19

the mirror used in the light field will

Answer 19

add to system’s inherent filtration

Question 20

positive beam limitation (PBL) devices

Answer 20

automatically collimates beam to size of image receptor

Question 21

examples of ancillary devices

Answer 21

lead blockers and lead masks

Question 22

higher Z# will cause

Answer 22

greater number of photoelectric absorption interactions and less scatter

Question 23

scatter is produced by what interaction

Answer 23

Compton interactions

Question 24

Compton interactions occur in

Answer 24

the outer shell

Question 25

reducing penumbra will

Answer 25

improve sharpness of recorded image

Question 26

describe the light field set up

Answer 26

a mirror is mounted in the path of the x-ray beam at a 45 degree angle; light source is placed opposite of the mirror

Question 27

aperture diaphragm

Answer 27

a flat sheet of metal with an opening cut in the center and attached to x-ray tube port

Question 28

aperture diaphragm is usually made of

Answer 28

lead

Question 29

cones and cylinders

Answer 29

essentially circular aperture diaphragms withe metal extensions

Question 30

the cone has an extension that

Answer 30

flares or diverges (upper diameter is smaller than bottom)

Question 31

ancillary devices are designed to

Answer 31

restrict the beam to a specific shape for a particular examination

Question 32

lead blocker

Answer 32

a sheet of impregnated rubber that can be cut to any size or shape

Question 33

lead blocker can be placed where

Answer 33

behind patient during LAT L-Spine; above shoulder during AP

Question 34

lead blockers are most helpful when

Answer 34

examining large patients

Question 35

lead mask

Answer 35

usually cut to correspond to particular field size and is secured to end of collimator