Radiographic Imaging Chapter 4

Front 1

Advantages of Digital IR

Back 1

brightness, density and contrast can be manipulated after image acquisition

Still, exposure should be carefully made so as to minimze patient radiation exposure

Front 2

Quantity of X-Rays Produced is Directly Proportional to

Back 2

mAs

mA x time

Front 3

Effect of different Generators

Back 3

more mAs required for single phase generators

single phase > 3-phase > high frequency

Front 4

Consequence of Inadquate mAs on Digital Image

Back 4

increased quantum noise

Front 5

Exposure Indicator

Back 5

indicates the level of x-ray exposure received to the digital IR (incident exposure)

displayed on the processed image

Front 6

Density on Film Images is Controlled by

Back 6

mAs

Front 7

Density Errors Should be Corrected by Adjusting the mAs by a factor of

Back 7

2

Front 8

Visible Changes in Film Density Can be Achieved with a Minimal mAs adjustment of

Back 8

30%

Front 9

kVp Effects on Digital Image

Back 9

increased kVp increases density

not a linear change - greater effect with high kVp

Front 10

15% Rule

Back 10

increase in kVp of 15% causes decrease in mAs of 50%

decrease in kVp of 15% causes increase in mAs of 100%

Front 11

Advantage of Higher kVp and Lower mAs

Back 11

less radiation to the patient

Front 12

kVp Effect on Density

Back 12

higher kVp results in lower contrast

also causes more scatter

Front 13

Should Radiographs be Repeated Because of Contrast Errors

Back 13

usually no

Front 14

What determines Focal Spot Size?

Back 14

filament size

Front 15

A small Focal Spot Results in

Back 15

improved recorded detail

more heat at the anode

Front 16

SID

Back 16

source to image distance

Front 17

Inverse Square Law

Back 17

(I1)(D1)^2 = (I2)(D2)^2

Front 18

mAs-Distance Compensation Formula

Back 18

mAs1 (SID)^2
____ = _____
mAs2 (SID)^2

Front 19

Standard Distances (SIDs)

Back 19

40, 48, 72 inches

quick rule:
72" to 56" = 0.5 mAs
40" to 56" = 2.0 mAs

Front 20

SID Effect on Size, Distortion, Recorded Detail

Back 20

as SID increases, distortion decreases

Front 21

SID for CXRs is usually

Back 21

72"

Front 22

OID

Back 22

object to image receptor distance

Front 23

Air Gap

Back 23

decreases scatter, increases contrast, increases distortion

OID should be as minimal as possible

Front 24

Magnification Formula

Back 24

MF = SID / SOD

MF of 1 equals no magnification

Front 25

SOD

Back 25

source to object distance

SOD = SID - OID

Front 26

Object Size Formula

Back 26

object size = image size / MF

Front 27

Effect of Magnification

Back 27

decreased recorded detail or spatial resolution

Front 28

Inaccurate Central Ray Alignment

Back 28

causes shape distortion

can also affect amount of mAs required

Front 29

Grid Factor Formula

Back 29

mAs1 GCF1
____ = ____
mAs2 GCF2

Front 30

What are the Grid Effects?

Back 30

improves image quality

increases needed mAs

Front 31

What are the effects of Collimation?

Back 31

decreases amount of radiated tissue

decreases scatter

increases contrast

increases needed mAs

Front 32

Effects of Collimation are Greatest When

Back 32

imaging large anatomic areas

using no grid

using high kVp

Front 33

Tube Filtration

Back 33

should have no effect on image

Front 34

Body Habitus

Back 34

form or build of patient's body

Front 35

Types of Body Habitus

Back 35

1) sthenic - normal build (50%)

2) hyposthenic - slender build (35%)

3) hypersthenic - large build (5%)

4) asthenic - very slender (10%)

Front 36

Effect of Part Thickness

Back 36

thick parts reuire more radiation

4 - 5 cm of additional thickness = increase by factor of 2

Front 37

What exposure changes are needed in pediatric patients?

Back 37

require faster exposures

bone density at adult levels by age 6

before age 6 decrease kVp by 15%

Front 38

What exposure changes are needed for Oblique Positions?

Back 38

requires more exposure because of increased amount of tissue

Front 39

What exposure changes are needed for Fiberglass Casts?

Back 39

usually require no additional exposure

Front 40

What exposure changes are needed for Plaster Casts?

Back 40

usually require additional exposure

Front 41

What exposure changes are needed for Splints?

Back 41

only require additional exposure if in path of primary beam

Front 42

What exposure changes are needed for Pathologic Conditions?

Back 42

additive conditions - require more exposure

destructive diseases - require less exposure

Front 43

What exposure changes are needed for Soft Tissue Images?

Back 43

Reduced mAs

Front 44

What are the image effects of Contrast Media?

Back 44

changes the absorption characteristics

effective method of increasing contrast in low-contrast areas

Front 45

Fill out the Grid Factor chart:

Back 45

Front 46

What is Positive Contrast Media?

Back 46

have a high atomic number and attenuate beam

Ex: barium, iodine

usually require increased exposure

Front 47

What is Negative Contrast Media?

Back 47

decrease attenuation

Ex: air

does not require a change in exposure

Front 48

Which of the following is accurate regarding the relationship between mA and exposure time to maintain the exposure to the image receptor?

A) Direct proportional

B) Direct

C) Inverse

D) Inverse proportional

Back 48

D

Front 49

A radiographic film image has excessive density. Which of the following is best in order to correct the exposure error?

A) Decrease kVp by 50%

B) Increase mAs by 15%

C) Decrease mAs by 50%

D) Decrease mAs by 15%

Back 49

C

Front 50

What exposure factor affects both the quality and quantity of the x-ray beam?

A) kVp

B) SID

C) mA

D) Focal spot size

Back 50

A

Front 51

Which of the following is NOT affected by kilovolage?

A) Compton interactions

B) Spatial resolution

C) Film density

D) Radiation quantity

Back 51

B

Front 52

How is the quality of the digital image affected when more than needed radiation exposure reaches the digital image receptor?

A) No effect

B) Decreased brightness

C) Increased brightness

D) Higher contrast

Back 52

A

Front 53

Which of the following would maintain radiation exposure to the image receptor when the kilovoltage is decreased by 15%?

A) Increase mAs by 15%

B) increase mAs by 50%

C) Double mAs

D) Halve the mAs

Back 53

C

Front 54

A quality image is produced using 70 kVp and 2.5 mAs at a 40" SID. What calculated change in exposure thechnique is necessary to maintain radiation exposure to the IR when the SID is increaset to 56"?

Back 54

70 kVp @ 50 mAs

Front 55

Without exposure technique compensation, increasing the OED by 4 inches for a knee image would: (Select all that are correct)

A) increase magnification

B) decrease density

C) increase contrast

D) decrease contrast

Back 55

A, B, & C

Front 56

A quality image is produced using 80 kVp @ 10 mAs with a 6:1 ratio grid. Calculate the change in exposure technique to maintain radiation exposure to the IR when changing to a 12:1 grid.

Back 56

80 kVp @ 17 mAs

Front 57

Which of the following factors does not affect the exposure of the IR?

A) Collimation

B) Focal spot size

C) Compensating filters

D) Body habitus

Back 57

B

Front 58

What exposure factor change is recommended to maintain radiation exposure to the IR when increasing patient thickness by 5 cm?

A) Double kVp

B) Double mAs

C) Increase kVp by 15%

D) Increase mAs by 15%

Back 58

B

Front 59

Installing a negative contrast agent in the GI tract has what effect in the area of interest on the image?

A) Increased brightness

B) Decreased contrast

C) Decreased brightness

D) No effect

Back 59

C