13. Radiographic image quality and contrast media

Question 1

what does absorbed radiation create on the image in terms of appearance and brightness

Answer 1

increased brightness and white areas

Question 2

what does transmitted radiation create on the image in terms of appearance and brightness

Answer 2

decreased brightness and black areas

Question 3

what are the 3 factors in terms of anatomy visibility

Answer 3

brightness

contrast

signal to noise ratio

Question 4

what are the 3 factors in terms of how accurately the image represents the anatomy (sharpness)

sharpness/accuracy of structural lines

Answer 4

spatial resolution

sharpness

distortion

Question 5

how is image brightness evaluated

2 things

Answer 5

by the amount of luminance/light emission of the display monitor

the amount of density or overall blackness after processing

Question 6

what is image brightness

Answer 6

amount of luminance/light emission from an image or display

Question 7

what does brightness depend on

2 things

Answer 7

absorption and transmission of x-ray through tissue

Question 8

what is the exposure intensity

Answer 8

amount and energy of x-rays reaching an area of the IR

Question 9

the exposure intensity must be high enough to__ and low enough to __

Answer 9

high enough to overcome quantum noise

low enough to minimise patient dose

Question 10

what causes noise in terms of primary exposure factors

Answer 10

mAs too low = grainy images

Question 11

what is image contrast

Answer 11

differences in brightness/density levels to differentiate between anatomic tissues

Question 12

the range of brightness levels/contrast is a result of what

Answer 12

the tissues differential absorption of the x-ray photons

Question 13

what is subject contrast

what 2 things is it the result of

Answer 13

different densities in the patient

result of absorption characteristics of the anatomic tissue radiographed and the quality of the x-ray beam

Question 14

what is the difference between the gray scale and scale of contrast

Answer 14

gray scale = number of different shades of grey that can be stored and displayed in a digital image

scale of contrast = range of densities visible on film

Question 15

higher contrast results from what

Answer 15

great differences in radiation absorption between tissues that vary greatly in composition

Question 16

what is contrast resolution

Answer 16

ability of IR to distinguish between tissues with similar subject contrast

Question 17

what is spatial resolution

Answer 17

how much system is able to give info about detail by distinguishing between different structures even though the structures might have similar appearance to each other

Question 18

what does spatial resolution refer to

Answer 18

the smallest object that can be detected in a digital image

Question 19

what is sharpness/spatial resolution

Answer 19

accuracy of representing anatomical structural boundaries

Question 20

what 2 things affects the sharpness/spatial resolution of an image

Answer 20

focal spot size

magnification

Question 21

what is distortion

what 2 features of the anatomic part is involved

Answer 21

misrepresentation of either the size or shape of the anatomic part

Question 22

what are the 3 things that can affect distortion

Answer 22

CR alignment or the x-ray tube

CR alignment of the part

CR alignment of IR

Question 23

what are the 2 types of shape distortion that can occur

Answer 23

foreshortening

elongation

Question 24

what is shape distortion

Answer 24

change in the imaged proportions of an object

Question 25

what 3 things is shape distortion affected by

Answer 25

orientation and alignment of object, IR and central ray

Question 26

how is the size and number of pixels in the matrix related to the spatial resolution

Answer 26

larger number of pixels = greater spatial resolution smaller pixel size = capture smaller entities and higher resolution

Question 27

anatomy must be aligned how to avoid shape distortion in terms of the IR and x-ray beam

Answer 27

anatomy must be parallel to the IR plate and perpendicular to the x-ray beam

Question 28

what is size distortion and what does it affect

Answer 28

magnification affects accuracy of representing anatomical structural boundaries

Question 29

what 3 things is size distortion due to

Answer 29

longer OID shorter SID larger focal spot size

Question 30

what should be done to the SID and OID to get rid of sharpness

Answer 30

shorter OID extend/larger SID

Question 31

what is motion unsharpness

Answer 31

decrease in sharpness resulting from voluntary or involuntary patient motion

Question 32

what is scatter

Answer 32

unwanted exposure to the image receptor resulting in fog

Question 33

what is scatter the result of

Answer 33

compton interactions

Question 34

what does scatter and fog do to the image contrast

Answer 34

decreases contrast

Question 35

what do you reduce scatter via the primary exposure factors

Answer 35

decrease kV

Question 36

what is quantum noise what is it dependent on

Answer 36

visible as brightness or density fluctuations and is photon dependent too few x-ray photons results in increased quantum noise

Question 37

what is contrast media

Answer 37

group of chemical agents developed to aid the characterization of pathology by improving the contrast resolution of an imaging modality

Question 38

what are the 3 types of contrast administration

Answer 38

swallowed/orally enemia/rectally intravenously/intra-arterially

Question 39

what is a barium enema what structures does it visualise

Answer 39

into large colon to see ascending, transverse and descending colon

Question 40

what are positive contrast in terms of what it does to the attenuation

Answer 40

increases attenuation

Question 41

what are 2 examples of positive contrast

Answer 41

barium, iodine

Question 42

what may need to be done when using positive contrast

Answer 42

may need to adjust exposure factors

Question 43

what are negative contrast in terms of what it does to the attenuation

Answer 43

decreases attenuation

Question 44

what is an example of negative contrast

Answer 44

air

Question 45

do exposure factors need to be adjusted when using negative contrast

Answer 45

no

Question 46

why can contrast agents be seen on images

Answer 46

due to differences in tissue density (increased x-ray absorption based on higher density)