Exam 3 Ch 21- Medical Image Descriptors

Question 1

Medical image quality-

Answer 1

refers to fidelity with which anatomy under investigation is rendered

Question 2

spatial resolution-

Answer 2

-ability to image small objects that have high subject contrast
-improves with smaller pixel size

Question 3

contrast resolution-

Answer 3

ability to distinguish anatomical structures of similar subject contrast such as liver-spleen & gray matter-white matter

Question 4

pixel-

Answer 4

element of the picture

Question 5

Dell

Answer 5

detector element

Question 6

noise-

Answer 6

random fluctuation of x-ray interaction on the IR
(simplified version- signal not caused by the subject)

Question 7

quantum mottle-

Answer 7

reduced with the use of high mAs & low kVp

Question 8

speed medical imaging quality rules-

Answer 8

-fast IR- high noise & low contrast resolution
-slow IR- low noise & high contrast resolution
-spatial resolution is limited to pixel size

Question 9

preferred technique-

Answer 9

high kVp & low mAs to reduce pt. dose

Question 10

3 types of radiographic quality-

Answer 10

-IR Factors
-Geometric Factors
-Subject Factors

Question 11

IR Factors-

Answer 11

pixel size, dynamic range, intensity response, signal to noise, & post-processing

Question 12

Geometric Factors-

Answer 12

magnification, distortion, & focal-spot blur

Question 13

Subject Factors-

Answer 13

contrast, thickness, density, atomic #, & motion

Question 14

magnification-

Answer 14

ability of system to draw/render image at appropriate size

Question 15

What is the magnification factor (MF) formula?

Answer 15

image size / object size

Question 16

When OID increases, what also increases?

Answer 16

magnification & distortion increase

Question 17

Which exams does magnification occur on?

Answer 17

all exams

Question 18

What is the formula used when the actual measurement of an object size may be impossible?

Answer 18

MF = SID / SOD

Question 19

When minimizing MF, what does a large SID do?

Answer 19

when SID increases, magnification decreases

Question 20

When minimizing MF, what does a small OID do?

Answer 20

when OID increases, it also increases magnification & distortion

Question 21

What is shape distortion caused by?

Answer 21

positioning the tube/part, or IR is angled

Question 22

distortion is concerned with-

Answer 22

with the part being imaged being unequal shape & size

Question 23

3 things distortion depends on-

Answer 23

-object thickness
-shape
-position

Question 24

foreshortening-

Answer 24

angled IR against a part

Question 25

elongation-

Answer 25

angled IR against the tube

Question 26

Teleradiology

Answer 26

sending images over a phone line

Question 27

Telerinkenology

Answer 27

long range radiology (x-rays at 72")

Question 28

What does magnification distortion reduce?

Answer 28

image quality

Question 29

thick objects are more ____ than thin objects

Answer 29

distorted

Question 30

proper positioning is important because-

Answer 30

irregular shapes appear more distorted when outside the center of the CR

Question 31

Objects that are further from the IR or Inclined (tilted back) objects aren't centered correctly & can present with-

Answer 31

distortion

Question 32

2 types of blur-

Answer 32

focal spot & motion

Question 33

focal-spot blur has to do with-

Answer 33

the shape of FS & the location on the IR relative to FS

Question 34

because of effective spot, the way it works is due to-

Answer 34

line focus principle

Question 35

What do you do to get a small affected FS?

Answer 35

angle the anode face

Question 36

the beam diversion of 1 source would cause FS itself to-

Answer 36

diverge

Question 37

presentation of projected FS will have-

Answer 37

different shapes depending where it lands on a rectangular IR

Question 38

____ will have the least amount of blur because of FS location relative to the IR-

Answer 38

anode side & center

Question 39

____ will have the most amount of blur because of FS location relative to the IR-

Answer 39

cathode side & not center

Question 40

helps reduce blurring on edges of anatomy-

Answer 40

short OID

Question 41

an increased OID is equal to-

Answer 41

a decreased SOD

Question 42

reduce FS blur-

Answer 42

short OID & centering

Question 43

subject factors- (5)

Answer 43

-subject contrast -part thickness -tissue mass density -effective atomic # -object shape

Question 44

the key to radiographic contrast

Answer 44

subject contrast

Question 45

helps display subj. contrast-

Answer 45

contrast capabilities of the IR, system, & monitor

Question 46

where is subject contrast inherent?

Answer 46

in the subject

Question 47

as part thickness increases-

Answer 47

-scatter & technique increase -transmission decreases

Question 48

tissue mass density-

Answer 48

photoelectric effect affected by atomic #

Question 49

when the effective atomic # is high, contrast is-

Answer 49

contrast is high

Question 50

transmitted x-rays demonstrated on a radiograph are-

Answer 50

black

Question 51

relative to cortical bone, on a radiograph soft tissue will show up-

Answer 51

black

Question 52

photoelectric effect is demonstrated on a radiograph as-

Answer 52

white

Question 53

job of contrast media-

Answer 53

artificially influence subject contrast

Question 54

the base of all imaging is-

Answer 54

subject contrast

Question 55

iodine Z#-

Answer 55

53

Question 56

barium Z#-

Answer 56

56

Question 57

Iodine & barium alter-

Answer 57

subject contrast to increase contrast

Question 58

when the Z# is high & increases, photoelectric effect-

Answer 58

increases rapidly

Question 59

2 types of contrast-

Answer 59

positive & negative

Question 60

site contrast-

Answer 60

iodine & barium

Question 61

iodine & barium shows up _____ on a radiograph

Answer 61

white

Question 62

as photoelectric effect increases, transmission ____.

Answer 62

decreases

Question 63

object shape-

Answer 63

the more the shape coincides with the x-ray beam, the greater the contrast

Question 64

the closer the shape of the object is closer to beam divergence at the level you're imaging at, you're going to get the least amount of-

Answer 64

least amount of distortion & blur demonstrated

Question 65

2 types of motion blur-

Answer 65

voluntary & involuntary

Question 66

voluntary motion-

Answer 66

movement from the patient such as breathing

Question 67

how can you reduce voluntary motion in a radiograph?

Answer 67

give good patient instructions

Question 68

involuntary motion-

Answer 68

peristalsis or the heart beating

Question 69

how can you reduce involuntary motion in a radiograph?

Answer 69

short exposure times

Question 70

reduce the likely hood of motion- (5)

Answer 70

-large SID -reduced OID -short exposure time -good patient instructions -immobilization devices

Question 71

tools for improving image quality- (5)

Answer 71

-proper patient positioning -AP v. PA -AEC selection -good patient instructions -breathing instructions

Question 72

method to improve image quality-

Answer 72

proper positioning of the entire patient so the part being imaged is displayed properly

Question 73

principle of imaging-

Answer 73

want the part of interest as close to IR as possible

Question 74

image receptor-

Answer 74

pixel size affects the patients relative dose

Question 75

small pixels require-

Answer 75

higher dose

Question 76

large pixel requires-

Answer 76

lower dose

Question 77

good technical factors selection-

Answer 77

high kVp aids in short exposure times & overall reduces patient dose & improves image quality