diagnostic quality

Question 1

diagnostic quality achieved with

Answer 1

• minimal magnification, distortion, penumbra
• anatomical accuracy
• adequate coverage
• density and contrast

Question 2

qualities of a diagnostic radiograph

Answer 2

• sharp

- shape and size same as object

Question 3

magnification

Answer 3

caused by divergent path of beam

-x rays travel in diverging straight lines

Question 4

2 rules to keep mag at a minimum

Answer 4

1. keep object as close to image receptor as possible

2. keep the focal spot to image receptor distance as large as possible

Question 5

distortion

Answer 5

unequal mag of an object

Question 6

paralleling technique

Answer 6

minimizes distortion and more anatomically accurate

Question 7

bisecting angle tech

Answer 7

inherent distortion

Question 8

what leads to foreshortening?

Answer 8

improper use of paralleling tech

Question 9

for the maxillary arch in paralleling tech, the image receptor must be where?

Answer 9

in center of oral cavity

-teeth biting on 1st/2nd groove

Question 10

where do teeth bite for mandible?

Answer 10

middle of block

Question 11

mag —- the farther away the image rec is from object

Answer 11

increases

Question 12

long cone paralleling tech

Answer 12

• better definition
• less mag
• less distortion
• better anatomic accuracy

Question 13

indications of bisecting angle tech

Answer 13

• narrow palate
• small mouth
• shallow floor of mouth (ankyloglossia)
• difficult patient/lack of cooperation

Question 14

penumbra

Answer 14

unsharpness

• bc focal spot has finite dimensions
• edge of an object is imaged many times

Question 15

how to minimize penumbra

Answer 15

• use as small a focal spot as possible (line focus principle)
• use a long focal spot to object distance
• minimize object to image receptor distance

Question 16

difference between long and short cone

Answer 16

• long cone is sharper

- magnification

Question 17

line focus principle

Answer 17

• focal spot large enough to dissipate heat

- small enough to have a sharp image

Question 18

rules for dimensional accuracy

Answer 18

• small focal spot
• long source-object distance
• short object-image receptor distance
• object parallel to image receptor
• central ray at right angle to teeth and image receptor

Question 19

how is anatomical accuracy obtained?

Answer 19

when the image receptor is placed parallel to the long axis of the teeth and beam is directed perpendicular to both the image receptor and teeth

Question 20

anatomical accuracy

Answer 20

• labial and lingual CEJs of ant teeth superimposed
• buccal and lingual cusps of molars superimposed
• contact open
• no superimposition of zygo bone
• buccal portion of alv crest is superimposed over lingual portion of alv crest

Question 21

adequate coverage

Answer 21

area of interest well covered in radiograph

Question 22

density

Answer 22

degree of image blackening

Question 23

contrast

Answer 23

difference in densities

Question 24

4 most important factors that control density

Answer 24

1. milliampere
2. exposure time
3. kilovoltage
4. source to image receptor distance

Question 25

what influences quantity ?

Answer 25

exposure time
mA
kV
BID

Question 26

what influences quantity and quality?

Answer 26

kV

Question 27

the density of the radiograph varies directly and proportionally with —- and —-

Answer 27

mA and exposure time

Question 28

kVp controls?

Answer 28

• penetrating power of the beam
• increase–> increase power
• the more penetrating beam, the more radiation strikes the image receptor

Question 29

increasing vs decreasing kVp

Answer 29

increasing kV darkens image

decreasing kV lightens image

Question 30

intensity of x ray beam is —– to the square of the distance from the source (focal spot)

Answer 30

inversely proportional

Question 31

doubling the distance does what?

Answer 31

produces 1/4 the density

Question 32

decreasing the distance by one half does what?

Answer 32

produces 4 times the density

Question 33

few x rays reach the film thru areas of what?

Answer 33

enamel and cortical bone

Question 34

many x rays are transmitted through what?

Answer 34

pulp, soft tissue, air around patient

Question 35

short scale contrast

Answer 35

few shades of gray
high contrast
low Kvp
-good for looking at caries

Question 36

long scale contrast

Answer 36

many shades of gray
high kvp
low contrast
-good for interpreting fine details–perio disease, periapical disease, bony lesions

Question 37

contrast depends on

Answer 37

subject contrast
image receptor contrast
scatter radiation
computer display

Question 38

subject contrast depends on

Answer 38

• make up of patient

- energy of beam

Question 39

what is the main controller of subject contrast

Answer 39

kVp

Question 40

what reduces radiographic contrast?

Answer 40

scatter radiation

Question 41

image receptor contrast depends on

Answer 41

• type of receptor
• film–also depends on chemistry
• extraoral film depends on type of screen phosphor

Question 42

characteristic curve

Answer 42

-describes contrast, latitude (exposure range), and speed of film and digital receptors

Question 43

digital imaging can help what?

Answer 43

reduce patient dose

Question 44

—- and —- have similar contrast and latitude

Answer 44

film and hard sensors

Question 45

PSP plates

Answer 45

lower contrast but greater latitude

Question 46

most desirable image

Answer 46

faint outline of soft tissue in edentulous spaces and area distal to molar teeth

Question 47

ideal viewing conditions

Answer 47

human eye = 60 gray levels

<30 in operator

Question 48

bit depth

Answer 48

digital contrast

• current–12 or 16 bits
• conventional computer can only see 8 bits =256 gray levels