CH 14 & 15 Vision and Perception_Beams

Question 1

Image Quality Factors

Answer 1

1)Density 2)Contrast 3)Detail 4) Distortion

Question 2

Density

Answer 2

Overall blackness of image (aka OD & brightness)

Question 3

Contrast

Answer 3

Differences in adjacent density & the ability to visualize the differences in structures.

Question 4

Detail

Answer 4

Sharpness/edges of the structures (Film/Lp/mm) (Digital- spatial rsn-pixel size & count)

Question 5

Distortion

Answer 5

misrepresentation of object size or shape.

Question 6

3 types of distortion

Answer 6

Shape: elongation and foreshortening. Size magnification.

Question 7

Threshold Detection is:

Answer 7

a visual phenomenon involving the perception of extremely small or faint details.

Question 8

Threshold Detection is affected by:

Answer 8

Anything that takes away detail, like radiographic fog (or any artifacts).

Question 9

Penumbra

Answer 9

Blurred or unsharp.

Question 10

Two main methods to control scatter:

Answer 10

Collimation and use of grid

Question 11

Collimation

Answer 11

Helps reduce the production of scatter.

Question 12

How does colliation help reduce scatter?

Answer 12

When using a smaller FOV there is 1)smaller xray field 2)less x rays 3)less compton interations 4) less scatter 5)less fog

Question 13

When is a grid used?

Answer 13

After it’s been produced.

Question 14

What is a grid?

Answer 14

Device that contains thin strips of lead to attenuate scatter and allow hard energies to pass through.

Question 15

Beam limitation devices:

Answer 15

Variable rectangular, PBL/Positive beam limitation device (these 2 are the most common), Cylinder Collimator, Cone, Diaphragm Aperature.

Question 16

What is a PBL?

Answer 16

Automatically restricts the size of the field to the size of the IR.

Question 17

What happens to image when kV is inc?

Answer 17

Force, interations, Compton, Scatter, and Fog all increase.

Question 18

Increasing part thickness does what to scatter?

Answer 18

Increases

Question 19

What happens to scatter when atomic # is decreased?

Answer 19

it increases.

Question 20

Umbra

Answer 20

Sharpness of shadow

Question 21

How do we control Umbra?

Answer 21

Use geometric factors like OID, SID, FSS

Question 22

What is Half Value Layer (HVL)?

Answer 22

Any absorbing material that reduces xray energy to half (50%).

Question 23

Short hard energies of xrays are called?

Answer 23

Hardening the beam

Question 24

How do we process visually?

Answer 24

The specialized cells of the retina, especially fovea centralis, convert the image to nervous impulses, and the optic nerve transmits the impulses to the brain for processing.

Question 25

Where does human image conversion occer?

Answer 25

The rod and cone cells.

Question 26

How do rods and cones work?

Answer 26

They contain photosensitive pigments that will respond to light by sending an electrical potential to specialized nerve cells.

Question 27

How many cones do humans have?

Answer 27

7,000,000 located only at the fovea centralis

Question 28

How many Rods do humans have?

Answer 28

120,000,000

Question 29

Photopic

Answer 29

Daylight vision, which is controlled by cones.

Question 30

Scotopic

Answer 30

Night vision, controlled by the rods.

Question 31

Visual acuity:

Answer 31

sharpness or focus

Question 32

Which is able to detect changes in brightness better? Rods or Cones?

Answer 32

Cones, reponsible for greater contrast perception.