Image Formation & Radiographic Quality Ch 3

Question 1

visible image

Answer 1

processed image

AKA manifest image

Question 2

transmission

Answer 2

incoming x-ray photon passes through the anatomic part without any interaction with anatomic structures

Question 3

tissue density

Answer 3

compactness of the atomic particles comprising the anatomic part
i.e. muscle effective atomic # 7.4
soft tissue effective atomic # 6.3
similar in atomic # but their atomic particles differ in compactness and their density varies

Question 4

subject contrast

Answer 4

absorption characteristics of the anatomic tissue imaged AND the quality of the x-ray beam

• differences in tissue thickness ie.e lung to bony thorax (high subject contrast & great difference in the brightness level recorded)
• abdomen is low subject contracts because of the similarity of tissue (i.e. liver/kidney)

*Quality of the x-ray beam affects the attenuation of tissue too…which can alter subject contrast
higher kVp DECREASES attenuation, REDUCES absorption and INCREASES transmission - result in fewer differences in brightness levels recorded on the image.

Question 5

spatial resolution

Answer 5

smallest object that can be detected in an image

i.e. ability of system to demonstrate sharp lines (geometric)

Question 6

secondary e-

Answer 6

Compton e-
ejected electron from Compton interaction

interaction between diagnostic x-rays and matter = Compton effect

Question 7

shape distortion

Answer 7

Can occur because of inaccurate CR align of tube, anatomic part, IR
elongation
foreshortening

Question 8

quantum noise

Answer 8

photon dependent
- quantum mottle

visible as a brightness or density fluctuation in image
- noise due not enough photos

Question 9

magnification

Answer 9

size distortion (OID or SID)

Question 10

latent image

Answer 10

invisible image
exit radiation that interacts with the IR
-not visible until processed

Question 11

dynamic range

Answer 11

range of exposure intensities an IR can accurately detect

Question 12

photoelectric effect

Answer 12

Photoelectric effect is responsible for the brighter (whiter) anatomic structures on an image.

1. incident photon interacts with an inner orbital or K or L e-, giving ALL of its energy to the e- ejecting it from orbit. The photon is absorbed
2. ejected e- (photoelectron) imparts the atom with the energy equal to the excess of the e- binding energy.
3. There is a vacancy in the inner orbital shell, K or L, which must be filled. One of the e- from the outer orbital shell, usually the next orbit out, drops to the void.
4. As the e- drops to the void, it may shed its excess energy as a secondary photon.

Question 13

contrast resolution

Answer 13

ability of the IR to to distinguish between objects have similar SUBJECT contrast.
Digital imaging has improved contrast resolution

Question 14

brightness

Answer 14

amount of luminance (light emission) on a display monitor

Increased brightness on computer monitor shows DECREASED density on a film image

Decreased brightness on a computer monitor shows INCREASED density on a film image

Question 15

artifact

Answer 15

unwanted image on a radiograph.

Artifacts can come from patient or imaging system.

Question 16

fog

Answer 16

unwanted exposure on the image

Question 17

exit radiation

Answer 17

remnant radiation

Both TRANSMITTED & SCATTERED RADIATION make up exit radiation

Question 18

distortion

Answer 18

misrepresentation of size or shape of the anatomic part

**When an image is distorted – spatial resolution IS REDUCED.

Question 19

absorption

Answer 19

As the x-ray beam deposits its ENERGY INTO ATOMS OF TISSUE/STRUCTURES some photons are completely absorbed
**Complete absorption of the incoming x-ray photon occurs when it has enough energy to remove (eject) an inner-shell electron

Question 20

attenuation

Answer 20

As the x-ray beam passes through anatomical tissues/structures it LOSES SOME ITS ENERGY (intensity).
Fewer x-rays remain in the beam after interacts with tissue/structures.

*reduction in the intensity or number of photons in the primary x-ray beam

Question 21

differential absorption

Answer 21

a process of IMAGE FORMATION whereby some amount of the x-ray beam is absorbed in the tissue and some passes through (transmits) the anatomic part

DIFFERENTIAL = varying anatomic parts do not absorb the primary beam to the same degree

What are the five radiographic densities?
hint; bone…