Exposure Contrast

Question 1

Receptor eposure/Optical density

Answer 1

Amount of overall blackness produced on the processed image
In digital, represented by exposure index/ S-Value
High EI = High exposure
Low EI = Low exposure
High S = Low exposure
Low S = High exposure

Question 2

Receptor exposure controlling/influencing factors

Answer 2

mAs - Determines quantity of xrays produced and eit the xray tube, has direct relationship with RE, governed by reciprocity law
kVp - manages quality of xrays, xrays wih high energy (short wave length, high frequency) are able to penetrate body & reach IR, Low energy = Long wave length, low frequency, exponential relationship with RE (small inrease in kVp, big increase in RE), governed by 15% rule
SID - Has inverse square relationship with RE, if SID is doubled, beam will have 1/4 its original intenity, changing SID means you have to adjust mAS, Beam intensity = new distance^2/old distance^2

Question 3

Beam intensity equation

Answer 3

Old intensity/new intensity = new distance ^2/ old distance^2

Question 4

Grids

Answer 4

Absorb scatter radiation = less radiation striking IR/detector
As grid ratio increases, RE decreases
mAs must be increased to compensate for decrease in RE

Question 5

Beam restriction

Answer 5

Decreases receptor exposure by limiting the size of xray beam, unless mAs is increased to compensate
Decreases receptor exposure by limiting the area of the patient being struck by photons
Reduces the amount of scatter radiation being produced, reducing receptor exposure by fog

Question 6

Anatomy and pathology

Answer 6

Anatomy effects receptor exposure through its variation of atomic number, tissue thickness, tissue density
Pathologic changes affect receptor exposure by altering tissue integrity, atomic number, tissue density, tissue thickness

Question 7

Anode heel effect

Answer 7

Xray intensity varies along the longitudinal axis of the beam
Exposure greatest near cathode end\Exposure less near the anode end, due to photons being absorbed by the heel
Thicker anatomy should be placed under the cathode side

Question 8

Filtration

Answer 8

Negligible effect on receptor exposure, its purpose is primarily for radiation protection
As filtration increases, RE decreases

Question 9

Contrast

Answer 9

Visible difference between two selected areas of brightness in the displayed radiographic image

Question 10

Effect of kVp on contrast using penetrometer

Answer 10

High kVp = long scale, low contrast
Low kVp = Short scale, High contrast

Question 11

kVp

Answer 11

influences contrast, but computer processing sets displayed contrast

Question 12

Grids

Answer 12

Allow most primary radiation through & absorb scatter radiation
Less fog = less shades of gray

Question 13

Collimation

Answer 13

Open collimation = more matter for xrays to interact with
Allows for more scatter production
Scatter decreases contrast
Collimating to necessary anatomy, reduces scatter production

Question 14

Filtration

Answer 14

Aluminum filtration used to absorb low energy xrays
Reduces patient skin dose
Filtration increase, contrast decreases by average energy of beam

Question 15

Subject contrast

Answer 15

Difference in tissue densities being xrayed

Question 16

Breast tissue

Answer 16

Similar density = low subject contrast, need to increase image contrast by decreasing kVp

Question 17

Chest

Answer 17

Large differences in tissue densities = High subject contrast
Need to decrease image contrast by increasing kVp

Question 18

Recorded detail

Answer 18

Sharpness of the structural edges in the images, smallest detail that can be detected
Also referred to as definition, sharpness, spatial resolution

Question 19

Recorded detail controlling and influencing factors

Answer 19

Pixel size - smaller pixels provide greater spatial resolution
Pixel pitch - space between pixels, less space between pixels provides greater spatial resolution

Question 20

OID

Answer 20

Distance from anatomic part being imaged to the image receptor
Shortest possible OID should be used
Increased OID causes magnification of the image, resulting in loss of recorded detail

Question 21

SID

Answer 21

Increased SID compensates for increased OID
Decreases magnification and increase in recorded detail

Question 22

Focal spot size

Answer 22

Small focal spot = better detail

Question 23

Contrast resolution

Answer 23

ability of the imaging system to distinguish the smallest change in exposure or signal that can be detected
provides visibility of small objects having similar shades of gray
controlled by bit depth, the number of bits per pixel (the larger the bit depth, the greater the number of levels of gray possible in an image)

Question 24

Distortion

Answer 24

Any geometric misrepresentation of an anatomic structure on an image receptor
Two types of distortion: size and shape
Controlling factors
Size
Magnification
Influencing factors
OID
SID
SOD
Causes anatomic structure to appear larger on the image than in reality
As SID increases, the amount of magnification decreases due to less beam divergence.
A shorter SID will cause more magnification to occur.