Factors Affecting Contrast/Spatial Resolution

Question 1

Increase Spatial Frequency

Answer 1

• Decrease contrast resolution b/c you are decreasing the object size and it is harder to get accurate images of smaller objects
• Has no effect on spatial resolution, spatial resolution is the ability of the scanner to display 2 separate objects immediately adjacent to each other w/o blurring them together

Question 2

Increase object size

Answer 2

• increase contrast resolution

- no effect on spatial resolution

Question 3

Increase kVp

Answer 3

• decreases contrast resolution, more photons make it the detector
• no effect on spatial resolution

Question 4

Increase focal spot size

Answer 4

• no effect on contrast resolution

- decrease spatial resolution, using larger filament for larger body parts

Question 5

Increase subject density

Answer 5

• decrease contrast resolution b/c more matter more scatter

- no effect on contrast resolution

Question 6

Increase subject thickness

Answer 6

• decrease contrast resolution b/c more matter more scatter

- no effect on spatial resolution

Question 7

Increase mAs

Answer 7

• no effect on contrast resolution, only if the image is extremely underexposed or SNR is bad, can show up at as quantum mottle
• no effect on spatial resolution, quantity of photons has no effect

Question 8

Increase pitch

Answer 8

• decrease contrast resolution, pitch will increase the amount of thickness covered for each slice (more matter, more scatter)
• decrease spatial resolution

Question 9

Increase slice acquisition thickness

Answer 9

• decrease contrast resolution b/c more partial averaging occurs
• decrease spatial resolution

Question 10

Increase matrix size

Answer 10

• decrease contrast resolution b/c pixel size is decreased (the smaller the pixel the less likely a photon will interact with it)
• increases spatial resolution b/c the pixel size is decreased

Question 11

Increase Pixel Size

Answer 11

• increase contrast resolution b/c a photon is more likely to interact with the pixel
• decrease the spatial resolution

Question 12

Bone Algorithm

Answer 12

• decrease contrast resolution

- increase contrast resolution

Question 13

Soft tissue or smoothing algorithm

Answer 13

• increase contrast resolution so many shades of grey are visible
• decrease spatial resolution

Question 14

Increase Window Width

Answer 14

• decrease contrast b/c many more shades of gray are shown

- no effect on spatial resolution

Question 15

Increase DFOV

Answer 15

• no effect on contrast resolution

- decrease spatial resolution b/c more is included in the DFOV

Question 16

Patient motion

Answer 16

• no effect on contrast resolution

- will decrease spatial resolution b/c structures become blurred

Question 17

Increase SNR

Answer 17

• increase contrast resolution

- decrease spatial resolution