Spatial Resolution, Contrast Resolution, MTF, Noise, DQE

Question 1

Spatial resolution is best defined as:
a) Ability to visualize different shades of gray
b) Ability to image small objects on the image
c) Amount of noise in an image
d) Image brightness

Answer 1

b) Ability to image small objects on the image — Spatial resolution describes detail sharpness.

Question 2

Which image display provides the highest contrast?
a) Gray on gray
b) White on white
c) Black on white
d) Color on black

Answer 2

c) Black on white — Maximum contrast occurs between black and white.

Question 3

Spatial frequency refers to:
a) Object size
b) Image brightness
c) Number of line pairs
d) Radiation dose

Answer 3

c) Number of line pairs — Spatial frequency is measured in line pairs per unit length.

Question 4

One line pair consists of:
a) Two dark lines
b) One line and one interspace of equal width
c) Two interspaces
d) One pixel

Answer 4

b) One line and one interspace of equal width — This defines a single line pair.

Question 5

Spatial frequency is expressed in:
a) Pixels per inch
b) Cycles per second
c) Line pairs per millimeter
d) Gray levels

Answer 5

c) Line pairs per millimeter — lp/mm is the standard unit.

Question 6

Higher spatial frequency response indicates:
a) Poor spatial resolution
b) Increased noise
c) Better spatial resolution
d) Reduced contrast

Answer 6

c) Better spatial resolution — Systems resolving higher frequencies show finer detail.

Question 7

Spatial resolution in digital imaging is limited primarily by:
a) kVp
b) Scintillator thickness
c) Pixel size
d) SID

Answer 7

c) Pixel size — Pixel dimensions cap resolution.

Question 8

Modulation transfer function (MTF) describes:
a) Image contrast
b) Radiation dose
c) Ratio of image to object contrast as a function of spatial frequency
d) Noise magnitude

Answer 8

c) Ratio of image to object contrast as a function of spatial frequency — MTF quantifies system performance.

Question 9

Imaging system spatial resolution is defined at:
a) 50% MTF
b) 25% MTF
c) 10% MTF
d) 1% MTF

Answer 9

c) 10% MTF — This is the standard cutoff for resolution.

Question 10

Dynamic range refers to:
a) Exposure time
b) Number of photons
c) Number of gray shades an imaging system can reproduce
d) Pixel size

Answer 10

c) Number of gray shades an imaging system can reproduce — Wider range means more visible detail.

Question 11

Postprocessing in digital imaging allows:
a) Increased spatial resolution
b) Visualization of all shades of gray
c) Reduced pixel size
d) Reduced noise

Answer 11

b) Visualization of all shades of gray — Windowing makes use of wide dynamic range.

Question 12

The signal in a radiographic image is:
a) All detected radiation
b) Scatter radiation only
c) Image-forming x-rays representing anatomy
d) Electronic noise

Answer 12

c) Image-forming x-rays representing anatomy — Signal conveys diagnostic information.

Question 13

Image noise primarily limits:
a) Spatial resolution
b) Contrast resolution
c) Distortion
d) Magnification

Answer 13

b) Contrast resolution — Noise obscures subtle differences.

Question 14

Excessive image noise in DR is usually caused by:
a) Overexposure
b) Excessive filtration
c) Quantum mottle from underexposure
d) Large focal spot

Answer 14

c) Quantum mottle from underexposure — Too few photons increase noise.

Question 15

DR systems can compensate for excessive noise:
a) Always
b) Sometimes
c) Only with postprocessing
d) Never

Answer 15

d) Never — Noise from low exposure cannot be corrected.

Question 16

Overexposed digital images:
a) Must always be repeated
b) Have excessive noise
c) Do not require repetition but should be avoided
d) Are underexposed

Answer 16

c) Do not require repetition but should be avoided — Leads to dose creep.

Question 17

Contrast resolution in digital imaging is:
a) Dose dependent
b) Lost with low dose
c) Preserved regardless of dose
d) Limited by filtration

Answer 17

c) Preserved regardless of dose — Digital systems maintain contrast latitude.

Question 18

Dose creep in DR should be replaced with:
a) Increased mAs
b) Technique creep
c) Higher kVp
d) Repeat imaging

Answer 18

b) Technique creep — Focus on proper technique rather than increasing dose.

Question 19

Detective quantum efficiency (DQE) measures:
a) Image contrast
b) Noise magnitude
c) X-ray absorption efficiency
d) Spatial resolution

Answer 19

c) X-ray absorption efficiency — Higher DQE means better dose utilization.

Question 20

High DQE allows:
a) Increased patient dose
b) Reduced patient dose
c) Reduced spatial resolution
d) Increased noise

Answer 20

b) Reduced patient dose — Efficient detectors need fewer photons.

Question 21

Compared to screen-film radiography, DR is primarily limited by:
a) Contrast resolution
b) Speed
c) Spatial resolution
d) Dynamic range

Answer 21

c) Spatial resolution — Pixel size limits DR detail.