1) Foundations of Medical Image Quality: Contrast, Sharpness, and Noise
1.
Sampling provides discretization of an analog image space into discrete spatial and intensity units.
A) True
B) False
Answer:
A) True
2.
Which one of these is true about Fourier transformation?
A) It enables dividing an image into multiple frequency bands.
B) It is the same thing as v-space in MRI.
C) It helps to reduce noise in medical images.
D) It restores resolution loss due to MTF degradation.
Answer:
A) It enables dividing an image into multiple frequency bands.
3.
If a background signal level is 100 and the lesion signal level is 80, what is the contrast?
A) 20
B) 2
C) 0.2
D) 0.02
Answer:
B) 2
4.
Which one of these is not true about sharpness
A) Sharpness is best described in terms of the MTF
B) The 20% MTF value reflect the limiting resolution of a system
C) Sharpness reflect how fine features of an image can be resolved
D) Loss of sharpness can be compensated with edge enhancement
Answer:
B) The 20% MTF value reflect the limiting resolution of a system
5.
Higher MTF implies
A) Higher resolution
B) Lower noise
C) Higher contrast
D) Lower scatter
Answer:
A) Higher resolution
6.
For a system with multiple components, the overall system MTF is the addition of all the component MTFs
A) True
B) False
Answer:
B) False
7.
Quantum noise refers to Fluctuations in the number of photons recorded by the detector due to
A) anatomical variations
B) scattered radiation
C) quantum state of the detector
D) finite number of photons
Answer:
D) finite number of photons
8.
Per Poission statistics, if the mean count of a pixel is 10,000, the standard deviation is
A) 10
B) 100
C) 10%
D) 100%
Answer:
B) 100
SD is square root of the number of counts
9.
Which one of these metrics reflect the texture of noise in an image:
A) SNR
B) NPS
C) CNR
D) NRQ
Answer:
B) NPS
Figure 14. Examples of a low noise mammographic image with a section of the image magnified to show image texture (top). The same image with added uncorrelated noise with characteristic flat NPS (middle) and with added correlated noise (bottom). Note that the two examples involve the same magnitude of added noise in terms of variance, but the NPS is different thus different noise textures.
10.
Contrast to noise ratio is
A) inversely proportional to the threshold size of a detectable target
B) directly proportional to threshold size of a detectable target
C) inversely proportional to contrast
D) directly proportional to image noise
Answer:
A) inversely proportional to the threshold size of a detectable target
11.
The DQE is a reflection of the inherent efficiency of an imaging system to utilize the x-ray flux to form a high quality image
A) True
B) False
Answer:
A) True
This ratio is known as the Detective Quantum Efficiency (DQE) and is commonly used as a metric to characterize the intrinsic performance of a digital radiographic system.
12.
The DQE is
A) Proportional to MTF
B) Proportional to MTF2
C) Proportional to the NPS
D) Proportional to the NPS2
Answer:
B) Proportional to MTF2
and
DQE is proportional to MTF2
13.
The DQE stands for
A) The detectable quantum energy
B) The detector quantum effectiveness
C) The detective quantum efficiency
D) The detectability quantum efficacy
Answer:
C) The detective quantum efficiency
This ratio is known as the Detective Quantum Efficiency (DQE) and is commonly used as a metric to characterize the intrinsic performance of a digital radiographic system.
14.
All else being equal, a higher MTF enables
A) Imaging at lower dose
B) Imaging with improved spatial resolution
C) Imaging with reduced scatter
Answer:
B) Imaging with improved spatial resolution
15.
All else being equal, a higher DQE enables
A) Imaging at lower dose
B) Imaging with improved spatial resolution
C) Imaging with reduced scatter
Answer:
A) Imaging at lower dose
Intuituvely, the more efficient the imaging system, the less dose you would need to use