Questions and Answers
The modulation transfer function (MTF) is a basic feature used to assess imaging system performance.
False
The Rose model equation is a basic feature used to assess imaging system performance.
False
The Wiener spectrum is a basic feature used to assess imaging system performance.
False
Resolution, contrast, and noise are intermediate measures of imaging system performance.
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The three basic features of imaging system performance are noise, spatial resolution, and signal-to-noise ratio.
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The receiver operating characteristic (ROC) analysis is a comprehensive measure of system performance.
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The modulation transfer function (MTF) is a comprehensive measure of system performance.
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The Rose model equation, contrast detail analysis, and receiver operating characteristic (ROC) analysis are intermediate measures of imaging system performance.
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The contrast of the disk relative to the background is a dimensionless quantity.
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Impressionist paintings are an example of how random noise affects image quality.
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Random noise in x-ray imaging is a result of using too many photons per area.
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Random noise can be measured as the mean of image values in a uniform region of the image.
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A scannning microdensitometer is used to measure the noise level in an x-ray image.
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Film contrast is always negative in x-ray imaging.
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The graph of relative exposure levels for phantom and background is a measure of image contrast.
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Random noise is reduced by increasing the number of photons per area in x-ray imaging.
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In medical images, contrast refers to the similarity between neighboring tissues.
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The contrast between bone and soft tissue is low in x-ray imaging.
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The type of device used to record the image is a factor that affects radiographic contrast.
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The energy spectrum of the x-ray beam does not affect radiographic contrast.
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Fogging or some other baseline signal is not present in the imaging device.
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Image contrast is calculated using the x-ray fluence (photons/area) of the object and its surrounding background.
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The x-ray exposure is higher beneath the plastic disk than in the background in the developed x-ray image.
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The chemical composition of the object does not affect radiographic contrast.
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Study Notes
IMAGING SYSTEM PERFORMANCE
- The basic features used to assess imaging system performance are resolution (spatial), contrast, and noise.
- Measurements of these basic features provide a foundation for studying and comparing medical imaging systems.
- Measures derived from pairs of these basic features provide further insight and include:
- Signal-to-noise ratio (SNR)
- Modulation transfer function (MTF)
- Wiener spectrum
- The most comprehensive measures of system performance incorporate all three basic features and include:
- Rose model equation
- Contrast detail analysis
- Receiver operating characteristic (ROC) analysis
Image Contrast
- Image contrast refers to differences between neighboring tissues in medical images.
- Contrast depends on several factors, including:
- Chemical composition of the object
- Type of device used to record the image (film or electronic detector)
- Energy spectrum of the x-ray beam (presence of scatter radiation)
- Fogging or baseline signal in the imaging device
- Contrast can be calculated using the fractional difference in x-ray exposure between the object and its surrounding background.
Random Noise
- Random noise relates to the uncertainty or imprecision with which a signal is recorded.
- Noise is similar to the concept of impressionist paintings, where the number of dots increases, the precision or certainty with which the image is represented increases.
- In x-ray and nuclear medicine imaging, an image recorded with a small number of photons/area generally has a high degree of uncertainty or is noisy, while an image recorded with a large number of photons/area is more precise and less noisy.
- Noise can be measured as the standard deviation (σ) of image values in a uniform region of the image.
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