Image Quality Flashcards
Image usefulness
Modality comparison: sensitivity, specificity, predictive value
Local contrast
Difference between some target region and the “background”. System resolution buried in the target size.
Modulation
More global, max and min of a modulation sine or cosine. Resolution implicit in the frequency
Intrinsic contrast depends on
Object parameters
Image metrics
Contrast, resolution, noise, artifacts, geometric accuracy, reproducibility
Image quality
Refers to the degree to which an image allows a radiologist to accomplish the clinical goals of the imaging study
Six most important factors influencing image quality
Contrast, resolution, noise, artifacts, distortion, and accuracy
Contrast
Refers to the difference in image intensity of an object or target and surrounding objects or background
Resolution
Is the ability of an imaging system to distinguish and depict two signals that differ in space, time, or energy as distinct
Noise
Is any random fluctuation in an image; noise generally interferes with the ability to detect a signal in an image
Artifacts
Are false signals in an image that do not represent any valid structural or functional signal in the patient
Distortion
Is any geometric inaccuracy in size or shape
Quantitative accuracy
Refers to the accuracy, compared with the truth, of numerical values obtained from an image
Diagnostic accuracy
Refers to the accuracy of interpretations and conclusions about the presence or absence of disease drawn from image patterns
Local Contrast
Contrast to Noise Ratio (CNR)
Modulation
Modulation transfer function
WIndow is related to
contrast (wide window, low contrast.)
Contrast change in a linear system
MTF is the …
frequency response of the system
Gaussian PSF
Triangle PSF
Exponential PSF
High frequencies are…
Low frequencies are…
High frequencies are “blue”
Low frequencies are “red”
Quantum Detection Efficiency
Nonrandom effects
- Artifacts
- Distortion
Artifacts
- Image features that do not correspond to a real object, and are not due to noise
- Star artifact
- Beam Hardening Artifact
- Ring Artifact
- Ghosts
Distortion
- Geometric or intensity changes not corresponding to the real object
- magnification
- barrel or pincushion distortion
- quantization
- saturation
Disease Prevalence
Sensitivity and Specificity
