6 Image Quality Flashcards
What is the definition of subject contrast?
Depiction of lesions results from differential attenuation of the x-ray beam between the lesion and background tissues.
Subject contrast is the difference in x-ray intensity that is transmitted through a lesion in comparison to the adjacent tissues.
What is the definition of subject contrast?
Depiction of lesions results from differential attenuation of the x-ray beam between the lesion and background tissues.
Subject contrast is the difference in x-ray intensity that is transmitted through a lesion in comparison to the adjacent tissues.
What is the definition of positive contrast?
Subject contrast can be positive if the lesion absorbs fewer x-rays compared to the surrounding tissues.
Positive contrast will result in darker lesions in conventional radiographs.
What is the definition of image contrast?
The difference in the film density of a lesion in comparison to the film density of the adjacent tissues.
What is the definition of image contrast?
The difference in the film density of a lesion in comparison to the film density of the adjacent tissues.
What is the definition of film latitude?
The range of air kerma values that results in a satisfactory image contrast. Latitude is known as dynamic range in engineering.
What are the benefits of breast compression?
Reduces variation of air kerma in mammography, and permits the use of high-contrast film.
What is the definition of image contrast in digital imaging?
The difference in the monitor brightness of a lesion in comparison to the monitor brightness of the adjacent tissues.
What is the definition of Resolution (spatial resolution, high-contrast resolution, sharpness, or blur)?
Resolution is the ability of an imaging system to display two adjacent objects as discrete entities.
What is the penumbra?
The result of x-rays arriving from slightly different locations in the focal spot.
What is the definition of focal spot blur or geometric unsharpness?
The resultant loss of sharpness.
What is the definition of noise?
Noise describes the content of an image that limits the ability to visualize lesions or pathology.
What is the definition of Standard deviation?
Used to describe the spread or distribution of a data set and is the square root of the average of the square of all the sample deviations.
What is the definition of Bias?
The presence of systematic error.
What is the definition of Precision?
The reproducibility of a result but does not imply accuracy.
What is the definition of Accuracy?
Refers to how close a measured value is to the true value.
What is the definition of True positives (TPs)?
Are positive test results in patients who have the disease.
What is the definition of True negatives (TNs)?
Are negative test results in patients who do not have the disease.
What is the definition of False positives (FPs)?
Are positive test results in patients who do not have the disease.
What is the definition of False negatives (FNs)?
Are negative test results in patients who have the disease.
What is the definition of Sensitivity?
The ability to detect disease and is TP/(TP + FN), also known as the true-positive fraction.
A sensitive test has a low false-negative rate.
What is the definition of Specificity?
The ability to identify the absence of disease and is TN/(TN + FP), also known as the true-negative fraction.
A specific test has a low false-positive rate.
What is the definition of Accuracy?
The fraction of correct diagnosis and is (TP + TN)/(TP + FP + TN + FN).
What is the definition of Positive predictive value?
The probability of having the disease given a positive test and is TP/(TP + FP).
What is the definition of Negative predictive value?
The probability of not having the disease given a negative test and is TN/(TN + FN).
What is the definition of Prevalence of the disease?
(TP + FN)/(TP + FP + TN + FN).
The achievable number of lp/mm is normally taken to be
∼1/(2 ×FWHM).
The limiting spatial resolution (lp/mm) of a (dedicated) chest screen–film unit is likely
5.
The detector air kerma in digital photospot imaging is
1 μGy.
The air kerma that produces a single digital fluoroscopy frame is
0.01 μGy.
