week 3: image quality Flashcards
image contrast is affected by
subject contrast, displayed contrast, detector contrast
contrast created by the computer hardware/software and then displayed on the viewing monitor
displayed contrast
contrast from the distribution of tissue densities and/or physiologic changes that are present in the anatomic part
subject contrast
Window width is the measure of the ___________________
range of gray shades that an image contains
Wide WW = (high/low) contrast image
low
Marrow WW = (high/low) contrast image
high
visibility of detail is affected by
Contrast resolution
Pixel brightness
Image contrast
Measured in digital imaging by DQE
visibility of detail is how well ___________________________-
the structures in the image can be seen in the displayed image
Ability of an imaging system to distinguish structures with similar tissue densities as separate entities
contrast resolution
how can contrast resolution be measured?
either signal-to-noise or contrast-to-noise ratio
Noise has a ____________ impact (increases/decreases) contrast resolution
negative, decreases
signal fluctuations that can randomly occur or be caused by internal electronics
electronic noise
noise that occurs in DR systems, also known as tiling; each tile may have slightly more or less amplification than surrounding chips, causing a tile-like appearance in the image
structured noise
patterns on the image generated by patient anatomy that is always present but not important for diagnosis
anatomical noise
caused by quantum mottle, uneven distribution of photons that is seen when not enough photons reach the image receptor; results in speckled appearance
quantum noise
DQE stands for
detector quantum efficiancy
DQE is one of the fundamental physical variables related to image quality and refers to the efficiency of a detector in ______________ into __________
converting incident x-ray energy, an image signal
DQE measures the __________________-
cleanliness or lack of noise in the image
DQE is affected by _____________________
the x-ray beam energy
x-ray photon quantity in detector area detector material
spatial frequency
the higher the DQE, the (higher/lower) the patient exposure dose
lower
The ability of an imaging system to create separate images of closely spaced objects and determines the edge definition capability
spatial resolution
what is spatial resolution affected by?
geometric factors
object factors
motion factors
image receptor factors
diagnostic performance measurement meanings
True Positive (TP)
True Positive (TP) – follow up test; image diagnosis was correct
diagnostic performance measurement meanings
False Positive (FP)
follow up test; image diagnosis was incorrect
diagnostic performance measurement meanings
True Negative (TN)
image diagnosis is negative and confirmed by follow up testing
diagnostic performance measurement meanings
Positive Negative (FN)
image diagnosis is negative but follow up testing shows presence of disease
Percentage or fraction of cases that are diagnosed correctly
diagnostic performance measurement accuracy
Indicates likelihood of obtaining a positive diagnosis in a patient with the disease
diagnostic performance measurement sensitivity
diagnostic performance measurement specificity
