Chapter 9 Exam Flashcards
A quality radiograph must include:
a. Accuracy of structural lines displayed
b. Minimal sharpness
c. Visibility of anatomic structures
d. All of the above
d. All of the above
Visibility factors of a quality radiograph include:
a. Brightness
b. Spatial resolution
c. Contrast
d. a and c
d. a and c
Which of the following results in a poor-quality digital image because of improper processing due to extreme over exposure to the image receptor
a. Distortion
b. Saturation
c. Quantum noise
d. Modulation transfer function
b. Saturation
What feature provides a numeric value indicating the level of radiation exposure to the digital image receptor?
a. Exposure indicator
b. Saturation
c. Pixel density
d. Grayscale
a. Exposure indicator
Anatomic tissues that attenuate the x-ray beam equally are said to have:
a. Quantum noise
b. High contrast
c. Low subject contrast
d. Less unsharpness
c. Low subject contrast
An imaging system that can resolve 10 Lp/mm instead of 6 Lp/mm is said to have:
a. Less distortion
b. More unsharpness
c. More distortion
d. Improved sharpness
d. Improved sharpness
Unwanted scatter exposure to the image receptor will likely increase:
a. Unsharpness
b. Brightness
c. Fog
d. Saturation
c. Fog
What is defined as “the range of exposure intensities an image receptor can accurately detect”?
a. Resolution
b. Contrast
c. Window level
d. Dynamic range
d. Dynamic range
For a given field of view (FOV), a _____ matrix size will result in _____ pixels
a. Large, fewer
b. Large, more
c. Small, more
d. None of the above
b. Large, more
In digital imaging, which of the following determines the range of grayscale available for display?
a. Pixel density
b. Matrix size
c. Pixel bit depth
d. Exposure indicator
c. Pixel bit depth
During digital image display, the contrast can be lowered (decreased) by increasing ______
a. Pixel density
b. Grayscale
c. Window level
d. Window width
d. Window width
The ability of the imaging system to distinguish between small objects that attenuate the x-ray beam similarly defines:
a. Dynamic range
b. Grayscale
c. insufficient detective quantum efficiency
d. Contrast resolution
d. Contrast resolution
Increasing the displayed field of view (FOV) for a fixed matrix size will result in:
a. Decreased pixel pitch
b. Increased pixel size
c. Decrease pixel size
d. Increased pixel bit depth
b. Increased pixel size
The visibility of anatomic structures is increased with:
a. Increased contrast-to-noise ratio (CNR)
b. Increased quantum noise
c. Increased signal-to-noise (SNR)
d. a and c only
d. a and c only
An imaging system with a higher detective quantum efficiency (DQE):
a. Is more efficient in converting x-ray exposure to a quality image
b. Produces images with decreased spatial resolution
c. Can display anatomic structures with less distortion
d. Produces images with decreased contrast resolution
a. Is more efficient in converting x-ray exposure to
Double exposing an image receptor will likely result in:
a. Pixel pitch
b. Foreshortening
c. Increased quantum noise
d. Image artifact
d. Image artifact
FOV/Matrix/pixel calculation
Pixel size (mm) = FOV (cm) / matrix size (mm)
the amount of luminance (light emission) of a display monitor
image brightness
The dynamic range in digital imaging is _____
linear
A _____ ______ _____ is only useful if the displayed image brightness can be optimized for human perception
wide dynamic range
The ability of the system to distinguish between small objects that attenuate the x-ray beam similarly
Contrast Resolution
a control that adjusts the contrast
Window width
the image has lower contrast, or more shades of gray
Wide window width
the image has higher contrast, or fewer shades of gray
Narrow window width
sets the midpoint of the range of brightness levels visible in the image, changing the this on the monitor allows the image brightness to be increased or decreased throughout the entire range of brightness levels
Window level
When an image is underexposed excessive _______ ______ may be visible
quantum noise
differential absorption, difference in brightness levels
Contrast
the combined result of multiple factors associated with the anatomic structure, quality of the radiation, capabilities of the image receptor
Radiographic contrast
refers to the absorption characteristics of the anatomic tissue radiographed and the quality of the x-ray beam
Subject contrast
What makes a good radiograph?
Accurately represents the anatomic area of interest. The characteristics evaluated for image quality are density or brightness, contrast, recorded detail or spatial resolution, distortion, and noise
The brightness of the image can be adjusted using the window level on the monitor to make the image looks better
Monitor brightness
Provides a numeric value indicating the level of radiation exposure to the digital image receptor
Exposure indicator
Distance measured from the center of a pixel to an adjacent pixel
Pixel pitch
Number of pixels per unit area
Pixel density
Measure of the imaging system’s ability to display the contrast of anatomic objects varying in size, measured 0 and 1.0
Modulation Transfer Function
in Modulation Transfer Function 0 =
no difference in brightness level
in Modulation Transfer Function 1.0 =
maximum difference in brightness levels
Modulation Transfer Function equation
MTF = (maximum intensity - minimum intensity) / (maximum intensity + minimum intensity)
Adds unwanted exposure to the radiographic image as a result of compton interactions
Decreases contrast
Scatter
- A concern in digital imaging, photon-dependent, is visible as brightness fluctuations on the image
- The fewer the photons reaching the IR to form the image, the more this will be visible on the digital image
- Fix this by increases mAs
Quantum noise
- A method of describing the strength of the radiation exposure on the comparison to the amount of noise apparent in the digital image
- Increasing this means that the strength of the signal is high compared to the amount of noise
- Increasing this will improve the quality of the digital image
Signal-to-Noise Ratio (SNR)
- Any unwanted brightness level on a radiographic image
- Can result from doubling exposing and IR, improper use of equipment, or patient clothing
Artifacts
results from the radiographic misrepresentation of either the size (magnification) or the shape of the anatomic part
Distortion
term used to evaluate accuracy of the anatomic structural lines
- A radiographic image cannot be an exact reconstruction of the anatomic structure
- Diagnostic quality is achieved by maximizing resolution and minimizing image distortion
Spatial resolution
A measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
Detective Quantum Efficiency (DQE)
The higher the DQE of a system, the _____ the radiation exposure to produce a quality image, thereby _________ patient exposure
lower, decreasing
refers to an increase in the image size compared with the object’s actual size
Size distortion
Shape distortion can appear in two different ways radiographically:
elongation & foreshortening
images of objects that appear longer than the true objects
elongation
images that appear shorter than the true objects
foreshortening
high-contrast =
short scale, fewer gray tones
low-contrast =
long scale, many gray tones
An imaging system that can resolve a greater number of line pairs per mm (higher spatial frequency) has increased ______ _______
spatial resolution
A pixel pair can be equivalent to a ____ ____
line pair
Coherent scatter =
radiationless scatter
_______ ________ is expressed in line pairs per mm of pixel size
Spatial frequency
