Chapter 17
If a digital radiography imaging system has a spatial resolution of 10 lp/mm, what is the pixel size of that system? A) 0.05 mm B) 0.5 mm C) 0.1 mm D) 0.01 mm
A) 0.05 mm pg. 310: 10 lp/mm = 20 objects/mm = 20 pixels/mm Therefore, pixel size is 1/20 mm = 0.05 mm
If an image receptor has a high probability of interacting with the x-ray beam, then it has a high _____. A) DQE B) SNR C) MTF D) lp/mm
A) DQE pg. 318: the probability that an x-ray will interact with an image receptor is determined by the thickness of the capture layer and its atomic composition. The descriptor used for medical imaging is detective quantum efficiency (DQE) (DQE) = is a measure of x-ray absorption efficiency.
A _____ test tool is used to acquire data for an MTF curve. A) bar pattern B) post processing C) signal-to-noise ratio D) contrast-detail curve
A) bar pattern pg. 309: Quality control test objects and tools have been designed to measure the amount of blurring as a function of spatial frequency. Bar pattern test tools are used with a microdensitometer to measure the modulation of each spatial frequency pattern ... this data is used to construct an MTF curve.
The bit capacity of each pixel identifies the _____ of a digital imaging system. A) dynamic range B) grey scale C) spatial frequency D) MTF
A) dynamic range pg. 312: the dynamic range of a digital imaging system is identified by the bit capacity of each pixel.
Image detail is also called _____. A) spatial resolution B) spatial frequency C) signal to noise ratio D) dynamic range
A) spatial resolution pg. 314: image detail (spatial resolution)
If there were such thing as a perfect imaging system, the MTF would be equal to _____. A) 5 B) 1 C) 2 D) 4
B) 1 pg. 309: The ideal imaging system is one that produces an image that appears exactly as the object, such a system would have an MTF of 1.
What is the spatial frequency of a digital system that can resolve 100 µm? A) 5 lp/mm B) 10 lp/mm C) 50 lp/mm D) 100 lp/mm
B) 10 lp/mm pg. 308: see example 1 lp / 100 µm —> need to convert to mm first (mili = 10^-3) 100 µm = 100 x 10^-3 m —> move decimal left 3 spaces for proper scientific notation (exp. goes up 3) = 0.1 x 10^0 mm = 0.1 mm 0.1 lp / 1 mm = # of objects per mm 1 lp/ 0.1 mm = size of object = 10 lp/mm
The human visual system can distinguish _____ shades of gray. A) 10 B) 30 C) 300 D) 1000
B) 30 pg. 311: no more than 30 shades of gray can be viewed because of the limitations of the human visual system.
As mAs is increased the signal to noise ratio is _____. A) decreased B) increased C) not affected D) doubled
B) increased pg. 313: noise limits contrast resolution; therefore radiographers strive for a high SNR ... in general as the mAs is increased, the SNR also is increased.
With digital imaging, patient dose can be reduced by using higher _____ techniques. A) mAs B) kVp C) optical density D) contrast
B) kVp pg. 317: Because digital image contrast is unrelated to dose, kVp becomes less important ... The kVp should start to be increased, and an accompanying reduction in mAs ... the result will be adequate contrast resolution, constant spatial resolution, and reduced patient dose.
The _____ digital imaging system uses the highest dynamic range. A) computed tomography B) mammography C) magnetic resonance D) angiography
B) mammography pg. 312: CT and MRI systems generally have a 12 bit dynamic range. DR may have a 14 bit dynamic range. Digital mammography (DM) and digital mammographic tomosynthesis (DMT) systems have a 16-bit dynamic range.
The two principal characteristics of a medical image are _____. A) spatial resolution and noise B) spatial resolution and contrast resolution C) contrast resolution and modular transfer function D) contrast resolution and dynamic range
B) spatial resolution and contrast resolution pg. 307: (in the blue box) - Each medical image has two principle characteristics: spatial resolution and contrast resolution.
Screen-film radiography has a dynamic range of _____. A) 10 B) 100 C) 1,000 D) 10,000
C) 1,000 pg. 311 the dynamic range of a screen film radiograph is essentially three orders of magnitude, from an optical density of near 0 to 3.0. This represents a dynamic range of 1000.
The use of two screens in imaging results in a higher _____. A) spatial frequency B) pixel size C) MTF D) spatial resolution
C) MTF pg. 310: the use of two screens amplifies the contrast of large objects with little blur.
As spatial frequency increases the object size _____ and the spatial resolution _____. A) increases, increases B) decreases, decreases C) decreases, increases D) increases, decreases
C) decreases, increases pg. 307: As the spatial frequency becomes larger, the objects become smaller. Higher spatial frequency = better spatial resolution. Large soft tissue objects (liver, kidneys, brain) have low spatial frequency and therefore are easy to image. Bone trabeculae, breast microcalcifications, and contrast-filled vessels are high-frequency objects; therefore they are more difficult to image.
DQE is _____. A) density quantum effect B) direct quantum efficiency C) detective quantum efficiency D) detective quantum energy
C) detective quantum efficiency pg. 318: the probability that an x-ray will interact with an image receptor is determined by the thickness of the capture layer and its atomic composition. The descriptor used for medical imaging is detective quantum efficiency (DQE) (DQE) = is a measure of x-ray absorption efficiency.
Spatial frequency is used to describe the quality of spatial resolution in terms of _____. A) pixel size B) modular transfer function C) line pairs D) contrast resolution
C) line pairs pg. 307: in medical imaging spatial resolution is described by the spatial frequency = relates to the number of line pairs in a given length.
The portion of useful image-forming x-rays is referred to as the _____. A) frequency B) MTF C) signal D) noise
C) signal pg. 313: the signal in a radiographic image is that portion of the image-forming x-rays that represents anatomy.
If a digital system has a spatial resolution of 4 lp/mm, it can resolve an object as small as _____ mm. A) 8 B) 4 C) 0.25 D) 0.125
D) 0.125 pg. 307: One line pair consists of the line and an interspace of the same width as the line = which means for this problem there are 8 objects in 1 line pair (8/1 mm) 4 lp/mm = 8 objects in 1 mm = 8/1 mm 1/8 = 0.125 mm A spatial resolution of 4 lp/mm resolves 8 objects per mm, each object being 1/8 mm, or 0.125 mm
The use of an image receptor with _____ DQE can result in _____ patient doses. I) low, lower II) high, lower III) high, higher IV) low, higher A) I B) II C) I & III D) II & IV
D) II & IV pg. 318: the relative value of DQE for various image receptors means that fewer x-rays are required by the higher DQE receptors to produce an image; this translates into lower patient radiation dose.
Of all radiographic imaging systems,_____ has the best contrast resolution. A) digital radiography B) mammography C) magnetic resonance imaging D) computed tomography
D) computed tomography pg. CT has the best contrast resolution of all x-ray imaging systems.
Recent studies have shown that denser breast tissue is best imaged with _____. A) xerography B) computed tomography C) screen-film mammography D) digital mammography
D) digital mammography pg. 313: in 2006, results of the Digital Mammography Imaging Screening Trial (DMIST) found that for younger, denser breasts, DM (digital mammography) was better.
The number of gray shades that an imaging system can reproduce is called its _____. A) spatial frequency B) contrast C) spatial resolution D) dynamic range
D) dynamic range pg. 311: Dynamic range is the number of shades of gray that an imaging system can reproduce.
Digital radiography images should be repeated if there is a problem with _____. A) contrast B) overexposure C) brightness D) none of the above
D) none of the above pg. 317: see box 17-1 Exposures should not be repeated in digital radiography because of brightness or contrast concerns. Overexposed images do not have to be repeated and should not become a habit.
In digital imaging, spatial resolution is ultimately limited by _____. A) focal spot size B) spatial frequency C) contrast resolution D) pixel size
D) pixel size pg. 309: spatial resolution in digital imaging is limited by pixel size. No digital imaging system can image an object smaller than 1 pixel.
