Image Acquisition

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2.2 Image processing & quality assurance (102)
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1

What information, located on each box of film, is important to note and has a direct relationship to image quality?

A Number of films in the box

B Manufacturer's name

C Expiration date

D Emulsion lot

he Correct Answer is: C
Every box of film comes with the expiration date noted. Film used after its expiration date usually will suffer a loss of speed and contrast and will exhibit fog. Film should be ordered in quantities that will ensure that it is used before it becomes outdated, and it should be rotated in storage so that the oldest is used first. (Fauber, p. 182)

2

What determines the quantity of fluorescent light emitted from a fluorescent screen?

  1. Thickness of the phosphor layer
  2. Type of phosphor used
  3. Phosphor size

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: D
The larger the phosphors and the thicker the layer of phosphors, the more fluorescent light is emitted from the screen. Different types of phosphors have different conversion efficiencies; rare earth phosphors emit more light during a given exposure than do calcium tungstate phosphors. In general, when manufacturing fast screens, better detail results from using smaller phosphors in a thicker layer. Kilovoltage also affects the amount of fluorescent light emitted. As the kilovoltage level is increased, so is the amount of fluoroscopic light emitted by intensifying screen phosphors. (Selman, 9th ed., pp. 181–183)

3

The x-ray tube used in CT must be capable of

  1. high-speed rotation
  2. short pulsed exposures
  3. withstanding millions of heat units

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: D
A CT imaging system has three component parts—a gantry, a computer, and an operating console. The gantry component includes an x-ray tube, a detector array, a high-voltage generator, a collimator assembly, and a patient couch with its motorized mechanism. Although the CT x-ray tube is similar to direct-projection x-ray tubes, it has several special requirements. The CT x-ray tube must have a very high short-exposure rating and must be capable of tolerating several million heat units while still having a small focal spot for optimal resolution. To help tolerate the very high production of heat units, the anode must be capable of high-speed rotation. The x-ray tube produces a pulsed x-ray beam (1–5 ms) using up to about 1,000 mA. (Bushong, 8th ed., pp. 429–430; Bontrager and Lampignano, 6th ed., p. 731)

4

Which of the following is the correct order of radiographic film processing?

A Developer, wash, fixer, dry

B Fixer, wash, developer, dry

C Developer, fixer, wash, dry

D Fixer, developer, wash, dry

The Correct Answer is: C
During automatic processing (Figure 4–33), radiographic film is first immersed in the developer solution, which functions to reduce the exposed silver bromide crystals in the film emulsion to black metallic silver (which constitutes the image). Next, the film goes directly into the fixer, which functions to remove the unexposed silver bromide crystals from the emulsion. The film then is transported to the wash tank, where chemicals are removed from the film, and then into the dryer section, where it is dried before leaving the processor. (Fauber, p. 162; Shephard, p. 134)

5

Which of the following is (are) tested as part of a quality assurance (QA) program?

  1. Beam alignment
  2. Reproducibility
  3. Linearity

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: D
Each of the three is included in a good QA program. Beam alignment must be accurate to within 2% of the SID. Reproducibility means that repeated exposures at a given technique must provide consistent intensity. Linearity means that a given milliampere-second setting, using different milliampere stations with appropriate exposure-time adjustments, will provide consistent intensity. (Bushong, 8th ed., p. 460)

6

The smallest digital detectors (approximately 100 microns) provide the best spatial resolution and, therefore, are best-suited for use in:

A Fluoroscopy procedures

B Mammography

C Pediatric radiography

D Long bone measurement to ensure measurement accuracy

The Correct Answer is: B
Although spatial resolution is important in all radiographic or fluoroscopic applications, the systems affording the maximum spatial resolution are applied to those examinations such as mammography (B) where microscopic lesions must be detected. Lesions typically detected in fluoroscopic images (A) are at the macroscopic level. Maximum spatial resolution in cassetteless digital systems is limited by the size of the digital detectors. In the case of mammography, the best possible spatial resolution is required to ensure the detection and display of micro-calcifications, which may be suggestive of malignant lesions (B). Spatial resolution is important in pediatric imaging (C) and those systems used for this application provide sufficient resolution to display diagnostically acceptable images. The spatial resolution is not as important for long-bone measurement (D) as it is in mammography. These radiographic procedures, regardless of the spatial resolution, are intended to provide measurements from one joint to another, which does not require optimal spatial resolution. (Seeram, 1 st ed., p. 98)

7

Which of the following can affect histogram appearance?

  1. Centering accuracy
  2. Positioning accuracy
  3. Processing algorithm accuracy

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: D
The computed radiography (CR) laser scanner recognizes the various tissue-density values and constructs a representative grayscale histogram. A histogram is a graphic representation showing the distribution of pixel values. Histogram analysis and use of the appropriate LUT together function to produce predictable image quality in CR. Histogram appearance can be affected by a number of things. Degree of accuracy in positioning and centering can have a significant effect on histogram appearance (as well as patient dose). Change is effected in average exposure level and exposure latitude; these changes will be reflected in the images informational numbers (i.e., S number and exposure index). Other factors affecting histogram appearance, and therefore these informational numbers, include selection of the correct processing algorithm (e.g., chest vs. femur vs. cervical spine) and changes in scatter, SID, OID, and collimation. Figure 7–21 illustrates the effect of incorrect collimation on histogram appearance—in short, anything that affects scatter and/or dose. (Carlton and Adler, 4th ed., pp. 361–362)

8

Factors that contribute to film fog include

  1. the age of the film
  2. excessive exposure to safelight
  3. processor chemistry

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: D
Film age is an important consideration when determining the causes of film fog. Outdated film will exhibit loss of contrast in the form of fog and loss of speed. A safelight is “safe” only for practical periods of time required for the necessary handling of film. Films that are left out on the darkroom counter can be fogged by excessive exposure to the safelight. Film emulsion is much more sensitive to safelight fog after exposure. The high temperatures required for automatic processors' rapid processing are a source of film fog. Daily QA ensures that fog levels do not exceed the upper limit of 0.2 density. (Shephard, pp. 110, 123, 137)

9

Bone densitometry is often performed to

  1. measure degree of bone (de)mineralization
  2. evaluate results of osteoporosis treatment/therapy
  3. evaluate condition of soft tissue adjacent to bone

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: B
Dual x-ray absorptiometry (DXA) imaging is used to evaluate bone mineral density (BMD). Bone densitometry/DXA can be used to evaluate bone mineral content of the body, or part of it, to diagnose osteoporosis, or to evaluate the effectiveness of treatments for osteoporosis. It is the most widely used method of bone densitometry—it is low dose, precise, and uncomplicated to use/perform. DXA uses two photon energies—one for soft tissue and one for bone. Since bone is denser and attenuates x-ray photons more readily, the attenuation is calculated to represent the degree of bone density. Soft tissue attenuation information is not used to measure bone density. (Frank, Long, and Smith, 11th ed., vol. 3, pp.

10

If obtaining multiple images on one image plate, it is important to:

A Allow for X-ray tube cooling between successive exposures

B Avoid shielding of the image plate at all times to avoid field recognition errors

C Properly shield each exposed and unexposed area during the imaging of each individual image

D Expose the AP or PA projection in the right lower portion of the image plate

The Correct Answer is: C
Successive static exposures taken on one or more image plates rarely would cause overheating of the X-ray tube (A). Shielding of the image plate for multiple exposures is important to avoid intrafield scatter radiation exposure and a possible field recognition error (B). The keys to multiple fields on one IP are symmetry and uniform distribution. One should only use 3-on-1 distribution for fingers and toes where the amount of intrafield scatter is low. If larger body structures are done 3-on-1, the intrafield scatter will reduce the contrast unless the unexposed areas are shielded between exposures (C). The specific location of any projection on an image plate does not discount the importance of including one projection on one image plate (D). (Seeram, 1 st ed., p. 93)

11

IRs/cassettes frequently have a lead-foil layer behind the rear screen that functions to

A improve penetration

B absorb backscatter

C preserve resolution

D increase the screen speed

The Correct Answer is: B
Many cassettes/IRs have a thin lead-foil layer behind the rear screen to absorb backscattered radiation that is energetic enough to exit the rear screen, strike the metal back, and bounce back to fog the image. When this happens, the IR's metal hinges or straps may be imaged in high-kilovoltage radiography. The lead foil absorbs the backscatter before it can fog the film. (Shephard, pp. 41–42)

12

Boxes of film stored in too warm an area may be subject to

A static marks

B film fog

C high contrast

D loss of density

he Correct Answer is: B
X-ray film emulsion is sensitive and requires proper handling and storage. It should be stored in a cool (40–60°F), dry (40–60% humidity) place. Exposure to excessive temperatures or humidity can lead to film fog and loss of contrast. Static marks are a result of low humidity. (Fauber, p. 182)

13

Which of the following affects both radiographic density and intensifying screen speed?

  1. Thickness of phosphor layer
  2. Type of phosphors used
  3. Thickness of spongy screen support

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: B
Factors that affect screen speed also will affect radiographic density. Rare earth–type phosphors absorb x-rays more efficiently and convert their energy into fluorescent light; therefore, they affect both screen speed and radiographic density. The thickness of the phosphor layer affects speed and density similarly. As the thickness of the phosphor layer increases, speed and density increase. The spongy layer behind each intensifying screen helps to ensure good screen–film contact and, therefore, good recorded detail. The spongy layer is unrelated to radiographic density. (Shephard, p. 68)

14

The processor rollers that are out of solution and function to transfer the film from one solution to another are the

A deflector plates

B guide shoes

C crossover rollers

D turnaround assembly

The Correct Answer is: C
Turnaround assemblies are located at the bottom of each solution tank and function to direct the film from a downward to an upward motion. Guide shoes, also called deflector plates, serve to keep the film on its proper course by directing or guiding it around corners. The crossover rollers are located at the top of the processor, out of the solution, and direct the film from one solution tank to the next. These are the racks that need daily cleaning to avoid chemical or emulsion buildup on their surface. Chemical or emulsion buildup on roller surfaces can cause film artifacts. (Shephard, pp. 141–143)

15

A QA program serves to

  1. keep patient dose to a minimum
  2. keep radiographic quality consistent
  3. ensure equipment efficiency

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: D
A QA program includes regular overseeing of all components of the imaging system—equipment calibration, film and cassettes, processor, x-ray equipment, and so on. With regular maintenance, testing, and repairs, equipment should operate efficiently and consistently. In turn, radiographic quality will be consistent, and repeat exposures will be minimized, thereby reducing patient exposure. (Carlton and Adler, 4th ed., pp. 480–4

16

The process of “leveling and windowing” of digital images determines the image

A spatial resolution

B contrast

C pixel size

D matrix size

The Correct Answer is: B
The digital images' scale of contrast, or contrast resolution, can be changed electronically through leveling and windowing of the image. It is often stated simply that window level controls density/brightness and window width controls contrast. However, the level control specifically determines the central or middensity of the scale of contrast, whereas the window control determines the total number of densities/grays (to the right and left of the central/middensity). Matrix and pixel sizes are related to (spatial) resolution of digital images. (Fosbinder and Kelsey, p. 289; Bushong 9th ed p. 328)

17

Before a flat-panel detector can be used for a radiographic exposure, it must be prepared. This preparation is referred to as:

A Propagation

B Initialization

C Augmentation

D Instrumentation

he Correct Answer is: B
In order to prepare a flat-panel detector for an X-ray exposure, it must be initialized, where all switching elements are held in an “off” state by the appropriate control voltage (e.g., -5 volts) (B). Once the x-ray exposure is made, the pixel’s sensing area contains the image information. That information is obtained, line by line, by changing the control voltage (e.g., +10 volts). The resulting signal is digitized and stored.

Propagation (A) refers to energy travelling through a medium, such as an anatomical part. In medical imaging, the term “augmentation” (C) refers to either forced accelerated venous blood return to the heart by manually compressing a patient’s leg during a venous ultrasound Doppler procedure or, in mammography, when imaging augmented breasts. Instrumentation (D) is a general term that refers to devices used in medical procedures or the development, and safe and effective use of medical technology. (Seeram, 1 st ed., p. 114)

18

The safe approach to avoid an exposure field recognition error when using CR is to:

A Expose one image on the smallest IP available with collimation margins aligned parallel to the edges of the IP

B Expose multiple images on one IP, but make sure all collimation margins overlap

C Expose one image on the IP, but do not collimate

D Expose multiple images on one IP, but make sure all collimation margins are parallel to each other and do not overlap

The Correct Answer is: A
The safe approach to avoid an exposure field recognition error when using CR is to acquire one image on the smallest IP available. Collimation margins should also be parallel to the edges of the cassette (A). Exposing multiple images on one image plate (B) with overlapping collimation borders can result in an exposure field recognition error. The ALARA principle should be applied for every radiographic exposure. Collimation is critical to minimize patient exposure and dose (C). It is best to expose one image on the smallest image plate that will include all pertinent anatomy. Making multiple exposures on one image plate, regardless of attention to proper collimation can result in an exposure field recognition error (D). (Seeram, 1 st ed., p. 92)

19

For the same FOV, spatial resolution will be improved using

A a smaller matrix

B a larger matrix

C fewer pixels

D faster screens

The Correct Answer is: B
Field of view (FOV) refers to the area being viewed. The FOV can be increased or decreased. As the FOV is increased, the part being examined is magnified; as the FOV is decreased, the part returns closer to actual size. Pixel size is affected by changes in either the FOV or matrix size. For example, if the matrix size is increased, for example, from 256 × 256 to 512 × 512, pixel size must decrease. If FOV increases, pixel size must increase. Pixel size is inversely related to resolution. As pixel size decreases, resolution increases. (Fosbinder and Kelsey, p. 285)

20

Phosphors suitable for use in intensifying screens should have which of the following characteristics?

  1. High conversion efficiency
  2. High x-ray absorption
  3. Afterglow

A 1 only B 1 and 2 only C 3 only D 1, 2, and 3

The Correct Answer is: B
Phosphors used in intensifying screens must absorb a high percentage of the incident x-ray photons and convert x-ray photon energy to fluorescent light energy. Afterglow is an undesirable characteristic of phosphors because continued fluorescence causes unpredictable and increased density. (Shephard, p. 65)

21

Phosphors classified as rare earth include

  1. lanthanum oxybromide.
  2. gadolinium oxysulfide.
  3. cesium iodide.

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: B
Rare earth phosphors have a greater conversion efficiency than do other phosphors. Lanthanum oxybromide is a blue-emitting phosphor, and gadolinium oxysulfide is a green-emitting phosphor. Cesium iodide is the phosphor used on the input screen of image intensifiers; it is not a rare earth phosphor. (Shephard, p. 66)

22

The term windowing describes the practice of

A varying the automatic brightness control

B changing the image contrast and/or density

C varying the FOV

D increasing resolution

The Correct Answer is: B
In electronic imaging (CR/DR), the radiographer can manipulate the digital image displayed on the CRT through postprocessing. One way to alter image contrast and/or density is through windowing. This refers to some change made to window width and/or window level. Change in window width changes the number of gray shades, that is, image contrast. Change in window level changes the image brightness, that is, optical density. Windowing and other postprocessing mechanisms permit the radiographer to produce “special effects” such as edge enhancement, image stitching, and image inversion, rotation, and reversal. A digital image is formed by a matrix of pixels in rows and columns. A matrix having 512 pixels in each row and column is a 512 × 512 matrix. The term field of view is used to describe how much of the patient (e.g., 150-mm diameter) is included in the matrix. The matrix or field of view can be changed without affecting the other, but changes in either will change pixel size. Automatic brightness control is associated with image intensification. (Fosbinder and Kelsey, p. 289; Selman, 9th ed., pp. 190–191)

23

: Which apparatus is needed for the construction of a sensitometric curve?

  1. Penetrometer
  2. Densitometer
  3. Electrolytic canister

A 1 and 2 only B 1 and 3 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: A
Only two pieces of apparatus are needed to construct a sensitometric curve (Figure 4–36). First, a penetrometer (aluminum step wedge) is used to expose a film. Once the film is processed, a densitometer is needed to read the resulting densities. Log-relative exposure is charted along the x (horizontal) axis; an increase in log-relative exposure of 0.3 results from doubling the exposure. Optical density is plotted on the y (vertical) axis and represents the amount of light transmitted through a film compared with the amount of light striking the film (expressed as a logarithm). (Bushong, 8th ed., p. 274)

24

The optimal alignment of the anatomical part being imaged for all digital receptors should be:

A Field centered to IP with at least two collimation margins and parallel to the IP edges

B Centered anywhere on the IP, but having four distinct collimation margins, regardless of parallel orientation to the IP edges

C Centered to the IP with at least one collimation margin aligned to nearest edge of IP

D Field centered to IP with four collimation margins parallel to the IP edges

The Correct Answer is: D
The optimal alignment when using CR is field centered to the plate with four collimation margins parallel to the IP edges (D). Otherwise, the exposure field may not be correctly identified, resulting in a processing error. An exposure field with only two collimation margins and parallel to the IP edges (A) results in extraneous radiation exposure in the top and bottom portions of the receptor. This exposure information may cause misidentification of the exposure field, causing a processing error. Simply exposing an anatomical part anywhere on the receptor (B) has the potential to cause misidentification of the exposure field, causing a processing error. If only one collimation margin is included on the receptor (C), the radiographer has improperly centered the anatomical part. This may result in misidentification of the exposure field and therefore, cause a processing error. (Seeram, 1 st ed., p. 91).

25

Silver reclamation may be accomplished in which of the following ways?

  1. Metallic replacement cartridge
  2. Electrolytic plating unit
  3. Removal from used film

A 1 only B 2 only C 1 and 2 only D 1, 2, and 3

he Correct Answer is: D
Unexposed, undeveloped silver is removed from film emulsion in the fixer solution. It is recovered (reclaimed) from the solution and sold. The silver may be reclaimed electrolytically or with a metallic replacement cartridge. Silver may also be reclaimed from processed radiographs or unexposed film. (Selman, 9th ed., p. 203; Shephard, pp. 155–160)

26

Which of the following is an abnormal intensifying screen action?

A Fluorescence

B Luminescence

C Speed

D Lag

he Correct Answer is: D
Luminescence is the production of energy in the form of light. Two types of luminescence are fluorescence and phosphorescence. Fluorescence occurs when an intensifying (radiographic) screen absorbs x-ray photon energy, emits light, and ceases to emit light as soon as the energizing source ceases. Fluoroscopic screens continue to emit light for a short time after the exposure has terminated. This characteristic (phosphorescence) is a desirable quality in fluoroscopic screens. Lag occurs when an intensifying (radiographic) screen continues to fluoresce after the x-ray stimulation has terminated. This characteristic is undesirable and causes excessive density. Screen speed is identified by the amount of light emitted by the phosphors. (Carlton and Adler, 4th ed., p. 320)

27

The X-ray scintillator layer used in in direct flat-panel digital detectors is usually either _____________ or ______________.

A Silicon dioxide, silver halide

B Cesium iodide, gadolinium oxysulfide

C Yttrium oxysulfide, barium fluoride

D Amorphous silicon dioxide, barium platinocyanide

The Correct Answer is: B
The X-ray scintillator used in the indirect flat-panel digital detector is usually either cesium iodide (CsI) or gadolinium oxysulfide (Gd 2 O 2 S). These phosphors are not new to X-ray imaging; they have been used in conventional X-ray image intensifiers (CsI) and in rare-earth intensifying screens (Gd 2 O 2 S) for many years (B). Silicon dioxide is a substance used in sonographic imaging, whereas silver halide is found in conventional radiographic film emulsions (A). Yttrium oxysulfide is a phosphor material used in conventional rare earth radiographic screen phosphors, whereas barium fluoride is a component of barium fluoride bromide crystals coated with europium in computed radiography (CR) image plate phosphors (C). Amorphous silicon dioxide is a material used in the photodiodes used in indirect digital flat panel detectors, whereas barium platinocyanide was a phosphor material used in experiments conducted by Wilhelm Roentgen. The latter material was responsible for detecting the X-ray energy Roentgen produced during his experiments using an energized Crookes tube. The material absorbed the energy produced in the tube and converted it into visible light. Thus, the new-found X-rays were originally called “X-light.” (Seeram, 1 st ed., p. 108)

28

Which of the following is (are) methods used for x-ray film silver reclamation?

  1. Photoelectric method
  2. Metallic replacement method
  3. Electrolytic method

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: C
About half the silver in a film emulsion remains to form the image. The other half is removed from the film during the fixing process. Therefore, fixer solution has a high silver content. Silver is a toxic metal and cannot simply be disposed of into the public sewer system. Since silver is also a precious metal, it becomes financially wise to recycle the silver removed from x-ray film. The three most commonly used silver recovery systems are the electrolytic, metallic replacement, and chemical precipitation methods. In electrolytic units, an electric current is passed through the fixer solution. Silver ions are attracted to and become plated onto the negative electrode of the unit. The plated silver is periodically scraped from the cathode and accurately measured so that the hospital can be reimbursed appropriately. The electrolytic method is a practical recovery system for moderate-and high-use processors. The metallic replacement (or displacement) method of silver recovery uses a steel mesh/steel wool type of cartridge that traps silver as fixer is run through it. This system is useful for low-volume processors and is often also used as a backup to the electrolytic unit. Chemical precipitation adds chemicals that release electrons into the fixer solution. This causes the metallic silver to precipitate out, fall to the bottom of the tank, and form a recoverable sludge. This method is used principally by commercial silver dealers. (Carlton and Adler, 4th ed., pp. 298–299)

29

As the CR laser scanner/reader recognizes the phosphostimulated luminescence (PSL) released by the PSP storage plate, it constructs a graphic representation of pixel value distribution called a

A processing algorithm

B histogram

C lookup table

D exposure index

The Correct Answer is: B
As the CR laser scanner/reader recognizes the phosphostimulated luminescence (PSL) released by the PSP storage plate, it constructs a graphic representation of pixel value distribution called a histogram.

The photostimulable storage phosphor (PSP) within the IP is the image receptor (IR). The PSP is a europium-doped barium fluorohalide coated storage plate. When the PSP is exposed by x-ray photons, the x-ray energy interacts with the crystals and a small amount of visible light is emitted, but most of the x-ray energy is stored (hence, the term storage plate). This stored energy represents the latent image.

The IP is placed in the CR scanner/reader where a helium–neon, or solid-state, laser beam scans the PSP and its stored energy is released as blue-violet light (phosphostimulated luminescence [PSL]). This light signal represents varying tissue densities and the latent image that is then transferred to an analog-to-digital converter (ADC)—converting the signal to a digital (electrical) one to be displayed on a monitor.

The PSL values will result in numerous image density/brightness values that represent various tissue densities (i.e., x-ray attenuation properties), for example, bone, muscle, blood-filled organs, air/gas, pathologic processes, and so on. The CR scanner/reader recognizes all these values and constructs a representative gray-scale histogram of them corresponding to the anatomical characteristics of the imaged part. Thus, all PA chest histograms will be similar, all lateral chest histograms will be similar, all pelvis histograms will be similar, and so on.

30

All of the following are potential digital pre-processing problems, except:

A Edge enhancement

B Defective pixel

C Image lag

D Line noise

The Correct Answer is: A
Edge enhancement (A) is a type of post-processing image manipulation, which can be effective for enhancing fractures and small, high-contrast tissues. Answers B, C and D are problems that may be encountered in pre-processed digital images. (Bushong, 10 th ed., p. 326).

31

The presence of dust or scratches on intensifying screens will cause

A decreased density in those areas of the image

B increased density in those areas of the image

C decreased density in all areas of the image

D increased density in all areas of the image

The Correct Answer is: A
If intensifying-screen phosphors are covered with dust, either they will not fluoresce or their fluorescence will not reach the IR emulsion. Similarly, if the screen is scratched and phosphors are removed, there will be no fluorescence to expose the IR. In both cases, then, those areas will exhibit little or no density. (Shephard, p. 75)

32

Cassetteless digital systems have a fixed spatial resolution determined by:

A The image plate laser divergence

B The focal spot size used

C The thin film transistor (TFT) detector element (DEL) size

D The proximity of the phosphor screen crystals

The Correct Answer is: C
A cassetteless system refers to direct or indirect digital systems where no cassette/IP is used. CR uses an IP containing a PSP (photostimulable phosphor plate). Laser divergence is a negative factor that occurs in computed radiography (CR) readers (A). However, with cassetteless digital systems, the spatial resolution of the detector elements (DEL) determines the maximum image resolution that can be obtained and is important in both CR and direct or indirect digital imaging systems. The thin film transistor (TFT) or detector element (DEL) size is fixed and, therefore, the maximum spatial resolution is defined by the physical size of the individual elements and their proximity to each other (C).

The focal spot size (B) appropriate for the anatomical part being imaged is important to render optimal image resolution. Proximity of the phosphor screen crystals refers to conventional film-screen radiography (D). (Seeram, 1 st ed., p. 97)

33

Geometric blur can be evaluated using all the following devices except

A star pattern

B slit camera

C penetrometer

D pinhole camera

he Correct Answer is: C
Focal-spot size accuracy is related to the degree of geometric blur, that is, edge gradient or penumbra. Manufacturer tolerance for new focal spots is 50%; that is, a 0.3-mm focal spot actually may be 0.45 mm. Additionally, the focal spot can increase in size as the x-ray tube ages—hence the importance of testing newly arrived focal spots and periodic testing to monitor focal-spot changes. Focal-spot size can be measured with a pinhole camera, slit camera, or star-pattern-type resolution device. The pinhole camera is rather difficult to use accurately and requires the use of excessive tube (heat) loading. With a slit camera, two exposures are made; one measures the length of the focal spot, and the other measures the width. The star pattern, or similar resolution device such as the bar pattern, can measure focal-spot size as a function of geometric blur and is readily adaptable in a QA program to monitor focal-spot changes over a period of time. It is recommended that focal-spot size be checked on installation of a new x-ray tube and annually thereafter. (Bushong, 8th ed., p. 462)

34

What information must be included on an x-ray image for it to be considered as legitimate legal evidence?

  1. Name of facility where exam performed
  2. Examination date
  3. Date of birth

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: B
X-ray images are often subpoenaed as court evidence in cases of medical litigation. In order to be considered as legitimate legal evidence, each x-ray image must contain certain essential and specific patient information. Essential information that must be included on each image is patient identification, the identity of the facility where the x-ray study was performed, the date that the study was performed, and a right- or left-side marker.

Other useful information that may be included, but that is not considered essential, is additional patient demographics such as their date of birth, the identity of the referring physician, the time of day that the study was performed, and the identity/initials of the radiographer performing the examination.

35

What is the purpose of the thin layer of lead that is often located behind the rear intensifying screen in an IR?

A To prevent crossover

B To increase screen speed

C To diffuse light photons

D To prevent scattered radiation fog

The Correct Answer is: D
The purpose of the thin layer of lead that is often located behind the rear intensifying screen in a cassette is to absorb x-rays that penetrate the screens, strike the rear of the cassette, and bounce back toward the film emulsion, resulting in scattered radiation fog. The thin layer of lead absorbs these x-ray photons and thus improves the radiographic image. (Shephard, pp. 41–42)

36

Which of the following materials may be used as grid interspace material?

  1. Lead
  2. Plastic
  3. Aluminum

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: C
A grid is composed of alternate strips of lead and interspace material. The lead strips serve to trap scattered radiation before it fogs the IR. The interspace material must be radiolucent; plastic or sturdier aluminum usually is used. Cardboard was used in the past as interspace material, but it had the disadvantage of being affected by humidity (moisture). (Selman, 9th ed., p. 234)

37

The pre-contrast image used to subtract pixel values from the post-contrast image showing contrast-filled blood vessels in digital subtraction angiography is called the:

A Mask image

B Ghost (phantom) image

C Moiré image

D Latent image

The Correct Answer is: A
In digital image subtraction, the pixel values from post-contrast images are electronically subtracted from pixel values from the first pre-contrast (mask) image (A) to show contrast-filled blood vessels with the other structures (e.g., bone) removed in order to enhance the diagnostic impressions of the radiologist. A ghost (or phantom) image (B) is an image artifact. The appearance of ghost images can be seen when CR image plates are incompletely erased. If an image plate has not been used for 24 hours, its phosphor storage plate should be erased again before using it for a diagnostic radiographic exposure. If a radiographic grid has a frequency that approximates the CR scan frequency and the grid strips are oriented in the same direction as the scan, the Moiré artifact may be observed (C); to decrease the possibility of this effect, high frequency grids are recommended for digital imaging. The latent image (D) is the image that exists in a radiographic film prior to chemical processing. It represents the collection of silver atoms around the sensitivity specks within the film emulsion. Upon chemical processing in a darkroom, the film will reveal an anatomical image with densities representing the varying levels of radiation exposure to the sensitivity specks contained within the film’s emulsion. (Seeram, p. 36).

38

Characteristics of DR imaging include

  1. solid-state detector receptor plates
  2. a direct-capture imaging system
  3. immediate image display

A 1 only B 1 and 3 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: D
Whereas CR uses traditional x-ray devices to enclose and protect the PSP/SPS, digital radiography (DR) requires the use of somewhat different equipment. DR does not use cassettes or a traditional x-ray table; it is a direct-capture system of x-ray imaging. DR uses solid-state detector plates as the x-ray IR (instead of a cassette in the Bucky tray) to intercept the collimated x-ray beam and form the latent image. The solid-state detector plates are made of barium fluorohalide compounds similar to that used in CR's PSP/SPSs. DR affords the advantage of immediate display of the image, compared with CR's delayed image display. (Shephard, p. 335)

39

The functions of a picture archiving and communication system (PACS) include

  1. storage of analog images
  2. acquisition of digital images
  3. storage of digital images

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: C
PACS refers to a picture archiving and communication system. Analog images (conventional images) can be digitized with a digitizer. PACS systems receive digital images and display them on monitors for interpretation. These systems also store images and allow their retrieval at a later time. PACS systems provide us with the option of a completely filmless radiology department. (Shephard, p

40

As the conversion efficiency of intensifying-screen phosphors increases,

  1. patient dose increases
  2. noise increases
  3. speed increases

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: C
Intensifying screens are made of phosphors that absorb a rather small quantity of x-ray energy and convert that energy to a considerable quantity of visible luminescent light (fluorescence in the case of cassette intensifying screens, phosphorescence in the case of fluoroscopic screens). Rare earth phosphors do this much more efficiently than the older calcium tungstate phosphors because rare earth phosphors have a higher DQE (Detective Quantum Efficiency). Thus, it is principally the luminescent light that exposes film emulsion, not x-rays. The more light the phosphors emit, the higher is the speed of the system, and the less patient dose is required. However, as speed increases, noise (in the form of quantum mottle) increases. (Bushong, 8th ed., p. 223)

41

When radiographing a cross-table lateral hip or axial shoulder using CR, one method of creating a collimation margin at the bottom of the radiograph is to:

A Use a narrow lead strip at the bottom edge of the IP, but out of the anatomy

B Only one collimation margin is necessary, so this would not be necessary

C Make two exposures with suspended respiration; one for the uppermost anatomy, then a second for the dependent anatomy

D Expose the anatomy as is and use the post-processing cropping feature

The Correct Answer is: A
The difference between cross-table hips or axial shoulders is that most often only one collimated edge is visible (because soft tissue extends to edge of table/IP). If a second collimated border is not detected, the exposure field is not accurately located, processing/rescaling errors will likely occur. One may create a second collimation margin by using a narrow (approx. 1 in.) lead strip at the bottom of the IP to generate a “margin” between the exposure field and the edge of the cassette (A). If only one collimation margin is included on the receptor (B), the radiographer has improperly centered the anatomical part. This may result in misidentification of the exposure field and therefore, cause a processing error. Two exposures at different central ray locations (C) would result in two images where a misaligned image of the anatomy for both exposures would result. The cropping feature (D) is a post-processing function that will not affect the system’s ability to recognize the exposure field. (Seeram, 1 st ed., p. 92)

42

Unopened boxes of radiographic film should be stored away from radiation and

A in the horizontal position

B in the vertical position

C stacked with the oldest on top

D stacked with the newest on top

The Correct Answer is: B
Boxes of x-ray film, especially the larger sizes, should be stored in the vertical (upright) position. If film boxes are stacked on one another, the sensitive emulsion can be affected by pressure from the boxes above. Pressure marks are produced and result in loss of contrast in that area of the radiographic image. When retrieving x-ray film from storage, the oldest should be used first. (Shephard, p. 110)

43

Which of the following can cause poor screen–film contact?

  1. Damaged IR frame
  2. Foreign body in IR
  3. Warped IR front

A 1 only B 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: D
Perfect contact between the intensifying screens and the film is essential to maintain image sharpness. Any separation between them allows diffusion of fluorescent light and subsequent blurriness and loss of detail. Screen–film contact can be diminished if the IR frame is damaged and misshapen, if the front is warped, or if there is a foreign body between the screens, elevating them. (Selman, 9th ed., p. 185)

44

Incorrect spectral matching between rare earth intensifying screens and film emulsion results in

A longer-scale contrast.

B insufficient density.

C decreased recorded detail.

D excessive density.

he Correct Answer is: B
Calcium tungstate intensifying screens have a broad range of emitted light, and it is more likely that somewhat different film emulsions still could be compatible with them. However, rare earth phosphors emit light over a relatively short range, usually in the green portion of the spectrum. The film emulsion must be sensitive and responsive to that particular color, or the expected results will not occur. If, for example, a blue-sensitive emulsion were matched with green-emitting screens, the resulting radiograph would be underexposed because the blue-sensitive film emulsion would not be responsive to the green-emitting phosphors. (Shephard, pp. 65–66

45

A wire-mesh test is performed to evaluate screen

A lag

B contact

C resolution

D intensification

The Correct Answer is: B
A wire mesh supported between two rigid pieces of clear plastic is used to evaluate screen–film contact. The mesh is placed on an IR and radiographed. On viewing, any areas that appear unsharp or blurry are indicative of poor screen–film contact. A screen lag test is performed by radiographing a phantom using an empty cassette/IR and then loading it with film and leaving it for a few minutes. If, after processing, there is any indication of an image, there is most probably screen lag. (Shephard, p. 54) Mark for Review Discussion Add to My Notes Performance Overall Time Spent 00:16:21

46

Which of the following contribute(s) to base-plus fog?

  1. Chemical fog
  2. Base tint
  3. Background radiation

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

he Correct Answer is: D
Base-plus fog is the small amount of measurable density on unexposed and processed x-ray film. This fog is a result of environmental background radiation that is present during film manufacture, transportation, and storage. The (usually blue) tint, given the base to enhance contrast, adds more density. Finally, the emulsion receives further fog as the film is chemically processed. Base-plus fog should not exceed 0.2D. (Carlton and Adler, 4th ed., p. 307)

47

Film base is currently made of which of the following materials?

A Cellulose nitrate

B Cellulose acetate

C Polyester

D Glass

he Correct Answer is: C
Film base functions to support the silver halide emulsion. Today's film base is made of tough, nonflammable polyester. Cellulose nitrate was used in the past, but it was highly flammable. Cellulose acetate, also used in the past, was not flammable, but it was not as durable as polyester. The earliest supports for emulsion were plates of glass (hence, the term flat plate). (Selman, 9th ed., p. 194)

48

Off-focus and scatter radiation outside of the exposure field when using CR can cause

A Narrowing of the histogram

B Widening of the histogram

C Improper alignment of the exposure field

D High contrast

The Correct Answer is: B
Off-focus and scatter radiation outside of the exposure field would be detected as additional information and, therefore, would widen the histogram (B), resulting in a processing error. Histogram analysis errors can result in rescaling errors and exposure indicator determination errors. Alignment of the exposure field (C) is set by the radiographer prior to the exposure. Any off-focus and scatter radiation exposure outside of the exposure field will not change this alignment. Scatter radiation decreases image contrast (D). (Seeram, 1 st ed., p. 91).

49

During measurement of blood pressure, which of the following occurs as the radiographer controls arterial tension with the sphygmomanometer?

A The brachial vein is collapsed.

B The brachial artery is temporarily collapsed.

C The antecubital vein is monitored.

D Oxygen saturation of arterial blood is monitored.

he Correct Answer is: B
A stethoscope and a sphygmomanometer are used together to measure blood pressure. The sphygmomanometer's cuff is placed around the midportion of the upper arm. The cuff is inflated to a value higher than the patient's systolic pressure to temporarily collapse the brachial artery. As the inflation is gradually released, the first sound heard is the systolic pressure; the normal range is 110 to 140 mmHg. When no more sound is heard, the diastolic pressure is recorded. The normal diastolic range is 60 to 90 mm Hg. Elevated blood pressure is called hypertension. Hypotension, low blood pressure, is not of concern unless it is caused by injury or disease; in that case, it can result in shock. (Adler and Carlton, 4th ed., pp. 200–201)

50

Resolution in CR increases as

  1. laser beam size decreases
  2. monitor matrix size decreases
  3. PSP crystal size decreases

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

The Correct Answer is: C
Spatial resolution in CR is impacted by the size of the PSP, the size of the scanning laser beam, and monitor matrix size. High-resolution monitors (2–4 MP, megapixels) are required for high-quality, high-resolution image display. The larger the matrix size, the better is the image resolution. Typical image matrix size (rows and columns) used in chest radiography is 2,048 × 2,048. As in traditional radiography, spatial resolution is measured in line pairs per millimeter. As matrix size is increased, there are more and smaller pixels in the matrix and, therefore, improved spatial resolution. Other factors contributing to image resolution are the size of the laser beam and the size of the PSP/SPS phosphors. Smaller phosphor size improves resolution in ways similar to that of intensifying screens—anything that causes an increase in light diffusion will result in a decrease in resolution. Smaller phosphors in the PSP (SPS) plate allow less light diffusion. Additionally, the scanning laser light must be of the correct intensity and size. A narrow laser beam is required for optimal resolution. (Shephard, p. 336)

51

In order for a phosphor to be suitable for use in intensifying screens, it should have which of the following characteristics?

  1. High conversion efficiency
  2. High x-ray absorption
  3. High atomic number

A 1 only B 3 only C 1 and 2 only D 1, 2, and 3

The Correct Answer is: D
Intensifying-screen phosphors that have a high atomic number are more likely to absorb a high percentage of the incident x-ray photons and convert x-ray photon energy to fluorescent light energy. How efficiently the phosphors detect and interact with the x-ray photons is termed quantum detection efficiency. How effectively the phosphors make this energy conversion is termed conversion efficiency. (Shephard, p. 65)

52

Pixel size and spacing determine the spatial resolution of the digital image. This is known as:

A Pixel pitch

B Focal resolution

C Nyquist resolution

D Frequency modulation

The Correct Answer is: A
The pixel size and spacing (i.e., pixel pitch, which is the distance from the midpoint of one pixel to the midpoint of the adjacent pixel) determine the spatial resolution of the image (A). The number of pixels can be obtained by multiplying the horizontal number of pixels by the vertical number of pixels in the image matrix (A). Focal resolution (B) is not a term used to describe spatial resolution in a digital radiographic image. However, the focal “spot” size does have an influence on image resolution. The smaller focal spot sizes should be used for smaller anatomical parts, whenever involuntary motion is absent. Nyquist “resolution” (C) is not a term used to describe spatial resolution in a digital radiographic image. However, the Nyquist “frequency,” which is 1/2X the pixel pitch (mm) is equivalent to the spatial resolution. Frequency modulation (D) is not a term used to describe spatial resolution in a digital radiographic image. However, modulation transfer function (MTF) measures the ability of a detector to transfer its spatial resolution characteristics to the image. (Seeram, 1 st ed., p. 110)

53

When a slow screen–film system is used with a fast screen–film AEC system, the resulting images

A are too light

B are too dark

C have improved detail

D have poor detail

he Correct Answer is: A
When an AEC (phototimer or ionization chamber) is used, the system is programmed for the use of a particular screen–film speed (e.g., 400 speed). If a slower-speed screen IR is placed in the Bucky tray, the AEC has no way of recognizing it as different and will time the exposure for the system for which it is programmed. For example, if the AEC is programmed for a 400-speed screen–film combination, and if a 200-speed screen IR is placed in the Bucky tray, the resulting radiograph will have half the required radiographic density. (Shephard, pp. 65–66)

54

A graphic diagram of signal values representing various densities within the part being imaged is called a

A processing algorithm

B DICOM

C histogram

D window

he Correct Answer is: C
A histogram is a graph usually having several peaks and valleys representing the pixel values/absorbing properties of the various tissues, and so on that make up the imaged part. These various attenuators include such things as bone, muscle, air, contrast agents, foreign bodies, and pathology. The various pixel values, then, represent image contrast. If the histogram has a rather flat “tail,” this represents underexposed areas at the periphery of the image, which can skew the overall histogram analysis. The radiographer selects the particular processing algorithm on the computer/control panel that corresponds to the anatomic part and projection being performed. DICOM (Digital Imaging and Communications in Medicine) refers to the standard for communication between PACS and HIS/RIS systems. Windowing refers to the radiographer's postprocessing adjustment of contrast and density (at the workstation). (Shephard, pp. 341, 345)

55

Due to the high sensitivity of digital detectors to low intensity radiation (background, scatter and/or off-focus radiation), there is likely to be scatter and off-focus radiation contributing to the image outside the collimation margins. Since many radiologists find this distracting, the most appropriate radiographer action would be to:

A Use film-screen imaging only

B Apply a black border to the image before it is printed or sent to PACS

C Expose the anatomical parts as is; there is nothing that can be done to improve the presentation of the image(s) due to the inherent sensitivity of the system

D Reduce exposure factors by one-half to ensure minimal scatter and off-focus radiation

he Correct Answer is: B
Film-screen radiography has been abandoned in most hospitals and imaging centers. Most of these institutions no longer maintain a darkroom or resources to produce film-screen images (A). Many radiologists find scatter and off-focus radiation distracting when viewing images. The appropriate response to scatter and off-focus exposure outside the collimation margin is to apply a black border to the image before it is printed or sent to PACS (B). Close collimation should be used to minimize scatter radiation (C). The exposure factors must be appropriate for the anatomical part being imaged. Halving the appropriate mAs or kVp (D) will result in image mottle or inadequate penetration of the part, respectively. (Seeram, 1 st ed., p. 94)

56

Histogram data that is skewed relative to the values of interest (VOI) of the histogram analysis used for a particular exam may be caused by all of the following, except:

A Anatomical structures not centered to the IP

B Excessive windowing

C The X-ray beam is not correctly aligned to the edges of the IP

D The beam edge is irregular because of overlap of a radiopaque shadow, such as a gonadal shield

he Correct Answer is: B
Windowing (B) is a post-processing method of adjusting the brightness and contrast in the digital image. Histogram analysis errors occur prior to post-processing of the image. There are two types of windowing: level and width. Window level adjusts the overall image brightness. When the window level is increased, the image becomes darker. When decreased, the image becomes brighter. Window width adjusts the ratio of white to black, thereby changing image contrast. Narrow window width provides higher contrast (short-scale contrast), whereas wide window width will produce an image with less contrast (long-scale contrast). Answers A, C and D can cause histogram data to be skewed relative to the values of interest (VOI) of the histogram analysis used for a particular exam. (Seeram, 1 st ed., p. 91).

57

An exposed image plate will retain its original image quality for about

A 2 hours

B 8 hours

C 24 hours

D 48 hours

The Correct Answer is: B
Computed radiography (CR) cassettes use no intensifying screens or film—hence, the term filmless radiography. The cassettes have a protective function (for the image plate within) and can be used in the Bucky tray or directly under the anatomic part; they need not be light-tight because the image plate is not light sensitive. The cassette has a thin lead-foil backing (similar to traditional cassettes) to absorb backscatter. Inside the cassette is the photostimulable phosphor (PSP) image plate, sometimes referred to simply as an image plate (IP). This PSP or IP within the cassette has a layer of europium-activated barium fluorohalide that serves as the IR as it is exposed in the traditional manner and receives the latent image. The PSP can store the latent image for several hours; after about 8 hours, noticeable image fading will occur. (Carlton and Adler, 4th ed., p. 358

58

Exposure-type artifacts include

  1. poor screen–film contact
  2. motion
  3. chemical fog

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: B
Artifacts can be a result of exposure, handling, and storage, or processing. Exposure artifacts include motion, double exposure, and poor screen–film contact—the effects of these are seen as a result of the exposure. Handling and storage artifacts include static electrical discharge, crinkle marks, scratches, and light or radiation fog—all these occur as a result of improper use or storage. Processing artifacts occur while the film is in the automatic processor and include pi lines, guide-shoe marks, and chemical fog. (Bushong, 8th ed., p. 473

59

A film emulsion having wide latitude is likely to exhibit

A high density

B low density

C high contrast

D low contrast

The Correct Answer is: D
Every film emulsion has a characteristic curve representative of that film's speed, contrast, and latitude. A gentle curve (as opposed to a steep curve) usually indicates a film with slow speed, low contrast, and more latitude. (Shephard, p. 105)

60

Which of the following requires two exposures to evaluate focal-spot accuracy?

A Pinhole camera

B Slit camera

C Star pattern

D Bar pattern

The Correct Answer is: B
Focal-spot size accuracy is related to the degree of geometric blur, that is, edge gradient or penumbra. Manufacturer tolerance for new focal spots is 50%; that is, a 0.3-mm focal spot actually may be 0.45 mm. Additionally, the focal spot can increase in size as the x-ray tube ages—hence, the importance of testing newly arrived focal spots and periodic testing to monitor focal-spot changes. Focal-spot size can be measured with a pinhole camera, slit camera, or star-pattern-type resolution device. The pinhole camera is rather difficult to use accurately and requires the use of excessive tube (heat) loading. With a slit camera, two exposures are made; one measures the length of the focal spot, and the other measures the width. The star pattern, or similar resolution device, such as the bar pattern, can measure focal-spot size as a function of geometric blur and is readily adaptable in a QA program to monitor focal-spot changes over a period of time. It is recommended that focal-spot size be checked on installation of a new x-ray tube and annually thereafter. (Bushong, 8th ed., p. 462)

61

What effect will a stained intensifying screen have on the finished radiograph?

A Blurring

B Magnification

C Decreased density

D Increased density

The Correct Answer is: C
Intensifying screens react to the presence of x-ray photons and change their energy to visible fluorescent light energy, which serves to expose the adjacent film emulsion. If an intensifying screen becomes stained, either partly or wholly, the stained area will not react to x-ray photons as completely and will emit less light. Therefore, the film emulsion adjacent to the stained area(s) will exhibit decreased density on the finished radiograph. (Shephard, p. 75)

62

All of the following are factors that cause low contrast in CR images, except:

A High kVp

B Inadequate grid efficiency or no grid

C Excessive beam limiting (collimation)

D Incomplete erasure of the image plate

he Correct Answer is: C
High kVp (beyond that which is optimal for the anatomical part being imaged) provides scattered X-ray photons enough energy to exit the anatomical part in various directions to strike the image receptor (A). This scatter radiation contributes nothing to the “true” anatomical image, but causes decreased contrast in the image. Inadequate grid efficiency, or not using a grid when needed (B), allows scatter radiation to strike the image receptor, causing decreased contrast. Many of the factors that cause low contrast in film-screen systems also cause low contrast in CR images: high kVp, inadequate grid efficiency or no grid, insufficient beam limiting, and incomplete erasure of the image plate (C). Incomplete erasure of an image plate from a previous exposure or background radiation will result in extraneous exposure data that reduces image contrast in the successive image (D). (Seeram, 1 st ed., p. 96)

63

Saturation” of an image in CR means that:

A The CR reader has difficulty converting insufficient exposure signals to produce a diagnostic image; all electronic enhancement mechanisms are maximized

B Beyond a certain exposure level, a large number of pixels will be at maximum digital value (black), resulting in loss of visibility of anatomical structures in that region.

C There is a large amount of scatter radiation that is contributing to loss of anatomical image detail due to loss of contrast, thus decreasing diagnostic quality of the image

D The CR image reader has adequately, and completely, read all the exposure intensities from the pixels resulting from the exposure

The Correct Answer is: B
“Saturation” of the CR image plate refers to overexposure of the image plate, not underexposure (A). “Saturation” means that, beyond a certain exposure level, a large number of the pixels will be at the maximum digital value, i.e., black (B). Therefore, there is no signal difference in the very high exposure areas, resulting in a loss of anatomical structures visualized in that region. It is therefore important for radiographers to use the appropriate exposure level for any particular anatomical part and not rely on the CR reader to adjust for overexposure. This is also critical to ensure proper adherence to the ALARA principle and to honor professional ethics. Although scatter radiation contributes to the exposure of the image plate (C), it is mainly the excessive exposure setting that “saturates” the pixels and prevents the CR reader from displaying densities darker than the blackest areas. The “saturation” exposure prevents the CR reader from reading exposure intensities beyond the blackest densities in the pixels (D). (Seeram, 1 st ed., p. 96).

64

The purpose of the automatic processor's transport system is to

A monitor and adjust temperature

B agitate, mix, and filter solutions

C move the film and change its direction

D monitor the solution and replace it as necessary

The Correct Answer is: C
The automatic film processor has a number of component systems. The transport system moves film from solution to solution between rollers, changing the direction of the film around critical turns. The circulation system functions to agitate, mix, and filter solutions. The temperature control system functions to monitor and control solution temperature. The replenishment system serves to monitor the solution and replace it as needed. (Bushong, 8th ed., p. 212)

65

The device used to give film emulsion a predetermined exposure in order to test its response to processing is called the

A sensitometer

B densitometer

C step wedge

D spinning top

The Correct Answer is: A
To test a film's response to processing, the film first must be given a predetermined exposure with a sensitometer. The film then is processed, and the densities are read using a densitometer. Any significant variation from the expected densities is further investigated. A step wedge is used to evaluate the effect of kilovoltage on contrast, and a spinningtop test is used to check timer accuracy. (Shephard, pp. 99–100)

66

which of the following possesses the widest dynamic range?

A High-speed screens

B Slow-speed screens

C AEC

D CR

The Correct Answer is: D
One of the biggest advantages of CR is the dynamic range, or latitude, it offers. The characteristic curve of x-ray film emulsion has a certain “range of correct exposure,” limited by the toe and shoulder of the curve. In CR, there is a linear relationship between the exposure, given the PSP (SPS) and its resulting luminescence as it is scanned by the laser. This affords much greater exposure latitude, and technical inaccuracies can be effectively eliminated. Overexposure of up to 500% and underexposure of up to 80% are reported as recoverable, thus eliminating most retakes. This surely affords increased efficiency; however, this does not mean that images can be exposed arbitrarily. The radiographer must keep dose reduction in mind. The same exposure factors as screen–film systems, or less, generally are recommended for CR. Intensifying screens used in screen–film x-ray imaging tend to produce high contrast. The faster the screens, the higher is the contrast; higher contrast often is associated with decreased latitude. AEC refers to automatic exposure control and is unrelated to dynamic range or latitude. (Shephard, pp. 330–332)

67

he automatic film processor's recirculation system functions to

  1. add quantities of solution as required.
  2. maintain uniform temperatures.
  3. mix and agitate solutions.

A 1 only B 1 and 3 only C 2 and 3 only D 1, 2, and 3

he Correct Answer is: C
The processor's pumping mechanisms transport/recirculate the solution through heating devices to maintain the proper temperature. The solution then is returned under pressure for further recirculation. The added pressure functions to agitate the solution and keep it in close contact with the film emulsion. Adding additional solutions at intervals is the function of the replenishment system. (Bushong, 8th ed., p. 212)

68

The instrument that is used frequently in quality-control programs to measure varying degrees of x-ray exposure is the

A aluminum step wedge.

B spinning top

. C densitometer.

D sensitometer.

The Correct Answer is: C
Every radiographic image is composed of a number of different densities. These densities may be measured and given a numeric value with a device called a densitometer. A sensitometer is another device used in QA programs; it is used to give a precise exposure to a film emulsion. An aluminum step wedge (penetrometer) may be used to show the effect of kilovoltage on contrast. A spinning top is used to test the accuracy of the x-ray machine's timer or rectifiers. (Bushong, 8th ed., p. 275)

69

Inadequate collimation in CR imaging can result in an image that is too

  1. light
  2. dark
  3. noisy

A 1 only B 1 and 2 only C 2 and 3 only D 1, 2, and 3

The Correct Answer is: D
It is important to note that histogram appearance as well as patient dose can be affected by the radiographer's knowledge and skill using digital imaging, in addition to his or her degree of accuracy in positioning and centering. Collimation is exceedingly important to avoid histogram analysis errors. Lack of adequate collimation can result in signals outside the anatomical area being included in the exposure data recognition/histogram analysis. This can result in a variety of histogram analysis errors, including excessively light, dark, or noisy images.

70

A fill factor of 80% in direct or indirect digital radiography means that:

A 20% of the pixel area is occupied by the detector electronics with 80% representing the sensing area

B 80% of the pixel area is occupied by the detector electronics with 20% representing the sensing area

C The saturation level will be unacceptable

D Only 20% of the image will be captured

The Correct Answer is: A
The fill factor is expressed as a percentage. In this case (A), 80% means that 20% of the pixel area is occupied by the detector electronics with 80% representing the sensing area which, in turn, represents the image. Larger fill factors indicate large sensing areas; larger fill factors (and sensing areas) indicate better spatial and contrast resolution. In (B), 20% means that 80% of the pixel area is occupied by the detector electronics with 20% representing the sensing area which, in turn, represents the image. Saturation (C) means that beyond a certain exposure level, a large number of the pixels will be at the maximum digital value (black) so that there is no signal difference in the very high exposure areas, resulting in a loss of anatomical structures in that region. This is an undesirable effect. Collimation defines the exposure field, so 20% of the image would only occur if 20% of the anatomical area were to be exposed and captured (D). (Seeram, 1 st ed., p. 112)

71

Which of the following digital post-processing methods remove high-frequency noise from the image?

A Edge enhancement

B Windowing

C Smoothing

D Aliasing

The Correct Answer is: C
Image smoothing (C) is a type of spatial frequency filtering performed during digital image post-processing. Also known as low-pass filtering, smoothing can be achieved by averaging each pixel’s frequency with surrounding pixel values to remove high-frequency noise. The result is reduction in noise and contrast. Smoothing (low-pass filtering) is useful for viewing small structures such as fine bone tissues. Edge enhancement (A) is a type of post-processing image manipulation, which can be effective for enhancing fractures and small, high-contrast tissues. In digital imaging, after the signal is obtained for each pixel, the signals are averaged to shorten processing time and decrease storage needs. The larger the number of pixels involved in the averaging, the smoother the image appears. The signal strength of one pixel is averaged with the strength of its neighboring pixels. Edge enhancement is achieved when fewer neighboring pixels are included in the signal average. Therefore, the smaller the number of neighboring pixels, the greater the edge enhancement. Windowing (B) is a post-processing method of adjusting the brightness and contrast in the digital image. There are two types of windowing: level and width. Window level adjusts the overall image brightness. When the window level is increased, the image becomes darker. When decreased, the image becomes brighter. Window width adjusts the ratio of white to black, thereby changing image contrast. Narrow window width provides higher contrast (short-scale contrast), whereas wide window width will produce an image with less contrast (long-scale contrast). Aliasing (D) is an image artifact that occurs when the spatial frequency is greater than the Nyquist frequency and the sampling occurs less than twice per cycle. This causes loss of information and a fluctuating signal and wrap-around image is produced, which appears as two superimposed images that are slightly out of alignment, resulting in a moiré effect. The Nyquist theorem states that when sampling a signal (such as the conversion from the analog to digital image), the sampling frequenc

72

While indirect digital detectors use a scintillator (phosphor) to convert X-ray energy, direct detectors use a

: A Photoconductor

B Scintillator

C Charged coupled device

D Histogram detector screen

The Correct Answer is: A
Indirect digital systems use scintillators/phosphors (B) to convert X-ray energy, whereas direct digital systems use a photoconductor (A) to covert this energy. This energy is subsequently converted by either a charged coupled device (CCD) array or photodiode array (coupled with a thin film transistor array) in the two types of indirect systems, or by a TFT array in a direct system. Finally, both indirect and direct digital system conversions result in an analog signal that is converted to a digital signal by the analog-to-digital convertor (ADC). A scintillator (phosphor) receives X-ray energy and converts it to light in an indirect digital detector system. In direct conversion digital detectors, an X-ray photoconductor (B) is used to convert this energy. Some indirect digital detectors use charged coupled devices (CCD), but a scintillator (phosphor) converts the X-ray energy and, through light optics, transfers this energy to the CCD (C). The histogram (D) is a computerized graphic display of the X-ray intensities received by the detectors in direct or indirect digital detector systems (or by the image plate in CR systems). There is no histogram detector screen (D). (Seeram, 1 st ed., p. 106)

73

Exposed silver halide crystals are changed to black metallic silver by the

A preservative

B reducers

C activators

D hardener

he Correct Answer is: B
As the film emulsion is exposed to light or x-rays, latent image formation takes place. The exposed silver halide crystals are reduced to black metallic silver in the developer solution. Automatic processor developer agents are hydroquinone and phenidone. The preservative—sodium sulfite—helps to prevent oxidation. The activator provides the necessary alkalinity for the developer solution, and hardener is added to the developer in automatic processing to keep emulsion swelling to a minimum. (Fauber, p. 164)

74

Base-plus fog is a result of

  1. blue-tinted film base
  2. chemical development
  3. the manufacturing process

A 1 only B 1 and 2 only C 1 and 3 only D 1, 2, and 3

he Correct Answer is: D
Every film emulsion has a particular base-plus fog, which should not exceed 0.2. This base density is a result of the manufacturing process (environmental radiation) and the blue tint added to the base to reduce glare. The remaining fog density is a result of the chemical development process, when exposed silver bromide grains are converted to black metallic silver. (Carlton and Adler, 4th ed., p. 307)

75

From which of the following primary beam sizes, all other factors remaining constant, will the greatest radiation exposure result?

A 8 × 10

B 10 × 12

C 11 × 14

D 14 × 17

The Correct Answer is: D
Limiting the irradiated field size, through collimation or other beam restriction, is perhaps the most effective way of controlling patient exposure dose. The smaller the irradiated area, the smaller the patient dose; the larger the irradiated area, the larger the patient dose. Therefore, the 14 × 17 primary beam size will result in the greatest patient exposure dose.

With greater beam restriction, less biologic material is irradiated, thereby reducing the possibility of harmful effects. Additionally, if less tissue is irradiated, less scattered radiation is produced, resulting in improved contrast and image quality. (Dowd & Tilson, p 231)

76

Methods of reducing radiation exposure to patients and/or personnel include

1. beam restriction. 2. shielding. 3. high-kV, low-mAs factors.

A 1 only

B 1 and 2 only

C 2 and 3 only

D 1, 2, and 3

The Correct Answer is: D
Beam restriction is probably the single best method of protecting your patient from excessive radiation. It is also an important factor in obtaining high-quality radiographs because there will be less fog from scattered radiation. Shielding areas not included in the radiograph, especially particularly radiosensitive areas, is another effective means of reducing patient dose. If the patient is subjected to less radiation exposure, then so is the operator. Shielding, distance, and time are the three cardinal rules of radiation protection. High-kV, low-mAs exposure factors employ the use of fewer and more penetrating x-rays. (Bontrager, p 58)

77

Which of the following functions to protect the x-ray tube and the patient from overexposure in the event that the phototimer fails to terminate an exposure?

A Circuit breake

r B Fuse

C Backup timer

D Rheostat

The Correct Answer is: C
A photo timer is one type of automatic exposure device. When it is installed in an x-ray unit, it is calibrated to produce radiographic densities as required by the radiologist. Once the part being radiographed has been exposed to produce the proper image density, the photo timer automatically terminates the exposure. The manual timer should be used as a backup timer should the photo timer fail to terminate the exposure, thus protecting the patient from overexposure and the x-ray tube from excessive heat load. Circuit breakers and fuses are circuit devices used to protect circuit elements from overload. In case of current surge, the circuit will be broken, thus preventing equipment damage. A rheostat is a type of variable resistor. (Shephard, p. 274)