CHAPTER 4 Image Acquisition and Evaluation (Review) cwilliamstulsa (found in MOSBY's class)
The number of pixels/mm in an image is called: a. Pixel density b. Bit depth c. Pixel pitch d. Matrix depth
A
A radiograph with few gray tones, primarily exhibiting black and white, would be described as having what type of contrast? 1. Long scale 2. Short scale 3. Low 4. High a. 2 and 4 b. 1 and 3 c.l and 4 d. 2
A.
Density may be defined as: a. Darkness on a radiographic image b. A combination of contrast and recorded detail c. The light areas of a radiographic image d. Differences in dark areas on a radiographic image
A.
Digital imaging is more sensitive to: a. Scatter and background radiation b. Fluorescent lights c. Free electrons d. Free radicals
A.
Quantum noise limits ability to see: a. Detail b. Contrast c. Fatty tissue d. Additive pathologies
A.
Magnification is caused by: 1. Short SID 2. Long SID 3. Short OlD 4. Long OlD a. 2, 3 b. 1,4 c. 1, 3 d. l only
B. The optimum conditions are longer SID and shorter OlD.
Which of the following describes the relationship between radiographic density and the use of grids? a. Grids always reduce density b. Grids reduce density unless mAs is increased to compensate c. Grids reduce density by absorbing scatter radiation d. Density increases as grid ratio increases
B. This necessitates the use of grid conversion factors.
What allows more anatomical structures to be captured during an exposure? a. Contrast resolution b. Spatial resolution c. Dynamic range d. MTF
C
As the amount of beam filtration is increased: a. Contrast increases b. There is no effect on contrast c. Contrast decreases d. Contrast increases because the beam is harder
C. The overall wavelength of the beam is shorter, resulting in lower contrast.
Which of the following describes the relationship between mAs and density? a. Density is directly proportional to mAs b. Density is inversely proportional to mAs c. Density is directly proportional to mAs2 d. mAs controls the number of electrons boiled off the anode and the number of x-rays produced
A. Whatever is changed in mAs directly impacts-density
The actual patient dose as measured by a meter embedded in the collimator is: a. RAD—radiation absorbed dose b. DAP—dose area product c. REM—radiation equivalent man d. Doubling dose
B. Digital imaging takes into account the total dose to the patient.
The active portion of a CR IP is(are): a. Calcium tungstate b. PSP c. Silver bromide crystals d. Rare earth phosphor
B. PSP - Photostimulable phosphor
The smallest area represented in a digital image is the: a. Image matrix b. Pixel c. Voxel d. Bit
B. Picture element.
Optimal recorded detail may be created using which of the following factors? a. Large focal spot b. Narrow pixel pitch c. Long OlD d. Short SID
B. Pixel pitch is very important to detail in digital imaging.
The space from the center of a pixel to the center of the adjacent pixel is called: a. Pixel density b. Bit depth c. Pixel pitch d. Matrix depth
C
The best scatter cleanup is achieved with the use of: a. Air gap technique b. Focused grids c. Crosshatch grids d. Parallel grids
C. But crosshatch grids prevent angling of the tube and are extremely susceptible to grid cutoff.
Inappropriate collimation causes: a. A fogged image b. Pixel unresponsiveness c. DICOM incompatibility d. Histogram analysis error
D.
Use of the air gap technique: a. Works because x-rays are absorbed in the air between the patient and the film b. Should occur when possible c. May cause some magnification because of decreased OlD d. Works because scatter radiation travels in divergent paths and misses the IR as a result of increased OlD
D. Even though not used much anymore, it is particularly effective on lateral cervical spine radiographs.
If SID is doubled, what may be said about radio graphic density? a. Density doubles b. Density is reduced by one-half c. Density is reduced by new mAs2 d. Density is reduced to one-fourth
D. This is another way of asking about the inverse square law.
Exposure technique in digital imaging may be adjusted by: a. Lowering kVp b. Increasing mAs c. Shortening SID d. Increasing kVp
D. This is in congruence with ALARA.
Poorer recorded detail may be caused by which of the following factors? a. Short OlD b. Long SID c. Small focal spot d. Pixel pitch wide
D. This is the space from center to center of adjacent pixels.
Distortion that occurs when the x-ray beam is angled against the long axis of a part is: a. Elongation b. Magnification c. Minification d. Foreshortening
D. This results in the part appearing shorter than it really is.
Bit depth is equal to: a. 2n (n equals the number of bits) b. 4096 shades of gray c. Pixel pitch d. Bits times bytes
A
A primary advantage to digital fluoroscopy is: a. Postprocessing manipulation of the image b. Radiation dose to the patient is substantially lower c. No radiologist is needed d. Lower cost
A.
The radiographic image is formed by: a. Exit rays striking the image receptor b. Laser light c. Cosmic rays d. Electrons and heat
A.
As speed class increases: a. The likelihood of noise increases b. The likelihood of noise decreases c. Patient exposure increases d. Sharpness increases
A. This may allow for higher kVp and lower mAs, which causes an increase in quantum mottle or noise.
Distortion that occurs when the x-ray beam is angled along the long axis of a part is: a. Elongation b. Magnification c. Minification d. Misrepresentation
A. This results in the part appearing longer than it really is.
Materials that make flat panel detectors possible are: a. Silicon dioxide b. Amorphous silicon c. Diodes d. Pixels
B.
Which of the following maintains image brightness over a wide range of exposures? a. AEC b. Bit depth c. Automatic rescaling d. Detector size
C
As beam restriction increases (becomes tighter): a. Density increases b. Density increases as a result of focusing of x-rays c. Density decreases d. Density is not affected
C.
Quality assurance and maintenance of CR cassettes includes cleaning and inspecting the plates at least: a. Daily b. Every 48 hours c. Every 3 months d. Weekly
C.
Smoothing software may result in: a. Enhanced fine detail b. Less distortion c. Loss of fine detail d. Increased distortion
C.
TFT is a: a. Thin film transistor—a diode used in rectifiers b. Thin film transistor—an electronic device used in CR cassettes c. Thin film transistor—an electronic switch used on flat panel detectors d. Thin film transistor—the electronics used with AECs
C.
Which of the following governs the relationship between SID and density? a. Reciprocity law b. 15% rule c. Inverse square law d. Ohm's law
C.
The law stating that any combinations of mA and time that produce the same mAs value will produce the same radiographic density is the: a. Inverse square law b. mAs-density law c. Reciprocity law d. 15% law
C. Sometimes written as mAs=mAs.
The primary controlling factor(s) of contrast is(are): a. mAs, which controls the energy of the x-rays produced b. kVp, which primarily controls the quantity of x-rays produced at the target c. Focal-spot size, which controls the quantity and quality of x-rays produced d. kVp and window width
D. kVp controls the wavelength and penetrating ability of the beam. In digital imaging window width can be used to manipulate contrast.
Low kVp produces which of the following? 1. High contrast 2. Few gray tones 3. Long-scale contrast 4. Short-scale contrast S. Low contrast 6. Many gray tones a. 1, 2, 4 b. 3, 5, 6 c. 5 d. 1
A.
Quality assurance of digital imaging requires the uniformity of processing codes to ensure: a. Image appearance consistency b. Faster throughput c. Less heat loading on the anode d. Smoother integration into PACS
A.
The 15% rule states that: a. Density maybe halved by decreasing kVp by 15% b. kVp should be 15% of the mAs selected c. Density may be halved by increasing kVp by 15% d. At least a 15% change in mAs is required to make a change visible
A.
The expression of image quality provided by a detector is called: a. MTF b. Matrix size c. SNR d. Nyquist frequency
A. Modulation transfer function
A material that absorbs x-ray energy and emits part of that energy as visible light is called: a. Diode b. Scintillator c. TFT d. Cathode
B
An indicator of the dose level needed to acquire an optimal image is: a. Detective quantum efficiency b. Dose area product c. Field of view d. Dynamic range
B
Mathematical codes used to generate the digital image are called: a. Binary codes b. Algorithms c. Binary digits d. Bytes
B
The available gray scale of an imaging system is determined by: a. Pixel pitch b. Bit depth c. Exposure latitude d. Image latitude
B
The number of pixels making up the digital image is the: a. Pixel depth b. Matrix size c. Pixel pitch d. Field of view
B
The range of receptor exposures that provides a quality image is called: a. Detector latitude b. Exposure latitude c. Histogram d. Dynamic range
B
The smallest resolvable area in a digital imaging device is: a. Detector size b. Detector element c. Matrix size d. Focal spot size
B
Which of the following affects radiographic density? a. Atomic mass of the x-ray tube anode b. X-ray tube angle c. Atomic number of the cathode filament
B. Due to a change in SID resulting from the tube angle.
The relationship between kVp and density may be described as: a. Directly proportional b. Direct, although not proportional c. Governed by the 15-50 rule d. Controlled by x-ray tube current
B. It is governed by the 15% rule.
Better recorded detail may be caused by which of the following factors? 1. Long SID 2. Long OlD 3. Short SID 4. Short OlD 5. Large focal spot 6. Small focal spot a. 2, 3, 5 b. 1, 4, 6 c. 1, 4, 5, 6 d. 2, 3, 6
B. This is a rather involved question that you're likely to see on the Registry exam, but it is a good view of factors related to recorded detail. Remember this is also a study guide, not just practice tests. sure to review these factors in Chapter 4 if any the answers don't seem right to you.
The process of assigning a value to each pixel to represent a gray tone is called: a. Quantization b. Scintillating c. Nyquist frequency d. Sampling
A
Distortion may be described as: a. Misrepresentation of an anatomical structure on film b. Foreshortening c. Elongation d. Magnification
A. Choices b, c, and d are all examples of distortion.
Beam-part-receptor alignment latitude describes: a. The latitude of collimation that still allows the software to detect collimated edges b. The alignment that maintains ALARA requirements c. Exposure latitude d. Acceptable distortion of the image
A. Detection of collimated edges is crucial to obtaining an accurate histogram.
A software function that evens the brightness displayed in the image is called: a. Smoothing b. Equalization c. Postprocessing d. Subtraction
A. However, smoothing may negatively impact resolution.
Which of the following statements concerning grids are true? 1. Contrast improvement factor is the measure of the ability of a grid to enhance contrast 2. Grid selectivity is the ratio of primary radiation transmitted through the grid to secondary radiation transmitted through the grid 3. Grids are used when part thickness is less than 10 cm 4. GCF is the amount of increase in kVp necessary when converting from nongrid to grid technique S. The primary purpose of grids is radiation protection 6. The main function of grids is to prevent Compton scatter from reaching the film 7. Grids prevent the production of scatter a. 1, 2, 6 b. 1, 2, 4, 6 c. 1, 2, 3, 5, 7 d. 1, 2, 6, 7
A. Keep in mind that grids are used over part thickness of 10 cm; the grid conversion factors are used to change mAs, not kVp; and grids don't prevent the production of scatter, they just try to absorb it after it's been produced.
When a nongrid technique using 10 mAs and 75 kVp is changed to a 12:1 grid using 75 kVp, what new mAs must be used to maintain the same density as the original film? a. 50 mAs b. 2mAs c. 40 mAs d. 120 mAs
A. The grid conversion factor or Bucky factor for a 12:1 grid is 5 times the original mAs.
Which of the following statements are true concerning the role of kVp in radiograph production? 1. As kVp is increased, penetrating ability of the x-rays increases 2. As kVp is increased, more x-rays exit the patient to strike the IR 3. As kVp is decreased, wavelength and density decrease 4. As kVp increases, radiographic density increases 5. As kVp decreases, radiographic density remains constant because mAs controls density a. 1, 2, 4 b. 1, 2, 3 c. 1, 3, 4 d. 5
A. Think about each answer individually before answer this question.
If SID is reduced by one-half, what must be done to mAs to maintain a constant density? a. Reduce mAs to one-fourth its original value b. Reduce mAs to one-half its original value c. Increase mAs by four times its original value d. Increase mAs by two times its original value
A. This is the density maintenance formula. Note the question asks what needs to be done to maintain density, not what happens to density if nothing is changed.
The useful image acquisition area of an image receptor is: a. Detector element b. Detector size c. TFT size d. Dynamic range
B
Undesirable fluctuations in brightness are called: a. MTF b. Image noise c. Quantization d. Scintillation
B
Elongation and foreshortening are examples of: a. Size distortion b. Shape distortion c. Motion d. Distortion caused by short SID and long OlD
B.
More uniform penetration of anatomical structures occurs when what level of kVp is used? a. Low b. High c. kVp does not affect penetration d. Level at which photoelectric interaction predominates
B.
Grid cutoff may be described as: a. Decreased density in the middle of the radiograph caused by the use of a parallel grid inserted upside down b. Decreased density on a radiograph as a result of absorption of image-forming rays c. Increased density in the center of a radiograph caused by the use of a focused grid inserted upside down d. Decreased density on the edges of a radiograph only
B. Choice A is incorrect because decreased density in the middle would not be caused by use of an inverted parallel grid. Choice C is incorrect because density would decrease in the middle of this radiograph. Choice D is incorrect because density could decrease across the entire radiograph, depending on how the grid has been positioned.
The thicker part of anatomy should be placed under which aspect of the x-ray tube? a. Central ray b. Cathode c. Anode d. Collimator
B. Anode heel effect.
Quality assurance and maintenance of CR cassettes includes erasing plates at least: a. Daily b. Every 48 hours c. Every 3 months d. Weekly
B. But erasing daily is better and preferred.
What effect does the use of radiographic grids have on contrast? a. Decreases contrast b. Increases contrast c. No effect on contrast d. Increases contrast by absorbing scatter radiation
B. Many of the scatter photons are being absorbed the grid resulting in higher contrast.
In digital fluoroscopy, what equipment should be used to view the image? a. Conventional view box b. High-resolution monitor capable of displaying millions of pixels c. High-definition television d. Plasma television required
B. The monitor must be high resolution, but can be plasma, LCD, LED, etc.
High kVp produces which of the following? 1. High contrast 2. Few gray tones 3. Long-scale contrast 4. Short-scale contrast S. Low contrast 6. Many gray tones a. 1,2,4 b. 3, 5, 6 c. 5 d. 1
B. The shorter wavelength beam more uniformly penetrates the various anatomic structures.
Given an original technique of 30 mAs and 80 kVp, which of the following would produce a radiograph with double the density? a. 60 mAs, 90 kVp b. 30 mAs, 92 kVp c. 15 mAs, 80 kVp d. 30 mAs, 70 kVp
B. The use of the 15% rule to increase kVp results in double the density.
A high SNR provides an image with: a. Poor spatial resolution b. Higher spatial resolution c. Poor contrast d. Higher distortion
B. There is a greater difference between the signal and any noise that may be present.
A grid with lead strips and aluminum interspacers that are angled to coincide with the divergence of the x-ray beam is called a: a. Parallel grid b. Focused grid c. Crosshatch grid d. Rhombic grid
B. These grids can be used only within a certain range of SIDs, as stated on the label on the grid.
An artificial increase in display contrast at an edge of the image is: a. Smoothing b. Edge enhancement c. Contrast resolution d. Spatial resolution
B. This enhances visibility of detail.
The primary controlling factors of density are: a. kVp and SID b. mAs and window level c. SID and OlD d. OlD and FSS
B. mAs controls the electrons flowing through the x-ray tube and striking the anode. Therefore it directly controls the number of x-rays produced. In digital imaging, brightness may be manipulated using window level.
Grid ratio is defined as: a. The ratio of the lead strips to the space between them b. The thickness of the lead strips divided by the thickness of the aluminum interspacers c. The ratio of the height of the lead strips over the distance between the lead strips d. The ratio of the distance between the lead strips over the height of the lead strips
C. Expressed as HID. Did you notice how choice B tried to get your attention? Be sure to read the entire answer.
As speed class decreases: a. The likelihood of noise increases b. Noise is unaffected c. Patient exposure increases d. Sharpness decreases
C. More total exposure is required to produce a useable image.
The appearance of images on technologists' monitors is: a. The same as on radiologists' monitors b. Substantially better than on radiologists' monitors c. Not as good as on radiologists' monitors
C. Technologists' monitors are not usually high definition (HD).
The variation of x-ray intensity along the longitudinal axis of the x-ray beam describes: a. Beam collimation b. Positive beam limitation c. Anode heel effect d. X-ray emission spectrum
C. The intensity of the x-ray beam is actually a little higher toward the cathode side of the tube.
The number of electrons boiled off the cathode and consequently the number of x-rays produced are controlled by: a. kVp b. SID c. mAs d. OlD
C. mAs controls the electrons flowing through the x-ray tube and striking the anode. Therefore it directly controls the number of x-rays produced.
Use of technique charts: a. Is unnecessary for any examination because of AECs b. Does not require that the part thickness be measured with calipers c. Is usually based on fixed mAs and variable kVp d. Is helpful when manual techniques are used
D. Technique charts are generally not needed for exams when AECs are used.
Digital imaging is driven by: a. kVp b. mAs c. JR speed class d. Exposure
D. Total exposure reaching the IR.
The range of SIDs that may be used with a focused grid is called: a. Grid ratio b. Objective plane c. Anticutoff distances d. Grid radius
D. Using a focused grid outside of its grid radius will result in grid cutoff.
The function of contrast is to: a. Make the image appear sharper b. Compensate for uneven anatomical structures c. Brighten the image d. Make detail visible
D. Without contrast, produced by differential absorption of the x-ray beam, detail cannot be visible.
mAs directly controls: a. The energy of the x-ray emission spectrum b. The quality and quantity of x-rays produced at the cathode c. The quality and quantity of x-rays produced at the anode d. The quantity of x-rays produced
D. mAs is a quantitative factor.
The smallest exposure change able to be captured by a detector is called: a. Spatial resolution b. Exposure latitude c. Pixel d. Contrast resolution
D
Poorer recorded detail may be caused by which of the following factors? 1. Long SID 2. Long OlD 3. Large focal spot 4. Small focal spot 5. Patient motion 6. Magnification a. 2, 3, 5, 6 b. 2, 3 c. 1, 4, 6 d. 5, 6
A. These factors all impact the geometry of the image.
Excessive processing of the digital image may: a. Degrade visibility of anatomy b. Provide additional anatomical information c. Enhance visibility of desired anatomy d. Increase patient dose
A. The more the image is processed the greater the opportunity for image degradation.
What converts light into a charge? a. Diode b. Cathode c. AC to DC converter d. Photodiode
D
Which of the following is a graphical representation of pixel values? a. Dynamic range b. Luminance c. Look-up table d. Histogram
D
Which of the following terms describes the highest spatial frequency that can be recorded by a digital detector? a. Spatial resolution b. Contrast resolution c. MTF d. Nyquist frequency
D
The adjustment in technical factors required when using beam restriction is: a. Increase kVp b. Decrease kVp to reduce the number of Compton interactions taking place c. Decrease mAs to reduce the number of Compton interactions taking place d. Increase mAs to compensate for the number of rays removed from the primary beam
D. Rays that have been removed from the beam must be restored by increasing mAs. The area being irradiated still remains smaller.
Differences in densities on a radiograph describe: a. Density b. Recorded detail c. Log relative exposure d. Contrast
D.
Digital systems operate at what speed class? a. 200 b. 400 c. 100 d. The speed class chosen by the radiographer
D.
Grid frequency is defined as: a. The same as grid ratio b. The amount of lead in the grid (expressed in terms of focusing distance) c. How often a grid is used d. The amount of lead in the grid (expressed as the number of lead strips per inch)
D.
If the exposure field is not accurately recognized, the histogram will contain data: a. Outside the exposure field, narrowing the histogram b. Inside the exposure field, widening the histogram c. Outside the exposure field, widening the histogram d. Inside the exposure field, narrowing the histogram
D.
The portion of contrast that is caused by variations in the anatomy or is secondary to pathological changes is called: a. Radiographic contrast b. Anatomical contrast c. Pathological contrast d. Subject contrast
D.
When AEC is used, increasing the kVp: a. Increases density proportionately b. Increases radiographic contrast c. Increases exposure time d. Has no effect on density
D. Automatic exposure controls are set to terminate the exposure after a certain amount of radiation has passed through the ionization chamber. Consequently, changes in kVp will have no effect on density. Some effect on contrast may occur if the change in kVp is substantial. The following answers relate to terminology used in digital imaging. Be certain to review these basic concepts. Keep in mind the ARRT exam will not ask questions related to specific brands of equipment made by various manufacturers. Therefore the concepts tested will be broad in nature, similar to these questions.
What effect does beam restriction have on contrast? a. Decreases contrast by focusing the x-ray beam b. Decreases contrast because of higher kVp level used c. Increases contrast by focusing the x-ray beam d. Increases contrast because of reduction in the number of Compton interactions that occur
D. Compton interactions produce scatter, which causes contrast to decrease.
Recorded detail is: a. Photographic representation of the part being radiographed b. Controlled by kVp c. Controlled by mAs d. Geometric representation of the part being radiographed
D. Controlled by SID, OlD, and focal spot size.
The use of filtration: a. Greatly reduces radiographic density because the absorption of short-wavelength x-rays b. Greatly reduces radiographic density because the absorption of high-energy x-rays c. Increases radiographic density by removing long-wavelength x-rays d. Has little effect on density because x-rays removed from beam are not image-producing rays
D. Overall the beam is harder so contrast may be lower.
Differential absorption of the x-ray beam is a function of: a. Compton interaction b. Atomic mass of anatomical structures c. mAs d. Photoelectric interaction
D. Photoelectic interaction results in absorption of incoming photons. It is also very influenced by the atomic number, not atomic mass, of anatomical structures.