Fundamentals of Diagnostic Imaging: Week 9 and 10
Although lower-than-necessary x-ray exposures can be detected and processed, image quality suffers and quantum noise results. This can lead to mistakes in diagnosis and can negatively impact our patients. a. true b. false
A
Considering the primary controller of radiographic density, which setting will produce the greatest density? A. 100 mA, 1 second B. 300 mA, 0.1 seconds C. 400 mA, 0.2 seconds D. 800 mA, .01 seconds
A
Pixels representing highly attenuating tissues (increased absorption) such as bone or metal are assigned a different numerical value for higher brightness than pixels representing tissues of low x-ray attenuation (decreased absorption). a. True b. False
A
Small objects have higher spatial frequency, and large objects have lower spatial frequency. It is more difficult to accurately image: A. small anatomic objects (high spatial frequency) than to image large ones (low spatial frequency). B. large anatomic objects (high spatial frequency than to image small ones (low spatial frequency). C. Spacial frequency only has to do with the speed. D. Both A and B
A
The ______________ of an imaging system refers to the ability of an IR to accurately capture the range of photon intensities that exit the patient. Digital IRs have a wide ________________ Which allows small errors in technique to still produce useable images. A. dynamic range B. Exposure range C. Constant range D. Imaging range
A
The computer can also process the data resulting from an IR exposed to higher-than-necessary radiation and produce a quality image but the increased exposure puts our patients at higher risk. a. true b. false
A
The relationship between mAs and density can be described as ________________. A. directly proportional B. direct exponential C. inversely proportional D. inverse exponential
A
Which kVp setting would produce the highest contrast on a radiographic image? A. 60 B. 75 C. 80 D. 110
A
Which of the following statements best describes the relationship between matrix size and pixel size if the field of view stays the same? A. Larger matrix size with smaller pixels will improve image quality. B. Larger matrix size with larger pixels will improve image quality. C. Smaller matrix size with larger pixels will improve image quality. D. None of the above are true.
A
Which statement best describes the relationship between kVp and density. A. kVp has a direct relationship with density, as kVp increases, optical density also increases. B. kVp has an indirect relationship with density, as kVp increases, optical density decreases. C. kVp has no relationship with density.
A
_______________ refers to the range of exposures that should be used to produce a diagnostic image and is likely established by the preferences or needs of the imaging department. A. exposure latitude B. IR latitude C. dynamic range D. all the above
A
Which of the following is true regarding spatial resolution? ( try to define spatial resolution and the terms to see the relationship) a. Increasing pixel density and decreasing pixel pitch increases spatial resolution. b. Decreasing pixel density and increasing pixel pitch decreases spatial resolution. c. decreasing pixel density and increasing pixel pitch increases spatial resolution. d. increasing pixel density and decreasing pixel pitch decreases spatial resolution.
A, B Pixel density (how many pixels) Pixel pitch (space between the center of one pixel to the next) If you increase the density your increasing the amount of pixels and if you decrease the pitch you are shortening the space that pixels take up ultimately creating more pixels per given area which increases detail allowing more visible structures defined in your image.
Increasing the matrix size for the field of view (FOV) will have what effect on pixel size? a. inverse relationship b. increasing matrix will decrease pixel size c. decreasing matrix will decrease pixel size. d. direct relationship
A, B This will increase spatial resolution of your image.
Increasing the field of view (FOV) will have what effect on the pixel size? a. directly related b. inversely related. c. Increasing field of view increases the pixel size for a given matrix. d. Increasing field of view decreases the pixel size for a given matrix.
A, C
A large focal spot should be used to decrease geometrical unsharpness and increase spatial resolution. A. True B. False
B
The line pair test is used to assess which of the following? A. The contrast resolution of the imaging system B. The spatial resolution of the imaging system C. The dynamic range of the imaging system D. None of the above
B
What would be the appropriate change in mAs if the kVp were decreased by 15% and the density of the image needs to be maintained? A. Decrease the mAs by 1/4 B. Double the mAS C. Halve the mAs D. Increase the mAs by 4x's
B
If a radiograph is done using an 80 inch FFD and 12 mAS and a second image is done using a 40 inch FFD, what is the new mAs that should be used to maintain the same amount of exposure? A. 2 B. 3 C. 6 D. 24
B Decrease the mAs by 1/4
Digital radiography has a wide dynamic range this means small amounts of underexposure or overexposure result in unusable images that must be re-taken and causes increased patient exposure. A. true B. False
B-false
MTF is a measure of the imaging system's ability to accurately display small anatomic objects having high spatial frequency. An imaging system that has a high MTF can display anatomic detail with improved visibility. For small anatomic structures with high spatial frequency you would expect an MTF of? A. 1 B. .8 C .3 D. 2
C
value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels). A. Variation Transfer Function (VTF) B. IR Receiver Function (IRF) C. Modulation transfer function (MTF) D. Regulator Transfer function (RTF)
C
Requires the use of a cassette Uses a photostimulable phosphor layer to generate the latent image The information must be digitized using a special scanner
CR
is a method of describing the contrast resolution compared with the amount of noise apparent in a digital image. Just as increased noise affects the SNR and visibility of the anatomic details, it also impacts the contrast displayed within the digital image.
Contrast-to-noise ratio (CNR)
If mAs were fixed, which kVp setting would produce the greatest density on a radiographic image? A. 55 B. 70 C. 85 D. 100
D
In digital imaging the number of shades of gray that can be displayed in the image is determined by? a. bit depth (larger = more shades of gray= better contrast resolution) b. bit depth (smaller = fewer shades of gray = decreased contrast resolution) c. bit depth (larger = fewer shades of gray = better contrast resolution) d. both a and b
D
The distance between x-ray tube and the bucky (the area that stores the film), is referred to as the _________________. A. object-image distance B. source-object distance C. focal-object distance D. source-image distance
D
Which of the following is true regarding the exposure indicator? A. This provides a numeric value regarding the level of radiation exposure detected by the imaging receptor B. It can help radiographers ensure they are using proper exposure techniques C. It can help radiographers adapt the amount of mAs and kVp they use which may reduce patient exposure D. All of the above are true.
D
Uses a scintillator such as Cesium iodide or a direct detector coated in selenium The information is digitized within the flat panel detector The imaging receptor is housed in the flat panel detector
DR
is a measurement of the efficiency of an IR in converting the x-ray exposure it receives to a quality radiographic image.
Detective quantum efficiency (DQE)
A system with higher contrast resolution means that anatomic tissues that attenuate the x-ray beam similarly (low subject contrast) can be better visualized. However, if the image has increased noise, the low subject contrast will not be as well visualized.
Digital imaging and CNR
Provides a standardized format for imaging files in healthcare
Digital imaging and communications in medicine
_____________________ will still produce a digital image with the appropriate level of brightness as a result of computer adjustment during image processing; however, the patient will be overexposed.
High kVp/high radiation
Increasing the CNR increases the visibility of anatomic details, whereas decreasing the CNR decreases the visibility.
Important Relationship Contrast-to-Noise Ratio and Image Quality
An IR with a higher DQUE requires less x-ray exposure to produce a quality radiographic image when compared to an IR with a lower DQE value.
Important Relationship Detective Quantum Efficiency and X-ray Exposure
Because digital IRs have a wide dynamic range, a quality image can be produced when using more radiation exposure than necessary. Radiographers must take extra precautions to not unnecessarily overexpose patients and select exposure techniques within the exposure latitude established by the department.
Important Relationship Digital Detectors and Dynamic Range
Digital IRs have a wide dynamic range; that is, they can accurately capture a wide range of x-ray intensities exiting the patient. The computer then processes the raw pixel data to compensate for an exposure error and create a diagnostic radiographic image. However, lower- or higher-than-necessary exposure techniques do not guarantee a quality digital image. Exposure latitude is the range of exposures that should be used to produce a diagnostic image.
Important Relationship Digital Detectors, Dynamic Range, and Exposure Latitude
As focal spot size increases, unsharpness increases and spatial resolution decreases; as focal spot size decreases, unsharpness decreases and spatial resolution increases.
Important Relationship Focal Spot Size and Spatial Resolution
Adding, removing, or changing a grid requires an adjustment in mAs to maintain radiation exposure to the IR. the more efficient a grid is in absorbing scatter, the greater is the increase in mAs
Important Relationship Grids and IR Exposure
For a fixed matrix size CR system, using a smaller IR for a given FOV results in improved spatial resolution of the digital image. Increasing the size of the IR for a given FOV results in decreased spatial resolution.
Important Relationship Image Receptor Size and Matrix Size
Increasing the OID increases magnification and decreases the spatial resolution, whereas decreasing the OID decreases magnification and increases the spatial resolution.
Important Relationship OID, Size Distortion, and Spatial Resolution
As SID increases, the x-ray beam intensity becomes spread over a larger area. This decreases the overall intensity of the x-ray beam reaching the IR.
Important Relationship SID and X-ray Beam Intensity
Increasing the SID requires the mAs to be increased to maintain exposure to the IR, and decreasing the SID requires a decrease in the mAs to maintain exposure to the IR.
Important Relationship SID and mAs
As SID increases, size distortion (magnification) decreases, and spatial resolution increases; as SID decreases, size distortion (magnification) increases, and spatial resolution decreases.
Important Relationship SID, Size Distortion, and Spatial Resolution
Increasing the SNR increases the visibility of anatomic details, whereas decreasing the SNR decreases the visibility.
Important Relationship Signal-to-Noise Ratio and Image Quality
A 15% increase in kVp has the same effect on exposure to the IR as doubling the mAs. A 15% decrease in kVp has the same effect on exposure to the IR as halving the mAs.
Important Relationship kVp and the 15% Rule
As mAs increases, the quantity of radiation reaching the IR increases. As mAs decreases, the amount of radiation reaching the IR decreases
Important Relationship mAs and Quantity of Radiation
__________________ will produce a digital image with the appropriate level of brightness, but the increased quantum noise will decrease the image quality.
Lower kVp/too little radiation
Software designed to transmit store display and otherwise manage digital image files in healthcare
Picture archival and communication system
The greater the pixel bit depth (i.e., 16-bit), the more precise the digitization of the analog signal and the greater the number of shades of gray available for image display. Increasing the number of shades of gray available to display in a digital image improves its contrast resolution.
Pixel depth and contrast resolution
In performing a radiographic examination, the radiographer should be aware of the anatomic area of interest and limit the x-ray field size to just beyond this area. ________________ to the appropriate field size is a basic method for protecting patients from unnecessary exposure.
Radiation Protection: Beam attenuation, Collimating
is a method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image. Noise is a concern with any electronic data set, in this case digital image noise. Because the photon intensities are converted to an electronic signal that is digitized by the ADC, the term signal refers to the strength or amount of radiation exposure captured by the IR to create the image.
Signal-to-noise ratio (SNR)
An image with increased contrast resolution increases the visibility of anatomic details and the ability to distinguish among small anatomic areas of interest. a. true b. false
True
If the ______________________ falls outside the manufacturer's suggested range, exposure to the digital IR, image quality, and patient exposure could be affected.
exposure indicator value
Placing a ___________ between the anatomic part and the IR absorbs scatter radiation exiting the patient and increases radiographic contrast.
grid
A low kVp results in more absorption and less x-ray transmission in the anatomic tissues but with more variation in the x-ray intensities exiting the patient, resulting in ____________________.
higher subject contrast
Increasing _________________ requires a lower mAs to maintain the desired exposure to the IR and decreases the radiation dose to the patient. Higher ___________ increases the beam penetration; therefore, less radiation is needed to achieve a desired exposure to the IR.
kilovoltage, kVp
A high kVp results in less absorption and more transmission in anatomic tissues, which results in less variation in the x-ray intensities exiting (remnant) the patient, producing _____________________.
lower subject contrast
For anatomic areas that produce a high percentage of scatter radiation, _____________is needed to increase image contrast than for anatomic areas that produce less scatter.
more OID
The unit of measure for _________________ is lp/mm. Increasing the number of lp/mm resolved in the imaging system (higher spatial frequency) results in improved spatial resolution.
spatial frequency
_________________________ determine the spatial resolution, and the pixel bit depth determines the system's ability to display a range of shades of gray to represent anatomic tissues.
the pixel size and pitch
