11. List the similarities between film/screen imaging and digital imaging when creating the beam and creating the image.
11. X-rays are produced in the same manner whether the result is an analog (film/screen) or digital image. Therefore the selection of technical factors, i.e. mAs, kVp, must be considered whenever an x-ray image is being created. Due to x-ray machines having variables from one unit to the next, technologists must familiarize themselves with each x-ray machine when creating the beam.
Another commonality between analog and digital imaging is the patient. The patient provides varying attenuation due to the tissues and organs within the collimated field as well as the pathology contribution. Other factors within the technologists control when creating the image are beam restriction and the use of a grid.
12. Consider the “Image Display” phase of the imaging process; what terms are used to describe this phase in film/screen versus digital imaging?
12. When viewing an image produced with film/screen, the x-ray image is produced on a physical (hard copy) x-ray film called a radiograph. Spatial resolution is dependent on the manufacturing properties of x-ray film (crystal size) and intensifying screens (phosphor size). To interpret a radiograph it must be placed on a viewbox. The viewbox must have adequate luminance (the amount of light emitted or scattered by a surface) to allow an accurate interpretation of the image. Contrast is a term to describe the difference in densities between adjacent tissues, e.g. low contrast, high contrast. The dynamic range is the range of gray shades that the imaging system can display. Film/screen has an optical density range of 0.2 to 2.5 which represents as dynamic range of approximately 1000 shades of gray.
Digital imaging allows for post processing capabilities, e.g. adjusting image brightness and contrast. Digital images are viewed on a monitor or soft copy. Similar characteristics of the image exist with the digital image including spatial resolution which depends on pixel matrix size and image brightness which may be altered by changing the window level on the monitor. Contrast or dynamic range is an impressive characteristic of digital imaging which has the capability of representing over 16,000 shades of gray.
Note that when viewing either a radiograph or a digital image ambient light is required.
7 | PIR: Part 1: Unit 7, Part 2: Unit 1 and 2 Worksheet
13. Consider the “Image Analysis” phase of the imaging process; (a) State the two-(2) factors that affect the visibility of detail and the controlling and influencing factors for each. (b) State the two-(2) factors that affect the geometric properties of an image and state the main factors that for each.
13. The two factors that affect visibility of detail are (1) density/IR exposure and (2) contrast.
(1) Density/IR exposure’s controlling factor is mAs and main influencing factor is kVp.
(2) Contrast’s controlling factor is kVp and main influencing factor is mAs.
The two factors that affect geometric properties are (1) recorded detail and (2) distortion
(1) Recorded detail is affected by geometry of the x-ray beam, characteristics of the image receptor, and the presence or absence of motion.
(2) Distortion is affected by the size and shape
Part 2: Unit 2
14. Define radiographic density/IR exposure.
14. Degree of overall blackening on the film.
15. What is the controlling factor of image density/IR exposure and how does it affect the image?
15. mAs is the controlling factor for density/IR exposure; an increase in mAs will result in an increase exposure which in turn will increase density/IR exposure
8 | PIR: Part 1: Unit 7, Part 2: Unit 1 and 2 Worksheet
16. How should density/IR exposure adjustments be made when changing kilovoltage?
16. Adjustments in kilovoltage to change density vary depending of the kV range used;
• 30 – 50 kV requires a 4 – 5% change in kV
• 50 – 90 kV requires a 8 – 9% change in kV
• 90 – 130 kV requires a 10 – 12% change in kV
• General rule-of- thumb when working in the diagnostic range (60 to 100 kVp); an increase or decrease of 15% will result in either a doubling or halving of exposure
17. How do the inverse square law and density maintenance formulas differ from one another?
17. The inverse square law indicates that as distance increases the intensity of the x-ray beam decreases; i.e. the intensity of the x-ray beam will be reduced to ¼ when moving from 80 cm to 160 cm distance.
I1 = (D2)2
I2 = (D1)2
The direct square law indicates that as distance increases the mAs (exposure) required to maintain density/IR exposure will also need to be increased; i.e. the mAs required at a distance of 90 cm would be half that required at 180 cm
mAs1 = (D1)2
mAs2 = (D2)2
18. How do variations in the anatomical part affect density/IR exposure?
18. As the anatomical part thickness increases; attenuation of the beam increases resulting in a decrease in density/IR exposure
9 | PIR: Part 1: Unit 7, Part 2: Unit 1 and 2 Worksheet
19. What relationships exist between the following grid characteristics and density/IR exposure? (1) grid ratio, (2) grid frequency (3) grid interspace material, and (4) grid use
19. High grid ratios with low frequency and dense interspace material; moving grids and improperly used grids (incorrect focal distance) ALL result in greater attenuation of scattered photons (as well as primary photons) which will reduce density/IR exposure. When changing grid ratios the mAs must be altered in an effort to maintain density/IR exposure. Note: kV is not altered because of its effect on contrast.
The Bucky factor or GCF (grid conversion factor) is required for the following formula;
mAs1 = GCF1
mAs2 = GCF2
20. What is the relationship between density/IR exposure and relative speed?
20. All factors remaining the same, as relative speed of an imaging system increases the density/IR exposure will increase; when changing relative speeds of imaging systems a change in mAs is required to maintain density.
mAs1 = RS2
mAs2 = RS1
21. How does film processing affect density/IR exposure?
21. An increase in developer temperature, immersion time or chemistry activity (over replenishment) will ALL result in an increase in density/IR exposure. Note: Developer solution contaminated by fixer solution will result in a decrease in density/IR exposure.
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22. The amount of blackness seen on a processed film is called __________________________.
22. density/IR exposure
23. The controlling factor for the overall blackness on an image is _____________________.
24. If the distance between the x-ray tube and image receptor is increased from 40 to 80 inches, what specific effect will it have on the radiographic density/IR exposure if other factors are not changed?
A. Increase density/IR exposure to 50%
B. Decrease density/IR exposure to 25%
C. No effect on density/IR exposure
D. Decrease density/IR exposure to 50%
24. B. Decrease density to 25%
25. Which term is used to describe an image that has too little density? _________________.
25. under exposed
26. Situation: An image of the foot is produced using a conventional film-screen IR. The resulting image is slightly under exposed and must be repeated. The original exposure was 5 mAs. What mAs setting is needed to correct the density/IR exposure?
A. 5 mAs B. 6.5 mAs C. 20 mAs D. 10 mAs
26. B. 6.5 mAs
11 | PIR: Part 1: Unit 7, Part 2: Unit 1 and 2 Worksheet
27. What percent increase in the original kVp is needed to double the IR exposure?
28. Situation: An image of the knee is underexposed and must be repeated. The original technique used was 62 kVp with 3.2 mAs. The technologist decides to keep the mAs at the same level but change the kVp to increase radiographic density/IR exposure. How much of an increase is needed in kVp to double the IR exposure?
A. 4 – 5%
B. 8 – 9%
C. 10 – 12%
D. 15 – 20%