Chapter 8 Challange Questions

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Apr 3, 2024

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Challenge Questions Yolanda Cuevas Chapter 8: X-ray Emission 1) Define or otherwise identify the following: a) Inherent filtration - The filtration provided by the window and oil bath of the x-ray tube. b) The unit of x-ray quantity - Milliroentgen (mR) or milligray (mGy a ). f) Half-value layer - The thickness of the filter or other absorbing material that will reduce intensity to half its original value. g) Wedge filter - A compensating filter designed to shape the useful x-ray beam to the anatomic structure under examination so that the exposure of the image receptor will be more uniform. h) The unit of x-ray quality - Identified numerically by half-value layer; also influenced by kVp and the added filtration in the useful beam. j) X-ray intensity - X-ray intensity is another term for x-ray quantity, measured in mR or mGy. 3) An abdominal radiograph taken at 84 kVp, 150 mAs result in patient radiation exposure of 6.5 mGy a . The image is too light and is repeated at 84 kVp, 250 mAs. What is the new radiation exposure? 10.83 mGy a (1083) mR 4) An image of the lateral skull taken at 68 kVp, 20 mAs has sufficient optical density but too much contrast. If the kVp is increased to 78 kVp, what should be the new mAs? 10 mAs 5) The chest radiograph taken at 180 cm SID results in an exposure of 120 uGy a . What would the exposure be if the same radiographic factors were used at 100 cm SID? 389 uGy a (38.9 mR) 6) The following data were obtained with a fluoroscopic x-ray tube operated at 80 kVp: The exposure levels were measured 50cm above the patient couch with aluminum absorbers positioned on the surface of the couch. Estimate the HVL through visual inspection of the data; then plot the data & determine the precise value of the HVL. Added mm Al uGy a None 650 1 480 3 300 5 210 7 160 9 130 One half of 650 uGy a (65 mR) is 325 uGy a (32.5 mR), which falls between 1 and 3 mm Al. A plot shows the correct answer to be 2.8 mm Al. 10) An extremity is radiographed at 60 kVp, 10 mAs, resulting in an x-ray intensity of 280 uGy a . If the technique is changed to 55 kVp, 10 mAs, what is the resultant x-ray intensity? 235 uGy a (23.5 mR). 11) What is the square law, and how is it used? The square law involves compensating for a change in SID by changing the mAs by the factor SID 2 . When SID is increased, the mAs must be increased by SID 2 to maintain constant exposure of the image receptor. 12) What is the primary purpose of x-ray beam filtration? To remove low-energy x-rays, which only increase patient dose without contributing to the image. 13) The kVp is reduced from 78 to 68 kVp. What, if anything, should be done with mAs to maintain exposure of the image receptor constant? Double the mAs.

14) What is the relationship between x-ray quantity and mAs? Directly proportional. Double mAs; double x-ray quantity. 15) Define half-value layer. The thickness of absorber necessary to reduce the x-ray beam intensity to half. 16) List the two ways an x-ray beam can be shifted to a higher average energy. Increase the kVp or add filtration. 17) Why is aluminum used for x-ray beam filtration? Because it is efficient at removing low-energy x-rays, and because it is readily available, inexpensive, and easily shaped into filters. 18) Describe the use of a wedge filter during radiography of a foot. The thicker part of the wedge should be positioned toward the toes in order to equalize optical density. 19) Does adding filtration to the x-ray beam affect the quantity of x-rays reaching the image receptor? Yes, the quantity is reduced with an increase in filtration. 20) Increasing Effect on X-ray Quality Effect of X-ray Quantity mAs None Increase kVp Increase Increase Distance None Reduce Filtration Increase Reduce

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