RTCA 218 Xray Emission Bushong Chapter 9 Xray
RTCA 218 X-ray Emission Bushong, Chapter 9
X-ray Emission Abstract: This section describes x-ray quality and x-ray quantity. Emphasis will be placed on factors affecting x-ray quality and quantity and discussing terms that relate to these issues. Objectives: At the end of this section, the student should be able to: n define and discuss radiation quantity. n list and discuss the factors affecting x-ray quantity. n define radiation quality and penetrability. n define and discuss half-value layer. n list and discuss the factors affecting radiation quality.
X-ray Emission X-ray Quantity – Output intensity n measured in _________ or m. R n machines operated at 70 k. Vp produce an x-ray intensity about ___ m. R/ m. As at 100 cm SID
Nomogram of x-ray intensity
Example An abdominal radiograph requires exposure factors of 70 k. Vp, 800 m. A, and 0. 10 seconds. If the exposure is made at a 40 -inch SID, what is the output intensity of this exposure? 800 m. A × 0. 10 sec. = 80 m. As Output (x-ray) intensity = 5 m. R/m. As @ 70 k. Vp & 100 cm Output intensity for this exposure would be calculated: 5 m. R × 80 m. As = 400 m. R
X-ray Emission n Factors affecting X-ray Quantity 1. m. As n _______ Proportional I 1 / I 2 = m. As 1 / m. As 2
X-ray Emission Example: Exposure utilizing 50 m. As results in an intensity of 200 m. R. What is the new intensity if the m. As is increased to 100? I 1 / I 2 = m. As 1 / m. As 2 200/x = 50/100 200/x = ½ x = 400 m. R
X-ray Emission 2. k. Vp n Proportional but not directly n ___% increase in k. Vp required cutting m. As in half to maintain same exposure and image _______ I 1 / I 2 = (k. Vp 1 /k. Vp 2)2
X-ray Emission Example: Exposure utilizing 70 k. Vp produces an intensity of 200 m. R. What is the intensity if the k. Vp is increased to 80? I 1 / I 2 = (k. Vp 1 /k. Vp 2)2 200 m. R/x = (7/8)2 200/x = 49/64 49 x = (200)(64) x = 261 m. R
X-ray Emission 3. Distance n Inversely Proportional n Inverse ______ Law I 1 / I 2 = d 22 / d 12
X-ray Emission Example: Exposure taken at a distance of 6 feet from the radiation source results in an intensity of 200 m. R. What is the new intensity if the distance is decreased to 2 feet? I 1 / I 2 = d 22 / d 12 200/x = 22 / 62 200/x = 4/36 200/x = 1/9 x = 1800 m. R
X-ray Emission 4. Filtration n calculated by Half _____ layer (HVL) n thickness of filtering material required to reduce the intensity of the x-ray beam to ___ its original value
X-ray Emission increasing filtration decreases x-ray quantity by removing unnecessary, ____________ x-ray photons n Increasing filtration increases the effective (average) energy of the x-ray beam n Filtration will have no affect on x-ray beam ___________ n Only a change in k. Vp (peak energy of the beam) will change the penetrating ability n
Example The following are scores of 10 quizzes given in a very exciting radiation physics course. To calculate the average add them up and divide by 10. 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55 55 ÷ 10 = 5. 5 average Now, your very kind and compassion teacher has allowed you to drop your 5 lowest quiz scores. To calculate that average, add the 5 highest scores and divide by 5. 6 + 7 + 8 + 9 + 10 = 40; 40 ÷ 5 = 8 average By dropping the 5 lowest quiz scores, the quantity of quizzes that counted toward the final grade decreased, but the effective (average) score of the quizzes increased.
X-ray Emission Problem: How many half-lifes are required to reduce an exposure with an intensity of 200 m. R to less than 10 m. R? 1 st half life – 200 to 100 2 nd half life – 100 to 50 3 rd half life – 50 to 25 4 th half life – 25 to 12. 5 5 th half life – 12. 5 to 6. 25 Answer: 5 half lives
X-ray Emission X-ray Quality n __________ 1. high energy = high penetrability = high quality = hard x-rays 2. low energy = low penetrability = low quality = soft x-rays
X-ray Emission n Factors Affecting X-ray Quality 1. ________ n increasing k. Vp increases beam quality
X-ray Emission 2. Filtration n Increasing filtration increases beam quality n Types of Filtration A. _________ n Filtration created by the parts of the x-ray tube and collimator housing B. Added C. Compensating n Thick part of the filter placed over the thin part of the anatomy n X-ray tubes that operate above 70 k. Vp require a minimum of 2. 5 mm Al equivalent of filtration
Inherent + Added = Total Filtration
Trough Filter Wedge Filter (Compensating)
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