Lab6 X-Ray Beam updated

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BME704 | Radiation Therapy Devices Lab 6 Department of Electrical, Computer, and Biomedical Engineering Program: Biomedical Engineering BME704: Radiation Therapy Devices Lab 6: Image Quality and Dose, Diagnostic X-Ray Beam Parameters NAME: Nourhan Chalhoub, Tori Butler ID: 500982281, 500920088 1

BME704 | Radiation Therapy Devices Lab 6 Objectives - Understand why the following statements are true: o “kV should be the lowest that will penetrate the area of interest” o ”mA should be as high as practical” o “mAs should be as low as practical” (acceptable noise level; ALARA; dose) - Understand how filtration affects the x-ray beam. - To understand how the factors that control the x-ray beam production (voltage and current) affect the image quality. Instructions: During the lab, the answers to the questions have to be directly filled into this instruction document. Extra time will be given, where the student must hand in their completed solutions at the beginning of the next scheduled laboratory time. *Note this is an individual lab assignment, and a department cover page must be included. References The following sections from the “X-Ray Imaging Physics for Nuclear Medicine Technologists. Part 2: X-Ray Interactions and Image Formation” article. - Review sections of article on “X-rays and Interaction with Matter” and “Attenuation Coefficients” found on pages 3 to 7. - Focus on section on “X-Ray Beam Attenuation” on pages 7-9 (stop at “Transmitted X-Ray Beam and Subject Contrast”) The following sections from the “Part 4: Principles of Patient Radiation Protection & ALARA” continuing education session found at: http://www.ceessentials.net/article5.html - Introduction - Section 4.1: Beam Filtration - Section 4.2: Achieve ALARA through technique selection Safety Code 35 http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/safety-code_35-securite/section-a3-eng. php#a353 2

BME704 | Radiation Therapy Devices Lab 6 X-Ray Beam Attenuation 1. Why is there x-ray beam filtration built into x-ray imaging systems? (1 point) There is an x-ray beam filtration built into x-ray imaging systems to absorb lower-energy x-ray photons emitted by the tube. This results in a less noisy image due to the increased scattering of lower-energy photons. 2. What is this analogous to in analog filters (i.e. low pass, high pass, or band pass)? (1 point) In analog filters, this process is similar to high pass filters, as it involves the removal of lower-energy photons, comparable to filtering out signals with low frequency. 3. Is there a reason to limit the amount of filtration you put in the x-ray beam? (2 points) Reducing the level of filtration may be warranted for specific applications, such as when examining small body parts or pediatric cases, as these scenarios require less X-ray penetration compared to adult examinations. 3

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BME704 | Radiation Therapy Devices Lab 6 X-ray Technique The amount of current that is applied to an x-ray tube to produce x-rays is measured in milliamperes (mA). This current is applied for a time period that is measured in seconds. Theses two characteristics are combined together in the “mAs”, or seconds of amperage that are applied to an x-ray tube. 4) Which curve (Upper or lower) in the above graph was produced with a higher mAs? (1 point) A higher mAs was produced in generating the upper curve in the provided graph. 5) What is the impact of increasing the mAs on dose? (1 point) The impact of increasing the mAs on dose results in the increase of electron production, consequently leading to an increased dose. 6) What is the relationship between mAs and dose? (1 point) The relationship between mAs and dose is that as mAs increases, so does the dose, indicating a proportional relationship between the two. 7) What happens to an x-ray image when the mAs is too low? (1 point) When the mAs is insufficiently low, the x-ray photons lack the necessary energy to interact effectively with the crystals, leading to the occurrence of quantum mottling in the x-ray image. 4

BME704 | Radiation Therapy Devices Lab 6 The amount of voltage (measure in kilovolts, kV) that is applied to an x-ray tube is another parameter that can be controlled in producing x-rays. 8) Which curve (Upper or lower) in the above graph was produced with a greater kV? (1 point) The upper curve on the graph corresponds to a higher applied kilovoltage (kV). 9) What is the impact of increasing the kV on dose? (1 point) The impact of increasing the kV on dose is that the dose will also increase. 10) What is the relationship between kV and dose? (1 point) The relationship between dose and kilovoltage (kV) is a squared and proportional relationship. 11) What X-Ray Interaction becomes predominant when kV is higher (e.g. 120 kV)? (1 point) The interaction that becomes predominant is the Compton effect when kV is higher. 12) What effect does increasing the kVp have on dose to imaging personnel? Is this a risk that is acceptable? (2 points) The effect is that when increasing the kilovoltage (kVp), this would result in increased photon penetration, leading to a higher overall dose. This potential risk is can sometimes be acceptable, as the imaging personnel routinely evaluate and prepare for such situations by employing protective measures. 13) How does the kVp level affect the x-rays beam's ability to penetrate an object? )? (1 point) An increase in the kVp levels enhances the penetration capability of the X-ray beam through an object. 5

BME704 | Radiation Therapy Devices Lab 6 Dose Reference Levels (DRLs) The Canadian federal governments “Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities” gives recommendations for radiation protection. One section deals with dose reference levels. These are the recommended limits for x-ray doses that a patient should receive for a given procedure. One does not want to exceed the amount of dose given as a reference level, unless there are unusual clinical conditions that require this. Table 1: Representative DRLs for radiographic procedures performed on adults (IPEM 2004), (IAEA 1996) from Safety Code 35 Examination Entrance Surface Dose (mGy) Chest (PA) 0.2 - 0.3 Chest (LAT) 0.7 - 1.5 Thoracic Spine (AP) 5 - 8 Thoracic Spine (LAT) 7 - 10 Lumbar Spine (AP) 7 - 10 Lumbar Spine (LAT) 15 - 30 Abdomen (AP) 7 - 15 Pelvis (AP) 5 - 10 Skull (AP) 4 - 5 Skull (LAT) 2 - 3 14) If the technique for an anterior posterior abdomen x-ray was 200mA, 30 ms (or 6 mAs) at 75kVp, resulted in a 10mGy exposure (intensity), determine the new exposure if: a) A change to 50 ms is made (I 1 /I 2 =mAs 1 /mAs 2 ) (one point) I 2 = (mAs 2 /mAs 1 ) x I 1 I 2 = ((50*200)/(30*200)) I 2 = 1.67 Gy I 2 = 16.67 mGy b) Is the change above appropriate? (one point) It is not appropriate because it does not fall in the range interval for the abdomen as it exceeds the 7-15 mGy level. 6

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BME704 | Radiation Therapy Devices Lab 6 c) A change to 90 kVp is made (I 1 /I 2 =(kVp 1 2 /kVp 2 2 ) (one point) I 2 = (kVp 2 2 /kVp 1 2 ) x I 1 I 2 = ((90^2)/(75^2)) I 2 = 1.44 Gy I 2 = 14.4 mGy d) Is the change above appropriate? (one point) The change is appropriate because it falls under the range interval for the abdomen at 7-15 mGy level. 7

BME704 | Radiation Therapy Devices Lab 6 Imaging Examples “Good” Quality Image of the Wrist. Details of the wrist bone structures, etc. can be clearly seen. “Poor” Quality Image of the wrist Details of the wrist bone structures are “blurry” and can to be seen clearly. The bone penetration and subject contrast are inadequate. 15) What steps would you take to adjust the mAs and/or kVp to improve the “Poor” quality wrist x-ray. (3 points) Some steps taken to adjust the mAs and or kVp to improve the “Poor” quality wrist X-ray would be to evaluate the exposure, adjust mAs for density and modify the kVp for contrast. Evaluating the exposure factors assess the current mAs and kVp settings use to ensure that it is appropriate for patients anatomy. If the image is underexposed, than increasing the mAs will enhance the density and visibility of structures. In short it provides more X-ray photons to the detector. Vise verse, if the image is overexposed, reducing the mAs wil decrease the amount of radiation reaching the detector. This improves contrast and prevents unnecessary radiation dose. When adjusting the kVp increasing it can improve penetration and provides a more detailed image, used mainly for thicker body parts. Whereas decreasing the kVps can lower the energy of the X-rays for better contrast in anatomical regions. 8

BME704 | Radiation Therapy Devices Lab 6 “Good” Image of Child’s Chest “Poor” Image of Child’s Chest due to effort to reduce patient exposure resulting in a photon starved radiograph that lacks subject detail. 16) What factors in the technique setting (kV and mAs) do you think contributed to the poor quality image. (2 points) Some factors in the technique setting that contribute to poor quality image are inadequate exposure and inappropriate kVp settings. When the image is underexposed it means the mAs is too low, meaning there will be an insufficient radiation exposure reaching the image receptor. If its overexposed, it means the mAs setting is too high, resulting in a darker imager with minimal detail. For the kVp settings a low kVp can lead to poor bone visualization and inadequate contrast in the image, resulting from low X-ray penetration. If the kVp setting is high, soft tissue may appear washed out and overall image can lack detail of diagnosis. 17) You have an x-ray system that is set up for imaging adult chests. You want to perform a chest x-ray on an infant. Please explain how you would change the following parameters (remain the same, raise or lower), with your reasoning. (3 points) a) kV Setting (one point) Lower the kV setting because infants have a smaller and less dense body structure than adults. It also helps produce images with better contrast for smaller body parts with minimal radiation dose. b) Beam Filtration (one point) 9

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BME704 | Radiation Therapy Devices Lab 6 Lower or remain the same beam filtration because reducing or keeping it the same can help maintain a higher proportion of lower-energy photons suitable for imaging pediatric patients. Contributes to better image quality in smaller less dense body structures. c) mAs Setting (one point) MAs settings should be adjusted based on the size and anatomy of the infant. Usually, they require a lower mAs setting compared to adults, however specific adjustments depends on factors such as age, size and condition of the infant. It’s crucial to balance the mAs setting to provide a sufficient exposure for image quality while minimizing the radiation dose. 10