What is the ratio of light incident on the film to amount of light transmitted through the film? As x-ray photon energy increases, the probability of that photon penetrating a given tissue without interaction increases. Repeated exposures made just under the limit over a long period can still jeopardize the life of the x-ray tube. The product of milliamperage and exposure time has a direct proportional relationship with the quantity of x-rays produced. Scatter radiation remains a concern at higher kVp and provides no useful information and always decreases the radiographic contrast. mAs/distance compensation formula The bigger the # in the ratio, the more ___ it is going to be at eliminating the scatter. Use these flashcards to help memorize information. A cumulative run through physics in Radiology, ARRT registry review covering Unit 5: Radiation Protection. Paper, LECTURE 5 - Controlling factors to density: mA & exposure Time. What is the primary controlling factor for contrast? The primary exposure technique factors the radiographer selects on the control panel are milliamperage, time of exposure, and kilovoltage peak (kVp). How does increasing grid ratio affect density? Recorded detail improves as OID decreases, SID is directly proportional to recorded detail. If a radiograph must be repeated because of another error, such as positioning, the radiographer may also use the opportunity to make an adjustment in density to produce a radiograph of optimal quality. Chapter 9 emphasizes that a good-quality radiographic image accurately represents the anatomic area of interest. To maintain exposure to the IR, when increasing the kVp by 15% (kVp 1.15), divide the original mAs by 2. As SID increases, recorded detail increases and vice versa. Then click the card to flip it. As the mAs is increased, the quantity of radiation reaching the IR is increased. Once the anatomic part is adequately penetrated, as the quantity of x-rays is increased, the exposure to the IR proportionally increases (. Knowledge of how these factors affect the image individually and in combination assists the radiographer to produce a radiographic image with the amount of information desired for diagnostic interpretation. However, the kVp has a greater effect on the image when using film-screen IRs. Calculate changes in mAs for changes in source-to-image receptor distance. body habitus Image Production This produces a high-contrast radiographic image (Figure 10-7). Bushong Stewart C. Radiologic science for technologists. mAs is called the total exposure because it controls the number of x-rays produced at exposure. optimal kVp Calculate changes in kVp to change or maintain exposure to the image receptor. As focal spot size changes, so does the amount of unsharpness. Small focal spot sizes are usually 0.5 or 0.6 mm, and large focal spot sizes are usually 1 or 1.2 mm in size. Kilovoltage is not a factor typically manipulated to vary the amount of IR exposure in film-screen imaging because the kVp also affects contrast. The actual focal spot is the area being bombarded by the filament electrons. Because kVp affects the amount of radiation reaching the IR, its effect on the digital image is similar to the effect of mAs. What are the two types of contrast seen in medical radiography? A) 50-800 (A 50 is a slow speed. improves contrast by removing scatter before it reaches the film which results in a shorter scale of contrast. However, with this increase in photon energy, the likelihood of Compton interactions relative to photoelectric interactions also increases. Additional Equipment 15% rule However, pathologic conditions, you are going to alter the penetration. image would be too light/inadequate density. A radiographic image repeated because of insufficient or excessive density requires a change in mAs by a factor of at least 2. and decreasing the kVp decreases IR exposure and the density produced on a film image (. Controls = amount of radiation produced by controlling amount of electrons flowing across X-ray tube. Because oceanographers require density measurements to be accurate to the . The selection of kVp alters its absorption and transmission through the anatomic part regardless of the type of IR used and therefore must be selected wisely. What factor causes foreshortening of the radiographic image? mAs and Digital Image Brightness Focal spot size influences the amount of unsharpness recorded in the image. To decrease exposure to the IR, multiply the kVp by 0.85 (original kVp 15%). Pediatric Patients Radiation Protection However, regardless of the type of IR, the patient should be exposed to the least amount of radiation necessary to produce a diagnostic-quality radiograph. Knowledge of how these factors affect the image individually and in combination assists the radiographer to produce a radiographic image with the amount of information desired for diagnostic interpretation. Because various types of IRs respond differently to the radiation exiting the patient (remnant), these differences are noted throughout this chapter. Major controlling factor of density = mAs. increase/decrease density and maintain density while increasing or decreasing contrast. For example, when the mAs is increased, density is increased; when the mAs is decreased, density is decreased (Figure 10-2). FIGURE 10-6 kVp and Exit-Beam Intensities.Higher kVp increases the penetrating power of the x-ray beam and results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient. Digital IRs can detect a wider range of radiation intensities (wider dynamic range) exiting the patient and therefore are not as dependent on the mAs as film-screen IRs. 2.2 A to 2.2 B). Focal Spot Size 1. The reciprocity law states that the reaction of a photographic emulsion to light will be equal to the products of the intensity of that light and the time of the exposure 1. Privacy Policy and Changes in mAs have a direct effect on density. Beam Restriction The mAs has a direct effect on the amount of radiographic density produced when using a film-screen IR. Higher kVp and lower mAs values are not recommended as a general rule during film-screen imaging because of the contrast required to best visualize the anatomic structures. As the quantity of x-rays is increased (mAs), the exposure to the image receptor proportionally increases. Recognize how to correct exposure factors for a density error. True. State exposure technique modifications for the following considerations: body habitus, pediatric patients, projections and positions, soft tissue, casts and splints, and pathologic conditions. On the control panel the radiographer can select whether to use a small or large focal spot size. However, the kVp has a greater effect on the image when using film-screen IRs. In general, for repeat radiographs necessitated by density errors, the mAs is adjusted by a factor of 2; therefore a minimum change involves doubling or halving the mAs. Contrast Media As the mAs is decreased, the amount of radiation reaching the IR is decreased. A 15% increase in kVp has the same effect as doubling the mAs. If you knew the answer, click the green Know box. When you need a break, try one of the other activities listed below the flashcards like Matching, Snowman, or Hungry Bug. Mas: What factors secondarily influence density? A low kVp results in more absorption and less transmission in the anatomic tissues, but with more variation in the x-ray intensities exiting the patient, resulting in a high-contrast (short-scale) image. In Chapter 6, variables that affect both the quantity and quality of the x-ray beam are presented. Bunsen R. W. and H. E. Roscoe. Everything else, we have changed mAs. Make the Physics Connection 10-4 80kVp0.85and mAs2 As SID increases, size distortion decreases, As OID increases, size distortion increases. Because of the anode hill effect, density is less at which end of the x-ray beam? Normal and pathologic. As mentioned previously, it may take more than doubling the mAs to correct for a density error. mAs controlling factor. FIGURE 10-3 Adjusting mAs for Density Errors.A, A greater increase in mAs, four times the original mAs, is needed. The mAs does not have a direct effect on image brightness when using digital IRs. mAs and Quantity of Radiation Although image contrast can be adjusted when using a kVp that is too high, increased scatter radiation reaches the IR and may adversely affect image quality. 800 is a fast) B) increase your mAs But how do you do this? 80kVp1.15=92kVp Factors Affecting Density of Water The density of a material is given in units of mass per unit volume and expressed in kilograms per cubic metre in the SI system of units. Because the mAs is the product of milliamperage and exposure time, increasing milliamperage or time has the same effect on the radiation exposure. The radiographer must weigh the importance of improved recorded detail for a particular examination or anatomic part against the amount of radiation exposure used. The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs, or reducing the mAs by 50%; for example, increasing the kVp from 82 to 94 (15%) produces the same exposure to the IR as increasing the mAs from 10 to 20. mA x t = mAs (strictly mA.s but the "." Altering the penetrating power of the x-ray beam affects its absorption and transmission through the anatomic tissue being radiographed. Image receptor (film) contrast and subject contrast. Additionally, for a given mAs, IRs respond differently. extrapolated This means that doubling the mA, doubles the number of x-rays and therefore doubles the density. Depending on the type of control panel, milliamperage and exposure time may be selected separately or combined as one factor, milliamperage/second (mAs). Changing the kVp affects its absorption and transmission as it interacts with anatomic tissue; however, using a higher kVp reduces the total number of interactions and increases the amount of x-rays transmitted. Milliamperage and time affect the quantity of radiation produced and kilovoltage affects both the quantity and quality. Maintaining or adjusting exposure to the IR can be accomplished with kVp by using the 15% rule. The distance between the source of the radiation and the IR, Essentials of Radiographic Physics and Imaging. At higher kVp, a greater proportion of Compton scattering occurs compared with x-ray absorption (photoelectric effect), which decreases radiographic contrast. B, A greater decrease in mAs, one-fourth the original mAs, is needed. However, regardless of the type of IR, the patient should be exposed to the least amount of radiation necessary to produce a diagnostic-quality radiograph. This typically brings the optical densities back within the straight-line portion of the films sensitometric curve to best visualize the anatomic area of interest. When adequate penetration is achieved, further increasing the kVp results in more radiation reaching the IR. Recognize how to correct exposure factors for a density error. patient motion; motion of the x-ray tube is not a problem. Unfortunately, exposure is limited with a small focal spot size. When the radiographer selects a particular focal spot size, he or she is actually selecting a filament size that is energized during x-ray production. Grids Central Ray Alignment If the mAs selected is too high (high exposure to the digital IR), the brightness can also be adjusted, but the patient has received more radiation than necessary. If you dont change your technique and you go to a higher grid ratio, your image will be ____. It is important for the radiographer to determine the amount of mAs needed to produce a diagnostic image. Outline If the radiograph necessitates an adjustment greater than a factor of 2, the radiographer should multiply or divide the mAs by 4 (, Radiographs that have sufficient but not optimal density usually are not repeated. Generator Output The controlling factor for density when using a film screen image receptor is: A mAs. adjustment during image processing; however, the patient has been overexposed. (From Fauber TL: Radiographic imaging and exposure, ed 3, St Louis, 2009, Mosby.) Density-dependent limiting factors can lead to a logistic pattern of growth, in which a population's size levels off at an environmentally determined maximum called the carrying capacity. What formula is used to calculate size distortion? However, exposure errors can adversely affect the quality of the digital image. kVp and the Radiographic Image Which of the two types of contrast exhibit wide exposure latitude? For example, single-phase generators produce less radiation for the same mAs when compared with a high-frequency generator. Feb 27, 2016 | Posted by admin in GENERAL RADIOLOGY | Comments Off on Radiographic Exposure Technique, Excessive Radiation Exposure and Digital Imaging. A radiographic image repeated because of insufficient or excessive density requires a change in mAs by a factor of at least 2. For most anatomic regions, an accepted range of kVp provides an appropriate level of radiographic contrast. This law pertains to mAs in the sense that all combinations of mA x seconds that amount to an equal quantity will produce the same amount of density. Exposure Technique Charts When a film image is too light (insufficient density), a greater increase in mAs may be needed to correct the density, or the mAs may need to be decreased to correct a film image that has excessive density. For example, using portable or mobile x-ray equipment may limit choices of mAs settings and therefore the radiographer must adjust the kVp to maintain sufficient exposure to the IR. It is due to this law that radiographers will have to take into consideration all other factors (mA, focal spot, source image receptor distance (SID), kVp) to reduce time to avoid motion blur. Kilovoltage and Digital Image Quality In addition, whenever a 15% change is made in the kVp to maintain the exposure to the IR, the radiographer must adjust the mAs by a factor of 2. Which of the two types of contrast is a product of low KVP? See our A 15% increase in kVp has the same effect as doubling the mAs. B, Smaller focal spot. Film-screen combos will range from __ - __. When using a film-screen IR, radiographers need to assess the level of density produced on the processed image and determine whether the density is sufficient to visualize the anatomic area of interest. DIGITAL IMAGING: similar to film screen in terms of density: Help reduce scatter. The product of milliamperage and exposure time has a direct proportional relationship with the quantity of x-rays produced. 1. A, Original image. The film characteristic, speed, and chemical processing determine the amount of optical density produced on the image for a given mAs. What are the 2 types? mAs should change proportionally to the square of the change in distance in the same direction. If the mAs is too low (low exposure to the digital IR), image brightness is adjusted during computer processing to achieve the desired level. Critical Concept 10-2 Your email address is only used to allow you to reset your password. Describe the use of grids and beam restriction, and their effect on image receptor exposure and image quality. To decrease exposure to the IR, multiply the kVp by 0.85 (original kVp 15%). The minimum change needed to correct for a density error is determined by multiplying or dividing the mAs by 2. 200mA50ms(0.05s)=10mAs Used to make adjustments to mAs if distance is increased or decreased. Digital IRs can detect a wider range of radiation intensities (wider dynamic range) exiting the patient and therefore are not as dependent on the mAs as film-screen IRs. What is the major controlling factor of density if SID is fixed? This relationship between radiation exposure intensity and density is discussed in more detail in Chapter 9. If you've accidentally put the card in the wrong box, just click on the card to take it out of the box. Focal spot size is determined by the filament size. This typically brings the optical densities back within the straight-line portion of the films sensitometric curve to best visualize the anatomic area of interest. density-dependent factor, also called regulating factor, in ecology, any force that affects the size of a population of living things in response to the density of the population (the number of individuals per unit area). The selection of kVp alters its absorption and transmission through the anatomic part regardless of the type of IR used and therefore must be selected wisely. Scatter radiation remains a concern at higher kVp and provides no useful information and always decreases the radiographic contrast. Exposure Technique Chart Development Primary Factors Milliamperage and Exposure Time Kilovoltage Secondary Factors Focal Spot Size Source-to-Image Receptor Distance Object-to-Image Receptor Distance Calculating Magnification Central Ray Alignment Grids Beam Restriction Generator Output Tube Filtration Compensating Filters Patient Factors Body Habitus Part Thickness Pediatric Patients When the radiographer selects a particular focal spot size, he or she is actually selecting a filament size that is energized during x-ray production. But how? The quantity of radiation reaching the patient affects the amount of remnant radiation reaching the IR. As a result, images with lower contrast are produced. More Dense than you expect it to be. The kVp affects the contrast in a digital image; however, image brightness and contrast are primarily controlled during computer processing. Milliampere-seconds, also more commonly known as mAs, is a measure of radiation produced (milliamperage) over a set amount of time (seconds) via an x-ray tube. The probability of Compton scattering is related to the energy of the photon. Table of Contents What Is the Density of Water? For film-screen IRs, the mAs controls the density produced in the image. This typically brings the optical densities back within the straight-line portion of the films sensitometric curve to best visualize the anatomic area of interest. Density-independent factors often arise from physical and chemical (rather than biological) phenomena. During computer processing, image brightness is maintained when the mAs is too low or too high. Explain how kVp affects radiation production and image receptor exposure. Radiographers have the responsibility of selecting the combination of exposure factors to produce a quality image. Why? When a kVp that is too low is selected, the brightness and contrast are adjusted, but quantum noise may be visible. Image C shows a lower contrast image due to an increase in kVp. To see how well you know the information, try the Quiz or Test activity. A greater change in the kVp is needed when operating at a high kVp (greater than 90) compared with operating at a low kVp (less than 70) (Figure 10-5). Critical Concept 10-5 To increase exposure to the IR, multiply the kVp by 1.15 (original kVp + 15%). In oceanography the density of seawater has been expressed historically in grams per cubic centimetre. Remember that a 15% change in kVp does not produce the same effect across the entire range of kVp used in radiography. mA is directly proportional to the intensity or quantity of the x-ray beam. To best visualize the anatomic area of interest, the mAs selected must produce a sufficient amount of radiation reaching the IR, regardless of type. There is an inverse relationship; as tissue thickness, average atomic number, and/or tissue density increases, radiographic density decreases. Pathologic Conditions When a low kVp is used, the x-ray beam penetration is decreased, resulting in more absorption and less transmission, which results in greater variation in the x-ray intensities exiting the patient (remnant). Tube Filtration Excessive or insufficient mAs adversely affects image quality and affects patient radiation exposure. Describe the use of grids and beam restriction, and their effect on image receptor exposure and image quality. Too much radiation reaching the IR (within reason) produces a digital image with the appropriate level of brightness as a result of computer adjustment during image processing; however, the patient has been overexposed. What will your image look like if you change from a 3 phase to a single phase with no change in technique? For film-screen IRs, the mAs controls the density produced in the image. These factors make achieving a desired level of radiographic contrast more complex than achieving a desired level of radiographic density, especially for film-screen imaging. Calculate changes in mAs when adding or removing a grid. Focal Spot Size Additionally, for a given mAs, IRs respond differently. Density-dependent factors are sometimes called regulating . Decreasing the kVp decreases the proportion of Compton scattering and increases radiographic contrast. mAs: True or False. Only gold members can continue reading. What is the controlling factor of density/IR exposure and how is it affected? Image Intensified Fluoroscopy For example, single-phase generators produce less radiation for the same mAs when compared with a high-frequency generator. Water is an odourless, tasteless, transparent, and colourless chemical substance, which is the main constituent of this planet's lakes, oceans, streams, and the fluids of most living organisms. The area of interest must be adequately penetrated before the mAs can be adjusted to produce a quality radiographic image. Calculate changes in mAs for changes in source-to-image receptor distance. Multitude of influencing factors; mAs reciprocity* Failure; Short exposure times of < than 0.01 seconds; . Explain how kVp affects radiation production and image receptor exposure. If you use 100 mAs for 14X17, you would have to ____ your mAs by 1.25 to maintain the same density. Identify the exposure factors that can affect patient radiation exposure. The level of radiographic contrast desired, and therefore the kVp selected, depends on the type and composition of the anatomic tissue, the structures that must be visualized, and to some extent the diagnosticians preference. Compare the effect of changes in milliamperage and exposure time on film-screen and digital images. Critical Concepts 10-10 How can we tell if our exposure is appropriate or not in digital? As mentioned previously, it may take more than doubling the mAs to correct for a density error. kVp and Radiographic Contrast 100mA0.1s=10mAs Or fluid: Because it increases the attenuation of the photon. Making a visible change in radiographic density requires that the minimum amount of change in mAs be approximately 30% (depending on equipment, this may vary between 25% and 35%). Milliampere-seconds (mAs). If a radiograph must be repeated because of another error, such as positioning, the radiographer may also use the opportunity to make an adjustment in density to produce a radiograph of optimal quality. As a result, images with lower contrast are produced (. Regardless, it is important to understand how changing each separately or in combination affects the radiation reaching the IR and the radiographic image. Critical Concept 10-9 The smaller this area of origin, the sharper the image. As mentioned earlier, the effects of changes in the kVp are not uniform throughout the range of kVp. Math Application 10-3 density requires that the minimum amount of change in mAs be approximately 30% (depending on equipment, this may vary between 25% and 35%). Similarly, too little radiation reaching the IR (within reason) produces a digital image with the appropriate level of brightness, but the increased noise decreases image quality. As a result, images with lower contrast are produced (Figure 10-6). The _____ factors should be used as the principle method for adjusting radiographic density. What is the misrepresentation (elongated or foreshortened) of the shape of the structure recorded as compared to the actual shape of the structure? SID is not a primary exposure technique factor; mAs and kVp are. 100mA100ms(0.1s)=10mAs What are the 2 primary types of compensating filters? If you switch from screen to grid, how do you know how to change your technique? A change in either milliamperage or exposure time proportionally changes the mAs. The efficiency of grids is referred to as the what? What does it control? Maintaining or adjusting exposure to the IR can be accomplished with kVp by using the 15% rule. 2.2 A to 2.2 C). What is the absorption of x-rays in the heel of the anode which results in decreased x-ray intensity of the anode side of the central ray? This relationship between radiation exposure intensity and density is discussed in more detail in, In general, for repeat radiographs necessitated by density errors, the mAs is adjusted by a factor of 2; therefore a minimum change involves doubling or halving the mAs. Recognize the factors that affect recorded detail and distortion. ADVERTISEMENT: Supporters see fewer/no ads, Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. 50 mA x 0.2 se = 10 mAs is equal to 300 mA x 0.03 s = 10 mAs. Chapter 6 Higher kVp increases the penetrating power of the x-ray beam and results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient (remnant). The mAs does not have a direct effect on image brightness when using digital IRs. If you are going from a 400 speed to a 200 speed, you will have to do what to maintain density? It directly influences the radiographic density, when all other factors are constant. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). Image brightness and contrast are primarily controlled during computer processing. 28 Q However, it is sometimes necessary to manipulate the kVp to maintain the required exposure to the IR. Image brightness and contrast are primarily controlled during computer processing. Because filtration alters beam intensity, density decreases slightly with increases in filtration. How does beam restriction affect density? Conversely, when the quantity of x-rays is decreased, the exposure to the IR decreases. For film-screen IRs, the mAs controls the density produced in the image. The radiographer must decide how much of a change in mAs is needed to correct for the density error. At the time the article was last revised Daniel J Bell had no recorded disclosures. More often, the radiographer evaluates the level of contrast achieved to improve the contrast for additional radiographs or similar circumstances that arise with a different patient. A patients age, condition, and the presence of a pathologic condition also affect the amount of mAs required for the procedure. Many secondary factors affect the radiation reaching the IR and image quality. The radiographer should be diligent in monitoring exposure indicator values to ensure that quality images are obtained with the lowest possible radiation dose to the patient. source-to-image receptor distance (SID) However, the kVp has a greater effect on the image when using film-screen IRs. Figure 3. 18 Q . Radiographic Exposure Technique Increasing or decreasing the contrast does what to density? Why should KVP not be used to control density? When low or high kVps are used, the amount of change in the kVp required to maintain the exposure to the IR may be greater or less than 15%. Will the thicker side of the wedge filter face the toes or the ankle? Kilovoltage When a small focal spot is used, the heat created during the x-ray exposure is concentrated in a smaller area and could cause tube damage. Recognize patient factors that may affect image receptor exposure. Calculate changes in milliamperage and exposure time to change or maintain exposure to the image receptor. If a repeat radiograph is necessary and kVp is to be adjusted to either increase or decrease the level of contrast, the 15% rule provides an acceptable method of adjustment. A greater increase is needed for high kVp (90 and above) than for low kVp (below 70). A lower-than-required mAs produces an image with increased quantum noise and a higher-than-needed mAs exposes the patient to unnecessary radiation. Image by Byron Inouye If the amount of matter is increased without changing the volume, then the density increases (Fig. Remember that a 15% change in, The actual focal spot is the area being bombarded by the filament electrons. Calculate changes in mAs when adding or removing a grid. Critical Concept 10-6 Remember that a 15% change in kVp does not produce the same effect across the entire range of kVp used in radiography. Adequate penetration of the anatomic area of interest is equally important when using digital IRs, and therefore kVp selection is important in producing a quality image. Many secondary factors affect the radiation reaching the IR and image quality. The smaller this stream, the greater the heat generated in a small area; therefore it is desirable to have a larger actual focal spot area. Increasing mAs causes more photons (radiation) of the particular kVp energy to be produced. High-frequency units produce x-rays much more efficiently than single-phase units. Because the milliamperage/second (mAs) controls the number of electrons boiled off of the filament and available to produce x-rays, it is considered the primary factor controlling quantity. The level of radiographic contrast desired, and therefore the kVp selected, depends on the type and composition of the anatomic tissue, the structures that must be visualized, and to some extent the diagnosticians preference. Which of the 2 contrast factors should be standardized? In Chapter 6, variables that affect both the quantity and quality of the x-ray beam are presented. Radiographs generally are not repeated because of contrast errors. By proper alignment of the tube, part and film (centering, keeping object parallel with fim and as close as possible, By using a resolution grid, resolution is measured in lines per millimeter (lp/mm), OID is inversely related to recorded detail. Radiographic contrast is the density difference between neighboring regions on a plain radiograph. Increasing or decreasing the kVp changes the amount of radiation exposure to the IR and the contrast produced within the image. When a small focal spot is used, the heat created during the x-ray exposure is concentrated in a smaller area and could cause tube damage. Density-dependent factors often arise from biological phenomena, rather than from physical and chemical phenomena. There is an increase in recorded detail as focal spot size decreases. 50mA200ms(0.2s)=10mAs Sample Problem: originally do something at 25 mAs and we want to know what our new mAs is going to be. Increasing the kVp increases the penetrating power of the radiation and increases the exposure to the image receptor. Introduction Depending on the type of control panel, milliamperage and exposure time may be selected separately or combined as one factor, milliamperage/second (mAs). Secondary Factors Part Thickness The minimum change needed to correct for a density error is determined by multiplying or dividing the mAs by 2. When a low kVp is used, the x-ray beam penetration is decreased, resulting in more absorption and less transmission, which results in greater variation in the x-ray intensities exiting the patient (remnant). Additive pathologies, ex: mass and tumor. Modern radiographic x-ray generators are equipped with safety circuits that prevent an exposure from being made if that exposure exceeds the tube loading capacity for the focal spot size selected. Although it may feel like you're playing a game, your brain is still making more connections with the information to help you out. It is not related to IR exposure. Once the anatomic part is adequately penetrated, as the quantity of x-rays is increased, the exposure to the IR proportionally increases (Figure 10-1). A 15% decrease in kVp has the same effect as decreasing the mAs by half. If you are changing from a single phase to a 3 phase, you will have to do what? Increasing the kVp increases IR exposure and the density produced on a film image, and decreasing the kVp decreases IR exposure and the density produced on a film image (Figure 10-4). Kilovoltage is not a factor typically manipulated to vary the amount of IR exposure in film-screen imaging because the kVp also affects contrast. mAs is NOT a primary controlling factor in the other 3 radiographic qualities; only density. A greater change in the kVp is needed when operating at a high kVp (greater than 90) compared with operating at a low kVp (less than 70) (, Because kVp affects the amount of radiation reaching the IR, its effect on the digital image is similar to the effect of mAs. magnification factor (MF) The effective focal spot is the origin of the x-ray beam and is the area as seen from the patients perspective. Chapter 9 emphasizes that a good-quality radiographic image accurately represents the anatomic area of interest. Film-Screen Speed The result is more photons (quantity) and higher energy photons (quality). The primary exposure technique factors the radiographer selects on the control panel are milliamperage, time of exposure, and kilovoltage peak (kVp). Focal Spot Size and Recorded Detail How does tissue thickness affect density? Using the 15% Rule As demonstrated in Math Application 10-1, mAs can be doubled by doubling the milliamperage or doubling the exposure time. What is the loss of radiographic quality caused by movement of the patient or x-ray tube during exposure? Differential absorption increases as the KVP is decreased; conversely, as KVP increases, more photons pass through and differential absorption decreases. This is the reason why we do what? Higher kVp increases the penetrating power of the x-ray beam and results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient (remnant). inverse square law Ex: you expose on a screen, you repeat it using a 16:1 grid, to maintain the same density, you have to use __ times your original mAs. A 10-kVp increase at 50 kVp (B) produces a greater change in density than a 10-kVp increase at 90 kVp (D). What is the difference between adjacent densities within the radiographic image? A MAJOR CONTROLLING FACTOR OF DENSITY. Conditions For best results enter two or more search terms. How does KVP relate to differential absorption? If volume increases without an increase in mass, then the density decreases (Fig. Key Terms It is desirable to keep this as small as practical to improve image quality (Figure 10-8). Modern radiographic x-ray generators are equipped with safety circuits that prevent an exposure from being made if that exposure exceeds the tube loading capacity for the focal spot size selected. As long as the kVp selected is sufficient to penetrate the anatomic part, the kVp can be further manipulated to alter the radiographic contrast. What is considered the useful range of optical densities? Make sure to remember your password. These slide into the guide shoes on the collimator box and are to aid and maintain an even density. Adding attenuation to photon beam = image will be less dense. Calculate changes in kVp to change or maintain exposure to the image receptor. Calculate changes in mAs when adding or removing a grid. decrease kVp by 15% OR, decrease mAs by half. This chapter discusses all of the primary and secondary factors and their effects on the radiation reaching the IR. are in the same box the next time you log in. If you forget it there is no way for StudyStack KVP, distance, beam restriction, anatomic part, grid, film/screen combination, processing, anode heel affect, Directly, as KVP increases density increases because penetrability increases so more photons are reaching the IR. 800 is a fast). Assuming that the anatomic part is adequately penetrated, changing the kVp does not affect the digital image in the same way as a film-screen image. When a film image is too light (insufficient density), a greater increase in mAs may be needed to correct the density, or the mAs may need to be decreased to correct a film image that has excessive density. How do intensifying screens affect density? Once the anatomic part is adequately penetrated, as the quantity of x-rays is increased, the exposure to the IR proportionally increases (Figure 10-1). Increasing either the current or time will increase the quantity of radiation; therefore the amount of radiation in an examination is represented as mAs. Additionally, when a kVp that is too high is selected, the image brightness and contrast are adjusted, but patient exposure may be increased. Purpose: Ischemic stroke (IS), one of the two main subtypes of stroke, occurs due to brain ischemia as a result of thrombosis of a cerebral blood vessel. State exposure technique modifications for the following considerations: body habitus, pediatric patients, projections and positions, soft tissue, casts and splints, and pathologic conditions. Related posts: A lower-than-required mAs produces an image with increased quantum noise and a higher-than-needed mAs exposes the patient to unnecessary radiation. This chapter discusses all of the primary and secondary factors and their effects on the radiation reaching the IR. Because the mAs is the product of milliamperage and exposure time, increasing milliamperage or time has the same effect on the radiation exposure. A high kVp results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient (remnant), producing a low-contrast (long-scale) image. In addition, whenever a 15% change is made in the kVp to maintain the exposure to the IR, the radiographer must adjust the mAs by a factor of 2. Destroying tissue and bone and therefore there is less material to attenuate the photon beam and will ultimately increase the density of your image. As focal spot size increases, unsharpness increases and recorded detail decreases; as focal spot size decreases, unsharpness decreases and recorded detail increases. A, Larger focal spot. For film-screen IRs, kVp has a direct relationship with density; however, the effect of the kVp on density is not equal throughout the range of kVp (low, middle, and high). Although image contrast can be adjusted when using a kVp that is too high, increased scatter radiation reaches the IR and may adversely affect image quality. A change in either milliamperage or exposure time proportionally changes the mAs. Your email address is only used to allow you to reset your password. When decreasing the kVp by 15% (kVp 0.85), multiply the mAs by 2. Make the Physics Connection 10-1 (From Fauber TL: Radiographic imaging and exposure, ed 3, St Louis, 2009, Mosby.) There is a direct proportional relationship between mAs and quantity of radiation; if the mAs are doubled, the amount of radiation is doubled. Explain the relationship between milliamperage and exposure time with radiation production and image receptor exposure. as grid ratio increases, density decreases because grids absorb scatter that would otherwise reach the image receptor, As SID increases, density decreases and vice versa (according to the inverse square law). Recognize how to correct exposure factors for a density error. Objectives The effective focal spot is the origin of the x-ray beam and is the area as seen from the patients perspective. For most anatomic regions, an accepted range of kVp provides an appropriate level of radiographic contrast. This chapter focuses on radiographic exposure techniques and the use of accessory devices, and their effect on the radiation reaching the image receptor (IR) and the image produced. What is different degrees of absorption in adjacent tissues that result in image contrast? Density is the mass per unit volume of a substance. All other factors remaining constant, an increase in milliamperage increases the amplitude of both the continuous and discrete portions of the spectrum. A 7 mAs. Compare the effect of changes in milliamperage and exposure time on film-screen and digital images. If a repeat radiograph is necessary and kVp is to be adjusted to either increase or decrease the level of contrast, the 15% rule provides an acceptable method of adjustment. Critical Concept 10-1 kVp does not produce the same effect across the entire range of kVp used in radiography. A high kVp results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient (remnant), producing a low-contrast (long-scale) image. Source-to-Image Receptor Distance What term means the misrepresentation of the size or shape of a structure recorded in the radiographic image? Small focal spot sizes are usually 0.5 or 0.6 mm, and large focal spot sizes are usually 1 or 1.2 mm in size. Characteristics of the film and processing, size, shape, and attenuating characteristics of the material being irradiated. During computer processing, image brightness is maintained when the mAs is too low or too high. plus or minus 50% of the correct technique range. Fourier transform and Nyquist sampling theorem. The time factor (s) is a measure of the electrons production duration in the tube; meaning 's' prescribes how long mA will last. It directly influences the radiographic density, when all other factors are constant. The X-ray Tube In addition, whenever a 15% change is made in the kVp to maintain the exposure to the IR, the radiographer must adjust the mAs by a factor of 2. Chapter 7 The film characteristic, speed, and chemical processing determine the amount of optical density produced on the image for a given mAs. Higher kVp increases the penetrating power of the x-ray beam and results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient. Soft Tissue The radiographer must decide how much of a change in mAs is needed to correct for the density error. detail, sharpness, definition and resolving power. Chapter 10 source-to-object distance (SOD) All other factors remaining constant, an increase in milliamperage increases the amplitude of both the continuous and discrete portions of the spectrum. "Photochemical Researches.--Part V. On the Measurement of the Chemical Action of Direct and Diffuse Sunlight.". Compensating Filters Change of image contrast related to change of kVp: Image A is used as a reference. (From Fauber TL: Radiographic imaging and exposure, ed 3, St Louis, 2009, Mosby.) As focal spot size changes, so does the amount of unsharpness. Density maintenance formula: MAS1/MAS2=D1(D1)/D2(D2), Density increases as developer temperature, immersion time, or replenishment rates increase: contaminated developer will decrease density. Higher kVp and lower mAs values are not recommended as a general rule during film-screen imaging because of the contrast required to best visualize the anatomic structures. In general, for repeat radiographs necessitated by density errors, the mAs is adjusted by a factor of 2; therefore a minimum change involves doubling or halving the mAs. Secondary Factors 80kVp0.85=68kVp When you've placed seven or more cards in the Don't know box, click "retry" to try those cards again. less contrast, longer scale of contrast is caused by: decreased kVp. Directly, as KVP increases density increases because penetrability increases so more photons are reaching the IR . Look at the large card and try to recall what is on the other side. Increasing the kVp increases IR exposure and the density produced on a film image. It reduces the amount of scatter radiation and therefore, reduces the overall density of the image. Differentiate between the types of exposure technique charts. Increasing the kVp increases IR exposure and the density produced on a film image, and decreasing the kVp decreases IR exposure and the density produced on a film image (Figure 10-4). The probability of Compton scattering is related to the energy of the photon. When a kVp that is too low is selected, the brightness and contrast are adjusted, but quantum noise may be visible. Additionally, for a given mAs, IRs respond differently. If the radiograph necessitates an adjustment greater than a factor of 2, the radiographer should multiply or divide the mAs by 4 (Figure 10-3). In general, the smallest focal spot size available should be used for every exposure. A high-frequency unit produces more x-rays using the same amount of electricity. Kilovoltage, Scatter Radiation, and Radiographic Contrast When making contrast changes on a radiograph, what changes in KVP should be made? Film-screen combos will range from __ - __ 2. What factors compose radiographic contrast? The radiographer should be diligent in monitoring exposure indicator values to ensure that quality images are obtained with the lowest possible radiation dose to the patient. Become a Gold Supporter and see no third-party ads. The factors that affect density are: Mass (direct effect, since it appears in the equation for density) Volume (direct effect, since it appears in the equation for density) State (indirect effect, since a change of state changes volume of a given mass) Patient Factors For film-screen IRs, kVp has a direct relationship with density; however, the effect of the kVp on density is not equal throughout the range of kVp (low, middle, and high). This relationship between radiation exposure intensity and density is discussed in more detail in Chapter 9. If a repeat radiograph is necessary and kVp is to be adjusted to either increase or decrease the level of contrast, the 15% rule provides an acceptable method of adjustment. A greater change in the kVp is needed when operating at a high kVp (greater than 90) compared with operating at a low kVp (less than 70) (Figure 10-5). Therefore, we will alter what? What influences image receptor (film) contrast? Calculate changes in milliamperage and exposure time to change or maintain exposure to the image receptor. Higher kVp increases the penetrating power of the x-ray beam and results in less absorption and more transmission in the anatomic tissues, which results in less variation in the x-ray intensities exiting the patient (remnant). Decreasing the kVp decreases the proportion of Compton scattering and increases radiographic contrast. variable kVpfixed mAs technique chart The kVp affects the exposure to the IR because it alters the amount and penetrating ability of the x-ray beam. Source-to-Image Receptor Distance to send you a reset link. To maintain the same mAs, the radiographer must increase the milliamperage and proportionally decrease the exposure time. Casts and Splints What is the controlling factor of density? Types of Technique Charts What is the enlargement of the recorded image as compared to the actual size of the structure? FIGURE 10-2 mAs and Radiographic Density.Changes in mAs have a direct effect on density. Adjusting Milliamperage or Exposure Time Because various types of IRs respond differently to the radiation exiting the patient (remnant), these differences are noted throughout this chapter. Identify the exposure factors that can affect patient radiation exposure. The smaller this area of origin, the sharper the image. in order to increase contrast, the technologist should: Increased mAs. Keywords: Controlling factors, Density-dependent factors, Density-independent factors, Correlation patterns, Covariance patterns, Loop models, Time averaging, Null hypotheses, Species interactions Abstract. increased density is caused by: increased kVp. There is a direct relationship between the amount of mAs and the amount of density produced when using film-screen IRs. As mentioned previously, it may take more than doubling the mAs to correct for a density error. Conversely, when the quantity of x-rays is decreased, the exposure to the IR decreases. To best visualize the anatomic area of interest, the mAs selected must produce a sufficient amount of radiation reaching the IR, regardless of type. The kVp affects the exposure to the IR because it alters the amount and penetrating ability of the x-ray beam. What states that the blackening on the film remains constant as long as MAS remains the same and usage of mA and time combinations? if you are going from a fast screen to a slow screen and you want to maintain your density you have to do what? A patients age, condition, and the presence of a pathologic condition also affect the amount of mAs required for the procedure. The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs, or reducing the mAs by 50%; for example, increasing the kVp from 82 to 94 (15%) produces the same exposure to the IR as increasing the mAs from 10 to 20. Because the milliamperage/second (mAs) controls the number of electrons boiled off of the filament and available to produce x-rays, it is considered the primary factor controlling quantity. To maintain the same mAs, the radiographer must increase the milliamperage and proportionally decrease the exposure time. increase your mAs to maintain the same density. What is the region of the anode target where electrons interact to produce x-rays? Image B shows a higher contrast image due to a decrease in kVp. How are density/IR exposure adjustments made for the change in kV? Similarly, too little radiation reaching the IR (within reason) produces a digital image with the appropriate level of brightness, but the increased noise decreases image quality. As mentioned earlier, the effects of changes in the kVp are not uniform throughout the range of kVp. Similarly, too little radiation reaching the IR (within reason) produces a digital image with the appropriate level of brightness, but the increased noise decreases image quality. ADVERTISEMENT: Radiopaedia is free thanks to our supporters and advertisers. Image Characteristics As the speed of the intensifying screen increases, density increases. Fixed kVp Variable mAs Technique Chart how does increasing filtration affect contrast? Adequate penetration of the anatomic area of interest is equally important when using digital IRs, and therefore kVp selection is important in producing a quality image. Exposure techniques using higher kVp with lower mAs exposure techniques are recommended in digital imaging because contrast is primarily controlled during computer processing. Assuming that the anatomic part is adequately penetrated, changing the kVp does not affect the digital image the same as a film-screen image. Thinner portion goes over the thicker portion of the body and visa versa. Too much radiation reaching the IR (within reason) produces a digital image with the appropriate level of brightness as a result of computer, Maintaining or adjusting exposure to the IR can be accomplished with kVp by using the, Altering the penetrating power of the x-ray beam affects its absorption and transmission through the anatomic tissue being radiographed. B, Decreased in density when the mAs is decreased by half. Low radiographic contrast is seen on radiographic images where adjacent regions have a low-density difference (black to grey). Variable kVp Fixed mAs Technique Chart To maintain the mAs, use: To maintain exposure to the IR, when increasing the kVp by 15% (kVp 1.15), divide the original mAs by 2. Make the Physics Connection 10-5 Chapter 6 Although the level of brightness has been adjusted, there may be increased quantum noise visible within the image. Calculate changes in kVp to change or maintain exposure to the image receptor. Increasing or decreasing the kVp changes the amount of radiation exposure to the IR and the contrast produced within the image. Milliamperage and time affect the quantity of radiation produced and kilovoltage affects both the quantity and quality. For example, when the mAs is increased, density is increased; when the mAs is decreased, density is decreased (. Calculate the magnification factor and determine image and object size. These factors make achieving a desired level of radiographic contrast more complex than achieving a desired level of radiographic density, especially for film-screen imaging. 200mA0.1s=20mAs 1. Focal spot size is an important consideration for the radiographer because the focal spot size affects recorded detail. Milliamperage and Exposure Time When the radiograph is deemed unacceptable, this means the optical densities lie outside the films sensitometric curves straight-line portion, and may need to be repeated. When a film image is too light (insufficient density), a greater increase in mAs may be needed to correct the density, or the mAs may need to be decreased to correct a film image that has excessive density. Milliamperage and Exposure Time How does tighter collimation affect contrast? Excessive Radiation Exposure and Digital Imaging elongation projects the object so it appears to be longer than it really is. What would the image be like if we went from a 6:1 Grid to a 16:1 grid and we didnt change our mAs? It is important for the radiographer to understand their effects individually and in combination. Unable to process the form. Recognize patient factors that may affect image receptor exposure. There is a direct relationship between the amount of mAs and the amount of density produced when using film-screen IRs. Calculate the magnification factor and determine image and object size. As a result, images with lower contrast are produced (Figure 10-6).
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