Which of the following projections is most likely to deliver the largest dose to the ovaries? A. AP lumbar spine, 7 x 17 in. cassette, 80 kVp The answer is B. EXPLANATION: Exposure dose to patients can be expressed as entrance skin exposure (ESE), sometimes referred to as skin entrance exposure (SEE). Exposure can also be expressed in terms of organ dose. Organ doses to the gonads, bone marrow, breast, thyroid, lens, and lung can be determined. Patient position and beam restriction often make a significant difference in patient dose. Examinations performed PA
rather than AP often decrease exposure to sensitive organs. This is so because the lower energy x-ray photons will be absorbed by the anatomic structures closer to the x-ray source, and the higher energy photons will penetrate and exit the part (penetrating the sensitive part rather than being absorbed by it). PA abdomen radiographs deliver less quantity dose to the reproductive organs than AP abdomen radiographs do. An AP lumbar spine radiograph, 7 x 17 in. cassette, 80 kVp delivers about 74
mrad to the ovaries, whereas the same projection using a 14 x 17 in. cassette delivers 92 mrad. An AP abdomen radiograph with 70 kVp delivers 80 mrad, whereas at 80 kVp, the ovarian dose is 68 mrad. All the following statements regarding mobile radiographic equipment are true except A. the exposure cord must permit the operator to stand at least 6 ft from the patient, x-ray tube, and
useful beam The answer is B. EXPLANATION: NCRP Report No. 102 states that the exposure switch on mobile radiographic units shall be so arranged
that the operator can stand at least 2 m (6 ft) from the patient, the x-ray tube, and the useful beam. An appropriately long exposure cord accomplishes this requirement. The fluoroscopic and/or radiographic exposure switch or switches must be of the "dead man" type; that is, the exposure will terminate should the switch be released. A lead apron should be carried with every mobile x-ray unit for the operator to wear during the exposure. Lastly, the radiographer must be certain to alert
individuals in the area, enabling unnecessary occupants to move away, before making the exposure. What is the annual TEDE limit for radiation workers? 50 mSv EXPLANATION: Whenever a radiation worker could receive 10% or more of the annual TEDE limit, that person must be provided with a
radiation monitor. The annual TEDE limit for radiation workers is 50 mSv (5 rem, 5,000 mrem), but it is the responsibility of the radiographer to practice the ALARA principle, that is, to keep radiation dose as low as reasonably achievable. According to the NCRP, the annual occupational dose-equivalent limit (50 rem) to the thyroid, skin, and extremities is 500 mSv EXPLANATION: According to the NCRP, the annual occupational whole-body dose-equivalent limit is 50 mSv (5 rem or 5,000 mrem). The annual occupational whole-body dose-equivalent limit for students under the age of 18 years is 1 mSv (100 mrem or 0.1 rem). The annual occupational dose-equivalent limit for the lens of the eye, a particularly radiosensitive organ, is 150 mSv (15 rem). The annual occupational
dose-equivalent limit for the thyroid, skin, and extremities is 500 mSv (50 rem). The total gestational dose-equivalent limit for embryo/fetus of a pregnant radiographer is 5 mSv (500 mrem), not to exceed 0.5 mSv in 1 month. The late effects of radiation are considered to 1 and 2 only EXPLANATION: Exposure to high doses of radiation results in early effects. Examples of early effects are blood changes and erythema. If the exposed individual survives, then late, or long-term, effects must be considered. Individuals who receive small amounts of low-level radiation (such as those who are occupationally exposed) are concerned with the late effects of radiation
exposure—effects that can occur many years after the initial exposure. Late effects of radiation exposure, such as carcinogenesis, are considered to be related to the linear nonthreshold dose–response curve. That is, there is no safe dose; theoretically, even one x-ray photon can induce a later response. Which of the following tissues or organs is the most radiosensitive? A.
Rectum Small bowel EXPLANATION: The most radiosensitive portion of the GI tract is the small bowel. Projecting from the lining of the small bowel are villi, from the crypts of Lieberkühich are responsible for the absorption of nutrients into the bloodstream. Because the cells of the villi are continually
being cast off, new cells must continually arise from the crypts of Lieberküeing highly mitotic, undifferentiated stem cells, they are very radiosensitive. Thus, the small bowel is the most radiosensitive portion of the GI tract. In the adult, the CNS is the most radioresistant system. Which of the following is (are) included in whole-body dose equivalents? 1.Gonads 1 and 2 only EXPLANATION: Whole-body dose is calculated to include all the especially radiosensitive organs. The gonads, the lens of the eye, and the blood-forming organs are particularly radiosensitive. The annual dose limit to the less sensitive skin, hands, and feet (extremities) is 50 rem/year. radiation dose. EXPLANATION: There are several radiation units that are used to express quantity and effects of radiation. Rad (radiation absorbed dose) expresses energy deposited (as a result of ionizations) in any kind of absorber. The unit of exposure, the roentgen, is used to express the quantity of ionization in air. The unit of dose equivalent is the rem (radiation equivalent man), which expresses dose to biologic material. Which interaction between x-ray photons and matter involves partial transfer of the incident photon energy to the involved atom? Compton scattering EXPLANATION: The photoelectric effect and Compton scattering are the two predominant interactions between x-ray photons and matter in diagnostic x-ray. In Compton scatter, the high-energy incident photon uses only part of its energy to eject an outer-shell electron. It retains most of its original energy in the form of a scattered x-ray. The outer-shell electron leaves the atom and is called a recoil electron. Compton scatter is the interaction between x-ray photons and matter that occurs most frequently in diagnostic x-ray and is the major contributor of scattered radiation fog. In the photoelectric effect, the low-energy incident photon uses all its energy to eject an atom's inner-shell electron. When photon ceases to exist, it means it has used all its energy to ionize the atom. The part has absorbed the x-ray photon. This interaction contributes to patient dose and produces short-scale contrast. Which of the following cells are the most radiosensitive? A. Myelocytes Erythroblasts EXPLANATION: Bergonié and Tribondeau theorized in 1906 that all precursor cells are particularly radiosensitive (e.g., stem cells found in bone marrow). There are several types of stem cells in bone marrow, and the different types differ in degree of radiosensitivity. Of these, red blood cell precursors, or erythroblasts, are the most radiosensitive. White blood cell precursors, or myelocytes, follow. Platelet precursor cells, or megakaryocytes, are the least radiosensitive. Myocytes are mature muscle cells that are fairly radioresistant. If a patient received 1,400 mrad during a 7-minute fluoroscopic examination, what was the dose rate? 0.2 rad/min EXPLANATION: A measure 1,400 mrad is equal to 1.4 rad. If 1.4 rad were delivered in 7 minutes, then the dose rate would be 0.2 rad/min: 1.4rad/7min = xrad/1min Which of the following statements regarding film badges is (are) correct? 1. Film badges should be read quarterly. 2 and 3 only EXPLANATION: Film badges are supplied by a dosimetry service. They contain pieces of dental film held within a holder containing filters. When used properly, film badges measure the quantity and quality of radiation exposure. Film within the badges is usually changed monthly. The sensitive film emulsion is susceptible to deterioration and false readings if the badges are worn for longer periods, or if they are damaged by water, heat, light, and so on. To avoid the possibility of damage or exposure, film badges should not leave the workplace. The annual dose limit for occupationally exposed individuals is valid for beta, x-, and gamma radiations. EXPLANATION: The occupational dose limit is valid for beta, x-, and gamma radiations. Because alpha radiation is so rapidly ionizing, traditional personal monitors will not record alpha radiation. Because alpha particles are capable of penetrating only a few centimeters of air, they are practically harmless as an external source Radiographers use monitoring devices to record their monthly exposure to radiation. The types of devices suited for this purpose include the 1. pocket dosimeter. 2 and 3 only EXPLANATION: The OSL is rapidly becoming the most commonly used personnel monitor today. Film badges and TLDs have been used successfully for years. A pocket dosimeter is used primarily when working with large amounts of radiation and when a daily reading is desired. For radiographic examinations of the skull, it is generally preferred that the skull be examined in the PA projection EXPLANATION: Because the primary x-ray beam has a poly-energetic (heterogeneous) nature, the entrance or skin dose is significantly greater than the exit dose. This principle may be employed in radiation protection by placing particularly radiosensitive organs away from the primary beam. To place the gonads further from the primary beam and reduce gonadal dose, abdominal radiography should be performed in the posteroanterior (PA) position whenever possible. Dose to the lens is decreased significantly when skull radiographs are performed in the PA position. Which of the following interactions between x-ray photons and matter involves a high-energy photon and the ejection of an outer shell electron? Compton scatter EXPLANATION: Compton scattering occurs when a relatively high-energy incident photon uses part of its energy to eject an outer shell electron, and in doing so changes its direction (is scattered). The energy retained by the scattered photon depends on the angle formed by the ejected electron and the scattered photon: The greater the angle of deflection, the less the retained energy. Compton scatter is very energetic scatter. It emerges from the patient and is responsible for scatter radiation reaching the image in the form of fog. In the photoelectric effect, a relatively low energy photon uses all its energy to eject an inner shell electron, leaving a vacancy. An electron from the shell above drops down to fill the vacancy, and in doing so gives up a characteristic ray. This type of interaction contributes most to patient dose, as all the photon energy is transferred to tissue. In coherent scatter, no energy is absorbed by the part; it all emerges as scattered photons. Pair production occurs only at very high energy levels, at least 1.02 MeV. What percentage of x-ray attenuation does a 0.5-mm lead equivalent apron at 100 kVp provide? 75% EXPLANATION: Lead aprons are worn by occupationally exposed individuals during fluoroscopic and mobile x-ray procedures. Lead aprons are available with various lead equivalents; 0.5 and 1.0 mm are the most common. The 1.0-mm lead equivalent apron will provide close to 100% protection at most kVp levels, but it is rarely used because it weighs anywhere from 12 to 24 lb! A 0.25-mm lead equivalent apron will attenuate about 97% of a 50-kVp x-ray beam, 66% of a 75-kVp beam, and 51% of a 100-kVp beam. A 0.5-mm lead equivalent apron will attenuate about 99.9% of a 50-kVp beam, 88% of a 75-kVp beam, and 75% of a 100-kVp beam. What is the intensity of scattered radiation perpendicular to and 1 m from a patient compared with the useful beam at the patient's surface? 0.1% EXPLANATION: The patient is the most important radiation scatterer during both radiography and fluoroscopy. In general, at 1 m from the patient, the intensity is reduced by a factor of 1,000 to about 0.1% of the original intensity. Successive scatterings can reduce the intensity to unimportant levels. The tabletop exposure rate during fluoroscopy shall not exceed Occupational exposure received by the radiographer is mostly from Compton scatter EXPLANATION: The photoelectric effect and Compton scattering are the two predominant interactions between x-ray photons and matter in diagnostic radiology. In the photoelectric effect, the low-energy-incident photon is absorbed by the tissues being radiographed. In Compton scatter, the high-energy-incident photon uses only part of its energy to eject an outer-shell electron. It retains much of its original energy in the form of a scattered x-ray. Radiologic personnel can be exposed to that high-energy scattered radiation, especially in fluoroscopy and mobile radiography. Lead aprons are used to protect us from exposure to scattered radiation during these procedures. A dose of 25 rad to the fetus during the seventh or eighth week of pregnancy is likely to cause what? Neurologic anomalies EXPLANATION: During the first trimester, specifically the second through eighth weeks of pregnancy (during major organogenesis), if the radiation dose is at least 20 rad, fetal anomalies can be produced. Skeletal anomalies usually appear if irradiation occurs in the early part of this time period, and neurologic anomalies are formed in the latter part; mental retardation and childhood malignant diseases, such as cancers or leukemia, also can result from irradiation during the first trimester. Fetal irradiation during the second and third trimesters is not likely to produce anomalies but rather, with sufficient dose, some type of childhood malignant disease. Fetal irradiation during the first 2 weeks of gestation can result in spontaneous abortion. It must be emphasized that the likelihood of producing fetal anomalies at doses below 20 rad is exceedingly small and that most general diagnostic examinations are likely to deliver fetal doses of less than 1 to 2 rad. The minimum requirement for lead-equivalent content in protective aprons is 0.25 mm Pb. EXPLANATION: Lead aprons are secondary radiation barriers and must contain at least 0.25 (1/4) mm Pb equivalent (according to 21 CFR), usually in the form of lead-impregnated vinyl. Many radiology departments routinely use lead aprons containing 0.5 mm Pb (the NCRP recommends 0.5 mm Pb equivalent minimum). These aprons are heavier, but they attenuate a higher percentage of scattered radiation. A minimum total amount of aluminum filtration (inherent plus added) of 2.5 mm is required in equipment operated above 70 kVp EXPLANATION: The x-ray tube's glass envelope and oil coolant are considered inherent (built-in) filtration. Thin sheets of aluminum are added to make a total of at least 2.5-mm-Al-equivalent filtration in equipment operated above 70 kVp. The function of the filtration is to remove the low-energy photons that serve only to contribute to skin dose. What contributes most to patient dose? The photoelectric effect EXPLANATION: In the photoelectric effect, a relatively low-energy photon uses all its energy to eject an inner-shell electron, leaving a vacancy. An electron from the shell above drops down to fill the vacancy and in so doing emits a characteristic ray. This type of interaction is most harmful to the patient because all the photon energy is transferred to tissue. In Compton scatter, a high-energy incident photon uses some of its energy to eject an outer-shell electron. In so doing, the incident photon is deflected with reduced energy but usually retains most of its energy and exits the body as an energetic scattered ray. The scattered radiation will either contribute to image fog or pose a radiation hazard to personnel depending on its direction of exit. In classic scatter, a low-energy photon interacts with an atom but causes no ionization; the incident photon disappears in the atom and then reappears immediately and is released as a photon of identical energy but with changed direction. Thompson scatter is another name for classic scatter. LET is best defined as 1 and 3 only EXPLANATION: When biologic material is irradiated, there are a number of modifying factors that determine what kind and how much response will occur in the material. One of these factors is LET, which expresses the rate at which particulate or photon energy is transferred to the absorber. Because different kinds of radiation have different degrees of penetration in different materials, it is also a useful way of expressing the quality of the radiation. Which of the following cells is the least radiosensitive? A. Myelocytes Myocytes EXPLANATION: Bergonié and Tribondeau theorized in 1906 that all precursor cells are particularly radiosensitive (e.g., stem cells found in bone marrow). There are several types of stem cells in bone marrow, and the different types differ in degree of radiosensitivity. Of these, red blood cell precursors, or erythroblasts, are the most radiosensitive. White blood cell precursors, or myelocytes, follow. Platelet precursor cells, or megakaryocytes, are even less radiosensitive. Myocytes are mature muscle cells and are fairly radioresistant. A controlled area is one that is... occupied by radiation workers EXPLANATION: A controlled area is one that is occupied by radiation workers; the exposure rate in a controlled area must not exceed 100 mR/week. An uncontrolled area is one that is occupied by the general population; the exposure rate must not exceed 10 mR/week. Shielding requirements vary according to several factors, one of them being occupancy factor. Patient dose increases as fluoroscopic... FOV decreases EXPLANATION: During fluoroscopic procedures, as field of view (FOV) decreases, magnification of the output screen image increases, and contrast and resolution improve. The focal point on an image intensifier's 6-in. field/mode is further away from the output phosphor than the focal point on the normal mode; therefore, the output image is magnified. Because less minification takes place, the image is not as bright. Exposure factors are increased automatically to compensate for the loss in brightness with smaller FOVs. Focal spot size (FSS) is unrelated to patient dose. The focal spot-to-table distance, in mobile fluoroscopy, must be a minimum of 12 inches. EXPLANATION: Lead and distance are the two most important ways to protect from radiation exposure. Fluoroscopy can be particularly hazardous because the SID is so much shorter than in overhead radiography. Therefore, for patient protection, it has been established that fixed (stationary) equipment must provide at least 15 inches (38 cm) source to tabletop/skin distance. Mobile fluoroscopic equipment must provide at least 12 inches (30 cm) source-to-tabletop/skin distance. Radiation dose to personnel is reduced by which of the following exposure control cord guidelines? 2. 3. Radiation dose to personnel is reduced by which of the following exposure control cord guidelines? 1 and 2 only EXPLANATION: Radiographic and fluoroscopic equipment is designed to help decrease the exposure dose to patient and operator. One of the design features is the exposure cord. Exposure cords on fixed equipment must be short enough to prevent the exposure from being made outside the control booth. Exposure cords on mobile equipment must be long enough to permit the operator to stand at least 6 ft from the x-ray tube. Which of the following is a measurement of dose to biologic tissue? Rem (Sv) EXPLANATION: Roentgen is the unit of exposure; it measures the quantity of ionization in air. Rad is an acronym for radiation absorbed dose; it measures the energy deposited in any material. Rem is an acronym for radiation equivalent man; it includes the RBE specific to the tissue irradiated, and therefore is a valid unit of measurement for the dose to biologic material. Which of the following is most likely to result in the greatest increase in patient exposure? A. Changing from a 400 speed system to a 200 speed system B. Increasing kVp 15% and cutting mAs in half C. Using two tomographic cuts instead of two plain images D. From nongrid technique to 8:1 grid From nongrid technique to 8:1 grid EXPLANATION: Converting from nongrid to an 8:1 grid requires about a fourfold increase in mAs. Increasing the kVp by 15% and cutting the mAs in half would reduce patient dose. When changing from general radiographic technical factors to tomographic factors, it is generally recommended that the kVp remain the same and that mAs be increased by 50%. Changing from a 400 speed system to a 200 speed system will require the mAs to be doubled. Therefore, the largest increase would be required by the addition of a grid. Which of the following factors can affect the amount or the nature of radiation damage
to biologic tissue? 1, 2, and 3 EXPLANATION: Radiation quality determines degree of penetration and the amount of energy transferred to the irradiated tissue (LET). Certainly, the larger the absorbed radiation dose, the greater is the effect. Biologic effect is increased as the size of the irradiated area is increased. The nature of the effect is influenced by the location of irradiated tissue (bone marrow vs. gonads). How does the use of rare earth intensifying screens contribute to lowering the patient dose? 2.It permits the use of lower kilovolts peak (kVp) 3.It eliminates the need for patient shielding 1 only EXPLANATION: The faster the intensifying screens used, the fewer are the required milliampere-seconds. Decreasing the intensity (i.e., mAs or quantity) of photons significantly contributes to reducing total patient dose. Decreasing the kilovoltage would increase patient dose because the primary beam would be made up of fewer penetrating photons, so the milliampere-seconds would have to be increased. The importance of patient shielding is never diminished. Which of the following has (have) an effect on the amount and type of radiation-induced tissue damage? 2.Type of tissue being irradiated 3.Fractionation 1, 2, and 3 EXPLANATION: All the factors listed influence the effect of radiation on tissue. Larger quantities, of course, increase radiation's effect on tissue. The energy (i.e., quality and penetration) of the radiation determines whether the effects will be superficial (erythema) or deep (organ dose). Certain tissues (such as blood-forming organs, the lens, and the gonads) are more radiosensitive than others (such as muscle and nerve). The length of time over which the exposure is spread (fractionation) is important; the longer the period of time, the less are the tissue effects. If the exposure rate to an individual standing 2.0 m from a source of radiation is 15 R/min, what will be the dose received after 2 minutes at a distance of 5 m from the source? 4.8 R EXPLANATION: The relationship between x-ray intensity and distance from the source is expressed in the inverse square law of radiation. The formula is Substituting known values: 25 x = 60 x = 2.4 R/minute at 2 m = 4.8 R after 2 minutes Distance has a profound effect on dose received and therefore is one of the cardinal rules of radiation protection. As distance from the source increases, dose received decreases. Stochastic effects of radiation include A. blood changes B. genetic alterations C. cataractogenesis D. reduced fertility genetic alterations EXPLANATION: Stochastic effects of radiation are nonthreshold and randomly occurring. Examples of stochastic effects include carcinogenesis and genetic effects. The chance of occurrence of stochastic effects is directly related to the radiation dose; that is, as radiation dose increases, there is a greater likelihood of genetic alterations or development of cancer. Nonstochastic effects are predictable threshold responses; that is, a certain quantity of radiation must be received before the effect will occur, and the greater the dose, the more severe is the effect. What is the minimum lead requirement for lead aprons, according to the NCRP? 0.50 mm Pb EXPLANATION: Lead aprons are secondary radiation barriers and must contain at least 0.25 mm Pb equivalent (according to 21 CFR), usually in the form of lead-impregnated vinyl. Many radiology departments routinely use lead aprons containing 0.5 mm Pb (the NCRP recommends 0.5 mm Pb equivalent minimum). These aprons are heavier, but they attenuate a higher percentage of scattered radiation. EXPLANATION: Lead aprons are secondary radiation barriers and must contain at least 0.25 mm Pb equivalent (according to 21 CFR), usually in the form of lead-impregnated vinyl. Many radiology departments routinely use lead aprons containing 0.5 mm Pb (the NCRP recommends 0.5 mm Pb equivalent minimum). These aprons are heavier, but they attenuate a higher percentage of scattered radiation. rad (Gy). The National Council on Radiation Protection and Measurements (NCRP) has recommended what total equivalent dose limit to the embryo/fetus? 5.0 mSv EXPLANATION: The NCRP recommends a total equivalent dose limit to the embryo/fetus of 5 mSv (500 mrem, 0.5 rem). This dose limit is the total for the entire gestational period. The dose limit for 1 month during pregnancy is 0.5 mSv (50 mrem, 0.05 rem). If a patient received 2000 mrad during a 10-minute fluoroscopic examination, what was the dose rate? 0.2 rad/min EXPLANATION: Two thousand mrad is equal to 2 rad. If 2 rad were delivered in 10 minutes, then the dose rate is 2 ÷ 10, or 0.2 rad/min. When an image intensifier's magnification mode is used, 1. output screen gain is increased. 2. resolution increases. 3. patient dose increases. 2 and 3 only EXPLANATION: During fluoroscopic procedures, as FOV decreases, magnification of the output screen image increases and contrast and resolution improve. The focal point on an image intensifier's 6-inch field/mode, is further away from the output phosphor than the focal point on the normal mode; therefore, the output image is magnified. Because less minification takes place, the image is not as bright. Exposure factors are automatically increased to compensate for the loss in brightness that occurs with smaller FOVs used in magnification mode. (Fosbinder, p 285) Which of the following radiation exposure responses exhibit a nonlinear threshold dose-response relationship? 1. Skin erythema 2. Hematologic depression 3. Lethality 1, 2, and 3 EXPLANATION: The genetic effects of radiation and some somatic effects, like leukemia, are plotted on a linear dose-response curve. The linear dose-response curve has no threshold; that is, there is no dose below which radiation is absolutely safe. The nonlinear/sigmoidal dose-response curve has a threshold and is thought to be generally correct for most somatic effects—such as skin erythema, hematologic depression, and radiation lethality (death). (Ballinger & Frank, vol 1, p 45) |
If a patient received 2000 mrad during a 10 min fluoroscopic examination, what was the dose rate
zusammenhängende Posts
Urheberrechte © © 2024 de.apacode Inc.
