PP 4.pdf
Transcript
Equipment Design for Radiation Protection Copyright © 2014 by Mosby, an imprint of Elsevier Inc. State-of-the-Art Diagnostic and Fluoroscopic Equipment Has been designed with many devices that radiologists and technologists can use To optimize the qualit...
Equipment Design for Radiation Protection Copyright © 2014 by Mosby, an imprint of Elsevier Inc. State-of-the-Art Diagnostic and Fluoroscopic Equipment Has been designed with many devices that radiologists and technologists can use To optimize the quality of the image To reduce radiation exposure for patients undergoing various imaging procedures Many safety features are built into x-ray-producing machines by their manufacturers to ensure radiation safety. Some safety features are included to meet federal regulations. Accessories are available to lower radiation dose for the patient. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 2 Radiation Safety Features of Radiographic Equipment, Devices, and Accessories Measures must be taken to ensure that radiographic equipment operates safely to protect General public Patients All personnel Every diagnostic imaging system must have a Inner is lead lined Protective tube housing Correctly functioning control panel A radiographic examination table and other devices and accessories must be designed to reduce the patient’s radiation dose. Radiolucent Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 3 Diagnostic-Type Protective Tube 15 to block off focus Housing 2nd to block primary beam Requirements A lead-lined metal diagnostic-type protective tube housing is required to protect the patient and imaging personnel from off-focus, or leakage, radiation by restricting the emission of x- rays to the area of the useful, or primary, beam. X-ray tube housing construction The housing enclosing the x-ray tube must be S constructed so that the leakage radiation measured at a distance of 1 m from the x-ray source does not exceed 1 mGya/hr (100 mR/hr) when the tube is operated at its highest voltage at the highest current in Air mGyA miligrays that allows continuous operation. = Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 4 Diagnostic-Type Protective Tube Housing (Cont.) Figure 11-01. A lead-lined metal diagnostic-type protective tube housing protects patients and imaging personnel from off-focus, or leakage, radiation by restricting x-ray emission to the area of the primary (useful) beam. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 5 Control Panel, or Console Must be located behind a suitable protective barrier that has a radiation-absorbent window that permits observation of the patient during any procedure Must “indicate the conditions of exposure and provide a positive indication when the x-ray tube is energized” Has visible mA and kVp digital readouts that permit the operator to assess exposure conditions When the exposure begins, a tone is emitted, and the sound stops when the exposure terminates. The audible sound clearly indicates to the operator that the x-ray tube is energized and ionizing radiation is being emitted. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 6 Radiographic Examination Table Must be strong Must adequately support the patient Frequently has a floating tabletop that makes it easier to maneuver the patient during an imaging procedure Must be of uniform thickness Must be as radiolucent as possible so that it will absorb only a minimal amount of radiation, thereby reducing the patient’s radiation dose Is frequently made of carbon fiber material Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 7 Square Direct Law Exposure Maintence law Source-to-Image Receptor Or mAs , (D )2. = Direct square mAsz (D2) Law Distance (SID) Indicator Provides a way to measure the distance from the anode focal spot to the image receptor (IR) to ensure that the correct source-to-image receptor distance (SID) is maintained Frequently, a simple device such as a tape measure is attached to the collimator or tube housing so that the radiographer can manually measure the SID. Lasers are also sometimes used to measure SID. “Distance and centering indicators must be accurate to within 2% and 1% of the SID, respectively.” Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 8 X-Ray Beam Limitation Devices The primary x-ray beam shall be adequately collimated so that it is no larger than the size of the IR being used for the examination. Accomplished by providing the x-ray unit with a light-localizing variable-aperture rectangular collimator to adjust the size and shape of the x-ray beam either automatically or manually Light-localizing variable-aperture rectangular collimator is currently the most popular x-ray beam limitation device. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 9 X-Ray Beam Limitation Devices Collimation = Beam (Cont.) Restriction Not field size Figure 11-02. Light-Localizing Variable-Aperture Rectangular Collimator. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 10 X-Ray Beam Limitation Devices (Cont.) Types of x-ray beam limitation devices Light-localizing variable-aperture rectangular collimator Aperture diaphragms Cones Cylinders Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 11 X-Ray Beam Limitation Devices (Cont.) All of these devices confine the useful, or primary, beam before it enters the area of clinical interest, thereby limiting the quantity of body tissue irradiated. This also reduces the amount of scattered radiation in the tissue and prevents unnecessary exposure to tissues not under examination. Benefit of restricting x-ray field size to include only the anatomic structures of clinical interest Significant reduction in patient dose because less scatter radiation is produced Improves the overall quality of the radiographic image Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 12 X-Ray Beam Limitation Devices Light-localizing variable-aperture rectangular collimators Construction Components Reduction of off-focus, or stem, radiation Confinement of the radiographic beam Skin sparing Minimizing skin exposure to electrons produced by photon interaction with the collimator Luminescence Coincidence between the radiographic beam and the localizing light beam Positive beam limitation (PBL) Alignment of the x-ray beam Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 13 X-Ray Beam Limitation Devices (Cont.) Figure 11-03. Diagram of a typical collimator demonstrating radiographic beam-defining system: 1, anode focal spot; 2, x- ray tube window; 3, first set of shutters, or upper shutters; 4, aluminum filter; 5, mirror; 6, light source; 7, second set of shutters, or lower shutters. The metal shutters collimate the radiographic beam so that it is no larger than the image receptor. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 14 X-Ray Beam Limitation Devices (Cont.) Light-localizing variable-aperture rectangular collimators (Cont.) Figure 11-04. Collimator containing the radiographic beam-defining system, which establishes the parameters (margins) of the beam. Adjustable lead shutters limit the cross-sectional area of the beam and confine it to the area of clinical interest. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 15 X-Ray Beam Limitation Devices (Cont.) Light-localizing variable- aperture rectangular collimators (Cont.) Positive beam limitation (PBL) The radiographer must ensure that collimation is adequate by collimating the radiographic beam so that it is no larger than the Figure 11-05. Collimate the radiographic beam so IR. that it is no larger than the image receptor. Limiting the beam to the area of clinical interest decreases the amount of tissue irradiated and minimizes patient exposure by reducing the amount of scattered and absorbed radiation. A, Good collimation. B, Poor collimation. C, Anteroposterior radiograph of the shoulder demonstrating good collimation. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 16 X-Ray Beam Limitation Devices (Cont.) Aperture diaphragm Cones Simplest of all beam Sometimes used for limitation devices radiographic examinations of specific areas such as the head Figure 11-06. An aperture diaphragm, a flat piece of lead with a hole of designated size and shape cut in its center, is Figure 11-08. Coned-Down Parietoacanthial placed directly below the window of the x-ray tube to confine Projection of the Maxillary Sinuses. (Frank ED, the primary radiographic beam dimensions suitable to cover Long BW, Smith BS: Merrill’s Atlas of Radiographic a given size of an image receptor at a specified source-to- Positioning & Procedures, ED 12, St. Louis, 2012, image receptor distance. Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 17 X-Ray Beam Limitation Devices (Cont.) Cones Flared metal tubes and straight cylinders Beam-defining cones used in dental radiography Figure 11-09. Radiographic cones are circular metal tubes that attach to the x-ray tube housing or variable rectangular collimator to limit the radiographic beam to a predetermined size and shape. A, Cone fashioned in the form of a flared metal tube. B, Cone fashioned in the form of a straight cylinder. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 18 Filtration Y & Filtration HVL Beam Hardening Purpose of radiographic beam filtration Effect of filtration on the absorbed dose to the patient Types of filtration Inherent Figure 11-10. Filtration removes low-energy photons (long-wavelength or “soft” x-rays) from the beam by Added absorbing them and permits higher energy photons to pass through. This reduces the amount of radiation Total filtration that the patient receives. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 19 Filtration Requirement for total filtration Figure 11-11. A minimum of 2.5 mm aluminum equivalent total filtration is required for fixed radiographic units operating at above 70 kVp. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 20 Filtration (Cont.) Filtration for mammographic equipment Metallic elements such as molybdenum and rhodium are commonly employed as filters. These filtration materials facilitate adequate contrast in the radiographic image over the clinical extent of compressed breast thickness by preferentially selecting a particular range or window of energies from the x-ray spectrum emerging from the x-ray tube target. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 21 Filtration (Cont.) Figure 11-12. A and B, X-ray emission spectra for tungsten and molybdenum anodes. Note that tungsten produces a high volume of x-ray photons above the 17- to 20-keV range considered ideal for mammography. These photons merely degrade the quality of the recorded image. The molybdenum anode produces few x-ray photons above the ideal energy range, initiating a higher-contrast image on the finished image. C, A rhodium anode produces a higher average energy x-ray beam than does the molybdenum anode. The energy range for rhodium-produced photons is 20 to 23 keV. Photons from this energy range can provide better penetration of larger, denser breasts. (Ballinger PW, Frank ED: Merrill’s Atlas of Radiographic Positions and Radiologic Procedures, ed 9, St Louis, 1999, Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 22 Filtration is ALWAYS Aluminum Filtration (Cont.) Filtration for general diagnostic radiology Aluminum is the metal most widely selected as a filter material because it effectively removes low- energy (soft) x-rays from a polyenergetic (heterogeneous) x-ray beam without severely decreasing the x-ray beam intensity. A diagnostic x-ray beam must always be AVL 5 mmAL = 2. adequately filtered. 1 TVL 3 3 NL =. Half-value layer (HVL) The thickness of a designated absorber (e.g., aluminum) required to decrease the intensity of the primary beam by 50% of its initial value Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 23 Filtration (Cont.) HVL (Cont.) Must be measured to verify that the x-ray beam is adequately filtered A radiologic physicist should obtain this measurement at least once a year and also after an x-ray tube is replaced or repairs have been made on the diagnostic x-ray tube housing or collimation system. HVL is expressed in millimeters of aluminum. HVL is a measure of beam quality, or effective energy of the x-ray beam. A minimal HVL is required at a given kVp. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 24 Filtration (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 25 Compensating Filters Made of aluminum, lead-acrylic, or other suitable materials Used to accomplish dose reduction and uniform imaging of body parts that vary considerably in thickness or tissue composition Partially attenuates x-rays that are directed toward the thinner, or less dense, area while permitting more x-radiation to strike the thicker, or more dense, area Types of compensating filters Wedge filter Trough, or bilateral wedge filter Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 26 Compensating Filters (Cont.) Figure 11-13. A, Wedged-shaped lead-acrylic compensating filter used to provide uniform density for (B) a dorsoplantar projection of the foot without a compensating filter. (C) A dorsoplantar projection of the foot with a wedge-shaped lead-acrylic compensating filter. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 27 Exposure Reproducibility/ Exposure Linearity Exposure reproducibility Exposure linearity Consistency in output in radiation Consistency in output radiation intensity for identical generator intensity at selected kVp settings settings from one individual when generator settings are exposure to subsequent changed from one mA and time exposures combination to another Variance of 5% or less is Linearity is the ratio of the difference acceptable. in mR/mAs values between two Reproducibility may be verified by successive generator settings to the using the same technical sum of those mR/mAs values. It exposure factors to make a series must be less than 0.1. of repeated radiation exposures When settings are changed from one and then, observing with a mA to a neighboring mA station, the calibrated ion chamber, how most that linearity can vary is 10%. radiation intensity typically varies. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 28 Radiopaque led strips Radiolucent inner space material Radiographic Grids Construction, purpose, technical value, and impact of a radiographic grid on patient dose A grid is a device made of parallel radiopaque strips alternately separated with low-attenuation strips of aluminum, plastic, or wood. Placement of a grid in relation to the patient and the IR Determining when to use a grid in accordance with body part thickness Function of a radiographic grid Grid ratio and patient dose Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 34 Radiographic Grids (Cont.) Figure 11-14. Radiographic grids remove scattered x- ray photons that emerge from the patient being radiographed before this scattered radiation reaches the image receptor and decreases radiographic quality. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 35 Minimal Source-to-Skin Distance (SSD) for Mobile Radiography minimum SSD Requirement Mobile-12" (30cm) Fixed-15" 38cm) Minimum SSD of at least 30 cm (12 inches) Distance generally used for mobile radiography is 100 cm (40 inches) or even 120 cm (48 inches) Effect of SSD on patient entrance exposure With Increased SSD such as 100 cm or 120 cm there is a more uniform distribution of exposure throughout the patient. Use of mobile units Only for patients who cannot be transported to a fixed radiographic installation Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 36 Minimal SSD for Mobile Radiography (Cont.) Figure 11-16. Mobile radiographic examinations require a minimal source-skin distance of 30 cm (12 inches). The 30 cm distance limits the effects of inverse square falloff of radiation intensity with distance. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 37 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories Digital imaging Use of the computer in almost all imaging modalities Conventional radiography: analog image Process of producing the conventional radiographic image Quality of the analog image Disadvantages to the use of this technology Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 38 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories (Cont.) Digital radiography (DR): Process of producing a digital radiographic image Components of the digital image Brightness of the digital image on a display monitor Resolution (detail) of the digital radiographic image Composition and function of digital radiography IRs Function of charge-coupled devices (CCDS) Access of DR images Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 39 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories (Cont.) Indirect conversion and direct conversion Figure 11-17. Some large area detectors provide indirect conversion of x-ray energy to electrical charge through intermediate steps involving photodiodes or charge-coupled devices. Other area detectors provide direct conversion of x-ray energy to electrical charge through the use of a photoconductor. (Hendee WR, Ritenour ER: Medical imaging physics, ed 4, Chicago, 2002, John Wiley & Sons) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 40 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories (Cont.) Repeat rates in DR DR eliminates the need for almost all retakes required because of improper technical selection, because image contrast and overall brightness may be manipulated after image acquisition. Repeat rates for mispositioning are not lowered. Mispositioning repeats should be monitored by an independent quality control technologist at a separate monitor, or a quality control system should be used, whereby the number of images per examination is compared with the number ordered for each technologist. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 41 Radiation Safety Features of - S Digital Imaging Equipment, - Devices, and Accessories (Cont.) Figure 11-18A. A, The images obtained with a screen-film image receptor system illustrate how changing technical Figure 11-18B. A, The images obtained with a screen-film exposure factors greatly affect film image quality. B, image receptor system illustrate how changing technical Computed radiography (CR) images obtained through the exposure factors greatly affect film image quality. B, same technique ranges as those used for A have much less Computed radiography (CR) images obtained through the effect on image quality because “CR image contrast is same technique ranges as those used for A have much constant, regardless of radiation exposure.” (Betsy Shields, less effect on image quality because “CR image contrast is Presbyterian Hospital, Charlotte, North Carolina, in Bushong constant, regardless of radiation exposure.” (Betsy Shields, SC: Radiologic science for technologists: physics, biology Presbyterian Hospital, Charlotte, North Carolina, in and protection, ed 10, St Louis, 2013, Elsevier/Mosby) Bushong SC: Radiologic science for technologists: physics, biology and protection, ed 10, St Louis, 2013, Elsevier/Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 42 - Radiation Safety Features of S Digital Imaging Equipment, - Devices, and Accessories (Cont.) Computed radiography (CR) Process involves Use of conventional radiographic equipment, traditional patient positioning, and standard technical exposure actors CR filmless cassette containing a photostimulable phosphor Use of an image reading unit to scan the photostimulable phosphor image plate with a helium-neon laser beam Function of a photomultiplier tube Digital image display monitor Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 43 - S Radiation Safety Features of Digital Imaging Equipment, - Devices, and Accessories (Cont.) Figure 11-19. The radiographer at the monitor uses the mouse to adjust the computed radiography image of the body part to the proper size, density, and contrast before electronically sending the image for reading. (Frank ED, Long BW, Smith BS: Merrill’s Atlas of Radiographic Positioning & Procedures, ED 12, St. Louis, 2012, Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 44 - S Radiation Safety Features of Digital Imaging Equipment, - Devices, and Accessories (Cont.) CR (Cont.) Avoiding overexposure of the patient Responsibility of the radiographer to minimize radiation exposure by using correct technical exposure factors the first time a patient is x-rayed Ability of the radiographer to manipulate the image Phenomenon known as dose creep CR phosphor sensitivity Sensitivity of the phosphor used in CR is approximately equal to a 200-speed screen-film combination. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 45 - Radiation Safety Features of Digital Imaging Equipment, S - Devices, and Accessories (Cont.) CR imaging kilovoltage flexibility CR has greater kilovoltage flexibility than does conventional screen-film radiography. X-ray beam collimation and centering of body part on CR cassette Body area or part must be positioned in or near the center of the CR IR. Use of radiographic grids in CR CR is more sensitive to scatter radiation, so a grid should probably be used more frequently except for the majority of pediatric patients. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 46 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories (Cont.) Fluoroscopic procedures Patient radiation exposure rate Dynamic, or active, motion images of selected anatomic structures Greatest patient radiation exposure rate in diagnostic radiology Responsibility of physician to evaluate the need for the examination Benefit versus risk Minimizing patient exposure time Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 47 Radiation Safety Features of Digital Imaging Equipment, Devices, and Accessories (Cont.) Figure 11-20. Fluoroscopic procedures produce the largest patient radiation exposure rate in diagnostic radiology. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 48 Radiation Safety Features of X-ray tubes Fluoroscopic Equipment, IR viewing system recording system Devices, and Accessories Fluoroscopic procedures Fluoroscopic imaging systems Possible equipment configurations Image intensification fluoroscopy Benefits Figure 11-21. Image intensification fluoroscopy unit. The x-ray tube used in this unit is mounted beneath the unit’s radiographic table, which supports the patient. The image intensifier and other image detection devices are then drawn forward and placed over the patient on the table to perform the examination. Other fluoroscopic equipment arrangements are possible. (Bushong SC: Radiologic science for technologists: Physics, biology and protection, ed 10, St Louis, 2013, Elsevier/Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 49 Radiation Safety Features of Fluoroscopic Equipment, Devices, and Accessories (Cont.) Fluoroscopic procedures Brightness of the fluoroscopic image Use of photopic or cone vision to view fluoroscopic image Figure 11-22. Basic Components of an Image Intensifier Tube. (Bushong SC: Radiologic science for technologists: Physics, biology and protection, ed 10, St Louis, 2013, Elsevier/Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 50 Radiation Safety Features of Fluoroscopic Equipment, Devices, and Accessories (Cont.) Milliamperage required and effect on patient dose Multifield, or magnification, image intensifier tubes Size Normal viewing mode Components Figure 11-23. A 25/17/12 image intensifier tube Method of operation produces a magnified image in 17-cm mode, Image quality whereas the 12-cm mode produces an image that is even more highly magnified. (Bushong SC: Patient dose considerations Radiologic science for technologists: Physics, biology and protection, ed 10, St Louis, 2013, Elsevier/Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 51 Radiation Safety Features of Fluoroscopic Equipment, Devices, and Accessories (Cont.) Fluoroscopic procedures Intermittent, or pulsed, fluoroscopy Effect on patient dose Practice significantly decreases patient dose, especially in long procedures Last-image-hold feature Limiting fluoroscopic field size Benefit of fluoroscopic field size limitation Fluoroscopic beam length and width limitation Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 52 Radiation Safety Features of Fluoroscopic Equipment, Devices, and Accessories (Cont.) Fluoroscopic procedures Technical exposure factors Selection of technical exposure factors for adult patients kVp Range: 75 to 110 kVp for adults, depending on the body area being examined SSD not less than 38 cm (15 inches) for stationary fluoroscopes; not less than 30 cm (12 inches) for mobile fluoroscopes Position of the input phosphor surface of the image intensifier in relation to the patient should be maintained as close as is practical to reduce the patient’s entrance exposure rate. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 53 Radiation Safety Features of Fluoroscopic Equipment, Devices, and Accessories (Cont.) Fluoroscopic procedures (Cont.) Selection of technical exposure factors for children Percentage of kVp decrease compared to an adult should be as much as 25% Decreasing technical exposure factors, maintaining SSD, and minimizing the height of the image intensifier entrance surface above the patient further limit excessive exposure of the pediatric patient. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 54 Radiation Safety Features of Fluoroscopic Equipment, Devices, And Accessories (Cont.) Fluoroscopic procedures Filtration Purpose and requirements Half-value layer (HVL) HVL of 3 to 4.5 mm aluminum is considered acceptable when kVp ranges from 80 to 100. SSD Requirement: no less than 38 cm (15 inches) for stationary fluoroscopes; no less than 30 cm (12 inches) for mobile fluoroscopes Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 55 Radiation Safety Features of Fluoroscopic Equipment, Devices, And Accessories (Cont.) Cumulative timing device Requirement Function Exposure rate limitation Current federal standard limit for entrance skin exposure rates General-purpose intensified fluoroscopic units Maximum of 100 mGya per minute (10 R/min) Fluoroscopic units equipped with high-level control (HLC) Maximum of 200 mGya per minute (20 R/min) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 56 Radiation Safety Features of Fluoroscopic Equipment, Devices, And Accessories (Cont.) Primary protective barrier 2-mm lead equivalent required for a fluoroscopic unit Fluoroscopic exposure control switch Must be of the dead-man type Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 57 Radiation Safety Features of Mobile C-Arm Fluoroscopy Equipment, Devices, and Accessories Mobile C-arm fluoroscopy Portable x-ray unit that is C-shaped Has an x-ray tube attached to one end of its arm and an image intensifier attached to the other end Frequently used in the operating room for orthopedic procedures, cardiac imaging, interventional procedures Use of C-arm in fluoroscopy procedures carries the potential for a relatively large patient radiation dose Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 58 Radiation Safety Features of Mobile C-Arm Fluoroscopy Equipment, Devices, and Accessories (Cont.) Mobile C-arm fluoroscopy (Cont.) C-arm operator, if standing close to the patient, could also receive a significant increase in occupational exposure from patient scatter radiation during such cases. C-arm equipment operators must have appropriate education and training to ensure that they will follow guidelines for safe operation and also meet radiation safety protocols essential to patient and personnel safety. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 59 Radiation Safety Features of Mobile C- Arm Fluoroscopy Equipment, Devices, and Accessories (Cont.) Figure 11-24. C-Arm Fluoroscope and Monitor. (Radiobiology and Radiation Protection: Mosby’s Radiographic Instructional Series, St. Louis, 1999, Mosby) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 60 Radiation Safety Features of Mobile C- Arm Fluoroscopy Equipment, Devices, and Accessories (Cont.) Mobile C-arm fluoroscopy Requirements Source-to-end of collimator assembly distance is required to be a minimum of 30 cm (12 inches) Patient-image intensifier distance should be as short as possible to reduce entrance dose Patient dose reduction Position of C-arm x-ray tube preferably under the patient Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 61 Radiation Safety Features of Mobile C-Arm Equipment, Devices, and Accessories (Cont.) Figure 11-25. To reduce the patient’s entrance dose during C-arm fluoroscopy, the patient-image intensifier distance should be as short as possible. (Mark Rzeszotarski) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 62 Radiation Safety Features of Mobile C-Arm Equipment, Devices, and Accessories (Cont.) Mobile C-arm fluoroscopy (Cont.) With the C-arm x-ray tube positioned under the patient, scatter radiation is less intense. When the C-arm x-ray tube is positioned over the patient, scatter radiation becomes more intense, and radiation exposure of personnel increases Figure 11-26. To reduce scatter radiation during C-arm fluoroscopy, position the C-arm correspondingly. so that the x-ray tube is under the patient whenever possible. (Mark Rzeszotarski) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 63 Radiation Safety Features of Cinefluoroscopy Equipment, Devices, and Accessories Film size for dose reduction High-dose-rate procedures Film frame rate Inference of patient dose from tabletop exposure levels Collimation Dose-reduction techniques Patient dose determined by procedure Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 64 Radiation Safety of Digital Fluoroscopic Equipment, Devices, and Accessories Use of pulsed progressive systems for dose reduction Methods for dose reduction Use of last-image-hold feature for dose reduction Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 65 Radiation Safety for High-Level- Control Interventional Procedures High-level-control interventional procedures Justification for use of high-level-control interventional procedures Public health advisory about the danger of overexposure of patients and exposure rate limits Procedures involving extended fluoroscopic time FDA has recommended that a notation be placed in the patient’s record if a skin dose in the range of 1 to 2 gray (Gyt) is received. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 66 Radiation Safety for High-Level- Control Interventional Procedures (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 67 Radiation Safety for High-Level- Control Interventional Procedures (Cont.) High-level-control interventional procedures (Cont.) Radiogenic skin injuries such as erythema or desquamation are deterministic effects in which the severity of the disorder increases with radiation dose. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 68 Radiation Safety for High-Level- Control Interventional Procedures (Cont.) High-level-control interventional procedures (Cont.) Use of fluoroscopic equipment by nonradiologist physicians Need for ongoing education and training Reasons for high radiation exposures during interventional procedures Need for monitoring and documenting procedural fluoroscopic time Responsibility for documentation Guidelines to assist physicians in developing strategies that will enable them to fulfill their interventional clinical objectives while controlling patient radiation dose and minimizing exposure to occupationally exposed personnel and other assisting personnel Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 69 Radiation Safety for High-Level- Control Interventional Procedures (Cont.) High-level control interventional procedures (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 70
