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Rad Protection Ch.11
Equipment Design for Radiation Protection
| Question | Answer |
|---|---|
| Protective Tube Housing | - Made of lead lined metal that surrounds the tube. - Protects personnel and patients from leakage radiation. - 1 mGya/hr at 1 meter (100 mR/hr). |
| Control Panel or Console Location: | - Located behind a protective barrier with a window for observation of patient. - Has and exposure indicator light and tone when energized. |
| Exam Table | - Durable enough to hold patient. - Thin enough to absorb minimal radiation. - Made of carbon fiber most often. |
| Distance and Centering Indicators | Must be within 2%. |
| SID indicator | Must be within 1% of the indicated SID. |
| Most tables may only accommodate up to ___________________. | 300lbs. |
| Beam Limitation Devices | - Limits scattered radiation. - Light localizing variable aperture. |
| Skin Sparing | The skin surface should never be closer than 15 cm to the patient. |
| Luminance | - Must adequately outline the margins of the radiographic beam on the area of interest. - 161 candela/square meter. |
| Types of beam limitation devices include: | PBL, cones aperture diaphragm and cylinders. |
| Leakage radiation from the radiographic tube housing should be kept to a minimum. What is the minimum standard? | 1 mGya/ hr or 100 mR/hr @ 1 meter. |
| Positive Beam Limitation (PBL) | - Should be within 2% accuracy of the collimator with the SID. - Alignment of the beam. |
| Filtration (total): | 2.5 mm Al equivalent. |
| Inherent Filtration | - Glass envelope, insulating oil surrounding the tube and the glass window. - 0.5mm al equivalent. |
| Added Filtration | Compensating filters. |
| Inherent + Added = | Total Filtration. |
| Types of compensating filters: | - Wedge. - Trough. - Bow tie (CT). - Conical (digital fluoro). |
| ________________ is the most widely used product for filtration in diagnostic radiology. | Aluminum. |
| What measures the amount of filtration needed to reduce the primary beam to 50% or half of its original value? | Half Value Layer. |
| Exposure Reproducibility | - Consistency in output in radiation intensity for identical generator settings from one individual exposure to subsequent exposures. - 5% variance is acceptable. |
| Exposure Linearity | - Must be able to reproduce a radiograph with any combinations of kVp, mA and time that will produce similar densities. - No more than 10% variability. |
| Which term is applied to the ability of an imaging system to expose in image receptor with any combination of mA and time and get comparable images? | Linearity. |
| High grid ratio = | High patient dose. |
| Low grid ratio = | Low patient dose. |
| Radiographic Grids | - Made of radiopaque strips alternately separated with low-attenuation strips of another material. - Functions include prevention of unwanted scatter caused from the patient in reaching the image receptor. |
| Radiographic Grids: | - As grid ratio increases, so does patient dose. - As grid ratio increases, so does image quality. |
| Source-Skin distance for mobile radiography | SSD of at least 12 inches on mobile and 15 inches on permanently installed equipment. |
| Computer | Play a many roles in diagnostic imaging today. |
| Analog -vs- Digital | Changes from film to digital has changed the way we produce and look at radiographic images. |
| CR -vs- DR | Updates in technology changes the way radiographers produce and look at images. |
| ________ of storage areas as well as personnel to manage these areas saves money to the company. | Deletion. |
| The major disadvantage of digital: | Is that Initial cost is much greater with digital imaging however after the initial set up, Digital is much cheaper. |
| ________________ to the patient is easy because the computer fixes the technologist errors. A conscious effort must be made to reduce the patient dose and maintain good image quality. | Overexposure. |
| _______ have the same sensitivity as a 200 screen film system therefore it is possible to bet a good quality image with lower patient dose with screen film radiography. | CR phosphors. |
| Reduce in repeats still make _______ more practical than screen film radiography. | CR. |
| kVp | - Analog kVp controls contrast. - Digital kVp is used to penetrate the patient part examined and the computer controls contrast. |
| Collimation | Must be accurate and part of interest in the center of the image to adequately image in CR/DR. |
| In digital imaging, what does kVp control? | Penetration. |
| In digital imaging, what controls contrast? | Computer. |
| Grids | - Digital imaging receptors are much more sensitive to radiation therefore it is very important to use grids to clean up scatter. - Are sometimes used when unnecessary in DR imaging due to the design of the room. |
| Fluoro Procedures | - Produce the greatest exposure rate of all of diagnostic imaging. - All efforts should be taken to maintain patient protection. |
| Brightness | - An increase of about 10,000 times that of non image intensification fluoro. - Makes it easier for radiologist so see the image. |
| Patient dose reduction: | Less mA is required for procedure. |
| Save time for radiologist: | Don't have to adjust eyes to darkness. |
| Intermittent or Pulsed Fluoro | - Reduces patient dose. - Last image hold also reduces patient dose. - Limiting field size reduces patient dose. * Controlled by the radiologist. |
| Fluoro Technical Factors | - Appropriate kVp should be used for the body part examined. - SSD should be at lease 12 inches for mobile and 15 inches for fixed units to minimize entrance skin exposure. - Spacers are used on mobile units to maintain distance to skin from tube. |
| Sometimes _____________ are put on the bottom of the x-ray tube to accommodate for distance. | Spacers. |
| Filtration | - A minimum of 2.5 mm al equivalent must be permanently installed in the path of the useful bean in fluoro units to reduce skin dose. - Measured by HV. |
| What is the minimum SSD for mobile fluroscopic units? | 12". |
| Cumulative Timing Device | - Each unit must have a timing device that has an audible sound for beam on time and an audible alarm that temporarily interrupts the exposure after 5 minutes of fluoro. - Beam on time is documented for each procedure. |
| Exposure Rate Limitations | - 100 mGya or 10R per minute for standard fluoro. - 200 mGya or 20R per minutes with high level control fluoro (those with boost capabilities). |
| __________ exposure rates allows for visualization of smaller and lower contrast objects. Usually used in cardiac and vascular imaging | Higher. |
| Primary Protective Barrier | 2mm lead equivalent is required for fluoro rooms. |
| Control Switch | - The fluoro control switch must be of the dead man type. - Continuous pressure must be applied to the exposure switch to operate. - If the person becomes incapacitated, it should not operate. |
Created by:
sassyrad
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