Term
| What are the two types of x-rays that are responsible for the OD or ___________ on a film? |
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Definition
| Contrast; Those that pass through the patient without interacting and those that are scattered in patient (compton) |
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Term
| What are the two names for the x-rays that transverse patients? |
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Definition
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Term
| What is the name for x-rays that enter the IR? |
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Definition
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Term
| What happens as scatter increases? |
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Definition
| The radiograph loses contrast and appears gray and dull because of fog |
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Term
| What are the three primary factors that influence the relative intensity of scatter? |
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Definition
Increased kVp Increased field size Increased patient thickness |
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Term
| As x-ray energy is increased, what happens? |
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Definition
| The absolute number of compton interactions decreases with increasing x-ray energy, number of photoelectric decreases RAPIDLY |
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Term
The absolute number of compton interactions ____ and what does this mean? (As x-ray energy is increased) |
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Definition
| Decreases; relative number of compton interactions increases |
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Term
| What happens to the number of photoelectric interactions and what does this mean? (As energy of x-ray increased) |
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Definition
| Decreases, increased kVp passes right on through and x-rays aren't absorbed by anatomic part |
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Term
| Why can't we take all radiographs with low kVp?? |
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Definition
| kVp must be high enough to ensure adequate penetration of the portion of the body being radiographed |
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Term
| As kVp is increased________ aslo increased |
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Definition
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Term
| _______ and ______ are used to reduce the level of scatter radiation |
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Definition
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Term
| Why is high kVp-low mAs preferred to low kVp-high mAs? |
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Definition
| High mAs causes much more patient dose |
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Term
| Who has control of field size? How is it controlled? |
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Definition
| Radiologic technologist; collimators |
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Term
| As field size is____ scatter is _____ |
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Definition
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Term
| When the beam is collimated, technique may have to be____? |
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Definition
| Increased, in order to maintain visible detail, make up for removed scattered radiation |
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Term
| Reduced scatter radiation results in ________ radiograph OD. |
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Definition
| Lower... In order to maintain optimum OD |
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Term
| Why is smaller beam size more important in fluoro? |
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Definition
| Collimation results in better image contrast due to less scatter |
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Term
| Scatter radiation is increased with ______ body parts. Why is this so? |
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Definition
| Thick... there are multiple interactions of x-rays |
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Term
True or false. Increasing patient thickness decreases multiple scatter. |
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Definition
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Term
| List any method you can think of that would give you control over body thickness |
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Definition
compression paddles compression in IVP doing PA vs. AP |
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Term
| How does the use of compression devices improve spatial resolution? |
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Definition
| by reducing patient thickness and bringing the object closer to IR |
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Term
| How would the use of compression devices affect patient dose? |
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Definition
| Compression reduces patient dose, improves contrast resolution |
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Term
| _____ limit the size of the x-ray field |
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Definition
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Term
| The two reasons to restrict beam are? |
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Definition
1. Only tissue being examined should be exposed to decrease exposure dose 2. Large x-ray fields result in more scatter radiation |
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Term
| The three types of beam restrictors are? |
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Definition
| Aperture diaphragm, cones or cylinders, variable aperture collimator |
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Term
| What does it mean that the aperture diaphragm is the simplest type of beam restrictor? |
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Definition
| Lead or lead lined metal diaphragm attached to x-ray tube head...very simple design. |
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Term
| How is aperture diaphragm designed? |
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Definition
| Opening in diaphragm usually designed to cover just less than size of IR used |
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Term
| True or False. The aperture diaphragm is used to cover the area of interest plus 1 cm larger. |
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Definition
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Term
| What does an unexposed border mean? What is the Ca. rule on this? |
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Definition
The IR receives an image that is 1 cm smaller on all sides. 2 sides of borders must be unexposed |
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Term
| Are aperture diaphragms always used alone, and if not, what are they used with? |
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Definition
| Sometimes used with cones and cylinders |
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Term
| The area where aperture diaphragms are most often used is _____ |
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Definition
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Term
| What can cause diaphragm cut off? |
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Definition
| Long axis of diaphragm must be parallel to long axis of IR |
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Term
| Cones and cylinders are considered to be modifications of____ |
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Definition
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Term
| How do cones and cylinders work? |
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Definition
| An extended metal structure restricts the useful beam to the required size |
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Term
| What is the normal shape of cones and cylinders? |
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Definition
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Term
| The most common type is _________(cylinder or cone) but it is still often called a ______? |
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Definition
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Term
| What is a difficulty of using cones and cylinders? |
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Definition
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Term
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Definition
| If x-ray source, cone, and IR not aligned on same axis. One side of radiograph may not be exposed, edge of cone interferes. |
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Term
| True or False. The openings to cones or cylinders can be adjusted? |
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Definition
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Term
| What anatomical structures are cones and cylinders often used for? |
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Definition
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Term
| Why is image contrast improved when using a beam-restricting device? |
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Definition
Reduced scatter radiation |
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Term
| What is the primary reason one uses beam restriction? |
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Definition
| Reduce patient dose, increase contrast |
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Term
| The most commonly used beam restrictor is the ______ |
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Definition
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Term
| What is off focus radiation and how is it controlled and presented on a radiograph? |
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Definition
| When projectile electrons stray and interact at positions on anode other than focal spot. Controlled by first-stage entrance shuttering device that has multiple collimator blades in tube housing. |
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Term
| True False. The projected light field must coincide with x-ray beam? |
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Definition
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Term
| Why must the projected light field coincinde with x-ray beam? |
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Definition
| Collimator cut off of anatomic structures may occur |
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Term
| What is the scale for that is marked on the collimator? |
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Definition
| To indicate field size at fixed SID's |
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Term
| What does PBL stand for and how do they work? |
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Definition
Positive Beam Limiting Sensing devices in tray identify size and alignment of cassette. |
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Term
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Definition
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Term
| What is added filtration? What are the most common filtration stations and what are they made of? |
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Definition
| Filtration added to tube housing. Collimator assembly is added filtration. |
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Term
| What is the most common added thickness of added filtration? |
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Definition
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