Term
| Recorded detail is known as _____ or _____. |
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Definition
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Term
| Recorded detail is defined as: |
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Definition
| the sharpness of structure lines or minute details in a radiograph. |
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Term
| The 4 factors that affect recorded detail are: |
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Definition
1. Geometric Factors
2. Motion
3. Image Receptor Factors
4. Object Factors |
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Term
| Geometric factors are defined as: |
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Definition
| The geometry of the x-ray beam coming out of the x-ray tube. |
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Term
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Definition
| Sopt size on the anode where the electrons hit. |
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Term
| What are the 2 types of Focal Spot Sizes? |
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Definition
1. Actual Focal Spot
2. Effective, Apparent, or Projected Focal Spot |
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Term
| Actual Focal Spot is defined as: |
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Definition
| The actual surface on the target (anode) where the electrons strike. |
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Term
| Effective, Apparent, or Projected Focal Spot is defined as: |
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Definition
| The appearance of the actual focal spot when viewed from the perspective of the image receptor. |
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Term
| What is the Line Focus Principle? |
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Definition
| The effective focal spot appears smaller than the acutal focal spot. |
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Term
| The effective focal spot size will be governed by 2 factors. What are they? |
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Definition
1. Size of actual focal spot
2. Anode angle |
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Term
| What is the effect of the size on actual focal spot? |
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Definition
| If it is smaller, the effecive focal spot will also be smaller. |
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Term
| What is the effect of the anode angle? |
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Definition
| The smaller the anode angle, the smaller the effective focus. |
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Term
| Advantages and disadvantages of small and large focal spot size: |
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Definition
Small: better detail, used with only 100 mA or less, poor heat dissipation
Large: detail not as sharp, used with any mA, better heat dissipation |
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Term
| What is the difference between umbra and penumbra? |
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Definition
| Umbra is the actual shadow. Penumbra is the "almost" shadow (blurry lines along the outside). |
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Term
| What is focal spot blooming? |
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Definition
| Over time the focal spot size increases. As focal spot size increases, so does the size of the penumbra. |
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Term
| What are the devices used to measure focal spot size? |
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Definition
Pinhole camera
Resolution chart (Star chart, slit chart, test tool) |
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Term
| What is NEMA and what does it stand for? |
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Definition
NEMA is the standards for focal spot blooming.
NEMA = National Electronics Manufacturers Association |
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Term
Geometric factors:
How does SID affect detail? |
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Definition
| As SID increases, detail increases |
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Term
Geometric factors:
how does OID affect detail? |
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Definition
| as the OID distance increases, detail decreases |
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Term
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Definition
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Term
Geometric Factors:
heel effect |
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Definition
| The effective focal spot appears smaller at the anode end and larger at the cathode end. Detail at anode end will have sharper image than at cathode end. |
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Term
4 sets of recorded detail
Motion: |
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Definition
any motion of the patient, the x-ray tube, or image receptor causes blur which destroys recorded detail.
To compensate for this give clear instructions, suspend respiration, short exposure times, and immobilize when necessary. |
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Term
4 sets of recorded detail
Image receptor factors: |
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Definition
| The faster the speed of the IR, the poorer the recorded detail |
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Term
| What are the three things that the loss of recorded detail can be caused by for image receptor factors? |
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Definition
film speed
intensifying screens
quantum mottle |
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Term
Image receptor factors:
Film speed: |
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Definition
| the faster the speed = the larger t silver halide crystals = decreased recorded detail |
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Term
Image receptor factors
Intensifying screens: |
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Definition
| less recorded detail because the light divergence from the intensifying screen before it reaches the film. |
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Term
| What are the three factors of intensifying screens? |
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Definition
crystal size and shape: faster speed screens = larger crystals = more divergent light pattern = decreased recorded detail
active phosphor layer thickness: faster speed screens have a thicker active layer which leads to more divergent light, reducing recorded detail
single vs double screen: double screen cassettes have less detail due to the crossover effect |
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Term
Image receptor factors
Quantum Mottle: |
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Definition
| a blotchy appearance of the radiographic image because of uneven distribution of x-ray photons across the surface of the IR. Occurs when low mAs is used. When enough x-rays are created distribution evens out. |
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Term
| Object factors definition |
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Definition
absortption unsharpness or object blur
the thicker the object the poorer the recorded detail
the closer you are to cone shaped the better the detail |
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Term
object factors related terms
visibility of detail: |
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Definition
how well the radiographic image can be seen
goverened by optical density and contrast (photographic factors) NOT GEOMETRIC FACTORS
it is possible to have good recorded detail but poor visibility of detail |
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Term
object factors related terms:
resolution: |
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Definition
| the ability of an imaging system to deliver recorded detail |
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Term
| What are the three types of resolution? |
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Definition
1. contrast
2. temporal time
3. spatial |
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Term
types of resolution:
contrast. |
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Definition
| the ability of an imaging system to distinguish structures of similar density and thickness as being separate. |
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Term
Types of resolution:
temporal time: |
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Definition
the ability of an imaging system to show events in time happening very close together as separate events.
the more images you take per unit time the better the detail but it increases patient dose. |
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Term
types of resolution:
Spatial: |
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Definition
| the ability of an imaging system to produce separate images of closely spaced objects |
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Term
| what factors are spatial resolution affected by? |
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Definition
| focal spot size, screen thickness, screen pohosphor crystal size and film/screen contact (image receptor factors) |
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Term
| What are the 5 ways to measure spatial resolution? |
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Definition
1. spatial frequency
2. point spread function (PSF)
3. line spread function
4. edge spread function
5. modulation transfer function (MTF) |
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Term
Spatial resolution:
spatial frequency is defined as?
what can the human eye read at? |
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Definition
a resolution chart made up of black and white lines (line pair per millimeter [LP/mm]) = one black and one white line
human eye at normal reading distance is about 5LP/mm. Most film/screen systems deliver about 2-4LP/mm |
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Term
Spatial resolution:
point spread function (PSF) is a graph that shows you what? |
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Definition
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Term
Spatial resolution:
line spread function is a what? |
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Definition
more accurate graph
you need an aperature with a slit cmaera 10 micrometeres wide instead of a pinhole |
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Term
Spatial resolution:
edge spread function is what? |
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Definition
a sheet of metal plate at the border between the black and white areas potted on a graph. Densitometer.
1/2 way up measures how far we are from "perfect". The wider the gap the poorer the spatial resolution |
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Term
Spatial resolution:
Modulation transfer function (MTF) is what? |
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Definition
a numeric value used to measure spatial resolution obtained from the LSF graph
mathematical process known as fourier transformation
ranges from 0-1. 1-100%
MTF = info not recorded in an image/info available in the part |
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Term
| The amount of size distortion can be calculated by what formula? |
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Definition
| Image size / object size = SID / SOD |
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Term
| Magnification factor can be measured by: |
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Definition
| Image size / object size or SID/SOD |
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Term
| Percent magnification can be measured by which formula? |
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Definition
| (Image size - object size) / object size x 100 |
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Term
| What is the purpose of a technique chart? |
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Definition
| to provide the radiographer with the technical factors necessary (kvp,mA, time) to produce an appropriate diagnostic radiograph. A balance between radiographic quality and patient exposure must be maintained. |
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Term
| ceiszynki's law of isometry |
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Definition
| an isometric angle of the CR equal to 1/2 of the angle formed between the object and the film, will eliminate or minimize foreshortening |
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Term
| What are the parameters of technique charts? |
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Definition
1. optical density = brightness
2. contrast = grey scale
3. recorded detail = sharpness of structure lines
4. distortion = treu shape, size, and spatial relationship
5. patient exposure = 1-4 balance against this
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Term
| What are the 14 factors that go into making a technique chart? |
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Definition
1. mA
2. exposure time
3. kVp
4. SID
5. IR system speed
6. Grid ration & type
7. field size
8. patient size
9. filtration
10. processing
11. voltage waveform of the x-ray generator
12. pathology
13. OID
14. focal spot size |
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Term
| What are the 9 major types of technique charts? |
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Definition
1. AEC
2. body habitus
3. Anatomically programmed systems
4. variable kilovoltage system
5. fixed kilovoltage system
6. high kilovoltage system
7. bit system
8. supertech calculator
9. proportional anatomy systems |
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Term
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Definition
| uses a radiation detector (usually 3 sensors [cells that measure radiation]) that terminate the exposure (comparator) when a sufficient amt of radiation has been measured |
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Term
| What 5 values do you have to set in an AEC device. |
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Definition
1. kVp: controls image contrast and exposure time only
2. mA: controls exposure time only
3. back-up time: terminates exposure at 6sec or 600mAs
4. correct cell selection
5. density selection: set level in comparator that will terminate the exposure |
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Term
| What is minimum response time? |
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Definition
| the length of time necessary for the AEC to respond to the radiaton and for the generator to terminate the exposure |
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Term
Density selections examples
how much change in optical density occrus between each setting? |
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Definition
| +1, +1/4, -1, -1/4, +2, +1/2, -2, -1/2 |
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Term
| Limitations of AEC systems |
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Definition
1. never use on anatomy that is too small or narrow to cover the cells
2. can only be used with bucky exams since the cells are part of he bucky
3. cannot be used on anatomy that is peripheral in relation to the beam
4. positioning and centering are critical
5. collimation is critical to reduce scatter
6. cannot be used with surgical apparatus, orthopedic devices, & orthodontic work |
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Term
| What is an anatomically programmed system? |
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Definition
| It is a computerized technique chart stored in a microprocessor in the control console. Can be used in bucky and non-bucky exams |
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Term
| What are the disadvantages of an anatomically programmed system? |
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Definition
| high captial cost, expensive to re-program |
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Term
| What is a variable kilovoltage system? Who founded it? |
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Definition
| Ed Jerman. Varying the kVp to compensate for changes in patient size while the mAs is kept constant. |
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Term
| What are the two ways to measure for a variable kilovoltage system? |
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Definition
1. measure the patient, multiply by 2, and add 30
2. set a base kVp and mAs for the normal size patient and increase 2 kVp for each cm change in patient thickness |
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Term
| What are the disadvantages of a Variable Kilovoltage system? |
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Definition
1. scale of contrast is always changing between patients
2. patient dose is higher since the kVp is relatively low and higher mAs values must be used
3. Low exposure latitude with hight contrast images
4. more heat produced in x-ray tube |
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Term
| What is a fixed kilovoltage system? |
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Definition
| most common manual technique. Developed by Fuch's. Keep kVp constant, vary the mAs according to changes in patient size. |
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Term
| What is the general rule for fixed kilovoltage systems? |
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Definition
| change the mAs by a factor of 2 times for every 5cm change in subject thickness. The kVp can be set at optimum levels (relatively high) so the mAs is lower. |
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Term
| What are the advantages/disadvantages of a fixed kilovoltage system? |
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Definition
Adv:
1. lower patinet dose since mAs is lower
2. increase consistency of contrast and optical density
3. wider exposure latitude with lower contrast
4. less wear on x-ray tube
Dis:
1. more scatter and a grid must be utilized
2. lower image contrast |
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Term
| What is a high kilovoltage system? |
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Definition
| uses high kilovoltage (100-300) to produce a long scale of contrast. Chest, barium, pre-natal studies |
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Term
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Definition
| developed by DuPont corporation in the 1970s. All possible variables such as part thickness, mA, time, kVp, etc are given a value called a bit. |
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Term
| What is a supertech calculator? |
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Definition
| slide rule device in 1973 |
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Term
| What is a porportional anatomy system? |
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Definition
| classifies body parts and gabitus into groups of similar part thickness and tissue density |
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Term
| What 6 things are classified as technique complications? |
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Definition
1. Pediatrics
2. Casts
3. Soft tissue
4. trauma
5. post mortem
6. single phase technique selection vs constant potential |
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Term
| What are the 4 types of Casts? |
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Definition
1. Plaster
2. Fiberglass
3. Plastic
4. Splint |
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Term
| What are the three types of plaster casts and what adjustments have to be made? |
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Definition
1. Wet: increase by 15kVp, or 3x normal mas
2. Dry: increase by 10 kVp, or 2x normal mass
3. Half: increase 8% kVp, or increase 50% mAs |
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Term
| What adjustment is made for fiberglass casts? |
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Definition
| Increase 5 kVp or 30% mAs |
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Term
| What adjustment is made for plastic casts? |
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Definition
| Increase 8% kVp or 50% mAs |
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Term
| What are the 2 categories of splints and what adjustments are made? |
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Definition
1. Wood and aluminum: increase 8% in kVp or 50% in mAs
2. Air : no adjustment made |
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Term
| What adjustments are made for soft tissue? |
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Definition
| decrease the kVp by 15% w/o changing the mAs |
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Term
| What adjustments are made for trauma? |
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Definition
| Internal bleeding will require 30% increase in mAs for abdominal or skull. 30-100% increase in mAs for chest. |
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Term
| What adjustments are made for post mortem? |
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Definition
| Increase mAs by 35% for head, thorax and abdomen studies. All the rest stay the same. |
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Term
| What adjustments are made for single phase technique selection vs constant potential? |
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Definition
Single phase requires 1.34-1.41 times more mAs than constant potential because of the average lower energy x-rays in single phase.
kVp should be at least 15% higher in single phase than constant potential. |
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