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Registry Review IP
| Question | Answer |
|---|---|
| when using a grid you must do what to your technique | increase the mAs |
| as grid ratio increases mAs should | increase |
| what measures the effectiveness of the grid | grid ratio |
| what is grid ratio | height of the lead strips over the distance between |
| grids remove scatter before/after reaching the IR | before |
| the number of grid lines per unit distance | grid frequency |
| a recirptrocating grid moves | back and forth |
| an oscvillating gird moves | in a circular pattern |
| when are stationary grids used | mobile |
| grid formula | old mAs/ new mAs = from / to |
| what is the mAs multiplication factor for - no grid - 5: 1 - 6:1 - 8:1 10:1 or 12: 1 16:1 | 1 2 3 4 5 6 |
| filtration _ receptor exposure | decreases |
| filtration _ average energy of the beam | increases; filters out the lower energy photons |
| what is the purpose of compensating filters | produces even contrast - uniform contrast - example: shoulder (boomerang) - example: toes |
| total filtration should be | 2.5 mm |
| how much inherent filtration should there be and what makes up inherent | 1.5 mm -glass of the xray tube - oil in the tube (help the ball bearings) -tube window -anode |
| how much added filtration should there be | 1 mm aluminum |
| what is the HVL | amount of absorber material used to reduce intensity of beam to 1/2 the original output |
| the higher the HVL the _ beam penetration | higher |
| the higher the energy the _ penetrability | more |
| what is the proper unit for measuring xray beam penetration | HVL |
| as thickness increases beam attenuation will _ and receptor exposure will _ | increase; decrease |
| as the atomic number increases attenuation will _ and receptor exposure will | increase; decrease |
| more attenuating will appear _ on images | white (bone) |
| list least to most attenuating | air fat water(tissue) muscle bone metal |
| for an additive disease like a hemothorax you need to _ technique therefore receptor exposure will _ | increase technique- less receptor exposure |
| for a destructive disease like osteoporosis you will need to _ technique therefore receptor exposure will_ | decrease technique- increase receptor exposure (less to pass through) |
| what is positive beam limitation (PBL) | shutters automatically collimate |
| increasing collimation will _ field size _ receptor exposure and _ scatter from reaching the IR | decrease, decrease, decrease |
| beam intensity is greater at the | cathode end |
| thicker anatomy should be placed on the | cathode end |
| when looking at the xray tube the anode is on the _ and the cathode is on the _ | left ; right |
| the anode heel effect is worsened with | 1. larger field sizes 2. shorter SID 3. steeper angle 4. larger FSS |
| area of unsharpness surrounding the edges of the image | penumbra |
| what is the area of sharpness on the image called | umbra |
| spatial resolution number one controlling factor | focal spot |
| we want a _ focal spot for better spatial resolution | small focal spot |
| the focal spot that is projected to the patient | effective focal spot |
| where is the actual focal spot | on the anode |
| which is larger the actual or effective | actual " actually larger" |
| which side of the xray tube has more sharpness | anode |
| for every inch of OID you need _ inch increase in SID | 7 |
| why should we increase SID when ther is OID | to minimize magnification (size distortion) |
| tilt from the object can cause | foreshortening |
| what causes elongation | tilt from the IR and improper beam angulation |
| what are the three main components of a DEL (dexel) | 1. semiconductor detection surface 2. microscopic capacitor 3. TFT ; thin film transistor "switching gate" |
| what is a con of smaller dels | we need more signal (exposure) which in turn is more patient dose |
| large dels have _ fill factor | high |
| amorphous selenium is used for | direct DR |
| which has lower pt dose direct or indirect | indirect |
| detector surface area for indirect TFT | amorphous silicon |
| what has better spatial resolution direct or indirect | direct |
| the crystals in indirect DR are made of | cesium iodide |
| which DR system uses a scintillator | indirect |
| TFT detectors are used for | direct and indirect |
| the PSP layer in CR cassettes are made of | barium fluorohalide crystals |
| we should erase cassettes every _ hours | 24-48 |
| _ is an electronic image of electrons stored / trapped until red laser in processor activates it | latent image |
| how many times does the plate glow for CR | 2 |
| to erase the plate we use _ light | white |
| image quality is best seen within the first _ hours for a cassette | 8 hours |
| deviation index has a _ relationship with exposure | direct |
| what are the types of noise | quantum noise (mottle) scatter electronic |
| we want a _ SNR | high |
| s number is has an _ relationship with exposure | inverse |
| exposure index has a _ relationship with exposure | direct |
| if you decrease your mA your exposure time will | increase |
| safety measure for AEC is | back-up timer |
| if you increase your kvp your exposure time with AEC will | decrease |
| what will happen if you are incorrectly centered over the AEC chamber | early termination - mottle |
| the input phophor is made of | cesium iodide |
| the photocathode converts _ to _ | light to electrons |
| what do the electrostatic focusing lens do | focus electron stream to the output screen |
| what is the output phosphor made of | zinc cadmium |
| what is the function of the anode in the image intensifier | allows electrons to pass through the output phosphor |
| if we mag the focal point will move | closer to the input phosphor |
| the output phosphor converts _ to _ | electrons to light |
| when you mag in the image intensifier does it increase or decrease spatial resolution | increase |
| what mA is used for image intensifier | 1-5 |
| minification | |
| flux gain is | the flow of electrons |
| for every xray photon how many light photons are made | thousands |
| how do you find brightness gain | minification gain x flux gain |
| processing used for correcting over or underexposure | rescaling |
| what is dead pixel correction | assigns a value to a dead pixel from values of adjacent pixels |
| averages of al pixel frequencies with surrounding pixels values to remove image noise | smoothing |
| t/f: it is impossible to obtain an MTF of 1 which is perfect | true |
| collimation must be within =/- _ of the collimation field | 2 |
| collimation can be tested using a _ test | penny |
| for linearity test for mAs variation cannot exceed | +/- 10 |
| reproducability should be within | +/- 5 |
| image does not get fully erased before exposing and analyzing the next image | ghosting |
| plate uniformity should be within | |
| what can we used to measure spatial resolution | wire mess, line pair tool |
Created by:
macummins1