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Normal Size Small Size show me how
Normal Size Small Size show me how
RADT 311 Unit #4
| Question | Answer |
|---|---|
| The function/purpose of field size limitation is to: | Minimize radiation exposure to the patient (Reduces irradiated tissue volume, and Reduces patient dose) and to preserve subject contrast in the remnant x-ray beam (Reduces scatter radiation) |
| T/F: Limitation of the field size is one of the most effective means of keeping patient exposure ALARA. | True |
| T/F: Field size should never be larger than necessary to include the anatomy of interest. | True |
| T/F: Field size should never be larger than the receptor plate necessary to include the anatomy of interest. | True |
| 1899 a dentist named _________________ developed the first x-ray beam filters as well as the first devices for limiting the size of the x-ray beam. | Williams Rollins |
| Rollins’ collimating devices were simple lead plates with different sizes of aperture openings cut into them, called _________ | diaphragms |
| What are a collimator's components? | Lead shutters and a light source |
| _________ is produced any-where outside of the focal spot when projectile electrons scatter and strikes the glass envelope, the cathode or other portions of the anode. | Off-focus radiation |
| The mirror in the collimator must be mounted at precisely ______ degrees from the light source to the side of the collimator. | 45 |
| A _________ test can be performed for QC checks to ensure the accuracy of the collimated beam | penny |
| The amount of scatter radiation present in the remnant beam is a direct function of the amount of tissue exposed, controlled by: | Size of the patient and the size of the x-ray field – the main factor we have control over |
| _________ is changed when the ratios between penetrating primary rays, photoelectric interactions, and Compton scatter interactions is altered. | Subject contrast |
| Subject contrast is _________ (degraded/improved) with smaller collimated field sizes. | improved |
| The reduction of __________ rays effected by tight collimation reduces the total exposure to the IR. | scatter |
| To the extent that field size affects scatter radiation produced, it _______ (does/does not) have an impact upon image noise. | does |
| T/F: Field size affects the visibility functions of the image. | True |
| Decreased SID = _________(Decreased/Increased) FOV | Decreased |
| The field size equation is: | mAs1/mAs2 = From/ To |
| The field size multiplication factor for a 14x17" FOV is: | 1 |
| The field size multiplication factor for a 10x12" FOV is: | 1.25 |
| The field size multiplication factor for a 8x10" FOV is: | 1.40 |
| The field size multiplication factor for a 9x9" FOV is: | 1.40 |
| The Line Focus Principle is controlled by: | 1. The width of the electron beam from the filament 2. The angle of the anode bevel |
| The ___________ (larger/smaller) the projected focal spot, the greater the sharpness of detail in the image. | smaller |
| The size of the projected or effective focal spot is crucial to the ___________ of any radiographic image | sharpness |
| The true _________ (actual/effective) focal spot is measured along the anode surface. | actual |
| The _________ (actual/effective) focal spot is the area available for dispersion of heat from electron bombardment. | actual |
| Standard x-ray tubes size of a large FS is: | 1.0 to 1.2 mm |
| Standard x-ray tubes size of a small FS is: | 0.5 to 0.6 mm |
| Special procedures tubes produce FS as small as __________ mm. | 0.2 – 0.3 mm |
| With a special procedure tube having an anode bevel of 7-10 degrees, will it produce a smaller or a larger effective focal spot than a standard tube? | Smaller since the bevel is steeper |
| From the anode end of the IR, the effective FS appears _______ (smaller/larger). | smaller |
| From the cathode end of the IR, the effective FS appears __________ (smaller/larger). | larger |
| Pertaining to the anode heel effect, intensity falls off toward the __________ (anode/cathode) end of the x-ray beam. | anode |
| Pertaining to the anode heel effect, intensity increases toward the ________ (anode/cathode) end of the beam. | cathode |
| T/F: The anode heel is defined as the lower back corner of the anode disc. | True |
| The anode material itself acts as a form of __________ filtration. | inherent |
| Inherent filtration refers to: | a permanently implemented filter in the useful beam (lower energy x-rays are absorbed so higher energy x-rays are what is left). |
| The heel effect is worsened with: | 1. Larger field sizes 2. Steeper (lesser) anode bevel angles 3. Larger focal spots 4. Shorter SIDs |
| Always place the _______________ end of the anatomy toward the anode end of the x-ray tube. | thinnest |
| The anode end of the x-ray tube is normally positioned to the _______ (left/right) as the radiographer approaches the table. | left |
| Suggestions for positioning an AP Chest: | Patient’s head to the left |
| Suggestions for positioning an AP T-Spine: | Patient’s head to the left |
| Suggestions for positioning an AP Femur: | Patient’s head to the right |
| Suggestions for positioning an AP Foot: | Patient’s head to the right |
| Suggestions for positioning an AP Humerus: | Patient’s head to the right |
| Small FS = ________ (More/Less) Image Sharpness | More |
| Large FS = ________ (More/Less) Image Sharpness | Less |
| _____________ is considered to be the controlling factor for sharpness of detail. | Focal Spot Size |
| T/F: Off-focus radiation is produced in the x-ray tube anode and is technically a form of primary radiation. | True |
Created by:
rdwilliams
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