Term
| Grid Problems - know a couple |
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Definition
Use of grids often increases patient dose of radiation due to increased kVp.
Moving grids require a bulky mechanism that is subject to failure.
The distance between the subject and the film is also increased with moving grids and may create an unwanted increase in magnification and image blur.
They often introduce motion into the film holding device, which can also result in image blur.
Moving grids may also produce a stroboscopic effect when used with half or full wave rectified x-ray generators because of synchronization between x-ray pulsation and grid movement. This gives us pronounced grid lines.
Also the exposure time is longer with moving grids.
These grids are also permanently mounted in the moving mechanism just below the tabletop or just behind the upright Bucky, so if they are installed wrong you will see grid lines. |
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Term
| most frequent grid problem |
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Definition
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Term
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Definition
| a properly functioning grid must lie in a plane perpendicular to the central axis of the x-ray beam. An error can be produced by having an improperly positioned radiographic tube head. This may result in grid cutoff and lower optical density |
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Term
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Definition
| a grid can be perpendicular to the central x-ray beam and still produce grid cutoff if it is shifted laterally. This is a problem with focused grids, and may also be a problem with tube head positioning. |
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Definition
| when radiographs are taken at SID’s unspecific for that grid. Grid cutoff will occur and radiographic density will decrease. |
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Term
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Definition
| it will show severe grid cutoff on either side of the central axis. |
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Term
| 4 situations that must be avoided to prevent error |
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Definition
off-level error
off-center error
off-focus error
upside-down grid error |
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Term
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Definition
| is an alternative technique to radiographic grid use. It is another method of reducing scatter radiation towards the film and enhancing image contrast. The image receptor is moved 10-15 cm from the patient. A portion of the scattered x-rays generated in the patient are scattered away from the film in the air gap between the patient and the film and are not detected. Since fewer scattered x-rays interact with the image receptor, the contrast is enhanced. The technique factors are about the same as those for an 8:1 grid. The problem with this technique is magnification. It is not affective with high kVp, above 90 because the direction of the scattered x-rays is toward the film. |
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Definition
| is the exactness of representation of the anatomic structure on the radiograph within the useful density range. |
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Term
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Definition
| is the ability to visually detect separate objects on a radiograph. |
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Term
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Definition
| refers to bone verses soft tissue interface. Detail or visibility of detail are terms commonly used when referring to this. is measured in line pairs per millimeter (lp/mm). |
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Term
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Definition
| Detail is defined as the degree of sharpness of structural lines on a radiograph. |
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Definition
| allows the viewer to see detail because image contrast and optical density are adequate |
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Definition
| refers to contrast differences between similar tissues, such as liver and spleen. |
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Term
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Definition
| is the undesirable fluctuation in the optical density of the image. This is like snow on the television. Some noise is controllable, some is not. |
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Term
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Definition
| refers to the distribution and size of the silver-halide crystals in the emulsion of the film. It is inherent noise on the radiograph. |
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Term
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Definition
| refers to the phosphor of the radiographic screen. Also inherent, but contributes little to radiographic noise. |
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Term
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Definition
| is the principle cause of radiographic noise. It refers to the randomness with which a low number of x-ray photons interact with the intensifying screens. The use of very fast intensifying screens may result in increased quantum mottle. It is evident using low mAs, high kVp, and fast-image receptors. More evident when using fewer x-rays. |
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Term
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Definition
film graininess
structure mottle
quantum mottle |
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Term
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Definition
| is the ability of an x-ray film to respond to an x-ray exposure. Also known as the measure of its sensitivity. |
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Term
| If image receptor speed is doubled, mAs must be |
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Definition
halved.
No change in kVp is necessary. |
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Term
| What 2 things are affected by image receptor speed |
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Definition
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Term
| Fast image receptors (400, 600 or above) |
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Definition
| have high noise and low resolution |
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Term
| Slow image receptors (50, 100, 200, and 300) |
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Definition
| have low noise and high resolution |
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Term
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Definition
| is designed to make sure the radiologist is provided with an optimal x-ray image and that the radiographer follows radiation safety procedures. Preventative maintenance and testing of x-ray equipment. |
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Term
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Definition
| is performed when a step-wedge is flashed to simulate an exposure. It shows shades of gray, which demonstrates radiographic contrast or variations in optical density. |
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Term
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Definition
| measures the light transmitted through the step wedge increments. |
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Term
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Definition
is the degree of blackening of a radiograph
Diagnostic useful range is 0.5-2.5 OD |
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Definition
| is the optical density inherent in the base of the film. It is due to the composition of the base and the tint added to the base. It has a value of approximately 0.05 OD. |
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Term
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Definition
| is the development of silver grains that contain no useful information. It results from inadvertent exposure of film during storage, undesirable chemical contamination, and improper processing. Higher _______ levels reduce the contrast of the radiograph. It should not exceed .05 OD. |
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Term
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Definition
| differences in optical densities. |
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Term
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Definition
| is inherent in the film and influenced by processing |
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Term
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Definition
| is determined by the size, shape, and x-ray attenuating characteristics of the anatomic part. |
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Term
| radiographic contrast is the product of these 2 things |
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Definition
film contrast
subject contrast |
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Term
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Definition
| refers to the range of exposures over which the x-ray film will respond with optical densities in the diagnostically useful range. Films that respond to a much wider range of exposures is said to have a “wider l_______”. |
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Term
| A wider latitude has a ________ gray scale |
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Definition
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Term
| A high contrast film has a ________ latitude |
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Definition
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Term
| a low contrast film has a _________latitude |
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Definition
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Term
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Definition
| all images on the radiograph are larger than the object they represent. |
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Term
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Definition
measure of magnification
image size divided by object size
MF = SID/SOD |
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Term
1) use as large a source-to-image receptor distance as possible, OR
2) place the object as close to the image receptor as possible. |
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Definition
| how do you minimize magnification? |
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Term
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Definition
| unequal magnification of different portions of the same object. It can produce inaccurate diagnosis. Object thickness and object position may create this. |
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Definition
| when the point of the object will not appear as a point in the image plane because the x-rays used to image that point originate throughout the target |
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Term
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Definition
| the most important factor in determining spatial resolution. it is small on the anode side, but large on the cathode side. |
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Term
a. Large effective focal spot
b. Short SID (x-ray source to object)
c. Long OID (object to image receptor distance) |
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Definition
| 3 conditions result in focal spot blur |
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Term
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Definition
| is described as a varying intensity across the x-ray field caused by attenuation of x-rays in the heel of the anode. It can affect the focal spot blur. It is small on the anode side and larger on the cathode side. Therefore images toward the cathode side have a higher blur and poorer spatial resolution than those on the anode side. |
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Term
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Definition
| may be caused by movement of the patient or x-ray tube during exposure. |
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Term
• Use the shortest possible exposure times
• Restrict patient movement by instructing the patient or using restraining devices
• Use a large SID
• Use a small OID |
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Definition
| 4 ways to prevent motion unshaprness |
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Term
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Definition
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Term
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Definition
| focal spot size, distance, and filtration |
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Term
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Definition
| refers to the characteristics of the radiographic image. These include optical density, contrast, image detail, and distortion |
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Term
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Definition
| is described as the blackening of the finished radiograph. Black is numerically equivalent to 3 or greater, whereas clear is less than 0.2. The blackening is a result of development of the silver-bromide crystals in the film emulsion. It relates directly to the amount of exposure received from x-rays, the conversion into visible light within the intensifying screens, and the film processing time, temperature, and chemical concentration. |
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Term
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Definition
| If the film is too dark then it has been ________ and is considered having a __________ optical density |
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Term
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Definition
| if the film is too light it is ________ and has a ________ optical density |
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Term
mAs
SID
SID is usually fixed, therefore mAs is the primary factor |
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Definition
| OD is controlled by these 2 things |
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Term
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Definition
| OD increases _______ with mAs. |
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Term
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Definition
mAs must increase at least _____% to produce a perceptible increase in OD.
As a general rule mAs is usually halved or doubled if it is the only factor that needs to be changed. |
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Term
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Definition
| an increase in kVp 15% is equivalent to ______ the mAs. |
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Term
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Definition
| function of this in the image is to make anatomic detail more visible. It is defined as the difference in optical density between adjacent anatomic structures or the variation in optical density present on a radiograph. It is necessary for the boarder or outline of a structure to be seen. |
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Term
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Definition
| a low contrast resolution may be enhanced with _____ kVp |
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Term
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Definition
| means the range of optical densities from the whitest to the blackest part of the radiograph. A high contrast radiograph has a short contrast scale, this means that there is little gray. To increase contrast you may decrease the kVp. A low contrast radiograph has a high contrast scale, or more shades of gray. To achieve this you must increase your kVp. |
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Term
*five percent rule*
30% reduction |
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Definition
| an increase of 5% in kVp may be accompanied by a _______ in mAs. |
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Term
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Definition
| describes the sharpness of small structures on the radiograph. |
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Term
| sharpness of image detail |
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Definition
| refers to the structural lines or borders of tissues in the image and the amount of clarity of the image. |
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Term
focal-spot size
SID
OID
It is also influenced by the type of intensifying screens and the presence of motion. You must use the smallest focal spot size appropriate and the longest standard SID and place the anatomic part as close to the image receptor as possible. |
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Definition
| 3 factors that control sharpness |
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Term
| visibility of image detail |
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Definition
| detail describes the ability to see the detail on the radiograph. Loss of visibility refers to any factor that causes the deterioration or obscuring of the image detail, like fog. |
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Term
collimation
use of grids
and other methods that prevent scatter radiation. |
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Definition
| key factors in visibility of image detail |
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Term
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Definition
| is the misrepresentation of object size and shape on the finished radiograph. |
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Term
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Definition
| poor alignment of the image receptor or the x-ray tube may result in _________ of the image. |
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Term
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Definition
| Poor alignment of the anatomical part may result in ____________ of the image. |
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