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Bushong ch 10, 13
Inverse square law ect..
| Question | Answer |
|---|---|
| The inverse square law states that - | Intensity is inversely proportional to the square of the distance |
| The inverse square law is the result of? | Divergence |
| The inverse square relationship applies to which of the following sources? a. Gamma Ray b. Plane c. Point d. Ultra Sound e. X-ray | c. Point |
| If the distance from a point is tripled, the intensity will be - | one ninth |
| If an instrument is 1 meter from a point source and is moved 50 cm closer to the source, the radiation intensity will - | Increase by a factor of 2 |
| A radiograph that faithfully reproduces structure and tissues is identified as a | high-quality radiograph |
| The most important characteristics of radiographic image quality are | spatial resolution, contrast resolution, noise, and artifacts |
| Spatial resolution improves as | screen blur decreases, motion blur decreases, and geometric blur decreases. |
| Contrast resolution is | the ability to distinguish anatomical structures of similar subject contrast such as liver–spleen and gray matter–white matter. |
| these terms refer to the degree of sharpness of structural lines on a radiograph | spatial resolution and contrast resolution or detail and recorded detail |
| Visibility of detail refers to the | ability to visualize recorded detail when image contrast and optical density (OD) are optimized. |
| x-rays and visible light photons travel | straight lines |
| What 3 principal geometric factors affect radiographic quality? | magnification, distortion, and focal-spot blur. |
| The Magnification Factor is the | ratio of image size to object size or source-to-image receptor distance (SID) to source-to-object distance (SOD). SID/SOD (divided by) |
| How to Minimizing Magnification | Large SID: Use as large a source-to-image receptor distance as possible. Small OID: Place the object as close to the image receptor as possible. |
| Unequal magnification of different portions of the same object is called | shape distortion. |
| Distortion Depends On what 3 factors | 1 Object thickness 2 Object position 3 Object shape |
| Inclination of an object results in a | a foreshortened image |
| What is possible in every radiographic examination if the patient is not properly positioned. | Distortion |
| What occurs if the object plane and the image plane are not parallel | Distortion |
| foreshortening, or the extent of reduction in image size, increases as the | angle of inclination increases |
| What occurs When objects of the same size are positioned at different distances from the image receptor | spatial distortion occurs |
| Focal-spot blur is caused by the | effective size of the focal spot |
| Focal-spot blur is small when the | OID is small |
| Focal-spot blur is larger on the | cathode side of the image |
| Focal-spot blur is the most important factor for determining | spatial resolution |
| To minimize focal-spot blur, you should use _____________ and ____________. | small focal spots and position the patient so that the anatomical part under examination is close to the image receptor. |
| radiographic contrast is simply the product | of image receptor contrast and subject contrast. Radiographic contrast = Image receptor contrast × Subject contrast |
| The degree of subject contrast is directly proportional to | to the relative number of x-rays leaving those sections of the body. |
| When the effective atomic number of adjacent tissues is very much different | subject contrast is very high |
| kVp is the most important influence on | subject contrast |
| high subject contrast, sometimes called short gray scale contrast because the radiographic image appears either black or white with few shades of gray has a value of | low kVp |
| results in low subject contrast or long gray scale contrast. | high kVp |
| Procedures for Reducing Motion Blur | Use the shortest possible exposure time. • Restrict patient motion by providing instruction or using a restraining device. • Use a large source-to-image receptor distance (SID). • Use a small object-to-image receptor distance (OID). |
| Movement of the patient or the x-ray tube during exposure results in blurring of the radiographic image is called | Motion Blur |
| Image quality is improved by _____________ that cause reduced motion blur. | short exposure times |
| The primary control of optical density is | mAs |
| The prime exposure factors are | kVp, mA, exposure time, and source-to-image receptor distance (SID) |
| kVp is the primary control of x-ray beam quality and therefore controls | beam penetrability |
| kVp controls screen-film | radiographic contrast |
| because kVp has higher energy, they also interact more by Compton effect and produce more scatter radiation, which results in ... | reduced image contrast |
| The mA selected determines the number of x-rays produced and therefore the... | radiation quantity |
| With a constant exposure time, mA controls the | quantity and therefore the patient radiation dose |
| X-ray quality remains fixed with a change in | mA |
| Radiographic exposure times usually are kept as short as possible. The purpose is not to minimize patient radiation dose but rather to | minimize motion blur that can occur because of patient motion. |
| when exposure time is reduced, the mA must be increased proportionately to provide the | required x-ray intensity |
| Milliamperes (mA) × exposure time (s) | mAs |
| What controls OD | mAs |
| The mAs value determines the number of x-rays in the primary beam; therefore, it principally controls radiation .... | quantity |
| Distance has no effect on ... | radiation quality |
| Distance (SID) affects | OD optical density |
| The use of a longer SID results in | less magnification, less focal spot blur, and improved spatial resolution. |
| With a longer SID more mAs must be used because of the effects of the..... | direct square law. |
| Radiographic techniques may be described by identifying three groups of factors which are... | 1- patient factors (as anatomical thickness and body composition) 2 -image-quality factors (such as OD, contrast, detail, and distortion) 3 -exposure technique factors (kVp, ma, exposure time, SID, grids, screens, focal-spot size, & filtration) |
| Sthenic | meaning “strong, active”—patients are average patients |
| Hyposthenic patients are | thin but healthy appearing; these patients require less radiographic technique. |
| Hypersthenic patients are | big in frame and usually overweight. |
| Asthenic patients are | small, frail, sometimes emaciated, and often elderly. |
| Radiographic technique charts are based on which body habitus? | sthenic |
| Patient thickness should not be | guessed |
| The chest has high | subject contrast |
| the abdomen has low | subject contrast |
| Tissues that attenuates few x-rays and appears black on the radiograph are called .... | Radiolucent |
| Tissues that absorbs x-rays and appears white on the radiograph | Radiopaque |
| Some pathology is destructive, causing the tissue to be more | Radiolucent |
| Some pathology can constructively increase mass density or composition, causing the tissue to be more .... | Radiopaque |
| image-quality factors refers to characteristics of the radiographic image; these include | OD, contrast, image detail, and distortion |
| factors that provide a means for the radiologic technologist to produce, review, and evaluate radiographs - also are considered the “language” of radiography; often, it is difficult to separate one factor from another. | Image-quality factors OD, contrast, image detail, and distortion |
| the degree of blackening of the finished radiograph is called | Optical density (OD) |
| A radiograph that is too dark has a high OD caused by .... | overexposure - when too much x-radiation reaches the image receptor |
| A radiograph that is too light has been exposed to too little x-radiation, resulting in low OD and is called ... | underexposed |
| Optical density can be controlled in radiography by two major factors... | mAs and SID |
| OD increases directly with mAs, which means that... | if the OD is to be increased on a radiograph, the mAs setting must be increased accordingly |
| A Normal chest radiograph taken at 100 cm SID - If the exposure technique factors are not changed, a similar radiograph at 90 cm SID will produce what time of xray ... | overexposed |
| A change in mAs of approximately what percent is required to produce a visible change in OD. | 30% |
| A Normal chest radiograph taken at 100 cm SID - If the exposure technique factors are not changed, a similar radiograph at 180 cm SID will produce what time of xray... | underexposed |
| It is generally accepted that if the OD on the radiograph is to be increased with the use of kVp, an increase in kVp of how much percentage is equivalent to doubling the mAs? | 15% - This is known as the 15% rule. |
| A 15% increase in kVp accompanied by a half reduction in mAs results in the same | OD |
| So, if only tissue thickness increases and no other factors changed, OD is ... | decreased |
| function of contrast in the image is to make anatomy more .... | visible |
| perhaps the most important factor in radiographic quality | Contrast |
| result of differences in attenuation of the x-ray beam as it passes through various tissues of the body | Contrast |
| The contrast resolution of soft tissues can be enhanced, at the expense of higher patient radiation dose, with with a reduction of... | kVp |
| High-contrast radiographs produce short | gray scale |
| Low-contrast radiographs produce long | gray scale |
| High contrast, “a lot of contrast,” or a “short scale of contrast” is obtained by using what time of kVp exposure techniques | low kVp |
| High Kilovolt Peak Produces | Long scale Low contrast Less contrast |
| Low Kilovolt Peak Produces | Short scale High contrast More contrast |
| The characteristic curve of a radiographic screen-film image receptor is the graphic relationship between .... and at the lowest it is called the ______ and at the highest it is called the _______. | optical density (OD) and radiation exposure toe & shoulder |
| An Increase in kVp effects contrast how? | decreases |
| spatial resolution = | distinguish small details of an object |
| Sharpness of image detail is best measured by | spatial resolution |
| This describes the sharpness of appearance of small structures on the radiograph | Detail |
| To produce the sharpest image detail, one should use the smallest appropriate ______ ____ and the longest ____ and place the anatomical part as close to the _______ ______ as possible. | focal spot SID image receptor |
| The visibility of image detail is best measured by... | contrast resolution |
| contrast resolution is the ability to.... | distinguish between differences in intensity in an image |
| the misrepresentation of object size and shape on the radiograph is ..... | Distortion |
| Poor alignment of the image receptor or the x-ray tube can result in | elongation |
| Elongation means ... | means that the anatomical part of interest appears bigger than normal. |
| Poor alignment of the anatomical part may result in .... | Foreshortening |
| Foreshortening means | that the anatomical part appears smaller than normal. |
| Distortion is reduced by positioning the anatomical part of interest in a.... | plane parallel to that of the image receptor. |
| Detail is controlled by | Focal-spot size |
| Optical density is controlled by | mAs |
| Contrast is controlled by | kVp |
| Distortion is controlled by | Patient positioning |
| The change in x-ray quantity is proportional to the square of the ratio of the | kVp |
| by increasing kVp and reducing mAs so that image receptor exposure remains constant, the patient dose is | reduced significantly |
| X-ray intensity varies inversely with the square of the distance from the x-ray tube target. This relationship is known as the | inverse square law |
| X-ray quantity is inversely proportional to the... | square of the distance from the source |
| When SID is increased, mAs must be increased by ..... (known as the square law) | SID2 to maintain constant exposure to the image receptor. |
| The purpose of the filters is to... | reduce the number of low-energy x-rays. |
| Adding filtration to the useful x-ray beam reduces... | patient dose |
| The disadvantage of x-ray beam filtration can be... | reduced image contrast when using screen film caused by x-ray beam hardening |
| X-ray beam hardening increases the number of high energy x-rays in the beam by... | removing the lower-energy non-penetrating x-rays |
| Penetrability refers to the ability of x-rays to... | penetrate deeper in tissue |
| The penetrability of an x-ray beam is called the... | x-ray quality |
| Attenuation is the reduction in x-ray intensity that results from... | absorption and scattering |
| HVL is the best method for specifying | x-ray quality |
| Increasing filtration increases the _________ and reduces the __________ . | quality of an x-ray beam X-ray Quantity |
| Filtration of useful x-ray beams provided by the permanently installed components of an x-ray tube housing assembly and the glass window of an x-ray tube is called.... | Inherent filtration |
| A thin sheet of Al positioned between the protective x-ray tube housing and the x-ray beam collimator is the usual form of... | Added Filtration |
| Distance has no effect on _________ but __________ quantity. | quality Reduces |
| mAs has no effect on _________ but __________ quantity. | quality Increases |
| Kvp has increases _________ & __________ . | quality quantity |
Created by:
wolfe9ah