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23 Cards in this Set
- Front
- Back
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Areas of film exposed to large # of light photons are (black/white) after film processing & are called (radiolucent/radiopaque).
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black
radiolucent |
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Areas of film exposed to small # of light photons are (black/white) after film processing & are called (radiolucent/radiopaque).
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white
radiopaque |
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What are the 5 radiopacites, from most radiolucent to least radiolucent.
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air
fat water/soft tissue bone metal |
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As thickness increases, radiopacity (increases/decreases).
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increases
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What is the definition of a radiograph?
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image of # & distribution of x-rays that pass thru patient & strike cassette
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What are some problems caused by the fact that radiographs are 2-D?
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loss of depth perception
superimposition summation shadows magnification & distortion silhouette sign |
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To evaluate depth perception with radiographs, what must you do?
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2 rads of objects are needed, w/ 1 at 90º to other (orthogonal projections)
some lesions are apparent in only 1 radiographic projection |
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What is superimposition?
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a normal structure appears in an unexpected location & is misinterpreted as a lesion (ex. nipples)
these structures are not particularly large, but they cast a disproportionately opaque shadow b/c they are surrounded by air & their margins are parallel to central x-ray beam, thus providing optimal geometry for visualization |
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What are summation shadows?
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special case of superimposition where overlapping structures create a summation opacity that is not really present in patient
result represents degree of x-ray absorption by all superimposed objects when a suspicious radiopacity or radiolucency is identified, must consider possibility that it represents a summation shadow produced by overlapping structures |
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A positive summation sign is more (radiolucent/radiopaque), while a negative summation sign in more (radiolucent/radiopaque).
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positive: more radiopaque (ex. overlap of 2 kidneys)
negative: more radiolucent (ex. overlying anal sac gas on ischium) |
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What factors affect the radiopacity of an object?
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physical density
atomic number thickness |
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What is magnification?
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= enlargement of image relative to its actual size
-as object-film distance ↑, magnification ↑ -in the magnified image, each bit of visual info is spread over a larger area of film --> ↓ image detail |
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What is distortion?
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-occurs when image misrepresents true shape or position of object
-results from unequal magnification of different parts of same object -can be minimized by keeping object & film planes parallel |
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What is a silhouette sign?
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= effacement (loss of visualization) of border of 2 structures of same radiography opacity that are in contact
-often results in diseases masking normal radiographic structures |
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What are some examples of silhouette signs?
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ex. can’t see coronary a. on heart b/c they are both soft tissue opacity, but can see pulmonary vessel superimposed on heart b/c air provides contrast b’twn them
ex. pleural effusion: can’t see heart in DV view b/c fluid surrounds heart, but can see heart in VD view because heart is dorsal to fluid ex. pneumonia can cause border effacement of heart if lung lobe touches heart |
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How are radiographs named?
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point of entrance --> point of exit of x-ray beam
use dorsal & palmar/plantar in digits rather than cranial & caudal names of lateral rads of abdomen & thorax are abbreviated to the recumbency of patient lying on x-ray table -rad of canine abdomen made w/ dog lying on left side is referred to as a left lateral |
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What are some rules for placing radiographs on the viewbox?
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-lateral views of any part should be viewed w/ cranial (rostral) aspect of animal to viewer’s left
-VD or DV rads of head, neck, or trunk should be placed w/ cranial (rostral) part of animal pointing up & w/ left side of animal to viewer’s right -when viewing lateromedial or mediolateral rads of extremities, incl. oblique projections, rad should be placed w/ proximal aspect of limb pointing up & cranial or dorsal aspect of limb to viewer’s left -caudocranial or craniocaudal rads of extremities should be placed w/ proximal end of extremity at top & lateral aspect of limb on viewer’s left |
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What are the major steps of radiographic interpretation?
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-signalment, hx, PE
-preliminary work: diagnostic quality -determine if radiograph is normal -describe abnormalities using Roentgen signs -determine if abnormalities are relevant -formulate list of ddx -plan on how to get to next step: more imaging, invasive procedures, etc. |
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What are the 6 Roentgen signs?
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size
shape number location margination opacity |
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What types of errors can be made in interpreting radiographs?
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errors of searching or scanning: result when reader fails to search image in systemic fashion & completely misses a lesion
-incl. tendency to overlook lesions located at periphery of rad satisfaction of search error: occurs when reader has preconceived ideas regarding what should be found -once reader has assessed rad for preconceived conclusion, becomes content that rest of rad is normal & stops searching recognition error: abnormality is identified but is either not taken into account in final analysis or is given too much weight & a misinterpretation results decision making errors: involve how radiographic info is interpreted & which abnormalities are assumed to be important egocentric errors: can be avoided by NOT reviewing rads in a sterile single person environment & seeking 2nd opinions |
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What are some things you should always do when interpreting radiographs to streamline the process?
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-review all rads in appropriate environment
-hang rads the same way each time -ensure that all views have been made -evaluate patient positioning -evaluation radiographic technique -evaluate for other technical errors & artifacts that may hinder interpretation -continuously review normal radiographic anatomy present on rads |
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How can the patient signalment, hx, & PE be used when interpreting radiographs?
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-clinical signs often precede radiographic changes
-even though rads are normal, rapid changes could develop & would be apparent if repeat rads where made w/in a short period -assessment of how patient is responding to therapy can be done using sequential rads |
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What are some ways to tell if a radiograph being interpreted is normal?
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use reference books
build a collection of normal rads radiograph opposite limb rely on experience get help |
