vet-120 diagnostic imaging
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DESCRIPTIONVET-120 Diagnostic Imaging. Course Set-up. 5 Lessons (Webinars) 5 Lesson Exams Final Proctored Exam Required Reading Diagnostic Imaging Study Guide Radiography in Veterinary Technology (Lavin 4 th edition). Studying for Exams. Make copy of Lesson PowerPoints - PowerPoint PPT Presentation
Course Set-up5 Lessons (Webinars)5 Lesson ExamsFinal Proctored ExamRequired ReadingDiagnostic Imaging Study GuideRadiography in Veterinary Technology (Lavin 4th edition)
Studying for ExamsMake copy of Lesson PowerPointsTake excellent notes during WebinarsRead & highlight Assigned Readings in Study Guide & Lavin bookPerform Self Checks in Study GuideLearn the Glossary at the beginning of each Chapter in Lavin bookStudy Key Points & Review Questions at end of each Chapter in Lavin book
Lesson 2 Producing a Radiographic Image
Glossary Terms Page 36
The 4 Exposure FactorsMilliamperage (mA)Time (S)Kilovoltage (kVp)Distance (SID)
The 4 Exposure FactorsExposure factors are THE KEY to taking good quality diagnostic x-raysDefinition Machine settings that a technician can adjust on the machine to take diagnostic x-raysSIBKIS when it comes to changing exposure factors!
Milliamperage (mA)Figure 4-1, Page 36Amount of electrons to produce x-raysFundamental Use the highest mA your machine can doAllows you to use much lower time settingsLess exposure time to x-raysThe higher the mA, the more exposed your film will be (the DARKER it will be) if all other exposure factors are kept the same
Exposure Time (S)The longer the exposure time, the greater the number of x-rays producedThe longer the exposure time, the greater the exposure to scatter radiationInverse relationship to mABenefits of shorter exposure timesLess movement on x-ray (thoracic films)Technician safety
Kilovoltage Peak (kVp)Figure 4-4, Page 38Speed of electrons used to create x-raysQuality of x-rayNot faster x-rays, but more penetratingAffects both exposure (darkness) of film, and contrast of filmSantes Rule (2 X thickness of body part) + 40 = kVp
CalipersFigure 4-5, Page 38 DefinitionA tool used to measure the thickness of a body part to be x-rayedUse centimeters (cm), not inchesIf in between numbers latitude
kVp rangeExposure latitude (kVp)40-50+270-80+490-100+6
Kilovoltage SummaryIt affects both contrast and exposureIncreased kVp more penetrating x-raysIncreased kVp increased scatter radiationIncreased kVp decreased contrast (leading to more latitude)
Milliamperage and TimeMilliamperesExposure timeFormula mAs = mA X sExamples same mAs, different mASame darkness (exposure)
Distance (SID)Source-image distance (SID)Aka Focal-film distance (FFD)Should be 40 inches for both table top technique and grid techniqueInverse Square Law Figure 4-6, Page 39Definition KISS Fundamental distance should always stay constant if possible
Greater Distance = Less Shadows
Greater Distance = Less Intensity (Exposure)Figure 4-6, Page 39
Review of X-ray ProductionFigure 4-7 on page 40X-ray tube partsPrimary vs. secondary radiationExposure factors
Glossary Terms Page 44
Radiographic QualityDefinitionHow easily details can be seen on an x-rayHow sharp the details are
Radiographic Quality FactorsRadiographic DensityRadiographic ContrastExposure FactorsScatter RadiationGrids
Radiographic DensityDefinition amount of darkness (exposure) in x-ray filmWhen looking at a film for exposure, look at the body part you are interested inWhat causes density, you ask? ---
Densities of Various StructuresSubject densities: 1, Air. 2, Fat. 3, Water. 4, Bone. 5, Metal. Air is least dense, allowing x-rays to penetrate and expose the film. Metal is the most dense, absorbing most of the x-rays and allowing only a few to penetrate, exposing the film.
Factors Affecting Radiographic DensityAll 4 exposure factorsFigure 5-2 on page 46Same mAs (exposure), different thickness of body partWhite structures on x-raysRadio-opaque.. Why?Black structures on x-raysRadio-translucent.. Why?
Density on X-raysFigure 5-3, Page 47
How is the Exposure on This X-ray?Overexposed (Figure 5-7 on page 49)Body parts too darkWhy? Under-exposed (Figure 5-6 on page 48)Body parts too lightMore common than overexposedCorrect exposure (just right!)
Overexposed Film (Too Dark)
Underexposed Film(Too Light)
Just Right, Goldilocks!
Underexposed or Overexposed?
Underexposed or Overexposed?
Underexposed or Overexposed?
Radiographic Contrast DefinitionThe density differences between 2 adjacent areas of an x-rayHigh contrast (short scale)Low contrast (long scale)Just like exposure, look at body parts (not background) on film
High Contrast vs. Low ContrastTable 5-1, Page 46
High Contrast X-raysLots of black and white on the film with very little shades of grayBone x-rays should be high contrast
Low Contrast X-raysThe film has black, white, and lots of shades of gray in betweenUsually soft tissue x-raysLatitude
Factors Affecting Radiographic ContrastkVp Relationship of contrast and kVp (Table 5-1 on page 46)***LatitudeSubject contrastDifference in density between 2 body partsDepends on thickness & density of part (Table 5-2 on page 46)
Exposure Factors and X-ray QualitymAskVpSID
Digital Control Panel with Exposure Factors
Milliamperage-Seconds (mAs)Affects density (darkness, exposure) onlyDoes not affect contrast
Kilovoltage (kVp)Affects both contrast and densityIncreased kVp causes increased scatter radiationIncreased kVp causes decreased contrast, which leads to more latitudeSoft tissue x-rays
Distance (SID)Affects density (exposure, darkness) onlyDoes not affect contrast
Scatter RadiationDefinitionSecondary radiation formed as a result of objects in the path of the primary beamMainly originates from the patient, but could come from increased kVpFogs the filmPotentially damages RVT!!!
Backscatter Definition When primary beam strikes patient, table, tray, or floor. scatter radiation bounces back to patient, film, and you!Therefore GLOVE UP, OR ELSE!
Grids Definition Device placed between patient & x-ray filmDesigned to absorb scatter radiationComposed of lead stripsAligned so that most of primary beam can get through them, but all secondary radiation is absorbedFound under table, usually permanently mounted
Grid Under Table
Figure 5-11, Page 50
Definition Relation of height of the lead strips to distance between themFigure 5-13 on page 51Example 10:1So what does it mean?
Grid FactorDefinitionAmount that mAs must be increased if a grid is usedExample grid factor of 2
Grid PatternsFigures 5-14 & 5-15 on Pages 51 & 52Linear gridsCrossed gridsFocused gridsGrid linesMovable gridsPotter-Bucky Diaphragm (Figure 5-18 on page 53)
Care of GridsLeave them aloneExpensive and delicate
To Use a Grid or Not?Grid TechniqueTable Top Technique
Grid TechniqueCapture of scatter radiationCaptures some of primary beam alsoLess foggingHigher exposure factors neededGenerally used for larger dogs & cats
Table Top TechniqueAnimal closer to the filmLower exposure factors needed Less shadowingFigures on page 55Object-Film Distance (OFD) lowerGenerally used for smaller animals/extremities
Table Top Less Shadowing
Glossary Terms Page 60
What Are Image Receptors?Definition Tools used to capture invisible x-rays in such a way that they can be seen with the naked eye
Types of Image ReceptorsRadiographyXeroradiographyComputed TomographyNuclear Scintigraphy
RadiographyLight-sensitive film in a light-proof cassetteFilm is sandwiched between 2 intensifying screens in this cassette95% of exposure on film due to light emitted on these screens!Only 5% from x-rays themselves
The Cassette Definition Lightproof encasement designed to hold x-ray film, with intensifying screens in close contact with film
Types of Cassettes
Cassette CareHandle with care! Or ELSE!
Some physical abuse in large animal practiceFilm-screen contact a MUSTCleaning cassettes regularly with mild soap & water
Intensifying ScreensDefinition Sheets of luminescent phosphor crystalsWhen these phosphor crystals are struck by x-rays they fluoresce2 screens per cassetteRequires less radiation exposure (mAs)~95% of exposure on film due to light from intensifying screens!
Cassette with Screens
Desired Properties of ScreensHigh level of x-ray absorptionHigh x-ray to light conversionLittle or no afterglow
AfterglowDefinition tendency of a phosphor to give off light after x-ray production has stopped
Intensifying Screen AnatomyFigure 6-5 on page 632 screens per cassette4 layersPlastic base support layer, tight to cassetteReflective layer thin Phosphor crystal layerLayer that fluorescesProtective coat thin, tight to film
Phosphor TypesThomas Edison 1896Calcium tungstateHigh x-ray absorptionStill used todayRare earth phosphors 1972ExpensiveGreat x-ray to light conversionNeeds a special type of film
Rare Earth Screens