Classification, Diagnostic Imaging, And Imaging Characteriza
VET-120 Diagnostic Imaging
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Transcript of VET-120 Diagnostic Imaging
VET-120Diagnostic
Imaging
Course Set-up
5 Lessons (Webinars) 5 Lesson Exams Final Proctored Exam Required Reading
– Diagnostic Imaging Study Guide– Radiography in Veterinary Technology
(Lavin – 4th edition)
Studying for Exams Make copy of Lesson PowerPoints Take excellent notes during Webinars Read & highlight Assigned Readings
in Study Guide & Lavin book Perform Self Checks in Study Guide Learn the Glossary at the beginning of
each Chapter in Lavin book Study 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 Factors Exposure factors are THE KEY
to taking good quality diagnostic x-rays
Definition – Machine settings that a technician
can adjust on the machine to take diagnostic x-rays
SIBKIS when it comes to changing exposure factors!
Milliamperage (mA)Figure 4-1, Page 36
Amount of electrons to produce x-rays Fundamental – Use the highest mA
your machine can do– Allows you to use much lower time
settings– Less exposure time to x-rays
The 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 produced
The longer the exposure time, the greater the exposure to scatter radiation
Inverse relationship to mA Benefits of shorter exposure times
– Less movement on x-ray (thoracic films)– Technician safety
Kilovoltage Peak (kVp)Figure 4-4, Page 38
Speed of electrons used to create x-rays
Quality of x-ray– Not faster x-rays, but more penetrating
Affects both exposure (darkness) of film, and contrast of film
Santes’ Rule – (2 X thickness of body part) + 40 =
kVp
CalipersFigure 4-5, Page 38
Definition– A tool used to measure the thickness
of a body part to be x-rayed– Use centimeters (cm), not inches– If in between numbers…… latitude
Latitude
kVp range Exposure latitude (kVp)
40-50 +2
70-80 +4
90-100 +6
Kilovoltage Summary
It affects both contrast and exposure
Increased kVp more penetrating x-rays
Increased kVp increased scatter radiation
Increased kVp decreased contrast (leading to more latitude)
Milliamperage and Time Milliamperes Exposure
time Formula
– mAs = mA X s
Examples – same mAs, different mA– Same
darkness (exposure)
Distance (SID) Source-image distance (SID)
– Aka Focal-film distance (FFD)– Should be 40 inches for both table
top technique and grid technique Inverse Square Law –
– Figure 4-6, Page 39– Definition
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 Production
Figure 4-7 on page 40 X-ray tube parts Primary vs. secondary radiation Exposure factors
Radiographic Quality
Glossary Terms – Page 44
Radiographic Quality
Definition– How easily details can be seen on an
x-ray– How sharp the details are
Radiographic Quality Factors
Radiographic DensityRadiographic ContrastExposure FactorsScatter RadiationGrids
Radiographic Density
Definition – amount of darkness (exposure) in x-ray film
When looking at a film for exposure, look at the body part you are interested in
What causes density, you ask? ---
Densities of Various Structures
Subject 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 Density
All 4 exposure factors Figure 5-2 on page 46
– Same mAs (exposure), different thickness of body part
White structures on x-rays– Radio-opaque….. Why?
Black structures on x-rays– Radio-translucent….. Why?
Density on X-raysFigure 5-3, Page 47
Subject Density/Exposure
How is the Exposure on This X-ray?
“Overexposed” (Figure 5-7 on page 49)– Body parts too dark– Why?
“Under-exposed” (Figure 5-6 on page 48)– Body parts too light– More common than overexposed
Correct 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
Definition– The density differences between 2
adjacent areas of an x-ray High contrast (short scale) Low contrast (long scale) Just like exposure, look at
body parts (not background) on film
High Contrast vs. Low Contrast
Table 5-1, Page 46
High Contrast X-rays
Lots of black and white on the film with very little shades of gray
Bone x-rays should be high contrast
Low Contrast X-rays
The film has black, white, and lots of shades of gray in between
Usually soft tissue x-rays Latitude
Factors Affecting Radiographic Contrast
kVp – Relationship of contrast and kVp
(Table 5-1 on page 46)***– Latitude
Subject contrast– Difference in density between 2 body
parts– Depends on thickness & density of
part (Table 5-2 on page 46)
Exposure Factors and X-ray Quality
mAskVpSID
Digital Control Panel with Exposure Factors
Milliamperage-Seconds (mAs)
Affects density (darkness, exposure) only
Does not affect contrast
Kilovoltage (kVp)
Affects both contrast and density
Increased kVp causes increased scatter radiation
Increased kVp causes decreased contrast, which leads to more latitude– Soft tissue x-rays
Distance (SID)
Affects density (exposure, darkness) only
Does not affect contrast
Scatter Radiation
Definition– Secondary radiation formed as a result
of objects in the path of the primary beam
Mainly originates from the patient, but could come from increased kVp
Fogs the film Potentially 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 film– Designed to absorb scatter radiation
Composed of lead strips Aligned so that most of primary
beam can get through them, but all secondary radiation is absorbed
Found under table, usually permanently mounted
Grid Under Table
Figure 5-11, Page 50
Grid Ratio
Definition – Relation of height of the lead strips to distance between them
Figure 5-13 on page 51 Example – 10:1 So what does it mean?
Grid Factor
Definition– Amount that mAs must be increased
if a grid is used– Example – grid factor of 2
Grid PatternsFigures 5-14 & 5-15 on Pages 51 & 52
Linear grids Crossed grids Focused grids Grid lines Movable grids
– Potter-Bucky Diaphragm (Figure 5-18 on page 53)
Potter-Bucky Diaphragm
Care of Grids
Leave them alone Expensive and delicate
To Use a Grid or Not?
Grid TechniqueTable Top Technique
Grid Technique
Capture of scatter radiation Captures some of primary beam
also Less fogging Higher exposure factors needed Generally used for larger dogs &
cats
Table Top Technique
Animal closer to the film Lower exposure factors needed Less shadowing
– Figures on page 55– Object-Film Distance (OFD) lower
Generally used for smaller animals/extremities
Table Top – Less Shadowing
Image Receptors
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 Receptors
RadiographyXeroradiographyComputed TomographyNuclear Scintigraphy
Radiography
Light-sensitive film in a light-proof cassette
Film is sandwiched between 2 intensifying screens in this cassette– 95% 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 Care Handle with care! Or ELSE!
Some physical abuse in large animal practice
Film-screen contact a MUST Cleaning cassettes – regularly with
mild soap & water
Intensifying Screens
Definition – Sheets of luminescent phosphor crystals– When these phosphor crystals are
struck by x-rays they fluoresce 2 screens per cassette Requires less radiation exposure
(mAs)– ~95% of exposure on film due to
light from intensifying screens!
Cassette with Screens
Desired Properties of Screens
High level of x-ray absorption High x-ray to light conversion Little or no “afterglow”
Afterglow– Definition – tendency of a phosphor to
give off light after x-ray production has stopped
Intensifying Screen Anatomy
Figure 6-5 on page 63– 2 screens per cassette
4 layers– Plastic base – support layer, tight to
cassette– Reflective layer – thin – Phosphor crystal layer
• Layer that fluoresces
– Protective coat – thin, tight to film
Cassette/Screen/Film Anatomy
Phosphor Types
Thomas Edison – 1896– Calcium tungstate
• High x-ray absorption• Still used today
Rare earth phosphors – 1972– Expensive– Great x-ray to light conversion
• Needs a special type of film
Rare Earth Screens
Screen Speed – 2 FactorsFigure 6-8 on page 64
Phosphor crystal size Thickness of crystal layer
Screen Speed Ratings
Slow – small crystals– Increased exposure time– High definition; more detail; sharp– Not grainy
Medium High – large crystals
– Decreased exposure time– More grainy– Less detail
Screen Care Critical, as
they are so expensive
Inspect and clean regularly
Use commercial cleaner only
Chemical spills on the screen
Don’t Develop the Screens!!!
Fluoroscopy
Figure 6-11 on page 67 Definition – “Live x-rays” Main feature is the screen, as there is
no film Image viewed is exactly opposite of an
x-ray Recorded on TV screen Old hand-held units illegal in USA
“Me & My Dog Tighe”
Button from 1910!
X-ray Film
Purpose of film– Provide a permanent record
Creates a latent image until developed
Film AnatomyFigure 6-14 on page 69
Base Emulsion layer
– Gel layer– Phosphors located here
•Silver halide crystals
– Easily penetrated by developing solutions
Protective coating
Layers of X-ray Film
Latent Image
In emulsion layer Physical change in film When developed, chemical change
takes place to produce visible image Unexposed film that is developed
– Clear after processing Film totally exposed to light or x-
rays– Black after processing
Film Types
Screen film– Silver crystals more sensitive to light
than x-rays– Matching film with screens
Non-screen film– Exposed by direct action of x-rays– No loss of detail due to screens– Dental radiography
(Video from St. Petersburg VTP)
Non-screen Film
Cassette for Screen Film
Film SpeedPage 70
Same concept as screen speed Slow film (High detail) Medium film (Standard speed)
– Most widely used in veterinary practice today
Fast film (Ultraspeed film) Film latitude
– Narrow latitude film – high contrast film
Film Care Fundamentals
Gentle with film, especially loading cassettes in dark room
Film boxes – store on end– No pressure creases in film
Storage temperature– Cool, low humidity
Expiration date – rotate film boxes so oldest film used first
Loading Film in Cassettes
When loading a cassette, use both hands to avoid kink marks, and carefully place the film into the cassette. The cassette must be closed and latched gently.
Film Processing
Chapter 7
Glossary Terms – Page 74
Film Processing
A chemical reaction Latent (invisible) image on film
converted to the visible image that is seen on developed film
The Darkroom
Most important place for turning out consistent, high quality x-rays
Where the greatest number of errors are made in producing a “diagnostic x-ray”
KISS PPPPP
Qualities Of A Good Darkroom
Clean Organized
– Dry side– Wet side– All things back in their proper place
Lightproof – no cracks of light– Fogged film
Climate control – cool with low humidity
Organization Of The Darkroom
Figure 7-1 on page 75
Dry side – Film exchange in cassettes– No splashing here!
Wet side – Chemical processing of exposed films– Drying of films
Dry Side
No “wet” stuff here Cassette unloading & reloading Empty film hangers on wall Film storage bin
Wet Side
Developing tank– Thermometer for determining
temperature of developer Rinse bath – usually 4X the size of
other tanks Fixing tank Film drying
Light-proofing
Film fogging without this – Film phosphors react
to room light– Light-colored walls… Why?
• More safelight reflection
Safelight – < 15 watts, 4 feet away from work
area– Filter to eliminate blue & green
light (shorter wavelengths)
Safelights
Dark Room with Safelight
Film Exposed to Light
Film-Processing Techniques
Manual processing– 10 steps (pages 79-82)
Automatic processing– Figure 7-17 on page 83– Processor maintenance
Digital x-rays! KOOL!– Latent image developed inside
computer
Film-Processing Solutions
Developer Rinse Bath Fixer Wash bath Drying
Reticulation – mottling of film from different temperatures in the solutions
Preparing Film For Developing
Opening cassettes– Keep closed always!
Hanging film Reloading cassettes
– When?– How?
Be humble if you don’t know something! (OR ELSE!)
Unexposed Film Stored in Dark Room
Figure 7-2, Page 75
Reloading Cassettes
Developing Solution
Developing AgentsAcceleratorsPreservativesHardenersRestrainersSolvent
Developing Solution
Purpose – to convert latent image to visible image– Done by converting exposed silver
crystals on film to BLACK metallic silver
How long here? – 5 minutes at 68 degrees
Fahrenheit– KISS!
Developing Solution
Developing agents – think emulsion layer of film– Hydroquinone or phenidone (alkaline
pH)– Converts exposed silver grains to
black metallic silver on the film
Accelerators – KCO3 or NaCO3
– Increase activity of developer– Increase pH
Developing Solution
Preservatives – prevent oxidation Hardeners – in auto-processors
– Prevent swelling of emulsion layer Restrainers – limit developer
action on exposed silver grains Solvent – water
Rinse Bath
Purpose – to rinse excess developer off before fixing film– If film is not rinsed, alkaline
developer will neutralize acid fixer No “backwash”! Stops developing process Rinse in circulating water for 30
seconds Not found in auto-processors
Fixing Solution
Clearing (Fixing) AgentsPreservativesHardenersAcidifiersBuffersSolvent
Fixing Solution
Purposes – To remove unexposed silver crystals,
and undeveloped exposed silver crystals
– To harden (preserve) emulsion layer of film
How long in fixer?– Ideally, 2X developing time (10
minutes)
Fixing Solution
Clearing (Fixing) Agents – sodium thiosulfate or ammonium thiosulfate– “Clears” film– “Fixes” film
Preservatives – sodium sulfite
Fixing Solution
Hardeners – aluminum salt– Prevent excessive swelling of
emulsion layer– Shortens drying time
Acidifiers – accelerate action of other chemicals– Neutralize developer
Buffers – maintain pH of solution Solvent – water
Wash Bath
Purpose– Remove ALL chemicals from film
Circulating water – 20 to 30 minutes
Prevents fading and discoloration
Drying Films
It takes time! Careful with shortcuts
– Water streaks
Solution “Issues”
Solution replenisher– One 14X17 radiograph takes 60 cc’s
of developer into rinse bath– “Fill it up!”
Solution replacement – about every 30 days– How to tell when?– Change the fixer solution first! Why?
Biologic Growth
Bacteria, fungi, algae can grow in rinse bath
Slime on sides of tanks? Treat this or metal can corrode
Manual Processing – Key Points
KISS PPPPP Unloading cassette Loading film on hanger Developing film – lid on! Rinsing film – no “backwash”! Drying film – water marks on film Filing film – cut the edges
Auto Processing – Key Points
Figure 7-17 on Page 83 Same procedure, but higher
temperatures and specialized chemicals. Why?
No rinse between developing & fixing Chemical replenishment Processor maintenance
– Have a reliable service company
Silver Recovery – Fixer & Films
Why?– Environmental– Economic – 1 ounce of silver in 40-45
small films Where is the silver?
– Fixer solution– Old x-ray films
Methods for Fixer Solution Harvesting
Metallic replacement– Iron (steel wool)
Electrolyte recovery– 2 electrodes into fix tank
Chemical precipitation– Adding more chemical compounds
Film Identification Every x-ray needs to be properly
identified– Medical reasons– Legal reasons
What is the minimal information?– Name & address of veterinary
practice– Date (including year)– Patient identification (owner name,
patient name, etc.)
Film Identification Tools
Lead MarkersLead-impregnated Tape Photo-imprinting Label System
Lead MarkersFigure 7-20 on Page 86
Easiest tool to use Letters and numbers used Lead absorbs x-ray…… are letters
and numbers black or white on film?
Lead Markers
Lead-Impregnated TapeFigure 7-21 on Page 86
Disposable after use Write on tape with ball point pen
– This displaces the lead when making letters & numbers
What color are the displaced letters & numbers – black or white? Why?
Photo-Imprinting Label System
Figure 7-22 on Page 87
Uses lead blocker on outside of cassette along with a typed-up ID card with information for identifying x-ray
Also uses a photo-imprinter in dark room
Lead blocker keeps a small portion of x-ray film clear of radiation for the imprinter
Label for Photo-Imprinting System
Film Filing & Storage
Cut the corners (manual processing)
Side by side, chronologically– Alphabetical, by owner– By case number– By date
Store for 7 years legally– Or until patient dies?