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?