Download Radiology basics → Making X-rays Digital Imaging Radiation Safety

07/10/2014
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James Montgomery, DVM, DACVR
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Know about different types of digital imaging systems
Have a refreshed knowledge of radiation safety and
radiographic technique
Understand why improved quality control at image
acquisition can improve report quality and turnaround
time
Know the benefits that teleradiology can provide to your
practice
Radiology basics  Making X-rays
Digital Imaging
Radiation Safety
Image Quality
Goldilocks histories
Teleradiology services
07/10/2014
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A little simplified, but for our purposes:
mAs
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Higher mA = MORE x-rays
Longer exposure time –
 Higher radiation dose, greater risk of motion
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kVp
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Higher kVp = more POWERFUL x-rays
 Penetrates tissue better
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Very important to have good quality radiographs
Radiology is hard enough with good images…
 Bad images just make all of our lives harder!
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 Less confident in your diagnosis
 Decreased utility of images as a diagnostic tool
 Waste of money
 Waste of time
 Wasted x-ray photons!
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General Practice
Radiography
 Ultrasound - becoming more common
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Larger private/Academic
Computed Tomography (CT)
Magnetic Resonance Imaging (MRI): larger private/academic
 Nuclear Scintigraphy
 Fluoroscopy
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PET-CT/PET-MRI: Mainly academic/research
X-Rays
• Radiography
• Fluoroscopy
• Computed Tomography (CT)
Electromagnetic Radiation
• Magnetic Resonance Imaging (MRI)
Sound Waves
• Ultrasound
Gamma (mostly) Radiation
• Nuclear Scintigraphy
• PET-CT/PET-MRI
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Radiographs  opacities: radiopaque, radiolucent
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A good general diagnostic tool
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CT  attenuation: hyperattenuating, hypoattenuating
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Good for assessing bony structures
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Ultrasound  echogenicity, echotexture
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MRI  signal intensity
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Gas – fat – soft tissue – mineral – metal
Nuclear medicine  increased uptake/activity
Film-screen technology
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Some soft tissue detail – depends on relative opacities of adjacent
structures
In its twilight…
Digital
More and more practices are joining the digital age
 Less spatial resolution than film-screen, but better
contrast resolution
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Ability to manipulate the image
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Multiple people can view same study in multiple areas
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No physical file to store/locate
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Ease of sharing information/consulting
 Slight loss of spatial resolution compensated for by being able
to manipulate the image on the screen
 Magnify, pan, change contrast
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Increased workflow
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Depending on system…
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No need for a darkroom  decreased operating cost
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Generally higher quality images than film
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More tolerant of imprecise exposure settings
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Improves image with public/clients
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Picture Archiving and Communication System
Includes:
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Initial expense
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Increased IT needs
Need robust backup system
 Should have off-site backup storage
 Need to stay current with software updates
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Device(s) acquiring the images: radiography unit, ultrasound, etc.
 Local image storage server
 Workstations that can view the images stored on the server
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File format just like .jpg, .tif, .png, .pdf
Must have DICOM viewing software to view images
 eFilm, Clear Canvas, Osirix, vendor specific viewers, other free viewers are
available
 Any computer can be set up as a workstation
Local area network
 Off site backup image storage
 The DICOM image communication protocol (DICOM compliance)
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Digital Imaging Communications in Medicine
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Standardized for medical imaging so that a Canon DR plate, a
Toshiba ultrasound, an eFilm workstation and a Philips PACS
will all use the same image format and same communication
protocol via the internet.
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Need three components:
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AE Title: Name of the computer, server or imaging device
IP address: Each device has its own number
Port number: Communication port
Your vendor will help you set this up so that everything
in your PACS communicates properly.
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Made up of pixels (Picture Elements)
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Smaller the pixel, the better the resolution
Smaller the pixel, more pixels per image  larger file
size
 Each pixel is assigned a shade of gray (or colour)
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300 PIXELS PER INCH
300 pixels per inch
75 pixels per inch
Pixels 16x larger
75 PIXELS PER INCH
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Lossless
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Lets the image file be broken into smaller components for
transmission and then put back together again exactly as it
was.
Lossy
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Compression program alters the individual pixel values and
discards “unnecessary” bits of information. Makes the file size
smaller and is irreversible on the receiving end.
Not recommended for diagnostic purposes.
Image source: http://www.verypdf.com/pdfinfoeditor/jpeg-jpeg2k-1.png
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Direct digital (DR)
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Computed radiography (CR)
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Can be used with existing x-ray machine
Most expensive system
Most current plates are wired
Wireless plates are available
Improved workflow
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Charge-coupled device (CCD)
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Image viewable in ~3 sec
Next exposure in 5-15 sec
+/- best image quality
Almost unlimited use
http://www.idshealthcare.com/hospital_management/us/Canon_Medical_Systems/Con
sumer_Imaging_Equipment/35_0/g_supplier.html
07/10/2014
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Can be used with existing x-ray machine
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Requires a laser reader
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Doesn’t improve workflow over film/screen
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Unless you have a multi-cassette reader
~1 min processing time
Have to buy x-ray machine as a
unit
Fluorescent screen converts x-ray
photons to light photons
Light captured by CCD digital
camera
Prone to image artifacts
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“It’s all about the lens…”
Zero portability
Lower image quality
Cheapest option
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Good image quality
Not light sensitive
Good portability
Plate is ‘activated’ for many
hours
Less expensive than DR
Plates wear out and have to be
replaced
http://www.flatpaneldr.com/?p=631
X-Rays
Intensifying
screen
Film blackness
(optical density)
Correctly exposed
Fiberoptic
Light collection
Focusing
lenses
CCD chip
Exposure
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Overexposed
Film blackness
(optical density)
Film blackness
(optical density)
Underexposed
Exposure
Exposure
Film/Screen = narrow margin of error
0.5 mAs
4.0 mAs
1.0 mAs
2.0 mAs
8.0 mAs
16.0 mAs
Adapted from Thrall, ed. Textbook of Veterinary Diagnostic Imaging, 6th ed
0.5 mAs
4.0 mAs
1.0 mAs
2.0 mAs
8.0 mAs
16.0 mAs
Adapted from Thrall, ed. Textbook of Veterinary Diagnostic Imaging, 6th ed
07/10/2014
70 kVp 1.5 mAs
70 kVp 6 mAs
0.5 mAs
2 mAs
4 mAs
Adapted from Thrall, ed. Textbook of Veterinary Diagnostic Imaging, 6th ed
There is a limit to
plate overexposure
‘The plate becomes
‘saturated’ and
anatomy disappears’
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Technique is not important with digital radiography 
FALSE
Radiation exposure is less with digital systems 
FALSE
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Because of increased exposure tolerance with digital there is a
trend towards “if in doubt, burn it out…”
Potential for reduced exposure because a less than optimal
radiographic technique can still give a diagnostic quality
image.
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Ultrasound, CT…MRI, yes, but not that common in
private practice yet.
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Particularly in the abdomen  normal radiographs may not =
normal abdomen
Great for imaging soft tissue
Real time imaging
Can see architecture of organs
Changes in echogenicity
Changes in echotexture
 Wall layering/Wall thickness
 Nodules within organs
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Upper range of human hearing – 20 kHz
Diagnostic ultrasound – 2-17 MHz
Based on the idea that sound passes through
tissues at a different velocity
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Sound waves sent out from transducer – bounce off
tissues and return to transducer
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Structures are placed in the image at different depths based on
the length of time of the round trip
Different structures absorb or reflect sound at different
intensities  different strength of returning sound waves –
represented as varying brightness in image
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Colour Doppler
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Power Doppler
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No directional or velocity information
Sensitive for detecting low blood flow
First developed in the 1970’s
Tomographic imaging
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Gives you velocity and direction of flow
Angle-dependent
No superimposition of structures
Excellent bone detail
Good soft tissue resolution
Excellent ability to manipulate the images
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Can reconstruct the raw data in any plane and in different
‘windows’ to emphasize bone or soft tissues
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Lung
Soft Tissue
Bone
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Naturally occurring:
Terrestrial
Soil and rocks contain
radioactive materials
 The sun
 Cosmic radiation
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Energy that is radiated or transmitted in the form of particles or
waves.
There is NO safe level of radiation exposure.
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Man Made
Nuclear reactor
Linear accelerators
 X-ray machines, etc.
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Depends on the energy of the radiation striking matter
With sufficient energy, it can physically knock out electrons from
atoms  Ionization
Radiation which can ionize atoms is Ionizing Radiation
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Ionizing radiation can break apart
water molecules to create free radicals
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H2O  H + OH
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OH + OH  H2O2
X-Rays, Gamma rays
Radiation lacking sufficient energy to ionize atoms is Nonionizing
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H2O2 is toxic
Ultrasound, MRI
Always wear lead apron, thyroid shield, and gloves
Never have gloves (or any body of your body parts!) in
the primary beam
Never just cover your hands with the gloves…
Collimate! – No dog-o-grams or cat-o-grams…
Remember ALARA
Use sedation so you aren’t in the room whenever
possible
http://www.aquasana.com/images/human.gif
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Effect of radiation on
rapidly reproducing cells is
the most pronounced
First trimester carries the
highest risk
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Radiation Doses Received from Some Familiar Activities
Event
Flight from LA to Paris
Thoracic radiograph
Apollo X astronauts’
moon flight
Radiation Dose Received
(mSv)
0.05
0.22
4.8
Population Group
Dose Limits: Over 5 Yrs
Dose Limits: Annual
Worker
100 mSv
50 mSv
Whole-mouth dental x-ray 9.1
Public
-
1 mSv
Exposure to accident at
Three Mile Island
Mammography
11.0
15.0
Barium enema
80.0
Heart catheterization
450.0
Reproduced from Thrall, Textbook of Veterinary Diagnostic Radiology, 5th ed
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Fundamental principle of radiation protection
Three Components:
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 Time
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 Distance
 Shielding
Limit the amount of time you are exposed
Use chemical restraint so technicians do not need
to be in the room for most radiographs
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We have very good, very safe drugs for sedation – USE
THEM!!!!
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Rotate personnel in room
Avoid repeat examinations
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Modern imaging system
Good processing technique
Personnel training
Accurate technique chart
Minimize patient holding
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Balance between dose and practice efficiency
Holding is not wrong if done correctly
X
Take advantage of the inverse square law!
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X
Intensity of radiation (x-rays/unit area) decreases with the square of the
distance from the source
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Doubling the distance reduces the x-ray intensity to 1/4th (1/2)2
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Tripling the distance reduces the x-ray intensity to 1/9th (1/3)2
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Do not hand-hold the x-ray machine or cassette
Use personal protective
equipment
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Distance very effective for radiation protection
Comes into play if you change the distance
between x-ray tube and patient  have to
calculate new mAs
Know the properties of the
type of radiation you are
working with so you can
choose the proper shield.
http://www.doh.wa.gov/ehp/rp/air/air-images/3%20What6.gif
07/10/2014
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Lead aprons
Must be properly cared for to preserve protective capability – hang them
up, don’t fold them
Gloves and gowns DO NOT protect from the primary beam
– only protect from scatter radiation
Gloves
Thyroid shield
Shielded glasses
Manually restrict beam to desired size
Decreases scattered radiation
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Use collimation – want 100% - 4 sided collimation
Increases image quality
Decreases personnel exposure
BAD
GOOD
07/10/2014
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What’s at stake
 Professional
reputation
 Employee health
 Your income
You could be sued