07/10/2014
James Montgomery, DVM, DACVR
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
A little simplified, but for our purposes: mAs
Higher mA = MORE x-rays Longer exposure time – Higher radiation dose, greater risk of motion
kVp
Higher kVp = more POWERFUL x-rays Penetrates tissue better
07/10/2014
Very important to have good quality radiographs Radiology is hard enough with good images… Bad images just make all of our lives harder!
Less confident in your diagnosis Decreased utility of images as a diagnostic tool Waste of money Waste of time Wasted x-ray photons!
General Practice Radiography Ultrasound - becoming more common
Larger private/Academic Computed Tomography (CT) Magnetic Resonance Imaging (MRI): larger private/academic Nuclear Scintigraphy Fluoroscopy
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
07/10/2014
Radiographs opacities: radiopaque, radiolucent
A good general diagnostic tool
CT attenuation: hyperattenuating, hypoattenuating
Good for assessing bony structures
Ultrasound echogenicity, echotexture
MRI signal intensity
Gas – fat – soft tissue – mineral – metal
Nuclear medicine increased uptake/activity
Film-screen technology
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
Ability to manipulate the image
Multiple people can view same study in multiple areas
No physical file to store/locate
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
07/10/2014
Increased workflow
Depending on system…
No need for a darkroom decreased operating cost
Generally higher quality images than film
More tolerant of imprecise exposure settings
Improves image with public/clients
Picture Archiving and Communication System Includes:
Initial expense
Increased IT needs Need robust backup system Should have off-site backup storage Need to stay current with software updates
Device(s) acquiring the images: radiography unit, ultrasound, etc. Local image storage server Workstations that can view the images stored on the server
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)
Digital Imaging Communications in Medicine
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.
07/10/2014
Need three components:
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.
Made up of pixels (Picture Elements)
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)
300 PIXELS PER INCH
300 pixels per inch
75 pixels per inch
Pixels 16x larger
75 PIXELS PER INCH
07/10/2014
Lossless
Lets the image file be broken into smaller components for transmission and then put back together again exactly as it was.
Lossy
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
Direct digital (DR)
Computed radiography (CR)
Can be used with existing x-ray machine Most expensive system Most current plates are wired Wireless plates are available Improved workflow
Charge-coupled device (CCD)
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
Can be used with existing x-ray machine
Requires a laser reader
Doesn’t improve workflow over film/screen
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
“It’s all about the lens…”
Zero portability Lower image quality Cheapest option
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
07/10/2014
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’
Technique is not important with digital radiography FALSE Radiation exposure is less with digital systems FALSE
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.
07/10/2014
Ultrasound, CT…MRI, yes, but not that common in private practice yet.
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
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
Sound waves sent out from transducer – bounce off tissues and return to transducer
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
07/10/2014
Colour Doppler
Power Doppler
No directional or velocity information Sensitive for detecting low blood flow
First developed in the 1970’s Tomographic imaging
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
Can reconstruct the raw data in any plane and in different ‘windows’ to emphasize bone or soft tissues
07/10/2014
Lung
Soft Tissue
Bone
Naturally occurring: Terrestrial Soil and rocks contain radioactive materials The sun Cosmic radiation
Energy that is radiated or transmitted in the form of particles or waves. There is NO safe level of radiation exposure.
Man Made Nuclear reactor Linear accelerators X-ray machines, etc.
07/10/2014
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
Ionizing radiation can break apart water molecules to create free radicals
H2O H + OH
OH + OH H2O2
X-Rays, Gamma rays
Radiation lacking sufficient energy to ionize atoms is Nonionizing
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
Effect of radiation on rapidly reproducing cells is the most pronounced First trimester carries the highest risk
07/10/2014
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
Fundamental principle of radiation protection
Three Components:
Time
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
We have very good, very safe drugs for sedation – USE THEM!!!!
07/10/2014
Rotate personnel in room Avoid repeat examinations
Modern imaging system Good processing technique Personnel training Accurate technique chart
Minimize patient holding
Balance between dose and practice efficiency Holding is not wrong if done correctly
X
Take advantage of the inverse square law!
X
Intensity of radiation (x-rays/unit area) decreases with the square of the distance from the source
Doubling the distance reduces the x-ray intensity to 1/4th (1/2)2
Tripling the distance reduces the x-ray intensity to 1/9th (1/3)2
Do not hand-hold the x-ray machine or cassette
Use personal protective equipment
X
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
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
Use collimation – want 100% - 4 sided collimation
Increases image quality Decreases personnel exposure
BAD
GOOD
07/10/2014
What’s at stake Professional reputation Employee health Your income You could be sued
