Diagnostic Imaging Notes
Introduction to Diagnostic Imaging
VTT 224 Diagnostic Imaging
PIMA MEDICAL INSTITUTE
References
Clinical Textbook for Veterinary Technicians (CTVT), 9th or 10th Edition- Chapter 16
Lavin’s Radiography for Veterinary Technicians (LRVT) 6th or 7th Edition- Chapters 1-9
Objectives
Discuss health risks associated with radiographic procedures and safety procedures to minimize risks. This includes understanding the ALARA principle (As Low As Reasonably Achievable) to minimize radiation exposure.
Describe preparation and maintenance of imaging site, radiographic equipment, and darkroom equipment. Proper maintenance ensures image quality and safety.
Describe types of intensifying screens and film speeds. Different screens and speeds affect image resolution and radiation dose.
Describe processing of exposed films to create diagnostic radiographic images with an automatic processor. Proper processing is crucial for optimal image quality.
Understand how to appropriately label, file, and store radiographs. Accurate labeling and proper storage are essential for future reference and legal purposes.
X-Rays
X-rays are a form of electromagnetic radiation used to produce an image. They are part of the electromagnetic spectrum with high energy and short wavelengths.
Radiograph is the image produced by the x-rays. It represents the varying densities of tissues in the body.
X-ray machine functionality:-
Electrons are fired at a target (usually tungsten) to produce x-rays and heat. High voltage is applied to accelerate electrons.
X-rays are focused into a controlled beam using collimators to reduce scatter radiation and improve image quality.
X-Rays & Chemistry
E=mc^2: Energy (E) equals mass/matter (m) times the speed of light squared (c^2). This equation illustrates the relationship between energy and mass.
Mass can be changed into energy and vice versa; neither can be created or destroyed, only changed in form. This principle is fundamental in understanding how x-rays are produced.
Element: smallest particle of a substance. Elements are the building blocks of matter.
Atom: smallest particle of any element. Atoms consist of protons, neutrons, and electrons.
Nucleus contains protons (+/- neutrons). Electrons orbit around the nucleus in specific energy levels.
Electrons can be “boiled off” their orbit around an atom if enough heat is applied. This is the process of thermionic emission, crucial for x-ray production.
X-Rays
The electromagnetic spectrum covers different energies. It ranges from radio waves to gamma rays.
Electromagnetic and electrical energy are used for x-ray technology. X-rays are high-energy photons.
In vet med, the field primarily deals with a specific range of energies. This range is optimized for imaging anatomical structures.
X-rays are very close to gamma rays in the electromagnetic spectrum. Both are high-energy and can penetrate tissues.
Properties of X-Rays
Invisible
Electrically neutral
Have no mass
Travel at the speed of light in a vacuum (3 x 10^8 m/s)
Cannot be focused by a lens; collimators are used instead
Form a polyenergetic (heterogenous) beam, meaning they consist of photons with varying energies
Useful range for DI is 25-125 kV (kilovolts)
Travel in straight lines
Cause fluorescence in certain substances- Effect of radiation on an intensifying screen
Can cause chemical changes to occur in radiographic and photographic film, leading to image formation
Can be absorbed or scattered by tissues in the body & can produce scattered/secondary radiation; this is why lead shielding is essential
Can cause chemical and biological damage to living tissue- USE PPE!!!
X-Rays
Energy can be expressed as waves or particles
Waves-
Wavelength: Distance between peaks of a wave. Shorter wavelengths have higher energy.
Frequency: Number of waves passing through a given unit of time. Measured in Hertz (Hz).
Important for penetration into tissues and time needed to make an x-ray.
Wavelength is inversely related to frequency: λ = c/f (λ = wavelength, c = speed of light, f = frequency)
Waves have height (amplitude) and move at the speed of light
Particles-
Photon: energy created when an electron is “boiled off” in the cathode- Smallest amount of electromagnetic radiation
They have no mass or electrical charge and interact with matter as though they are particles.
The photons energy is directly proportional to frequency- Better penetration E = hf (E = energy, h = Planck’s constant, f = frequency)
X-rays
Filament superheated in cathode (overall -)
Electrons “boil off” the outer layer of their atoms through thermionic emission
kVp will give the energy of the electrons- kVp=high frequency/low wavelength highly penetrating x-rays. Higher kVp increases the speed of electrons and the energy of x-ray photons.
Electrons slam into the anode and produce energy or photons. This interaction generates x-rays (bremsstrahlung and characteristic radiation) and heat. Most of the energy is converted into heat.
X-Rays: Radiation Safety
X-rays can alter animal tissues (including humans) either temporarily or permanently
Damage may be repaired without incident- Most cellular damage is sucessfully repaired in the body
Damage may be repaired with errors- Can lead to risk of cancer, birth defects, etc.
Damage may be lethal/lead to tissue damage- Cataracts, hypothyroidism, etc.
X-Rays: Radiation Safety
Need to protect ourselves and our patients from excess radiation. ALARA (As Low As Reasonably Achievable) principle is crucial.
Methods of protection:-
Personal Protective equipment (PPE)
Radiation Monitoring using dosimeters
Specialized x-ray machine components like collimators and filters
Fewest required exposures to minimize radiation dose
HANDS FREE RADIOLOGY
X-Rays: Radiation Safety
Radiation units-
Measured radiation- The dose measured by service personnel calibrating your x-ray unit
Was the Roentgen (R), now is the air Kerma (Gya). 1 Gya = 100 rads
Absorbed dose- The amount of radiation absorbed per unit of mass (not monitored in DI b/c of minimal effects)
Was the radiation absorbed dose (RAD), now is called gray (Gy). 1 Gy = 100 rads
Dose equivalent- The unit measured on dosimeters
Was the radiation equivalent Man/mammal (REM), now is called the sievert (Sv). 1 Sv = 100 rem
X-Rays: Radiation Safety
Maximum Permissible Doses-
Whole body- 50 mSv per year
Skin/extremities- 500 mSv per year
Eye/lens- 150 mSv per year
Pregnancy-total dose should not exceed 0.5 mSv per month!
Under 18-should not be taking rads!
X-Rays: PPE
Lead shielding-
Gown/apron (0.5 mm lead equivalent)
Thyroid shield (0.5 mm lead equivalent)
Gloves (0.5 mm lead equivalent)
Cap
Glasses
X-Rays: PPE
Lead apparel should be
Stored properly to prevent cracking and damage, extending their lifespan and effectiveness.
Radiographed at least annually to check for damage (cracks) that may compromise protection. Damaged PPE should be replaced immediately.
Other safety factors
Chemical Hygiene
Adequate ventilation and use of PPE when handling chemicals in the darkroom or automatic processor.
Proper disposal of chemicals to minimize environmental impact.
Imaging site & equipment preparation
Cleanliness:
Keep the imaging room and equipment clean to reduce the risk of contamination and artifacts on radiographs.
Regularly clean the cassette and intensifying screens to remove dust and debris.
Maintenance:
Schedule regular maintenance for the X-ray machine and processor to ensure they are functioning correctly.
Check cables, connections, and filters for wear and tear.
Darkroom
A darkroom is a completely dark room where x-ray film can be handled and processed without exposure to light.
Light-tight:
Ensure the darkroom is entirely light-tight to prevent film fogging.
Check for and seal any light leaks around doors, windows, and vents.
Darkroom equipment
Safelight:
Use a safelight with the correct filter (usually red or amber) to provide minimal illumination without exposing the film.
Position the safelight at the appropriate distance from the work surface.
Manual processing versus automatic processor
Manual Processing involves developing, rinsing, fixing, washing, and drying the film in separate tanks.
Automatic Processing uses a machine to perform these steps in a controlled and consistent manner.
Intensifying Screens
Intensifying screens are located inside the cassette and convert x-ray energy into visible light, which exposes the film.
Types:
Rare earth screens are more efficient at converting x-rays to light, reducing the radiation dose needed.
Calcium tungstate screens are older and less efficient but still used in some practices.
Film speed
Film speed refers to the sensitivity of the film to light and radiation. It affects image resolution and the amount of radiation required.
Film Types
Blue-sensitive film is designed to be exposed by blue light emitted from certain intensifying screens.
Green-sensitive film is designed to be exposed by green light emitted from rare earth intensifying screens.
Radiographic Film Composition
Base: Flexible support layer.
Emulsion: Radiation and light-sensitive layer containing silver halide crystals.
Supercoat: Protective layer over the emulsion.
Film artifacts
Film artifacts are unwanted marks or blemishes on a radiograph that can interfere with diagnosis.
Types of film artifacts
Pressure marks
Scratches
Fingerprints
Static electricity
Chemical stains
General Steps to Developing Film
Developing: Converts exposed silver halide crystals to black metallic silver, creating the visible image.
Rinsing/Stop Bath: Removes developer and stops the developing process.
Fixing: Removes unexposed silver halide crystals, making the image permanent.
Washing: Removes all residual chemicals.
Drying: Removes water and prepares the film for viewing and storage.
Digital Radiography (DR)
Digital Radiography (DR) systems capture X-ray images directly using digital detectors, eliminating the need for film and chemical processing.
Computed Radiography (CR)
Computed Radiography (CR) uses a cassette with an imaging plate that stores the X-ray image. The cassette is then run through a reader that converts the image to digital format.
Advantages of Digital Radiography
Immediate image availability
Reduced radiation exposure
Image manipulation and enhancement
Easy storage and retrieval
Elimination of film and processing costs
Disadvantages of Digital Radiography
High initial cost
Potential for image manipulation (ethical considerations)
Dependence on technology and power
PACS
PACS (Picture Archiving and Communication System) is a medical imaging technology that provides storage, retrieval, distribution, and presentation of medical images.
DICOM
DICOM (Digital Imaging and Communications in Medicine) is a standard for handling, storing, printing, and transmitting information in medical imaging.
Labeling & Filing
Label each radiograph with patient information, date, and clinic details.
Store radiographs in a cool, dry place, away from light and radiation.
Labeling and Filing:
Patient Identification