VT120 reading radiology

The Discovery of X-Rays

• X-rays were discovered by German scientist Wilhelm Conrad Roentgen in 1895.
• Roentgen was in his laboratory setting up experiments for the next morning when he observed a platinocyanide plate glowing a few feet away from his work area.
• His curiosity led him to investigate the cause of the glow, ultimately leading to the development of the field known as diagnostic imaging.
• Roentgen named the radiation “x-rays” due to their unknown characteristics.
• He was also the first to patent his discovery at a registry office.
• Through his experiments, he listed 12 unique properties of x-rays (see Table 1.1).

Table 1.1: Roentgen's List of Unique Properties of X-Rays

Properties of X-Rays

• Invisible: Cannot be seen, heard, or smelled.
• Electrically Neutral: Carry neither positive nor negative charge.
• No Mass: Do not possess mass or weight.
• Travel at Speed of Light: Move at a speed of approximately $186,000$ miles/second (or $3 imes 10^8$ meters/second) in a vacuum.
• Cannot Be Focused by a Lens: The beam does not change when passing through a lens.
• Form a Polyenergetic Beam: A mix of different photon energies is present in one exposure. The term peak kilovoltage (kVp) refers to the maximum energy in one exposure.
• Produced in Varying Energies: Diagnostic imaging typically uses energies from 25kV to 125kV, with 25-40kV used for specialized imaging.
• Travel in Straight Lines: Individual photons move in a divergent beam from the x-ray tube.
• Cause Fluorescence: Certain substances fluoresce when exposed to x-rays which amplifies the effect of x-ray on film using intensifying screens.
• Producing Chemical Changes: X-rays can penetrate matter or be absorbed by it, creating images on radiographic and photographic films.
• Absorb or Scatter: X-rays interact with body tissues, causing scattering or secondary radiation as a result of photon interaction with matter.
• Damage to Living Tissue: Can cause chemical and biological damage through excitation and ionization (removal of electrons) of atoms comprising cells.

Elements and Atomic Theory

• An element is the smallest particle of a substance, arranged on the Table of Elements to aid in understanding atomic nature.
• Atoms mainly consist of empty space. The smallest particles of elements are called atoms, which have a nucleus of protons (positive charge) and neutrons (neutral charge), surrounded by negatively charged electrons.
• Electrons orbit the nucleus, held in place by the positive charge of protons and their own negative charge.
• Electrons are placed in specific rings around the nucleus; as the number of protons increases, corresponding increases in electrons are seen, sometimes resulting in electrons leaving their orbits (i.e., boiled off during x-ray production process).
• Thermionic emission: When the cathode is heated, electrons are boiled off, marking the start of x-ray production.

Matter and Energy

• Every element has substance either in the form of matter (mass) or energy.
• Matter: Characterized by mass and weight, influenced by gravity.
• Energy: Defined by movement. Matter can become energy and vice versa, following the law of conservation (neither can be created or destroyed but can change in form).
• Related Equation:
  • Dr. Einstein’s formula: $E = mc^2$
  • Where E = energy, m = mass, c = speed of light.

Application Information

• The production of x-rays relies on tungsten wire within the cathode. When heated, electrons are emitted and drawn across to the anode utilizing thermionic emission.

The Electromagnetic Spectrum

• Various forms of energy exist, including mechanical, chemical, thermal, nuclear, electromagnetic, and electrical.
• In imaging, the focus is on electrical and electromagnetic energy.
• Visible light and radiation portions of the electromagnetic spectrum manifest energy in differing ways.

The Dual Nature of X-Rays

• Wave and Particle: X-rays can behave as waves or as photons (particles of energy).
• Photon: The smallest quantity of electromagnetic radiation, traveling in waves at the speed of light.

Energy as Wavelengths and Frequencies

• Wavelength represents distance between crests and troughs of waves.
• Frequency: The number of waves that pass a point in a set time interval, related to the current and voltage settings of the x-ray generator.
• Inverse relationship between wavelength and frequency: as wavelength increases, frequency decreases.

Energy as Particles

• Photons lack mass or charge but interact with matter like particles.
• The energy of a photon can be quantified mathematically, following the direct proportional relationship between frequency and energy: if frequency increases, the photon energy increases.

Summary

• Roentgen's discovery of x-rays in the late 1800s established characteristics.
• The electromagnetic spectrum categorizes energy forms by wavelength, with x-rays positioned high on the scale.
• X-rays demonstrate dual characteristics as waves and particles. The line focus principle explains how x-ray direction is influenced by the anode's bevel angle.
• X-ray Circuit Components: Four main criteria for proper x-ray production: power, adjustable selections, unidirectional flow, and free electrons generation.
• X-Ray Tube Design: The x-ray tube comprises a cathode and anode.

The Cathode

• The cathode typically has two tungsten filaments for different exposure needs.

Filaments

• Large filament (1.4mm wide, 1cm length): for larger body parts.
• Small filament (0.7mm wide, 0.75mm length): for detailed radiography work.

Thermionic Emission and Space Charge

• Filaments, upon heating, produce electrons via thermionic emission leading to the development of a space charge effect.

The Anode

• The anode indicates energy absorption from electrons. X-ray production occurs primarily at the target area known as the focal spot.
• Varieties of anodes: Rotating (used in small animal units) and stationary (utilized in portable units).

Rotating Anodes

• Mounted on stem with moving mechanisms to dissipate heat over a larger area, crucial for high-powered x-ray machines.

Stationary Anodes

• Commonly made of copper, with tungsten to absorb heat. Used when mobility isn't necessary.

Anode Heel Effect

• Explains unequal distribution of x-ray intensity: more intense on cathode side than anode side.

Tube Rating Chart

• Outline limits of exposure time based on kVp and mA settings to prevent tube damage. Important for large patients or outdated machines.

Scatter Radiation

• Scatter radiation decreases image quality and contributes to technician exposure. Controlled by collimation and proper kVp settings.

Types of X-Ray Units

• Types of x-ray units in veterinary practice include portable, mobile, and stationary systems, used for varied patient sizes and locations.
• Portable Units: Ideal for on-site use, lighter but with limited mA and kVp.
• Mobile Units: Medium-powered, often used in mixed practices.
• Stationary Units: More powerful, integrated into veterinary hospitals for diagnostic operations.

Producing X-Rays

• Factors: mA, kVp, exposure time, and FFD.
• Importance of optimizing technical factors for diagnostic quality.

Exposure Factors

• Milliamperage (mA): Controls quantity of x-rays produced.
• Kilovoltage (kVp): Impacts energy of the x-ray beam and contrast. Higher settings lead to darker images, while lower settings provide higher contrast. Factor for anatomical thickness considered in exposure settings.
• Focal Film Distance (FFD): Distance impacts exposure and detail. Changes in FFD require adjustments in mAs settings to maintain image quality.
• Grids: Used to reduce scatter radiation and improve image quality; can absorb some primary x-ray but are necessary when thickness exceeds 10 cm.

Technique Chart

• Provides standardized exposure factors based on anatomical thickness to produce quality radiographs without unnecessary exposure.

Capturing the Image

• Two modalities: film screen and digital imaging.

Film-Screen Systems

• Cassettes and intensifying screens enhance film sensitivity and reduce radiation exposure.
• Screen speed influences radiation dose and image quality. Each type of film and screen is compatible for effective imaging.

Darkroom Techniques

• Proper darkroom setup essential for exposure preparation and film processing.
• Equipment must be maintained for optimal function, especially with automatic processors.

Digital Radiography

• Includes both computed radiography (CR) and digital radiography (DR) methods, allowing efficient storage and retrieval of images.

Radiation Safety

• Careful adherence to safety practices required to protect staff and patients from excess exposure.

Regulations and Practices

• Understanding dose limits, monitoring exposure, and utilizing protective practices are critical to ensuring safety standards in the veterinary environment.
• PPE and shielding regulations, including leaded aprons and thyroid shields, are vital in minimizing radiation exposure.

Personal Monitoring and Protection Officer

• Dosimeters record exposure levels. A designated radiation protection officer in every veterinary facility ensures compliance with safety and operational standards.

Patient Preparation and Restraint

• Proper techniques are crucial for obtaining quality images while minimizing discomfort and risk to both patient and technician.

Radiographic Contrast Agents

-Positive Contrast Media, like barium sulfate and organic iodides, enhance visualization of structures. Negative contrast agents consist of gases that provide intrinsic challenges.

Endoscopy and Alternative Imaging Modalities

• Specific benefits within veterinary laboratories, allowing for non-invasive diagnostic capabilities across various species.

Ultrasound and CT Imaging

• These modalities extend the reach of diagnosis through advanced imaging techniques, providing more significant surgical and medical insights for veterinary care.

Overall Technician Note

• Proper education and care of imaging equipment assures smooth operations and reduces risks associated with radiation handling and usage in veterinary practices, leading to better diagnostic works.