Introduction to SI Units and Atomic Structure

SI Units

• Standard units of measurement are length, mass, and time
• Mass is the amount of matter in an object, measured in kilograms
• Length is the distance light travels in a vacuum in 1/299792485th of a second, measured in meters
• Time is measured in seconds, relating to vibrations of cesium
• SI units were adopted by the 11th General Conference of Weights and Measures.
• There are 7 base SI units.

Matter and Energy

• Matter is the substance of all physical objects, has shape, form, and occupies space.
• Mass is the quantity of matter in an object.
• Weight is the force of gravity acting on an object.
• Substances have definite and constant composition.
• Elements are substances that cannot be broken down.
• Compounds are substances that can be broken down.
• The smallest particle of an element is an atom.
• The smallest particle of a compound is a molecule.
• Einstein's theory of relativity states matter and energy cannot be created or destroyed but can be converted from one to the other (E=mc²).

Atoms and Elements

• Z number is the number of protons in an atom, determining element classification.
• Changing the Z number changes the element.
• Changing the number of neutrons or electrons causes ionization, not a change in element, but can disrupt metabolic relationships.
• Atomic mass number is the total mass of protons and neutrons in an atom.
• Valence is an element's combining ability.

X-Ray Tube Components

• X-ray tubes (Coolidge tubes) are inefficient, producing 1% x-rays and 99% heat.
• Cathode is the negative side, containing the filament.
• Anode is the positive side, containing the target.
• Filament is composed of thoriated tungsten.
• Dual focus filaments allow for better resolution with small filaments and high heat with large filaments.
• A focussing cup surrounds the filament.
• Thermionic emission occurs when electrical energy heats the filament.
• Anodes are either stationary or rotating.
• Stationary anodes use tungsten alloy embedded in a copper anode.
• Rotating anodes use tungsten rhenium alloy for increased heat capacity (300x).
• Target is where electrons collide, causing x-ray production.
• Actual focal spot is the physical area hit by electrons.
• Effective focal spot is the projected area of the x-ray beam.
• Focal spot size and target angle influence effective focal spot size (inverse relationship).
• Stator is a bank of electromagnets.
• Rotor is made of ferromagnetic bars, connected to the anode by a molybdenum stem.
• Target interactions (bremsstrahlung and characteristic) occur close to the target surface (0.25 - 0.5 cm).
• Bremsstrahlung interactions are major component of x-ray production.
• Characteristic interactions involve inner shell electrons.
• Off-focus radiation is not produced at the focal spot.

Image Quality and Radiation Safety

• Filtration removes low-energy x-rays (inherent and added).
• Total Filtration is inherent + added filtration.
• mAs (milliampere-seconds) controls the quantity of x-rays.
• kVp (kilovoltage peak) controls the quality of x-rays.
• Distance and intensity are inversely related (inverse square law).
• Attenuation is the reduction of photons passing through matter.
• Photon interactions: Coherent (no change in initial photon, only direction), photoelectric (absorption), Compton (scattering).
• Beam restrictors (collimators, cones, cylinders) reduce scatter and the primary beam.
• Grids reduce scatter radiation, but can cause grid cutoff.
• Grid ratio is the height/distance of grid lines.
• Filtration and beam restriction are inversely related to exposure.

Image Receptor, Display, and Processing

• Visibility of detail involves image contrast and spatial resolution.
• Contrast is the difference in brightness between adjacent areas.
• Spatial resolution (or frequency) is the sharpness of detail.
• Quantum mottle is underexposure noise.
• Noise is expressed as signal-to-noise ratio.
• Magnification and distortion (elongation/foreshortening) are geometric distortions.
• Digital radiography uses direct and indirect conversion detectors.

Other Topics

• Radiation protection principles (ALARA, time, distance, shielding).
• Radiation sources (natural and man-made).
• Personnel monitoring devices, radiation protection standards, regulatory agencies.
• Biological effects (stochastic and deterministic).
• Image processing in digital imaging (point, local, geometric).
• Exposure index determines exposure to the image receptor (Digital).

Fluoroscopy and Tomography

• Fluoroscopy uses high image frame rates for the moving body.
• Tomography demonstrates coronal sections.
• Tomography uses synchronized movement of the tube and image receptor.
• Focal plane reveals the clearest structures.
• Section interval separates tomographic planes.

CR and DR

• CR uses phosphor plates in a cassette.
• DR uses flat panel detectors for direct or indirect electronic conversion.
• Image acquisition using PSP (phosphor storage plates) or Flat panel detectors .

Image Intensification

• Image intensification tubes (ITT) increase brightness gain.
• Input screen converts x-rays into light.
• Output screen converts electrons into light.
• Magnification gain is input diameter squared/ output diameter squared.
• Interrogation and extinction times affect fluoro speed.
• Image quality (spatial resolution, contrast) significantly influence the use of radiographic and fluoro imaging.

General Concepts

• Informatics relates to information processing.
• Platforms and specific medical applications such as Body Mass Index.