Radiologic Science: Essential Concepts

Essential Concepts of Radiologic Science

• This chapter explores the fundamental principles of x-ray imaging, including the study of matter, energy, the electromagnetic spectrum, and ionizing radiation.
• Radiographers, who specialize in x-ray imaging, hold significant responsibility for conducting x-ray examinations in accordance with established radiation protection standards for the safety of patients and medical personnel.
• The physics of radiography encompasses the production and interaction of x-rays, evident from the moment an x-ray tube generates x-rays.

Nature of Our Surroundings

• In a physical analysis, all things can be classified as either matter or energy.
• Matter occupies space and possesses mass, composing physical objects.
• Atoms are the fundamental building blocks of matter, arranged in complex ways.

Matter and Energy

• Matter is defined as anything that occupies space and has mass.
• Atoms and molecules serve as the complex building blocks of matter.
• Mass, described by its energy equivalence, is measured in kilograms (kg).
• Energy, the ability to do work, is measured in joules (J) in the International System (SI). In radiology, the electron volt (eV) is often used.
• Potential energy is the ability to perform work due to position.
• Kinetic energy is the energy of motion.
• Chemical energy is the energy released during a chemical reaction.
• Electrical energy is the work achievable when an electron moves through an electric potential difference.
• Thermal energy (heat) is the energy of motion at the molecular level, related to temperature.
• Nuclear energy resides within the nucleus of an atom.
• Electromagnetic energy, critical for x-ray imaging, encompasses x-rays, gamma rays, radio waves, microwaves, ultraviolet, infrared, and visible light.
• Matter and energy are interchangeable.

Radiation

• Radiation is energy emitted and transferred through space.
• Electromagnetic energy is commonly referred to as electromagnetic radiation or simply radiation.
• Matter that intercepts and absorbs radiation is exposed or irradiated.
• Ionizing radiation is a specific type of radiation, including x-rays, capable of removing an orbital electron from an atom.
• An ion pair consists of the orbital electron and the remaining atom after ionization.

Sources of Ionizing Radiation

• Ionizing radiation can be harmful, and individuals are exposed to it from various sources categorized as natural environmental radiation and man-made radiation.
• Natural environmental radiation contributes approximately 3 millisieverts (mSv) annually.
• Man-made radiation contribute 3.2 mSv annually.
• Natural environmental radiation includes cosmic rays, terrestrial radiation, internally deposited radionuclides, and radon.
• The largest man-made source of ionizing radiation is diagnostic x-rays (3.2 mSv/yr).

Discovery of X-rays

• X-rays were discovered accidentally by Wilhelm Roentgen on November 8, 1895.
• Roentgen received the first Nobel Prize in physics in 1901 for his work.
• He produced and published the first medical x-ray image in early 1896, an image of his wife's hand.
• Roentgen described x-radiation with nearly all of its recognized properties within a month of his discovery.

Development of Medical Imaging

• Radiography utilizes film or a solid-state image receptor, with an x-ray tube typically mounted from the ceiling.
• Fluoroscopy uses a moving image on a television monitor or flat panel display.
• Computed tomography reconstructs fixed images in any anatomical plane using a rotating x-ray source and detector array.
• X-ray voltages are measured in kilovolt peak (kVp), while x-ray currents are measured in milliampere (mA).
• Early radiographic procedures required long exposure times, which was reduced by using a fluorescent intensifying screen.
• The demands during World War I led to the use of film rather than glass plates.
• Thomas A. Edison developed the fluoroscope in 1898.
• William Rollins first applied collimation and filtration to reduce patient exposure.
• In 1907, H.C. Snook introduced the interrupterless transformer.
• William D. Coolidge unveiled the hot-cathode x-ray tube in 1913.
• The Potter-Bucky grid was introduced in 1921.

Reports of Radiation Injury

• The first x-ray fatality in the United States occurred in 1904.
• Physicians and patients were frequently injured due to the low energy of radiation, necessitating long exposure times.
• Protective devices and apparel were developed for radiologists, and x-ray workers were monitored for occupational exposure effects.

Basic Radiation Protection

• Emphasis has shifted to protection of patients due to concerns about latent harmful effects and the sensitivity of human fetuses to radiation.

Radiation Protection Devices

• Metal filters, typically aluminum or copper, absorb low-energy x-rays that have little diagnostic value.
• Collimation restricts the x-ray beam to the area of interest in the body, reducing scatter radiation and improving image contrast.
• Lead-impregnated material is used to make protective aprons and gloves.
• Gonadal shielding should be used for all individuals of childbearing age when it does not interfere with the examination.
• Radiographic control consoles are located behind protective barriers.

Standard Units of Measurement

• Physics strives for exactness by eliminating subjective descriptions and using base quantities: mass, length, and time.
• Secondary quantities are derived from combinations of base quantities, such as volume, mass density, and velocity.
• The standard unit of length was initially the distance between two lines on a platinum-iridium bar in Paris, now defined in terms of the wavelength of orange light emitted from krypton-86.
• The kilogram was originally defined as the mass of 1000 cm³ of water at 4° Celsius, now represented by a platinum-iridium cylinder.
• The second, the standard unit of time, is measured by an atomic clock based on the vibration of cesium atoms.
• Every measurement has two parts: a magnitude and a unit.
• The International System (SI) represents the current state of units.

Mechanics

• Mechanics deals with objects at rest (statics) and objects in motion (dynamics).
• Velocity is a measure of how fast something is moving.
• Acceleration is the rate of change of velocity with time.
• Isaac Newton's three laws of motion:
  • A body at rest will remain at rest, or a body in motion will continue to move with constant velocity in a straight line unless acted on by an external force.
  • The force acting on an object is equal to the mass of the object multiplied by the acceleration produced.
  • For every action, there is an equal and opposite reaction.
• Weight is a force on a body caused by the pull of gravity.
• Momentum is the product of the mass of an object and its velocity.
• Work is the force applied times the distance over which it is applied.
• Power is the rate of doing work.
• The law of conservation of energy states that energy may be transformed from one form to another, but it cannot be created or destroyed; the total amount of energy is constant.
• Kinetic energy is the energy associated with the motion of an object.
• Potential energy is the stored energy of position or configuration.

Heat

• Heat is a form of energy related to the kinetic energy of the random motion of molecules.
• The unit of heat is the calorie.
• Heat is transferred by conduction, convection, and radiation.
• Temperature is measured with a thermometer, often calibrated at the freezing and boiling points of water, using Celsius (°C), Fahrenheit (°F), and Kelvin (K) scales.

Terminology for Radiologic Science

• It's essential to become familiar with the language associated with radiologic science.
• Numeric prefixes are used to express large or small multiples of standard units.

Radiologic Units

• Four units are used to measure radiation:
  • Air Kerma (Gya): Kinetic energy released in matter, measured in joules per kilogram (J/kg), where 1 J/kg is 1 gray (Gy).
  • Absorbed Dose (Gyt): Radiation energy absorbed per unit mass, with units of J/kg or Gy.
  • Effective Dose, Sievert (Sv): Used to express radiation received by radiation workers and populations.
  • Radioactivity, Becquerel (Bq): Quantity of radioactive material, with one becquerel being one nucleus disintegration per second.

The Medical Imaging Team

• Radiographers need to complete academic courses, gain clinical experience, and pass the national certification examination given by the American Registry of Radiologic Technologists (ARRT).