Introduction to Radiography

The Discovery of X-Rays

• Wilhelm Conrad Roentgen: The discovery of x-rays occurred on November 8, 1895, at the University of Würzburg in Germany.
• Experimental Set-up: Roentgen was working with a Crookes tube, which is a type of cathode ray tube. To ensure no visible light escaped, he enclosed the tube in black photographic paper.
• Initial Observation: He noticed a fluorescent plate located elsewhere in the room began to glow. He observed that the plate fluoresced in direct relation to its distance from the tube, appearing brighter as it was moved closer.
• Hittorf-Crookes Tube: The specific equipment used in these initial experiments was a pear-shaped Hittorf-Crookes tube.
• Naming: Because the nature of this radiation was initially unknown, Roentgen named it "x-radiation" or x-rays.
• Early Findings: Roentgen discovered several fundamental properties of x-rays:
  • They could penetrate certain materials.
  • They could expose photographic plates.
  • They could create images of internal structures.
  • They behaved differently than visible light.
  • They could not be seen directly by the human eye.
• Recognition: Roentgen received the first Nobel Prize in Physics in 1901 for this discovery.

Pioneers of Radiography

• H.C. Snook: He utilized an alternating current generator to develop the interrupterless transformer, which significantly improved the electrical supply for x-ray production.
• Thomas Edison:
  • Edison experimented with various fluorescent materials and invented the first fluoroscope.
  • He discovered many fluorescent chemicals utilized in radiography for years to follow.
  • Cessation of Research: Edison abandoned his x-ray research after his assistant and friend, Clarence Dally, suffered severe radiation burns. Dally served as the subject for many of Edison's experiments; his arms required amputation, and he eventually died in 1904. This was the first recorded x-ray fatality in the United States, illustrating the serious biological hazards of radiation.
• Michael Pupin: In 1896, Pupin demonstrated that fluorescent screens could intensify the effect of x-rays, thereby reducing exposure time. These screens are now known as intensifying screens.
• William Coolidge:
  • He designed the hot cathode x-ray tube in 1910 to work with Snook's electrical supply improvements.
  • This design became the prototype for all modern x-ray tubes.
• George Eastman: Eastman, who had previously invented photographic film using cellulose nitrate (a plastic material) to replace glass, produced the first radiographic film in 1914.

Evolution of the Radiographer Profession

• The First Radiograph: Roentgen produced the first anatomic radiograph, which was an image of his wife’s hand.
• Early Practitioner Roles: Initially, physicians performed all tasks themselves, including:
  1. Positioning the patients.
  2. Operating the equipment.
  3. Developing the photographic plates.
• Emergence of Assistants: As the popularity of radiography grew, physicians trained assistants to perform these tasks. These assistants evolved into the first professional radiographers.
• Education Transition:
  • Originally, education was primarily hospital-based programs.
  • Colleges became involved when hospital programs began utilizing academic offerings at local institutions for basic sciences like anatomy and physiology.
  • Today, most programs have transitioned to community colleges, colleges, and universities, though some hospital-based programs still exist.
• Curriculum Structure: Modern programs combine classroom education, laboratory practice, and clinical experience. Students must learn scientific principles alongside safe examination techniques for actual patients.

Essentials of X-Ray Production

• Basic Process: The general workflow involves the x-ray tube, positioning the patient, using an image receptor (IR), and processing the resulting image.
• The Four Essential Requirements:

1. A Vacuum: The x-ray tube is made of borosilicate glass to withstand extreme heat. The vacuum ensures that electrons can travel without colliding with gas molecules.

2. A Source of Electrons: The cathode (negative end) contains a wire filament made of tungsten ($Z = 74$). When heated, electrons are released through thermionic emission, creating an "electron cloud" or space charge around the filament.

3. A Target for Electrons: The anode (positive end) contains a target, also made of tungsten due to its high melting point. This smooth, hard surface is where x-rays are generated as electrons travel from the cathode to the anode.

4. High Potential Difference: A high-voltage transformer provides the voltage. During exposure, the positive target attracts the negative electrons at high speeds. When they strike the target, their kinetic energy is converted into:

   • $> 99\%$ heat.
   • A small amount of x-rays.

Fundamentals of Electromagnetic Energy

• Spectrum Examples: X-rays are a form of electromagnetic energy, alongside radio waves, microwaves, infrared, visible light, ultraviolet, and gamma rays.
• Wave Properties:
  • Amplitude: The height of the wave, measuring the distance from the resting position to the crest or valley.
  • Wavelength ($\lambda$): The distance between corresponding points on consecutive waves (e.g., crest to crest).
  • Frequency ($f$): The number of waves passing a given point per second.
• Inverse Relationship: Wavelength and frequency are inversely related. Short wavelengths have high frequencies, and long wavelengths have low frequencies.
• Energy Relationship: Energy is directly proportional to frequency ($E \propto f$). Therefore, x-rays, which have extremely short wavelengths and high frequencies, possess very high energy.
• Ionization Classification:
  • Ionizing Radiation: Includes x-rays and gamma rays; they have enough energy to cause ionization.
  • Nonionizing Radiation: Includes ultraviolet, visible light, infrared, and radio waves; they lack the energy to ionize atoms.
• The Photon: Also called a quantum, a photon is the smallest unit or "packet" of electromagnetic energy.

Characteristics and Behavior of X-Rays

• Shared Traits with Visible Light:
  • Travel in straight lines.
  • Travel at approximately the speed of light ($3 \times 10^8\,m/s$).
  • Produce photographic/image-receptor effects.
  • Produce biological effects.
• Distinguishing Traits of X-Rays:
  • Invisible to the human eye.
  • Have no mass.
  • Have no electrical charge.
  • Can penetrate matter opaque to visible light.
  • Can ionize matter.
  • Can produce fluorescence in specific crystals.
• Wave-Particle Duality: X-rays exhibit characteristics of both waves and particles.
• Attenuation: This is the reduction of the x-ray beam as it passes through matter due to absorption. More dense or thicker materials cause higher absorption. The density hierarchy of absorption is: $\text{Air} \rightarrow \text{Fat} \rightarrow \text{Water/Muscle} \rightarrow \text{Bone}$.
• Exit Radiation: Also known as remnant radiation, these are the x-rays that remain after passing through the body. This pattern reflects the different absorption characteristics of tissues and creates the radiographic image.

Types of Radiation

• Primary Radiation: The x-ray beam produced at the tube's focal spot on the anode. It spreads outward from this point.
  • Central Ray (CR): The imaginary line through the center of the beam, perpendicular to the tube's long axis.
  • Radiation Field: The cross-sectional area of the beam.
• Scatter Radiation: Created when the primary beam is attenuated by solid matter (the patient or table). It travels in unpredictable directions and generally has less energy than the primary beam. It is the principal source of occupational exposure for radiographers and can cause image "fog."
• Remnant Radiation: The radiation that exits the patient to reach the image receptor. It contains the data used to produce the image.

Radiographic Equipment and Components

• Collimator: Attached beneath the tube housing, it uses lead shutters to restrict the beam size and shape. It contains a light source to show the operator the radiation field. Smaller fields reduce patient exposure and improve image quality by reducing scatter.
• X-Ray Tube Housing: A barrel-shaped housing that protects the tube, insulates electrical components, reduces leakage radiation, and provides support.
• Tube Support Systems: Can be ceiling-mounted (allowing movement in multiple directions), floor-mounted, or tube stands.
  • Motions: Longitudinal (along the table), Transverse (across the table), Vertical (up/down), Rotation (around tube axis), and Angulation/Roll.
  • Safety: Locking mechanisms must be released before moving the tube to prevent damage.
• Detents: Specific mechanical stops that help line up the tube with the table or upright receptor quickly.
• Radiographic Table: Supports the patient. Features include vertical movement, floating tabletops for easier positioning, and tilting capabilities.
  • Trendelenburg Position: A tilting table position where the head is lowered at least $15$ degrees.
  • Table Safety: Requires the use of footboards, shoulder guards, and handgrips when tilting.
• Grids and Bucky Systems:
  • Grid: Placed between the patient and IR to absorb scatter radiation. It is generally used for body parts thicker than approximately $10\text{--}12\,cm$.
  • Bucky: A moving grid device. The grid moves during exposure to prevent the lead strips from appearing on the image.
• Control Console: Where the radiographer selects exposure factors:
  • mA (Milliamperage): Sets the rate of x-ray production and determines focal spot size.
  • kVp (Kilovoltage peak): Controls wavelengths, penetrating power, and potential difference.
  • Timer: Controls exposure duration.
  • mAs: The product of mA and time, determining the total quantity of radiation.

Fluoroscopy

• Definition: A method of x-ray imaging that allows the visualization of movement in real time (dynamic imaging), similar to a video.
• Applications: Watching contrast move through the GI tract or tracking catheters/instruments through the body.
• Equipment: Modern digital systems allow radiologists to view images on a monitor in real time.
• Radiation Safety: Because x-rays may be produced continuously, equipment includes a fluoroscopy timer that alarms after a preset period—typically $5$ minutes—to encourage time reduction.
• Radiographer Duties:
  • Taking patient history (including dietary/cleansing prep).
  • Paperwork (Consent, Time-Out, Patient Education).
  • Assisting with gowning and explaining the procedure.
  • Taking preliminary "scout" images.
  • Setting control panel and preparing equipment (attaching footboards/guards).
  • Entering data and preparing contrast agents.
  • Assisting the radiologist with patient positioning and contrast administration.
  • Handling digital images and providing post-procedural instructions.