Lesson1:History, Physics, and Basic Concepts of Radiography Study Guide

Discovery and Basic Concepts of X-rays

• Wilhelm Conrad Rankin:

  • Identified as the father and grandfather of X-ray.

  • German mechanical engineer and physicist.

  • Known as the father of radiography.

  • Discovered X-rays by accident on 11/08/1895.

  • Used the Crookes tube for the discovery.

The Vacuum Tube and Historical Experiments

• The Crookes Tube:

  • A vacuum-sealed glass tube designed to carry electricity.

  • Rays emitted from the tube accidentally passed through it and created a shadow-like image on radio-sensitive paper.

• Early Implementation and Safety:

  • Mr. Rankin experimented on his wife, taking the first X-ray of her hand (visible wearing rings).

  • Rankin's wife ultimately died from radiation-induced illness due to a lack of knowledge regarding radiation effects.

  • Historically, X-rays were used in shoe stores to see if children's feet fit properly inside shoes before the dangers were understood.

Honorable Mentions: Key Figures in Radiologic History

• H. C. Snook: Developed the interrupless transformer.

• William Coolidge: Designed the hot cathode X-ray tube and created the prototype for modern-day tubes.

• Michael Pupin: Implemented the use of fluorescent screens and the modern intensifying screen.

  • Fluoro screens are still in use today.

  • Early screens were Cathode Ray Tubes (CRT), used in "old school" large televisions, whereas modern hospitals primarily use LCD and LED screens.

• Clarence Daly:

  • Worked closely with Thomas Edison.

  • Conducted experiments to understand fluorescent properties.

  • Suffered radiation burns leading to arm amputation and died of radiation exposure in 1904.

  • Recorded as the first X-ray fatality in the United States.

Evolution of Radiologic Education

• Training History:

  • X-ray education began as on-the-job training.

  • On-the-job training remains common in specific avenues like the cath lab, NIR, and CT.

• Formalization:

  • CT and MRI now have educational proportions and clinical training requirements.

  • Technicians must complete 12 credits of cross-sectional anatomy for these modalities.

  • In the cath lab, a license test must be passed for certification.

• Program Development:

  • Radiation therapy became a separate training field in the 1950s.

  • The GI Bill after World War II aided in the formation of modern community colleges offering hospital-based program affiliations.

  • Examples of affiliations include Fairleigh Dickinson, Bloomsburg, and Englewood.

  • Valley Hospital's first independent class will graduate next year.

Essential Requirements for X-ray Production

• Four Basic Requirements:

  1. A vacuum (glass envelope).

  2. A source of electrons (filament).

  3. A target for the electrons (anode).

  4. A high potential difference between the source and target (voltage/$kVp$).

• The Vacuum:

  • Referred to as the glass envelope.

  • Made of silica glass (Pyrex) with a high melting point.

  • All air is removed from the tube.

• Electron Source:

  • Consists of a filament through which electric current flows to create heat.

  • Contains 74 electrons orbiting the nucleus.

  • Heat forms an electron cloud via thermionic emission (boiling off electrons).

  • The resulting free electrons form a "space charge."

• The Target:

  • The target is the electrically positive anode, made of tungsten.

  • When electrons collide with the target at high speed, kinetic energy is converted into heat ($99\%$) and X-rays ($1\%$).

Electromagnetic Energy and Wave Properties

• Nature of X-rays: Electromagnetic waves possessing both electrical and magnetic properties.

• Wave Pattern: They travel in a sinusoidal form (sine wave).

• Wave Terminology:

  • Wavelength: The distance from one crest to the next.

  • Amplitude: The distance from the graph bottom line up to the top middle (crest) of the wave.

  • Frequency: The number of times per second that a crest passes a given point.

• Mathematical Relationships:

  • Relationship between wavelength and frequency: Shorter wavelengths result in higher frequency because crests are closer together.

  • Relationship for velocity:       $\text{Velocity} = \text{Wavelength} \times \text{Frequency}$

The Electromagnetic Spectrum

• Ordering (Left to Right):

  1. Radio waves (far left).

  2. Infrared.

  3. Ultraviolet rays (sun, light bulbs).

  4. X-rays.

  5. Gamma rays (nuclear medicine).

Characteristics and Effects of X-rays

• Straight-line travel (until interacting with matter).

• Photographic effect.

• Biological effects.

• Cannot be refracted by a lens.

• Cannot be detected by human senses (sight, touch, smell, etc.).

• Penetrate matter that is opaque to light.

Interaction with Matter: Attenuation

• Attenuation: The effect on the X-ray beam caused by passing through matter (absorption by mass, structures, water, muscle, and bone).

• The Image: The visible image is the result of absorption and attenuation.

• Atomic Number Impact:

  • The atomic number of the structure determines the shade of gray, black, or white.

  • Lungs: Low atomic number, air-filled; X-rays pass through easily, creating dark shades.

  • Bone: High atomic number; absorbs more radiation, creating white shades.

The X-ray Beam and Imaging Terminology

• Primary Beam: The radiation emitting from the tube that has not yet passed through any matter.

• Remnant Radiation (Exit Radiation): The radiation that has passed through the body; the "scraps" left over that create the radiographic image.

• Fluorescence: Crystals giving off light when exposed to radiation.

• Focal Spot: The small area on the target (anode) where the primary beam is formed.

• Radiation Field: The plate of use where the cone-shaped beam is directed.

• Central Ray (CR):

  • The photon in the center of the beam, perpendicular to the long axis of the tube.

  • The only place where X-rays move in a perfectly straight line.

  • Divergence: As rays move further from the central ray, they diverge (go diagonal), which can cause distortion of the joint or body part.

• Latent Image: The radiation exposure image that has been captured on the receptor but has not yet been processed into a digital image.

Scatter Radiation and Occupational Exposure

• Scatter Radiation:

  • Has less energy than the primary beam.

  • Comprised of radiation scattered after the primary beam is attenuated by matter (the patient or the X-ray table).

  • Principal source of occupational exposure for radiographers.

  • Technologists must use appropriate radiation levels to minimize scatter production.

The X-ray Tube Construction and Housing

• Dual Focus Tubes: Modern tubes have two filaments:

  1. Small filament/focal spot: Used for fine details (e.g., toes).

  2. Large filament/focal spot: Used for larger target areas (e.g., chest or abdomen).

• Tube Housing:

  • Shielding that absorbs the non-useful portion of the beam.

  • Protects internal components.

  • Allows manipulation by the technologist.

  • Contains collimators, rulers for distance, and laser lights for the central ray.

Tube Movements and Distance

• Longitudinal: Movement along the long axis of the table.

• Transverse: Side-to-side movement.

• Vertical: Up-and-down movement (controls SID).

• Roll: Tilting or angling the tube along the longitudinal axis (toward head/cephalic or feet).

• Detent: Stops built into the tube support for specific Source-to-Image Distances (SID).

  • Common SIDs: $40\text{ inches}$, $48\text{ inches}$, and $72\text{ inches}$.

  • $72\text{ inches}$ is used for chest X-rays and cross-table cervical spine laterals to decrease magnification.

  • $40\text{ inches}$ is used for most extremity work and abdomens.

Secondary Equipment

• Collimator: Attachment on the housing used to change the size of the radiation field.

• Grid: A device used to clean up/prevent scatter radiation from reaching the Image Receptor (IR).

• Bucky: Located under the table or on the wall (wall bucky) to hold the cassette and grid.

• Transformer: Provides the high voltage necessary for production.

• Control Console: Allows control of $mA$, $kVp$, and the Automatic Exposure Control (AEC).

• Rotor Switch: Pressed halfway to "rotor" and fully to expose.

Fluoroscopy (Real-Time Imaging)

• Nature: Designed for direct viewing of motion in real-time.

• Capabilities: Tilts from $89\text{ degrees}$ to flat; can perform negative head tilts.

• Clinical Applications:

  • GI studies (barium enemas).

  • Myelograms.

  • VCUG.

  • Hysterosalpingograms (fertility testing/injecting contrast into cervix/uterus).

  • Arthrograms (injecting contrast into joint spaces like the rotator cuff).

  • Thoracentesis follow-ups (draining fluid from lungs/joints).

The Radiographer's Role in Fluoroscopic Exams

• Obtain patient history and proper consent.

• Perform time-outs and patient education.

• Assist in changing the patient and explaining procedures.

• Set up control panels and splash films.

• Prepare sterile trays, anesthesia, and contrast media for the radiologist.