Study Notes on the History of Medical Imaging (MEDI 317)

INTRODUCTION TO MEDICAL IMAGING

MEDI 317

LECTURER:
  • Patience Addo
  • University of Health and Allied Sciences

LEARNING OBJECTIVES

  • Upon completion of this lesson, students will be able to:
    • Understand the history of radiography practice.
    • Understand the other sources of radiation.
    • Understand the health concerns following the discovery of X-rays.

DISCOVERY OF X-RAYS

Background Context

  • In the 1870s and 1880s, scientists were investigating cathode rays through partially evacuated glass tubes.
  • Wilhelm Conrad Roentgen experimented with a Crookes tube.

Roentgen's Experiment

  • Conducted in a darkened lab to prevent escape of visible light.
  • Used a plate coated with barium platinocyanide, which fluoresced when exposed to the rays produced by the tube.
  • On November 8, 1895, Roentgen accidentally discovered X-rays.

Characteristics of X-rays

  • X-rays were produced in a glass envelope that contained positive and negative electrodes.
  • The air in the tube was evacuated.
  • A high voltage was applied, resulting in a fluorescent glow from the tube.
  • Roentgen shielded the tube with heavy black paper and noted green light generated by materials meters away, leading him to conclude a new type of ray was emitted from the tube.

Application and Reception

  • Roentgen found the ray capable of passing through most substances, casting shadows of solid objects.
  • Discovered that X-rays could penetrate human tissue but were stopped by bones and metals.
  • One of Roentgen's first experiments involved radiographing his wife Bertha's hand.
  • Initial industrial application was demonstrated via radiographing a set of weights before moving to medical uses, which created a significant impact in science and media alike.

Significance

  • The 'X-Light' led to the adjective 'X' for unknown.
  • The first medical X-ray image was produced in 1896.
  • Roentgen received the first Nobel Prize in Physics in 1901, and IUPAC named the 111th element after him, Roentgenium.

Scientific Interest

  • Roentgen's work led to widespread duplication of his experiments by scientists globally.
  • This spark in interest generated numerous articles and stories in newspapers and magazines, varying in truthfulness.

ROENTGEN’S LABORATORY

Forms of Tube Used by Roentgen

  • Presentation of various tube forms utilized by Roentgen for X-ray production during 1895-1896.

HISTORY OF RADIOGRAPHY

Initial Public Fascination

  • Public interest was captivated by the notion of an invisible ray that could pass through solid matter, providing images of bones and internal body parts through photographic plates.
  • Scientific interest paralleled this with the demonstration of wavelengths shorter than visible light, creating enthusiasm for medical and surgical applications.

Early Medical Applications

  • Within a month of Roentgen's announcement, medical radiographs were made in Europe and the U.S. for surgical guidance.
  • By June 1896, X-rays were utilized by battlefield physicians for locating bullets in wounded soldiers.

Industrial Adoption Timeline

  • Before 1912, X-rays had limited application outside medicine and dentistry, primarily used in research of metals due to the fragility of X-ray tubes.
  • The introduction of high vacuum X-ray tubes by Coolidge in 1913 changed the situation, allowing for a reliable source at voltages up to 100 kilovolts.

Advancements in Industrial Radiography

  • In 1922, the 200-kilovolt X-ray tube made it feasible to radiograph thick steel parts efficiently.
  • In 1931, GE developed 1,000 kilovolt X-ray generators, facilitating industrial radiography.
  • That year, the ASME approved X-ray use on fusion welded pressure vessels, enhancing industrial acceptance.

A SECOND SOURCE OF RADIATION

Henri Becquerel's Discovery

  • In 1896, Henri Becquerel discovered natural radioactivity concurrently as others studied cathode rays.
  • His research focused on fluorescent minerals, which glow under sunlight.
  • Becquerel utilized photographic plates to study this fluorescence.

Accidental Discovery of Radiation

  • A cloudy day limited his ability to expose samples to sunlight, prompting him to store uranium compounds with photographic plates.
  • Upon developing the plates, he found them fogged, indicating exposure that could not be attributed to stray light.
  • Only the plates stored with uranium were fogged, leading him to conclude that the uranium compound emitted radiation that could penetrate the wrapping.

Interest and Follow-Up Research

  • Despite his findings, few scientists initially pursued Becquerel's research on radioactivity.
  • The interest in radioactivity surged following the discovery of radium by the Curies two years later.
  • Marie Curie and her husband Pierre sought other radioactive elements in pitchblende, which led to the discovery of polonium and radium in 1898.

Industrial Applications of Radioactivity

  • Radium served as the first gamma-ray source in industry, allowing thicker castings to be radiographed.
  • Industrial radiography significantly expanded during WWII as part of the Navy's shipbuilding initiatives.
  • By 1946, man-made gamma-ray sources like cobalt and iridium emerged, proving stronger and less expensive than radium, thus accelerating growth in industrial radiography.

DEVELOPMENT OF MODERN RADIOLOGY

Basic Requirements for X-ray Production

  • A satisfactory x-ray beam requires high voltage (measured in kilovolt peak, kVp, where 1kV = 1000V) and sufficient electric current (measured in milliampere, mA).

Advancements from Roentgen's Time

  • In Roentgen's era, few mA and voltages up to 50kVp were used, leading to longer exposure times that could blur images.
  • Two significant technological advances transformed X-ray usage, transitioning from a physicist's novelty to a large-scale medical specialty.
Key Developments
  • In 1907, H.C. Snook introduced a high-voltage power supply, an interrupt-less transformer suitable for existing static machines.
  • In 1913, William D. Coolidge introduced a hot-cathode X-ray tube that allowed for independent selection of voltage and current, standardizing output.

20th Century Advancements

  • The 20th century marked significant advancements in X-ray imaging across the human body.
  • The evolution included treatment options leveraging radioactive sources alongside diagnostic tools.
  • Imaging technologies expanded to include ultrasound (sonography), computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetoencephalography (MEG) under investigation.
  • Therapeutic modalities like linear accelerators (Linac), intensity-modulated radiation therapy (IMRT), and CyberKnife were developed.

HEALTH CONCERNS

Emergence of Health Physics

  • The field of radiation protection, known as "health physics," emerged alongside the discoveries of X-rays and radioactivity at the close of the 19th century.
  • Experimenters and physicians operated X-ray apparatuses with minimal regard for health risks, primarily due to a lack of precedent suggesting hazards from X-rays.

Misconceptions about X-rays

  • Initially, many believed X-rays could benefit health, as they were similar to light yet invisible, unfelt, and undetectable.
  • The prevailing belief led to unrestrained use, resulting in significant injuries attributed only later to X-ray exposure due to delayed symptom onset and lack of awareness of X-ray hazards.
Early Warnings and Recognition of Dangers
  • Pioneers like Thomas Edison, William J. Morton, and Nikola Tesla began correlating X-ray exposure with skin burns.
  • These figures provided the first alerts about potential adverse effects of X-rays.

Understanding Radiation Damage

  • Today, radiation damage has been investigated extensively at molecular, cellular, and organ system levels.
  • Quantitative data on dose-response relationships enables health physicists to establish safe radiation levels for medical, scientific, and industrial applications, maintaining risks comparable or lower than those associated with other technologies.

Nature and Properties of X-rays and Gamma rays

  • X-rays and gamma rays are types of electromagnetic radiation described by their shorter wavelengths compared to visible light.
  • The wavelength of visible light is approximately 600 nanometers, whereas the wavelengths of X-rays are on the order of one angstrom (10⁻¹⁰ meters) and gamma rays about 0.0001 angstrom (10⁻¹² meters).

CONCLUSION

  • Understanding the history, development, and health implications of medical imaging, particularly X-rays, is vital as these technologies continue to evolve and impact both diagnosis and treatment practices in medicine.