X-ray History: Discovery, Development, and Impact

Halifax Radiology Museum and the Halifax Building

• Halifax opened its doors in $1928$ and included a radiology department from the start.
• The Halifax Radiology Museum is located just inside the entrance; it was made possible by Bud Hinkle, who served as radiology manager from $1985$ to $1995$ and was known for being a bit of a pack rat, preserving Americana for study.
• Some of the original radiology equipment from the hospital’s early days remains on display, allowing a direct comparison with today’s technology.
• X-rays are a fundamental part of modern society: we encounter them in airports (luggage scans) and in manufacturing (defect inspection in structural materials like airplane wings).
• The building’s history situates this discussion in the broader context of early radiology adoption and institutional memory.

X-rays in daily life, industry, and science

• X-rays are now ubiquitous in everyday life and industry, far beyond medical radiography.
• In manufacturing, X-rays inspect for defects in structural materials (e.g., airplane wings).
• In genetics and biology, X-ray information contributed to foundational discoveries (e.g., DNA structure).
• In medicine, chest and skull radiographs became routine, transforming diagnostic capabilities.
• Rosalyn Franklin used X-ray diffraction data to study DNA.
• Watson and Crick used the same diffraction information to define the double-helix structure of DNA in $1953$.
• X-ray technology intersects with societal expectations and safety concerns, as implied by historical anecdotes about early enthusiasm and misconceptions.

The dawn of X-rays: discovery and public reception

• The discovery occurred in the late 19th century, with a surge of “X-ray mania” as electricity entered households and new devices emerged.
• Early X-ray devices were sometimes used for entertainment (bone portrait studios in New York studios) where people could see radiographs of hands, heads, or chests and frame them as curiosities.
• Paranoia and misconceptions circulated, such as fears about using goggles at the opera to see through clothing.
• The first American medical X-ray was performed at Dartmouth College on $02/03/1896$; the event is commemorated with a photo showing a patient with a distal ulna fracture, flanked by a physician and a physicist who timed the exposure.
• A handheld fluoroscope, designed by Thomas Edison, was marketed for per-house use, enabling people to view their own bones by looking through the tube.
• Eye exposure and radiation exposure to the hands were significant early concerns.

The early experiments and the first radiographs

• The discoverer: Wilhelm Conrad Roentgen, a physics professor at the University of Würzburg, Germany, in a lab on the First Floor of the Würzburg Physics building.
• Initial apparatus: a Crookes tube (a high-vacuum tube with a cathode and anode) connected to a high-voltage supply producing a bluish-green glow from the tube.
• Roentgen conducted a landmark experiment on 11/08/1895 in which he covered the tube with a black box to block light and observed a faint glow on a nearby barium platinocyanide (phosphorescent) paper, eight feet away, indicating the emission of penetrating rays.
• He demonstrated that placing various objects between the tube and paper affected the paper’s glow: metal keys blocked the rays, while paper did not, revealing that the rays could produce silhouettes of bones.
• Over the next six weeks, Roentgen characterized this new ray, naming it with the letter X for the unknown.
• He produced what is considered the first human radiograph of a hand (Roentgen’s radiograph), sometimes associated with Miss Rankin, a patient used for demonstration.
• He presented his findings publicly to the Würzburg Physical Medical Society, featuring a radiograph of Rudolph Albert von Kollicker’s hand; this event helped popularize the discovery.
• Von Kollicker lauded the new ray and suggested naming it after Roentgen; the crowd reportedly proposed labeling the ray “Rincken” (a misspelling of Röentgen/Röntgen).

Early radiography equipment and entertainment devices

• An iconic device from the era was a shoe-store radiography unit used in the 1940s–1960s:
  • A platform with a hole at the front and three viewports (one for you, one for your mom, one for the salesman).
  • An X-ray source beneath the feet allowed buyers to see the bones of the feet inside a shoe.
  • The device was discontinued in the $1960s$ due to safety concerns and overexposure risks, highlighting early radiation safety lessons.
• These early demonstrations exemplified both public fascination and the need for better understanding of radiation safety.

How the Crookes tube produces X-rays (the physics in plain terms)

• The Crookes tube consists of a cathode (negative) and an anode (positive) with a high voltage between them; electrons are emitted from the cathode and accelerate toward the anode.
• Most of the electrons’ energy is converted into heat (the tube is inefficient): about $1\%$ or less of the electrons’ energy yields X-ray photons; the rest becomes heat in the glass and components.
• When electrons strike the glass or other materials, a portion of the energy is emitted as X-rays via Bremsstrahlung (breaking radiation): the energy of the X-ray photons depends on the voltage potential between the poles.
• The tube emits X-rays in all directions (unfocused) because the anode is off-center and the radiant energy is not collimated.
• The process was inefficient and required long exposure times for imaging (e.g., about $20$ minutes to obtain a single foot image).
• The energy of the emitted X-rays increases with higher voltage (higher kVp), giving better penetrating power, enabling clearer radiographs for thicker or denser regions.
• The Crookes tube’s early inefficiency and lack of directionality motivated critical design improvements.

Evolution of X-ray tube design and imaging quality

• Major design changes:
  • Move the anode to be directly opposite the cathode, and bevel the anode to focus X-rays in one direction, which significantly reduced exposure time and improved image quality.
  • Enhance the cathode with a heated filament (thermionic emission) to emit more electrons when the tube is energized, increasing X-ray production.
• In modern terms, the two primary adjustable settings in X-ray imaging are:
  • The voltage, commonly referred to as $kVp$, which controls the energy and penetrating power of individual X-ray photons.
  • The current, represented in $mAs$ (the product of milliamperes and time), which controls the number of photons produced.
• The radiologic technologist adjusts these settings to optimize image quality for each patient and body part, accounting for size and thickness.
• The final major design change: a rotating anode.
  • A rotating disc spreads the heat over a larger area, preventing local overheating and extending tube life.
  • This innovation is essential for high-energy imaging, such as CT, where energy demands are much higher.
• The rotating anode is a standard feature in modern X-ray tubes; listening for the telltale whirring sound at the start of an exam is a sign that the anode is spinning up.
• The Crookes tube analogy: a cathode ray tube (old TV) is conceptually similar—the cathode emits electrons that create a visible image on a phosphor screen; however, in X-ray tubes the emitted X-rays are used to form radiographic images in photographic film or digital detectors.
• Older TVs emitted some X-radiation, prompting safety warnings in the past; modern displays rely on non-radiative technologies (LCD, LED).

From radiographs to images: the electromagnetic spectrum and image formation

• X-rays are part of the electromagnetic spectrum, alongside visible light and radio waves.
• The spectrum ranges from low-energy radio waves (AM) through visible light to high-energy X-rays and gamma rays.
• Higher-energy X-rays can pass through various tissues with different degrees of attenuation, depending on thickness and density.
• Air-filled lungs attenuate very little, allowing most X-ray energy to reach the film; the heart is denser and attenuates more than lungs, and bones are even denser and attenuate most X-rays.
• An X-ray exposure creates a composite radiographic image (a negative shadow) that represents the varying attenuation of X-rays by tissues.
• With knowledge of normal radiographic anatomy, X-ray images can diagnose conditions such as pneumonia, evidenced by the radiographic appearance in the right lung in this discussion.

Roentgen’s legacy, safety, and ethical implications

• Roentgen died in $1923$; despite strong encouragement from friends and family, he did not pursue patent protection for X-rays.
• He believed scientific discoveries should stay with the scientific community to be thoroughly investigated and developed by future generations; his generosity to humankind is described as immeasurable in terms of lives saved in medicine and industry.
• In a broader scientific context, X-rays have provided insight into the world around us—from genetics and materials science to astronomical studies—demonstrating the broad, transformative impact of this chance discovery in a small German laboratory in November $1895$.
• Ethical and practical implications discussed include early misperceptions about safety, entertainment uses, and the development of protocols to minimize exposure while maximizing diagnostic benefit.

Key takeaways and connections to foundational principles

• The discovery of X-rays arose from curiosity-driven research using the Crookes tube and a black-box experiment, leading to a tool that reshaped medicine, industry, and science.
• The evolution of X-ray technology—from unfocused, inefficient tubes to focused, thermionically heated, and rotating-anode tubes—paralleled advances in our understanding of radiation physics and imaging science.
• The expanding range of applications—from medical radiography to non-destructive testing and DNA structural elucidation—highlights the interdisciplinary impact of a single technological breakthrough.
• Safety, ethics, and public perception have continually shaped the development and use of X-ray technology, underscoring the importance of responsible innovation and risk management.

Quick glossary of major terms (for quick study)

• Crookes tube: an evacuated glass tube with a cathode and anode used to produce cathode rays and, under certain conditions, X-rays.
• Cathode: negative electrode in a vacuum tube that emits electrons when heated.
• Anode: positive electrode in a vacuum tube that attracts electrons.
• Thermionic emission: emission of electrons from a heated filament, increasing the available electrons for X-ray production.
• Bremsstrahlung (breaking Radiation): the mechanism by which high-energy electrons emit X-rays when deflected by atomic nuclei.
• kVp: kilovolt peak, the voltage across the X-ray tube that determines the energy of X-ray photons.
• mAs: product of tube current (in milliamperes) and exposure time; controls the quantity of X-rays produced.
• Rotating anode: a rotating disc in an X-ray tube that spreads heat, prolonging tube life and enabling higher energy imaging.
• Radiograph: the X-ray image produced on film or a digital detector.
• Fluoroscope: an imaging device that provides real-time X-ray viewing, historically used as a handheld device.
• Bone portrait studios: early entertainment venues offering radiographs of body parts as novelty.”