99 Fun Facts About Radiology

On a standard X-ray image, which of these appears black?

Air. Dense bone and metal block most of the rays and show white, muscle and fat come out in shades of grey, and air-filled lungs let nearly everything through, so they look dark.

Röntgen named his discovery 'X-rays' because, in mathematics, x stands for what?

An unknown quantity. He meant the label as a stopgap while he worked out what the rays were, but it stuck in English; many other languages call them Röntgen rays instead.

Whose hand appears in Röntgen's famous first X-ray photograph of the human body, taken in 1895?

His wife's. Anna Bertha Röntgen kept her hand still over a photographic plate, and the developed picture showed the shadows of its bones and of the ring she was wearing.

Röntgen won which award in 1901 for discovering X-rays?

The first Nobel Prize in Physics. He accepted the award but, shy of public speaking, declined to give the lecture that laureates are expected to deliver.

A DEXA scan uses low-dose X-rays to measure what?

Bone density. Two X-ray beams of different energies pass through the bones, and the difference in how they are absorbed reveals thinning that an ordinary X-ray would miss.

Which two men shared the 1979 Nobel Prize in Medicine for developing the CT scanner?

Godfrey Hounsfield and Allan Cormack. They never worked together: Cormack published the mathematics in 1963 and 1964, and Hounsfield, unaware of it, engineered a scanner of his own.

The first CT scanner was built at which electronics company, better known for its record label?

EMI. Its engineers had worked on radar and built an early all-transistor computer before turning to medicine, and the first machines were sold as the EMI-Scanner.

In 1971 the first CT scan of a patient was carried out at Atkinson Morley Hospital in which city?

London. The scan picked out a cyst in the patient's brain; the experimental rig had been tested on bullocks' brains, which its inventor carried across the city on public transport.

On the scale that CT scanners use to grade how dense each tissue is, which substance is fixed at zero?

Water. Everything else is scored against it, denser tissue above zero and lighter material below, so every shade of grey in a CT image is really a number.

The word tomography comes from Greek words meaning what?

Slice and write. The name fits a method that records the body one cross-section at a time, where an ordinary X-ray piles every layer into a single overlapping shadow.

Instead of X-rays, an MRI scanner builds its images using a powerful magnet and pulses of what?

Radio waves. Each pulse knocks nuclei in the body's tissues out of line with the magnetic field, and the scanner reads the faint signals they give off as they swing back.

Who shared the 2003 Nobel Prize in Physiology or Medicine for discoveries concerning MRI?

Paul Lauterbur and Peter Mansfield. Lauterbur showed that varying the magnetic field across a sample could turn its signals into a picture, and Mansfield made the method fast enough for hospitals.

Who performed the first full-body MRI scan of a human being, in 1977?

Raymond Damadian. He named his hand-built machine Indomitable, and the first person it scanned was not Damadian himself but his graduate assistant, Larry Minkoff.

In what unit is the field strength of an MRI magnet measured?

Tesla. The unit honours the inventor Nikola Tesla, and a hospital scanner's field is strong enough to fling a steel wheelchair across the room, which is why metal is kept out.

Which nuclei does conventional MRI image, because they are so abundant in the body's water and fat?

Hydrogen protons. Each one behaves like a tiny magnet that lines up with the scanner's field, and with so much water in every tissue there are enough of them to give a clear signal.

Marie Curie's mobile X-ray units for First World War field hospitals were nicknamed what?

Little Curies, or petites Curies. Curie drove one of the vans herself and worked near the front with her teenage daughter Irène, using the X-rays to find metal splinters in wounded soldiers.

Marie Curie named which element, the first she discovered, after her native country?

Polonium. She was born in Warsaw at a time when Poland had been carved up between its neighbours, and the name was a way of putting her country back on the map.

Which Glasgow professor pioneered obstetric ultrasound, with a landmark Lancet paper in 1958?

Ian Donald. He borrowed an industrial technology built to find flaws in metal welds and pressure vessels, and worked with an engineer to turn it into a scanner for unborn babies.

The ultrasound technique for measuring blood flow is named after which 19th-century physicist?

Christian Doppler. He was really writing about starlight, arguing that a moving star's colour should shift just as a moving sound's pitch does; the sound version was confirmed three years later.

Why is sharper, higher-frequency ultrasound reserved for structures close to the skin?

It cannot penetrate deep tissue. The body absorbs high-pitched sound more quickly, so scans trade detail for depth: high frequencies for tendons, lower ones for the liver or kidneys.

Which inventor built an early commercial fluoroscope, then gave up X-ray work after his assistant was fatally injured by radiation?

Thomas Edison. The assistant was a glassblower, Clarence Dally, who died in 1904 after losing a hand to radiation burns; Edison himself came close to losing his eyesight.

What is the most common radiographic examination in medicine?

The chest X-ray. It shows the heart, lungs and ribs in a single exposure, for a dose matching only days of the natural background radiation everyone receives.

Which two elements are the classic contrast agents swallowed or injected to show up on X-rays?

Iodine and barium. Both are heavy elements that block X-rays, so a barium drink outlines the stomach and gut on the image, while iodine compounds are the ones given by injection.

Which Portuguese neurologist developed cerebral angiography in 1927?

Egas Moniz. He went on to share the 1949 Nobel Prize in Medicine, not for this work but for devising the brain operation known as lobotomy.

Who invented angioplasty and the catheter-delivered stent, the 'father of interventional radiology'?

Charles Dotter. In 1964 he slid a catheter through a blocked leg artery in a woman who had refused amputation, opening it without surgery; the method has since saved thousands of limbs.

What is the most commonly used medical radioisotope in the world?

Technetium-99m. Its gamma rays are easy for a camera outside the body to detect, and with a half-life of six hours nearly all of it has decayed within a day, keeping the dose low.

Radioactive iodine is used to scan and treat which gland, which naturally soaks up the element from the blood?

Thyroid. Because the gland collects iodine to make its hormones and no other organ absorbs much, a dose of radioactive iodine homes in on thyroid cells and destroys them from within.

The most common tracer in PET cancer scans is a radioactive look-alike of which nutrient?

Glucose. Cancer cells are more metabolically active and take up sugar faster than their neighbours, so they hoard the tracer and show up as bright spots on the scan.

What does the 'P' in PET scan stand for?

Positron. The tracer gives off these antimatter twins of the electron; each soon meets an electron and the pair vanish in a flash of gamma rays that the scanner's ring of detectors picks up.

The SI unit of absorbed radiation dose, one joule per kilogram, is named after which physicist?

Louis Harold Gray. A hospital physicist by trade, he pioneered ways of measuring how much energy X-rays and radium deposit in living tissue, which is exactly what his unit counts.

Which natural source gives the average person the largest share of their yearly background radiation dose?

Radon gas. It seeps out of the ground and collects inside buildings, so the dose a person gets varies widely depending on where they live.

What does the radiation-safety acronym ALARA stand for?

As Low As Reasonably Achievable. In practice the rule comes down to three habits: spend less time near the radiation, keep further away from it, and put shielding in between.

On a mammogram, the tiny white specks that doctors check for signs of early cancer are deposits of what?

Calcium. The deposits have nothing to do with how much calcium you eat, and they are too small to feel, which is why it takes the X-ray to find them when there is no lump to notice.

The Radiological Society of North America holds its vast annual meeting at McCormick Place in which city?

Chicago. The meeting once travelled from city to city, stopping in Washington as late as 1984, before the society made McCormick Place its regular home.

In an imaging department, who is the medical doctor who interprets the scans and writes the report?

The radiologist. The job takes medical school plus years of specialist training; the radiographer, by contrast, is the professional who positions the patient and takes the images.

From the 1930s to the 1950s, many shops used X-ray fluoroscopes to check the fit of what?

Shoes. Child, parent and salesman each peered through a viewing port at the glowing bones of the feet inside the new pair, while the customer stood right on top of the X-ray tube.

Which protective garment is traditionally worn during dental and fluoroscopic X-rays?

A lead apron. Lead's atoms are so heavy and tightly packed that a thin sheet sewn into the fabric stops most stray X-rays, which would sail through ordinary cloth.

Why is gel spread on the skin before an ultrasound scan?

To let the sound through. Ultrasound bounces back from even a tiny gap between probe and skin, so the gel fills it and lets the pulses pass into the body and their echoes return.

Where in the electromagnetic spectrum does X-radiation sit?

Between ultraviolet and gamma. Their waves are so short, some no longer than a single atom is wide, that scientists usually describe X-rays by their energy instead of their wavelength.

The workhorse isotope of nuclear medicine is 'milked' each day from hospital generators loaded with which parent element?

Molybdenum. Its isotope molybdenum-99 lasts just long enough, with a half-life of 66 hours, to be shipped to hospitals, where the short-lived isotope it decays into is flushed out as needed.

At which university's Physical Institute was Röntgen working when he discovered X-rays in 1895?

Würzburg. Working in a darkened room with his vacuum tube sealed in black card, he noticed a chemically coated screen glowing two metres away, where no known ray could have reached it.

The young Röntgen was expelled from school after being wrongly blamed for what?

A caricature of a teacher. Someone else had drawn it, and without a school diploma he could attend a Dutch university only as a visitor, so he sat the entrance exam for Zurich's Polytechnic instead.

An angiogram is an X-ray examination, made with injected dye, of which part of the body?

Blood vessels. They do not show clearly on an ordinary X-ray, so a contrast dye is injected first and the pictures are taken as it flows through them.

What was the title of Röntgen's first paper announcing X-rays, written at the end of 1895?

On a New Kind of Rays. He wrote it up after seven weeks shut away in his laboratory, and the journal Nature printed an English translation the following month.

Which element is the basis of most contrast agents injected for MRI scans?

Gadolinium. It speeds up the signal coming from the tissue around it, and the faster that signal recovers, the brighter the area appears on the scan.

Why did Röntgen, like the Curies, refuse to patent his discovery?

He wanted society as a whole to benefit. It did so quickly: within weeks of his announcement, doctors were using X-rays to look inside their patients.

Most MRI scanners keep their superconducting magnets cold with which liquefied gas?

Helium. It has the lowest boiling point of any element, cold enough for the magnet's coils to superconduct, so a conventional scanner keeps them in a large bath of it.

Functional MRI maps which parts of the brain are active by tracking changes in what?

Blood oxygen. Busy brain cells use more oxygen and draw in fresh blood to replace it, so the scanner can spot working regions with no injection and no radiation.

CT scans were long known as 'CAT scans', short for computed what tomography?

Axial. The X-ray beam circles the patient and a computer turns the readings into cross-sections of the body, which can then be stacked into a three-dimensional picture.

In a Harvard study, most experts checking lung CT scans for nodules missed which animal pasted into the images?

A gorilla 48 times the size of a typical nodule went unseen by 83% of the 24 specialists tested. Eye tracking showed that most of those who missed it had looked straight at it.

Soviet bootleggers cut banned music onto discarded hospital X-ray films, making records known by which nickname?

Ribs were cut into seven-inch discs from films bought or fished out of hospital bins, and the centre hole was burned through with a cigarette. The trade thrived in the 1950s and 1960s.

A 2005 CT scan of which Egyptian pharaoh's mummy ruled out the old theory of murder by a blow to the head?

Tutankhamun's loose skull fragments turned out to have moved after death, which cleared the murder theory. The scan pointed instead to a previously unnoticed leg fracture.

X-rays and a CT scan in 2001 revealed what lodged in the left shoulder of Ötzi the Iceman?

An arrowhead had gone unnoticed for a decade after the mummy was found in the Alps in 1991. With his other wounds, it convinced researchers that Ötzi was killed by another person.

The 'Radium Girls' were American factory workers poisoned while painting glowing numbers onto what?

Watch dials needed a fine brush tip, so the women were told to point their brushes on their lips and swallowed radium daily. Their lawsuits left a lasting mark on labour law.

A franchised American beauty system once aimed X-rays at women's bodies for which cosmetic purpose?

Hair removal by X-ray worked, and usually for good, but it left thousands of women with skin burns, ulcers and tumours. The method is illegal in the United States.

Which fruit lends its name to an informal unit for explaining tiny radiation doses?

Banana equivalent dose compares an exposure with eating one average-sized fruit, which carries a trace of naturally radioactive potassium-40. The body excretes the surplus, so the dose never builds up.

An early X-ray machine at the 1901 Pan-American Exposition went unused when which US president was shot there?

William McKinley died of gangrene eight days later, and one bullet in his abdomen was never found. A surgeon later said the machine might have disturbed the patient for no real gain.

Physicist Paul Langevin built an early ultrasound transducer during the First World War to detect what?

Submarines were the target of his device, a thin sheet of quartz sandwiched between two steel plates. The idea had reached the French government from a Russian engineer named Chilowski.

Mass miniature radiography, widely adopted in the 1950s, screened entire populations for which lung disease?

Tuberculosis laws in Brazil and Japan once obliged about 60% of the population to be screened this way. The method, a small photograph of an X-ray screen image, was largely dropped in the 1970s.

Which handheld radiation detector, known for audible clicks, grew from 1908 work under Ernest Rutherford?

Geiger counter clicks each mark one ionising event inside a gas-filled tube. Hans Geiger's 1908 technique only became a practical instrument in 1928, once the Geiger–Müller tube arrived.

Which metal, once the standard filament in light bulbs, forms the target that electrons strike in most X-ray tubes?

Tungsten has the highest melting point of any metal, at 3,422 °C. It needs it, because only about 1% of the energy striking the target leaves as X-rays and the rest turns to heat.

Which childhood disease of vitamin D shortage shows on radiographs as bowed legs with cupped, frayed bone ends?

Rickets leaves growing bone under-mineralised, so the changes show first where growth is fastest. A full survey needs only pictures of the knees, wrists and ankles.

Which substance, the hardest in the human body, appears lightest of all the tooth layers on a dental X-ray?

Enamel is about 96% mineral, the highest share of anything in the body, so it stops more of the beam than the dentine or pulp beneath it.

Before an ultrasound scan of the pelvis through the abdomen, patients are often asked to arrive with which organ full?

The bladder, when full, acts as an acoustic window. Sound crosses fluid with less loss, which gives a clearer view of the uterus and ovaries lying behind it.

What is the medical name for the condition often called a collapsed lung, usually confirmed with an X-ray or CT scan?

Pneumothorax is the usual meaning, though 'collapsed lung' can also refer to atelectasis. The first picture is ideally taken from behind while the patient holds a full breath.

Which allied health professional performs ultrasound scans and may specialise in obstetric, cardiac or vascular work?

Sonographer is the title of the person holding the probe. A sonologist, by contrast, is a medical doctor with extra ultrasound training who can report scans independently.

In radiographic positioning, which way does a patient lie when placed supine, the opposite of prone?

Face up is supine: the patient lies flat with the torso facing the ceiling. Putting babies to sleep this way is said to explain the decline in sudden infant death syndrome.

Which precious metal, held as light-sensitive crystals in traditional X-ray film, can be reclaimed from spent films?

Silver sits in the film as halide grains, mainly silver bromide. Developing turns the exposed grains into opaque metal, darkest where the most radiation arrived.

Which French physicist discovered radioactivity in 1896 while testing uranium salts for X-ray-like radiation?

Henri Becquerel was inspired by news of X-rays weeks earlier and expected bright sunlight to trigger the glow. He shared the 1903 Nobel with Marie and Pierre Curie.

X-rays, like visible light, travel as massless packets of electromagnetic energy known by what name?

Photons in an X-ray beam each carry enough energy to ionise atoms, which visible light cannot manage. The name comes from the Greek word for light.

What small badge-like device do X-ray staff wear on the torso to record their cumulative radiation exposure?

A dosimeter matters because radiation damage adds up over a career. Electronic models sound an alarm when a set limit is passed, while film types must be processed before they give a reading.

The international warning sign for ionising radiation, three black blades around a dot, is known by what name?

Trefoil signs were first drawn in 1946 at the Berkeley Radiation Laboratory, in magenta on a blue background. The magenta was picked because it was expensive and unlikely to turn up on other signs.

What term describes a material, such as metal, that blocks X-rays and therefore looks white on a radiograph?

Radiopaque materials such as bone look white or light grey, while radiolucent ones let the beam pass and show dark. Contrast agents work by being deliberately radiopaque.

Which dental X-ray view, used to find decay between the back teeth, takes its name from a paper or plastic tab?

Bitewing films carry the tab at their centre, and the patient clamps it between the teeth. That holds the film so it catches the upper and lower crowns in equal measure.

The Cobb angle, measured on a standing radiograph of the back, grades the severity of which condition?

Scoliosis curves are measured standing because lying down shrinks the angle by around 7 to 10 degrees. Beyond 60 degrees, breathing complications are usual.

Ultrasound is defined as sound above roughly which frequency, the upper limit of healthy young human hearing?

20 kilohertz is the ceiling set by the limits of the middle ear. Medical scanners generally work far above it, at between 1 and 18 megahertz.

In 1929, burning X-ray film filled which American medical centre with poisonous gas in a fire that claimed 123 lives?

Cleveland Clinic kept thousands of pounds of nitrocellulose film in a basement room, and the fumes spread through the building's pipe shafts. The dead included one of its own founders.

Which Swedish medical physicist gives his name to the SI unit that expresses the health risk of a radiation dose?

Rolf Sievert spent his career on the biological effects of ionising radiation, heading the physics laboratory at Sweden's Radiumhemmet from 1924 to 1937.

Which law of physics explains why stepping twice as far from an X-ray source cuts the exposure to a quarter?

The inverse-square law says intensity falls with the square of the distance, so tripling the distance brings a ninefold drop. It guides both diagnostic radiography and radiotherapy planning.

Which anatomical plane, named from the Latin for arrow, divides the body into left and right sections on a scan?

Sagittal was coined by Gerard of Cremona. One way to picture it is an arrow passing through the body from front to back, with the plane running along its flight.

What nickname do doctors give a symptomless lump, often on the adrenal gland, found by chance on an unrelated scan?

Incidentaloma lumps on the adrenal gland are common and seldom cancerous. Suspicious ones, or those 4 cm or more across, are usually recommended for removal.

Which central compartment of the thorax, seen between the lungs on a radiograph, holds the heart, windpipe and gullet?

The mediastinum also packs in the thymus, lymph nodes and several major nerves. Anatomy texts divide it in various ways, but Felson's radiological scheme uses just three compartments.

A hysterosalpingogram uses X-ray dye in fertility tests to show whether which structures are blocked?

Fallopian tubes count as open only when the dye is seen spilling from their far ends into the abdominal cavity. The same pictures outline the shape of the womb.

Myelography, an X-ray test using contrast injected after a lumbar puncture, looks for disease of which structure?

The spinal cord is outlined by dye placed in the fluid-filled sac around it. Doctors use the test to find cysts, tumours and the level of an injury in patients who are unable to have an MRI.

Which hazy lung pattern, greyer than normal lung but not solid white, was among the commonest CT findings in COVID-19?

Ground-glass opacity is haze where the lung should look dark, seen when fluid, collapse, scarring or a tumour displaces what normally fills the airspaces.

What name is given to the frame of a CT scanner that carries the rotating X-ray tube and the row of detectors?

The gantry of a hybrid PET-CT machine holds two scanners at once, so both sets of pictures are taken in a single session and laid over each other.

Until about 1918 a radiographer was called a 'skiagrapher', from the Ancient Greek for writer and which other word?

Shadow fits because a plain radiograph records what is left of the beam after the body has absorbed part of it. The pictures themselves were first known as roentgenograms.

Marie Curie died in 1934 of which disorder, blamed on radiation from her research and wartime X-ray work?

Aplastic anaemia killed her at the age of 66 in the Sancellemoz sanatorium at Passy, in the French Alps. Her radiological work at field hospitals is thought to have added to the damage.

Ultrasound probes make and detect sound using crystals that change shape under voltage, a property known as what?

The piezoelectric effect was discovered in 1880 by the brothers Jacques and Pierre Curie. It runs both ways: squeezing the crystal produces a charge, which is how returning echoes are read.

Wilhelm Röntgen was running which vacuum apparatus, named after an English chemist, when he first noticed X-rays?

A Crookes tube wrapped in black cardboard was running on 8 November 1895 when a fluorescent screen nearby began to glow faintly. Seven weeks later Röntgen published the first paper on the rays.

Which worldwide standard for storing and sending medical images grew out of an ACR and NEMA document released in 1985?

DICOM stands for Digital Imaging and Communications in Medicine. It exists so that scanners, archives and viewing stations made by different manufacturers can exchange pictures.

Which German doctor threaded a catheter into his own heart in 1929, then had it recorded on X-ray film?

Werner Forssmann let a nurse believe the catheter was going into her arm, then walked with her to the X-ray department on the floor below. He shared the 1956 Nobel Prize in Medicine.

Which General Electric physicist invented the hot-cathode X-ray tube in 1913?

William Coolidge had already transformed the light bulb at General Electric with experiments on a tougher metal filament. He lived to the age of 101.

Which German word names the X-rays given off when fast electrons are abruptly slowed near atomic nuclei?

Bremsstrahlung means 'braking radiation'. It supplies the smooth, continuous part of an X-ray tube's output, on which sharp spikes characteristic of the target metal are superimposed.

Which process, named after an American physics Nobel laureate of 1927, sees X-rays bounce off electrons and lose energy?

Compton scattering was discovered in 1923 by Arthur Holly Compton, who was studying how light elements deflect X-rays. The lost energy shows up as a longer wavelength.

A memorial unveiled in 1936 in which German city names X-ray and radium pioneers who died from their work?

Hamburg's memorial stands outside St Georg Hospital and began with 169 names from fifteen nations. By 1959 the list had grown to 359.

Which Swedish doctor gives his name to the 1953 needle-and-guidewire technique used to pass catheters into arteries?

Sven Seldinger's method slides a round-tipped guidewire through a hollow needle, withdraws the needle, then passes the catheter over the wire. The same trick places kidney drains and pacemaker wires.

Which Oxford doctor showed in the 1950s that X-raying pregnant women raised the cancer risk in their children?

Alice Stewart's findings were eventually accepted worldwide, but it took around two and a half decades for X-rays in pregnancy and early childhood to be curtailed.

A boot-shaped heart on an infant's radiograph is the classic sign of which congenital heart defect?

Tetralogy of Fallot thickens the wall of the right ventricle, producing the outline the French call coeur en sabot. Most affected infants, though, never show it.