Autopsy of the living  pg. 3

The discovery of naturally-occurring radioactive elements, like uranium, polonium and radium, in the late 19th century sparked the “atomic age.” However, these naturally radioactive elements are not normally found in the body, so their medical use was limited.

In 1934, the creation of artificial radioisotopes of normally non-radioactive elements common in the body (including carbon, oxygen, nitrogen and fluorine) gave physicians the tools they needed to adapt radioactive compounds for medical purposes. As these radioisotopes decayed, they produced gamma rays, which could be detected with a Geiger counter.

Deriving an image was not the priority at first; the goal was to detect “hot spots” in the body where the radioactive compounds accumulated. But, in 1951, Benedict Cassen, Ph.D., at UCLA built the scintiscanner, a device that scanned the body using pen-sized gamma ray detectors and created a crude print-out of those hot spots. Acquiring a usable image from these radioactive compounds suddenly seemed possible.

In 1968, the first nuclear imaging machine, single photon emission computed tomography (SPECT) was built. However, the seminal advance in nuclear imaging came in 1975, when Michael Phelps, Ph.D., and Edward Hoffman, Ph.D., at Washington University in St. Louis reported their development of PETT (positron emission transaxial tomography), later shortened to “PET.”

When a positron emitted by a decaying radioisotope collides with a nearby electron, two gamma rays traveling in opposite directions are produced. Using a hexagonal array of gamma detectors and computational methods similar to those that generated CT images, the Washington University scientists built a device that could construct three-dimensional “maps” of positron emission deep within the body.

PET was primarily used for research purposes until 1979, when another milestone—the development of radioactive FDG (fluorodeoxyglucose), a glucose analog—further propelled the technology into the medical field. With FDG, physicians can track the metabolic activity of cells, aiding in the diagnosis of cancer and other diseases.

Smiling in the womb

In 1877, the discovery of piezoelectricity laid the foundation for one of the safest and most economical methods of seeing into the body—ultrasound.

Piezoelectric crystals generate a voltage in response to applied mechanical stress, including sound waves. During World War I, they were used in the first sonar devices to detect sound waves bounced off enemy submarines.

In 1937, sound waves were first transmitted through a patient’s head to derive a crude image of the brain. Ultrasound ultimately found its niche in obstetrics and gynecology in the 1950s following reports of the damaging effects of X-rays on the fetus.

Since then, ultrasound has morphed from flat black-and-white, two-dimensional images intelligible only to trained professionals to the sharp and startling 4-D “movies” of the fetus kicking, yawning and smiling in the womb.

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