Learn all about the developments of medical imaging and radiology, which thankfully allow us to view inside the living human body without having to cut it open.
Introduction
Medical imaging, also referred to as radiology, consists of different types of technology that are used to view inside the living human body without having to cut it open. Each technology provides different information which can assist with the diagnosis and treatment of a specific disease or injury. Medical imaging offers invaluable anatomical and functional information and has contributed significantly to the advancement of modern medicine, changing the landscape of illness prevention and treatment, and saving countless lives each year.
In recognition of the impact and remarkable contribution that medical imaging has had on healthcare, International Day of Radiology is celebrated on 8th November each year, which is the anniversary of X-ray discovery by German physicist Wilhelm Roentgen.
The Discovery of the X-Ray
On November 8th, 1895, German physicist Wilhelm Roentgen was the first to observe X-rays. X-rays are a type of radiation called electromagnetic waves that act similar to light rays but at much shorter wavelengths. Roentgen noticed a glow coming from a chemically coated screen while he was testing cathode rays and their ability to pass through glass. The glow was caused by invisible rays originating from the glass tube he was using by penetrating the opaque black paper he had wrapped around the tube.
Fascinated, Roentgen experimented further, discovering that this new type of ray was capable of passing through the skin and other soft tissues of the body while leaving bones and metals visible. One of his first experiments shows a film of his wife Bertha’s hand with her wedding ring clearly visible. The only reason he called these rays “X-rays” was because of their unknown nature.
Roentgen’s discovery had made the invisible visible and was hailed a miracle by the medical community around the world. In 1901, he was awarded the Nobel Prize in Physics.
Computed Tomography
Computed tomography (CT) is a computerized X-ray imaging technique. During a CT scan, a narrow beam of X-rays is aimed at a patient while quickly rotating around the body, and the signals produced are then processed by the machine’s computer to generate cross-sectional images of the body, also known as ‘slices.’ These slices offer a lot more detailed information than conventional X-rays, showing soft tissue contrasted with anatomic details, thus allowing unprecedented diagnostic accuracy.
The first CT machine, considered one of the most important innovations of all time, was invented in 1967 by Sir Godfrey Hounsfield, a British engineer. American physicist Alan M. Cormack developed the early mathematical models used in CT. In 1979, both were awarded the Nobel Prize for Physiology or Medicine.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is very different to CT as it uses different physical principles and doesn’t involve X-rays. It is based on a phenomenon called ‘nuclear magnetic resonance’ (NMR) and was discovered in the 1930s simultaneously and independently by two American scientists – Felix Bloch at Stanford University and Edward Purcell at Harvard – and involves magnetic fields and radio waves that cause atoms to give off tiny signals.
The first MR scanner was completed in 1977 by Raymond Damadian, an American physician who wanted to invent a machine that would show human tissue and diagnose disease. And he did just that. In MRI technology, a powerful magnet produces a fixed magnetic field around the patient while radiofrequency pulses excite protons within the body. An image is created by capturing the return signals from the excited protons as they relax back to a resting state.
MRI is considered the ultimate medical imaging technique because of the soft tissue contrast and anatomical details it provides, and today it is used in almost every medical subspecialty.
Ultrasound
Ultrasound uses high-frequency soundwaves that are above the range of human hearing and are transmitted into the body. The echoes produced and reflected are plotted into an image.
The beginning of ultrasound technology can be traced back to 1790 when Italian biologist Lazzaro Spallanzani discovered the echolocation used by bats to maneuver through the air; they use their hearing to capture the return of the high-frequency sound they emit, in order to navigate in the dark.
The first use of ultrasound as a medical diagnostic imaging technique was in 1942, when neurologist Karl Dussik attempted to locate brain tumors through the human skull. In 1958, gynecologist Ian Donald was the first to use ultrasound to study the unborn fetus, uterus, and the pelvis in pregnant women. Since then, ultrasound technology has continued to advance, making it an inexpensive and widely available imaging modality.
Positron Emission Tomography
Positron emission tomography (PET) is a result of advances across several scientific fields such as physics, mathematic, chemistry, computer science and biology. Dr Michel Ter-Pogossian, a nuclear scientist at Washington University, is considered the father of PET as his experiments in the 1950s led to the development of PET as a medical diagnostic tool.
According to Johns Hopkins Medicine, PET is “a type of nuclear medicine procedure that measures metabolic activity of the cells of body tissues. PET is actually a combination of nuclear medicine and biochemical analysis.”
In PET scans, patients are injected with a radioactive drug called tracer which will then collect in areas of the body with higher level of metabolic or biochemical activity, thus indicating disease. The huge advantage of this type of imaging is that the tracer can detect diseases before they show up in CT or MRI, and today it can be used in combination with those to provide exceedingly accurate disease detection and diagnosis.
Challenges in Medical Imaging
Medical imaging has grown faster than any other medical service. As a result, doctors are increasingly relying on imaging and laboratory testing, thus increasing healthcare costs.
However, as much as medical imaging plays a part in diagnosis, it is also a potential source of diagnostic errors. The interpretation of diagnostic medical imaging is dificult to mechanize or automate; it is very dependent on radiologists’ knowledge and perception. In fact, most missed radiological diagnoses are attributable to interpretation errors of radiologists.
Another challenge is the increased exposure of patients to ionizing radiation and nuclear medicine, which, in turn, increases malignancy risks. According to the National Research Council of the National Academies, while high doses of ionizing radiation can produce damaging effects within days after exposure, low levels used in diagnostic imaging can produce ‘late’ effects, like cancer, many years after initial exposure.
