By Assoc Prof Dr Y Faridah, MRad and Assoc Prof  Dr B J J Abdullah FRCR
Department of Radiology,  University of Malaya, Kuala Lumpur, Malaysia

The Discovery
On November 8th 1895, Wilhelm Conrad Roentgen, a physics professor at the University of Wurzburg, made a startling discovery. While experimenting with a cathode-ray tube with evacuated glass bulbs, Roentgen noted that when a current was passed across the bulb, a barium platinocyanide screen was seen to fluoresce. He realized that the glow seen on the screen had to have been produced by a more penetration radiation than cathode rays. He sequestered himself in a darkened laboratory and while passing his hand between the tube and fluorescing screen, he was amazed to see what appeared to be shadows of his bones (1-5).

On January 23rd 1896, approximately two months after his discovery, he presented his findings on “A New Kind of Ray” (“Eine Neue Arte von Strahlen”) to the Physico Medical Society of Wurzburg, using as evidence the now-famous radiograph of a human hand (either the hand of his wife, Bertha Roentgen, or Professor Killiken, his colleague). Hence the birth of Radiology as a medical specialty could be traced to that exact moment in history (6).

These new rays were called ‘x-rays’ because x was the mathematical symbol for an unknown quantity. It was found that x-rays interact with atoms in the material being exposed, leaving atoms that have an electrical charge (ions). Till this day, ‘x-rays’ are called ionizing radiation. The equipments used by Roentgen were easily available and soon his experiment was duplicated. The apparatus was demonstrated in scientific and medical meetings but was equally popular at fun fairs. Within four months of Roentgen’s discovery, the first clinical diagnostic radiograph with an exposure time of 20 minutes made its appearance in America and was being used in Europe and other English-speaking countries. Within a year of Roentgen’s work there were nearly 1000 scientific papers published regarding x-ray. For this momentous discovery, Roentgen was awarded the first Nobel Prize in Physics in 1901 (4-6).
 

In the early years, radiographs were initially made onto glass photographic plates which were coated with emulsion only on one side. In 1918, Eastman introduced film coated with emulsion on two surfaces (4). Radiography at this time was focused on imaging of extremities, mainly to detect fractures and to localize position of bullets. This was due to the fact that bone, soft tissue and dense foreign bodies provided the only contrast between materials. In 1910, orally administered contrast medium (bismuth nitrate later replaced by barium sulphate) was used to image the gastrointestinal system. Further development brought about an intravenous contrast agent marketed for urinary tract radiography in 1927 (5).
 

The next development involved the use of fluorescent screen, an x-ray tube, an x-ray table and red goggles and required the radiologist to stare directly into the screen so that x-ray images could be displayed in real time. This was a rather primitive method as the fluorescence emitted was very dim. Residents trying to learn the art at that time were at a tremendous disadvantage and had a particularly difficult and frustrating time to see what their professor’s claim they saw on the fluoroscope (7). It was not until the 1950s that image intensifiers alleviated this situation by producing an image bright enough to be viewed. This allowed better depiction of real time radiographic image, paving the way for angiography (7).  

An x-ray system in the early years in which patients had to hold the cassettes themselves

The first iodine-based contrast arteriogram in a patient was reported in 1929 by Dos Santos, approximately 34 years after the discovery of x-ray. However without the benefit of the image intensifiers at this time, arterial access was obtained via a blind translumbar puncture. The emergence of image intensifiers gave a much-needed boost to this flagging enterprise. Greater steps were taken when Seldinger introduced a safer, simpler and more effective method of accessing the femoral artery (8). Despite the advent of the Seldinger technique, real advances in diagnostic angiography were still stunted, as fluoroscopy remains primitive. In the late 1980s and early 1990s however, two essential technologies have greatly impacted the evolution of angiography: movable multiple-angle C-arm fluoroscopy and digital image acquisition (8). 

By this time however, advances in cross-sectional image technologies were eroding the traditional diagnostic arteriography base. By the 1970s, ultrasound (US) and computed tomography (CT) had arrived displacing angiography as the supreme imaging tool in radiology. By the late 1990s, duplex US, CT angiography and Magnetic Resonance (MR) angiography began to replace diagnostic arteriography for the direct study of vascular pathology. It had seemed by necessity that emphasis was then given to therapeutic use of angiography. In most radiology departments today, that catheter-based angiography is reserved mainly for diagnosis of atherosclerotic vessels and as an adjunct to interventional procedure (8).
 

Early imaging studies were projections of 3-Dimensional (3D) body parts displayed as if a steamroller as in our favourite cartoons had flattened the human body. This results in much overlap of the body parts making interpretation of disease difficult. The emergence of three powerhouse imaging tools namely ultrasound, computed tomography and magnetic resonance imaging have revolutionized the care of patients across the continuum of medicine and surgery. Sound energy, researched and used by the defense department as wartime sonar, was the basis of ultrasound imaging, which emerged in the 1960s. Ironically sonar technology initially used as an aid to destruction of humanity during the Second World War was channeled to create a tool for saving lives. For the first time, there is an imaging tool that does not use ionizing radiation. Radiology is now often referred to as ‘imaging’ reflecting the fact that it is no longer dependant on x-rays alone. Over the years, ultrasound has stood the test of time proving to be a safe, reliable, portable and cheap imaging modality.  

Further advancement in ultrasound includes the development of high frequency probes and Doppler technology. Currently ultrasound scanners are a must have in all hospitals and medical outfits not just for diagnostic work but also for image guided biopsies and catheter placements. But it was not until 1972 that cross-sectional imaging became a catch phrase. This was attributed to the invention of computed tomography (also known as computed axial tomography or CT Scan). A British engineer, Godfrey Hounsfield incorporating methods of inversion technique previously described by a South African-born physicist, Allan Cormack; presented a way to use CT for clinical use, and developed a machine to do so. Derived from the Greek words tomos, meaning slice, and graphein, meaning representation, CT imaging from the outset showed the ability to give detailed axial images of the human body (9, 10).  

Hounsfield initially used gamma ray, which took 9 days to produce a picture. Replacing the gamma source with a more powerful x-ray tube source reduced the scanning time to 9 hours. The first picture of a brain showing grey and white matter was produced then (11).

CT scan image of one section of the brain in 1970 (left) compared to 1980.

The earliest CT scanners were limited to imaging of the head. By 1976 the technology had evolved to whole body scanners, and by the 1980s CT Scans had gained worldwide acceptance. Today there are an estimated 30,000 locations around the world where this diagnostic tool is in use. The prototype CT Scanners took roughly four minutes of lapsed time to acquire a single image. Currently, modern units produce images in less than 0.5 seconds.  

The advent of CT had an enormous effect on our ability to ‘see’ inside the body and immediately changed the practice of medicine. Lauterbur reported in 1973 that he could use a similar strategy to reconstruct the nuclear magnetic properties of materials. At about the same time, Mansfield also suggested that appropriate analysis of nuclear magnetic resonance (NMR) signals could be used to infer the spatial arrangement of their sources. Lauterbur and Mansfield realized that an image of the distribution of nuclei in the body could be produced by analyzing the frequencies of the currents (i.e. NMR signals) recorded when the magnetic field is varied. Within a year, this method was used to obtain an image of a dead mouse (12). By 1982, first images obtained using a 1.5 Tesla system were displayed. Today, imaging of the human body is being attempted at field strength of more than 9 T - once again stretching the limits of radiofrequency coil and magnet technology. 

The momentum created by CT scanners fueled the commercial development of MRI systems. In its infancy, many thought that MRI would have a limited impact because of its high cost, the technical difficulties associated with it and the belief that CT scanning was a superior method of imaging. MRI has quickly become the primary imaging method for brain and spine imaging as well as functional imaging of the heart (12).
 

Early radiology was rooted in morphology, namely skeletal morphology. The change towards imaging of physiology of the human body began with nuclear medicine. With this transformation comes the ability to not only display presence of diseases but also the mechanism of disease and the biology of treatments. In the midst of the excitement brought about by Roentgen’s discovery, Becquerel discovered radioactivity in the early 1896. Thus began the dawn of the nuclear age. Similar to the discovery of x-rays, the discovery of phosphorescence was accidental. Becquerel had placed some photographic plates in a drawer with some crystals of uranium. Upon retrieving the plates, he found that the plates had been exposed. He deduced that exposure must have been from rays of a radioactive source i.e. the uranium crystals themselves (13). 

Next: Into the world of digital imaging >>>

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Last Updated:
Tuesday, 04 January 2005