One could not have missed the ubiquitous X-ray images during visits to hospitals. Medical imaging has been around since the discovery of X-rays (a form of electromagnetic radiation; light is also a form of electromagnetic radiation) more than a century ago. Wilmhelm Conrad Röntgen, a professor of Physics discovered X-rays on 8 November 1895, while working with cathode ray tubes in his laboratory in Würzburg, Germany. He called them X-rays because at first he did not understand what they were. X is used as a scientific symbol for the unknown. In a heart-stopping moment, he chanced to pass his hand through the beam. He could see the outline of the bones of his hand. A few days later Röntgen made a photographic image of his wife’s hand, using the new rays instead of light for the exposure. The news of the first radiograph of Mrs. Röntgen’s hand spread fast by the press.
The first clinical images were taken in February 1896. Since then the use of X-rays has been the most important diagnostic imaging method and X-rays still have a central role in radiography. While new techniques such as computed tomography (CT) have been developed, the means of producing X-rays using special tubes (similar to a television picture tube) has altered little since the time of Röntgen.
There is another source of electromagnetic radiation, namely the synchrotron radiation (SR), which is much more powerful than the traditional X-rays. The existence and properties of SR was predicted long before the discovery of the X-rays. SR was experimentally observed for the first time on 24 April 1947, in the visible part of the electromagnetic spectrum, in the electron synchrotron, built at the General Electric Company in Schenectady, New York and hence the name synchrotron radiation.
SR has numerous advantages over the traditional X-Ray sources and lasers. Synchrotron radiation laboratories are large sources of X-rays used to study materials at the molecular and atomic level. SR is produced by accelerating electrons in a large ring (several hundred meters in circumference) almost at the speed of light. This causes the electrons to emit X-rays with additional special properties. The X-rays produced in a synchrotron are a billion times brighter than the ones from a typical clinical X-ray source. This makes SR the most powerful light produced by humans.
Most applications of the X-rays are based on their ability to pass through matter. This ability varies with different substances; for example, wood and flesh are easily penetrated, but denser substances such as metals and bones are more opaque. The penetrating power of the X-rays, primarily depend on their energy, more the energetic the deeper they penetrate. Beams of X-rays emerge from the ring in pipes called beamlines, set at intervals around the synchrotron ring. Instruments at the ends of the beamlines hold samples of the material to be studied and produce 3-D images of a variety of substances.
The applications of the SR span a wide range of domains in fundamental science (chemistry, physics, biology, molecular medicine, etc.), applied research (materials science, medical imaging, pharmaceutical research & development, advanced radiology, etc.,) and industrial technology (micro-fabrication, micro-analysis, photo-chemistry, etc.). SR facilities are technologically challenging, requiring a team of dozens of experts even for their day-to-day running. At the same time these facilities are prohibitively costly, about several hundred million US$. In contrast the X-Ray machines can be run by a single person and costs just a few thousand US$. Because of these reasons, there are very few SR facilities in despite of their numerous applications.
There are about seventy-five synchrotron radiation sources in various stages of operation, construction or planning in countries like Armenia, Australia, Brazil, Canada, China, Denmark, France, Germany, India, Iran, Italy, Japan, Jordan, Korea, Russia, Singapore, Spain, Sweden, Switzerland, Taiwan, Thailand, The Netherlands, Ukraine, the United Kingdom and the USA. It requires several years and government patronage to build such facilities. Iran is the most recent country to join this elite group. The Iranian Light Source Facility (ILSF) is a 3GeV facility, presently in the design phase and to be located at Qazvin 150km northwest of the capital Tehran. From this list it is evident that the world of synchrotron sources has its own share of haves and have-nots! The continent of Africa is yet to have a synchrotron.
The synchrotron radiation sources provide multiple, extremely intense and tunable beams of radiation over a huge range of energies from infrared through hard X-rays. Their advent has revolutionised many experimental techniques adding a new dimension to medical imaging and therapy. Applications range from the imaging of single cells to the imaging of the human cerebrum and heart. In radiation therapy research, applications range from fundamental radiation cell biology studies to new modalities of therapy. It has spawned several methods for studying live and wet tissues samples, yielding information on both structure and composition on all length scales down to atomic resolution. Such techniques have played a crucial role in the development of molecular biology and the solution of protein structure. The application of SR in the field of radiography is now expanding and it is clear that very substantial improvements in image quality and patient dose can be realised. Using SR, it is possible to obtain high- resolution images of small structures, for example, in the heart, lungs, cartilage, and other soft tissues.
Synchrotron images of the heart, the lungs or the brain can be obtained using smaller and less invasive radiation doses than those currently used in hospitals and the high precision of these images means that they can be used in the studies, something that has not been possible up to now. Angiography and imaging technique carried out in hospitals is used to visualise coronary arteries, either to detect narrowing (stenosis) which could lead to heart-attack, or to examine the condition of an artery after an operation such as angioplasty. But angiography is invasive. During the procedure a long flexible tube is inserted into the femoral artery of a leg in order to inject an opaque substance directly into the coronary artery.
Using SR, it has become possible to carry out angiography in a less invasive way. The reason? The use of SR makes it possible to obtain images of excellent quality even with diluted contrast agent. It is therefore possible to inject the contrast agent intravenously in the arm, which is far less invasive than the artery administration mode. Although it results in high dilution of the contrast material prior to arrival in the heart arteries, the SR allows its detection.
Synchrotron-based medical imaging offers major advances in both diagnosis and precision image-guided therapy. Research opportunities include, in neuroscience, orthopedics, cancer, environmental toxicology/ epidemiology, perfusion, and imaging modality development, aging, dementia, multiple sclerosis, arthritis, trauma, sports medicine, enhanced radiation therapies for cancer and heavy metal toxicology, among others. In the emerging post-genomic era opportunities exist for molecular imaging to contribute substantially to accelerated drug discovery, to establish new methods of assessing outcome, and to ultimately improve early disease detection, prevention and therapy.
The field of synchrotron radiation in medicine is growing rapidly. As new facilities come up around the world, it is certain that the growth will continue. Efforts are underway to bring the SR facilities to the clinical environment, however challenging the task may be. But even with little progress in this effort, SR medical research is playing an important role in clarifying the limitations of conventional imaging technologies in the clinical world today. Equipped with such knowledge we can hope for a betterment of medical practice. The year 2014 is being celebrated as the International Year of Crystallography. Light has been at the helm of observational/experimental sciences. The year 2015 has been declared as the International Year of Light and Light-based Technologies. Both the events are a time to recognise the place of X-rays and synchrotron radiation in our lives.
[SAMEEN AHMED KHAN is on the Engineering Department, Salalah College of Technology (SCOT), Salalah, Sultanate of Oman. rohelakhan@yahoo.com]