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Medical imaging of
bulky patients
Trends |
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Medical
imaging of bulky patients Researchers identified abdominal obesity as a problem in India. But I do not know of any publication from India on the difficulties of imaging obese patients. In “Radiology Rounds”, the July 2005 newsletter from Massachusetts General Hospital (MGH), Dr Janet Cochrane Miller says that 4.7 per cent of Americans are extremely obese. Technologists have to increase the tube current and also exposure time to improve the quality of x-ray pictures of bulky patients. Radiation dose to patient increases. Increased exposure time causes blurred pictures. The issue is so important that on November 30, the Radiological Society of North America (RSNA) held a special focus session on “Obesity: The Impact on Radiology” during its Annual convention (RSNA 2005) at Chicago. Dr Peter Mueller, division head of abdominal imaging and interventional radiology at MGH, who moderated the session, noted that obesity surgery is the fastest growing area of elective surgery in the abdomen. All radiologists should have working knowledge of this type of surgery and the potential problems these patients may have. Dr Paul Uppot, an assistant radiologist at the Massachusetts General Hospital (MGH), had presented his study on how obesity affects medical imaging during RSNA 2004. He received many phone calls since then. He observed that in a 15-year-old retrospective study of radiologic exams at MGH, researchers found that the diagnostic information of 0.15 per cent of the five million studies was limited by the body weight of patients. They did not include patients whose examinations were cancelled because they could not fit on the table. Dr Walter Pories, professor at the Brody School of Medicine, East Carolina University revealed that 10 to 15 per cent of all images of obese patients had Dr Janet Cochrane Miller noted that fat affects ultrasound images to a greater degree than any other medical imaging modality. At the frequency range normally used for abdominal imaging, one cm of fat attenuates 50 per cent of the beam intensity. At lower frequencies attenuation is less; image resolution is also less. According to Dr Miller, 20 patients in 1000 may not get the benefit of ultrasound scans because of excess body weight. Corresponding data for MRI scan is one in 1000; abdominal CT is 4 in 1000; chest x-ray is 5 Some obese patients are too large to image using even x-ray films of large size. They need multiple cassettes. “When they exceed the weight limit for x-ray tables, patients can sometimes be imaged while standing” Dr Miller wrote. Dr Miller observed that poor image quality in CT exam due x-ray attenuation can be corrected by increasing the tube current and the speed of rotation of the gantry. But the bore of the gantry is only 70 cm, at times too small for some patients; the weight limit for the CT tables is 425-450 pounds. Absorption and scatter of photons affect the quality of image in nuclear medicine. Miller’s prescription is to choose the appropriate radioisotope. This also has limitations. In 1881, Roentgen watched helplessly while his mother was dying of some vague disease. His family physician could not diagnose the malady as he could not see inside the human body. Fourteen years later Roentgen discovered x rays. Many medical imaging modalities made rapid strides. But for many obese patients, the physician has to depend on observation. He may have to operate to identify the problem. Physics of imaging does not offer any
solution till now. — Dr K.S. Parthasarathy is a former Secretary, Atomic Energy Regulatory |
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THIS UNIVERSE
It is a general belief that life is not possible without oxygen. But if the universe contains planets very
different from the earth, why cannot living beings that have evolved there live on some
other gas? When we think of life, we usually have in mind creatures like us. We forget that even on the Earth, there are anaerobic bacteria for which oxygen would be poison. Bacteria also represent life. We do not know what other forms of life might be possible. Viruses can “live” without oxygen and under extreme conditions, including high vacuum; these may be considered as entities that exploit other life forms to reproduce themselves. In that sense, these represent a parasitic form of life. No sensible exobiologist would insist that when we find life on any other planet, we would encounter beings with similar features and physical, social or psychological characteristics identical to what we find on the Earth; yet we can be excused for suspecting that given the universal abundance of elements and the universality of the laws of nature, a pathway to life somewhat analogous to that which developed on the Earth is not too unlikely. Even then, the finer manifestations would be hard to predict, considering the enormous variety of life forms that have evolved even on our own planet. Except for planets in our immediate neighborhood (to which we can send unmanned probes), we may be constrained to detecting only those extraterrestrial civilisations that have developed the technological capability to communicate with us. If the tongue of an animal were replaced with the tongue of a man, would the animal be able to talk? How can we understand the language of
animals? Besides the difficulty of transplanting a human tongue in to an animal, such an experiment would be cruel, foolhardy and useless. The tongue by itself does not do the talking. The brain is also centrally involved. If the brain remains the same, and the nature of the animal is not altered, we may be much worse off. The animal may become incapable of making the sounds it now makes for communicating with other animals or with humans. You have also asked how we can understand the language of animals. I think those who are close to animals and care for them do manage to establish a communication system with them. They understand each other’s language. Remember that we can also learn to communicate with those who are deaf and dumb. I have learnt that conservation of angular momentum is an absolute symmetry of nature. Do you know of anything in nature that violates it? No, Class-9th Ms Gupta, I do not. It would be like saying that the Earth could suddenly stop rotating without anything from outside disturbing it. |
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Trends Using building blocks that make up ordinary plastics, but putting them together in a whole new way, University of Michigan researchers have created a class of lightweight, rigid polymers they predict will be useful for storing hydrogen fuel. The work is described in the November 17 issue of the journal Science. The trick to making the new materials, called covalent organic frameworks (COFs), was coaxing them to assume predictable crystal structures — something that never had been done with rigid plastics. “Normally, rigid plastics are synthesised by rapid reactions that randomly cross-link polymers,” said postdoctoral fellow Adrien Côté, who is first author on the Science paper. “Just as in anything you might do, if you do it really fast, it can get disorganised.” For that reason, the exact internal structures of such materials are poorly understood, making it difficult to predict their properties. But Côté and colleagues tweaked reaction conditions to slow down the process, allowing the materials to crystallise in an organised fashion instead of assembling helter
skelter.
Gravitational tractor When a wayward asteroid is about to smash into the Earth, scriptwriters for the movie Armageddon called in Bruce Willis to drill into the rock and nuke it. He succeeds but sacrifices his own life. Now, two NASA scientists, both also astronauts, suggest a simpler, safer, and much more plausible way of diverting an offending asteroid. Their method relies on the gravitational tug of a massive, unmanned spacecraft to pull the rock away from a damaging rendezvous with the Earth. The gravitational tractor, as the researchers call their proposed craft, would require the sustained power of a nuclear-propulsion system to reach the asteroid and perform the manoeuvers that would be required to deflect it. For general space exploration, NASA has already proposed a fleet of suitable vehicles, although their funding is currently uncertain.
Internet telephony Ever since the government deregulated internet telephony three years back, more and more Indians are turning to this new technology to keep in touch with their loved ones abroad as it is far cheaper than the normal telephone calls. Despite tight regulations, bandwith problems and the quality of service issues, it is estimated that more than 50 per cent of all international long distance calls from India are made over the Internet, and this is set to go further up in the coming years, say experts. According to a survey by iLocus, by 2007, about 70 per cent of all long distance calls would be made through internet telephony or voice over internet protocol
(VoIP). — PTI |
It
is difficult to x-ray bulky patients. They seldom receive the benefits
of other life-saving, medical imaging techniques such as computed
tomography (CT), magnetic resonance imaging (MRI) or ultra-sonography.