|SCIENCE TRIBUNE||Thursday, October 17, 2002, Chandigarh, India|
Code division multiple access
PRODUCTS & DISCOVERIES
Routine CT screening can be dangerous
ON April 26, 2002, the US Food and Drug Administration (USFDA) noted that some medical imaging facilities promote and market whole body CT scanning or screening as a preventive or proactive health measure to healthy individuals who have no symptoms or suspicions of disease. FDA does not know of any scientific study, which demonstrates that whole body CT screening is effective in detecting any particular disease early enough for the disease to be managed, treated or cured.
"Any such presumed benefit of whole body CT screening is currently uncertain, and such benefit may not be great enough to offset the potential harms such screening could cause. Public health agencies and national medical societies — the American College of Radiology, the American College of Cardiology and the American Heart Association — do not recommend CT screening" FDA asserted.
CT is a unique tool. Often it is useful to diagnose disease, trauma or abnormality and to plan, guide and monitor treatment. CT scans may help to determine the extent of the disease. But it must not be used indiscriminately.
If symptom-less patients are screened, the benefit is uncertain. However, there is potential for some risk. In a CT examination, patient receives a much larger radiation dose compared to most conventional X-ray procedures. The effective dose in a CT examination is not much less than the lowest dose received by some of the survivors of the atomic bombs. FDA cautioned that these survivors have demonstrated a small but increased radiation related excess risk for cancer.
The comments of FDA on the indiscriminate use of CT procedures, reminded me of an eminently readable book entitled "Radiation — What It Is and How It Affects You" by Jack Schubert and Ralph E Lapp. All medical practitioners must read it. The authors wrote about a medical practice that had, in the fifties, become almost a standard, among such firms as General Motors, Ford and Chrysler and many other companies. They used to send their executives off to clinics for a complete annual medical checkup which included X-ray screening of the lungs, heart, stomach, upper and lower intestinal tract, kidneys and other organs.
The medical examination lasted two or three days. The executives received a whopping radiation dosage equal to that received in over 500 chest x-ray examinations in the bargain! This fact was not known to many. Even the American Medical Association had then urged broader use of "executive examination" by industry! General Motors had 5000 executives with his dubious "privilege", visiting any one of the one hundred authorised clinics and hospitals. Ironically, history seems to repeat itself in the case of CT screening.
All radiation doses have an associated risk, a small possibility of developing radiation-induced cancer some time later in life. In a medically needed procedure, the benefit to the patient far outweighs the risks. FDA warns that for a person without symptoms, CT screening is unlikely to discover serious disease and the potential harm to the individual may be greater than the presumed benefit.
Schubert and Lapp quote a 1956 communication of the National Committee on Radiation Protect: "one of the important sources of radiation exposure is that applied by general practitioners. Here we cannot expect for many, many years, at best, to have any really good idea of what exposures these people are using. They do not know themselves. They have no techniques by which you can really estimate the exposure given in a gastrointestinal tract examination."
The situation does not appear to be any different now. A consultant radiologist K. Grower Thomas and his colleagues from several other hospitals compiled a simple questionnaire and interviewed 130 doctors of all grades, including consultant radiologists (British Medical Journal, 13th April 2002).
They asked the physicians for an approximate dose of radiation in a chest radiograph. This dose was to be taken as a unit of one to calculate how many units a patient would receive for several types of medical X-ray examinations carried out in a busy radiology department (17 examinations in total).
Believe it or not, only 3 out of 130 scored a pass mark of 50 per cent in spite of a generous marking scheme and no negative marking. "The degree of knowledge was inversely proportional to seniority, with consultants scoring less than junior colleagues. It was clear and worrying that doctors have no real knowledge of radiation doses that their patients receive," the study revealed.
This is nothing new. A few years ago, the Royal College of Radiologists, UK, found that 20 per cent of the physicians in UK did not know that Computerised Axial Tomography (CAT) units involved X-ray exposure!
I regret to say that Indian experience in related areas is similar. The Atomic Energy Regulatory Board organised appreciation programmes on X-ray safety for the benefit of radiologists, physicians, medical students and para-medical staff. Invariably, a popular question was on the effect of irradiation on the unborn child. Many specialists were not equipped to offer advice on the magnitude of radiation doses in different medical X-ray procedures. Responding to a popular science article, on medical X-ray protection, I wrote a few years ago, some patients approached their radiologists to get some idea about the radiation doses they receive in medical X-ray examinations. Even senior specialists did not know.
I wrote about the Indian experience in the British Medical Journal (E-response, BMJ, 13 April 2002). Dr Adrian K. Midgley, a general practitioner from the UK reacted: "You cannot make it feasible for all of us to remember the radiation dose in an examination since this is changeable and we have other things to do than replace minimally useful numbers in our memory with new improved and minimally useful numbers."
He is correct up to a point. I have heard such remarks from his Indian counterparts. But if the physician knew about the relative magnitude of the doses in various procedures, it may help to reduce unwanted referrals of symptom-free patients, a point very relevant in the case of CT procedures.
Code division multiple access
CODE Division Multiple Access (CDMA) can help in achieving the convergence of voice, video and data on one network. Mobile networks in India are dominated by GSM technology. CDMA in the form of Wireless in Local Loop (WLL) is an alternative providing both fixed telephony and limited mobility with additional benefits.
The Interface Standard IS-95 Code Division Multiple Access (CDMA) has emerged as a powerful alternative standard for digital cellular and wireless personal communication standards. CDMA is a type of Spread-Spectrum and has been successfully used earlier in military applications to jam the communications. Currently CDMA has achieved paramount success as a mobile standard and is being used in Wireless in Local Loop (WLL) technology. The limited mobility application of this technology is attributed to the CDMA standard and it has emerged as a powerful alternative to GSM mobile telephony standard.
Spread-Spectrum is a method of transmission where the signal occupies a bandwidth in excess of the minimum required to send the information. This spreading of bandwidth is achieved with the help of a code, which is independent of the data. The receiver is synchronised to despread the bandwidth and to receive the data. Spread-Spectrum can either be "Frequency hopping" or "Direct sequence". Frequency hopping results in signal switching between different frequencies within the hoping bandwidth.
Direct sequence methodology incorporates the coding of digital data at a much higher frequency. The process of code generation is pseudo-random with the receiver also correlating the code to extract the relevant information.
CDMA is a Direct Sequence Spread-Spectrum system and works on 64 Kbps digital signals. The modulation process here refers to the multiplication of a radio frequency carrier with a pseudo-noise. The pseudo noise is itself a binary signal produced at a much higher frequency than the data to be sent. This higher frequency has a larger bandwidth, which spreads the original signal in the frequency domain. Information signal is first spread at the base band and then modulated. At the receiving end the signal is first demodulated and then "despread" to retrieve the original signal.
Integrating voice, video and data on one network is convergence. CDMA can help in achieving convergence. Mobile networks based on GSM technology dominates India’s mobile market. CDMA technology incorporated in the form of Wireless in Local Loop is an alternative providing limited mobility. A wireless Local Loop is a replacement for the existing Copper twisted-pair loop. It provides the fixed telephone access and as well as the limited mobility. The parameters worth consideration here are the services, capacity, PSTN connectivity, cost and maintainability.
The benefits offered by CDMA are
manifold. It offers capacity improvement of about five times that of
GSM system. The call quality and the privacy achieved are higher. The
size of the phones is smaller and the power requirement is also less
and varies as the distance from the cell changes. The day is not far,
when the CDMA will make the third generation phone, having the feature
of voice, video and data a household item.
NEW PRODUCTS & DISCOVERIES
It’s the most promising audio advance in years. Hypersonic speakers, from American Technology (headed by the irrepressible Woody Norris, matter of a radical personal flying machine) focus sound in a tight beam, much like a laser focuses light. When it rolls out in Coke machines and other products over the next few months, audio quality will rival that of compact discs.
The applications are many, from targeted advertising to virtual rear-channel speakers. The key is frequency: The ultrasonic speakers create sound at more than 20,000 cycles per second, a rate high enough to keep in a focused beam and beyond the range of human hearing. As the waves disperse, properties of the air cause them to break into three additional frequencies, one of which you can hear. This sonic frequency gets trapped within the other three, so it stays within the ultrasonic cone to create directional audio.
Step into the beam and you hear the sound as if it were being generated inside your head. Reflect it off a surface and it sounds like it originated there. At 30,000 cycles, the sound can travel 150 yards without any distortion or loss of volume. Here’s a look at a few of the first applications.
1. Virtual Home Theatre: How about 3.1-speaker Dolby Digital sound? With hypersonic, you can eliminate the rear speakers in a 5.1 setup. Instead, you create virtual speakers on the back wall.
2. Targeted Advertising: "Get $1 off your next purchase of Wheaties," you might hear at the supermarket. Take a step to the right, and a different voice hawks Crunch Berries.
3. Sound Bullets: Jack the sound level up to 145 decibels, or 50 times the human threshold of pain, and an offshoot of hypersonic sound technology becomes a nonlethal weapon.
4. Moving Movie voices: For heightened realism, an array of directional speakers could follow actors as they walk across the silver screen, the sound shifting subtly as they turn their heads.
5. Pointed Messages: "You’re out too far," a lifeguard could yell into his hypersonic megaphone, disturbing none of the bathing beauties nearby.
SCIENCE & TECHNOLOGY CROSSWORD
1. In a loose DNA of prophase, the type of coiling is this.
8. A building’s remains after its demolition.
9. The tool for boring holes.
11. ....bytes, tell the capacity of a hard disk.
13. Telecommunication terminology for electronic Push Button Telephone.
16. A bird’s ovum.
17. A kind of beer having light colour.
18. Space provided above the cupboard in a house.
20. Horizontally rotating vane of helicopter.
21. An acidic hydrocarbon obtained from petroleum fractions.
23. Slow and continuous deterioration of metals due to action of environment.
25. Abbr. for an accelerator that can raise energy of a proton to 20thousand billion electron volts.
1. Science of water or liquids conveyed through pipes.
2. A PSU engaged in construction of fertilizer plants in India.
3. A device used to record a physical event taking place at a distance.
4. Having four straight sides and angles of 90 degrees.
5. This function gives a solution to wave equation satisfying a set of boundary conditions.
6. A five nation programme to modernize F-16 planes.
7. Tanned skin of animals.
10. Symbol for Radium.
12. Short for gigabyte.
14. The way to go out; exit.
15. Impurity added to a semi-conductor to increase the charge carriers.
17. ....meter, an instrument used to measure the rate of evaporation of water.
19. Abbr. for a black box kept in aero planes for flight data recording.
22. Abbr. for a school set up by Govt of India to provide continuing development education to groups through teaching learning strategies.
24. Symbol for Sodium.