– the construction workers – which rip down the worn-out bone; and osteoblasts – the architects – which utilize calcium, magnesium, boron and other minerals to build up healthy new tissue. This process is called ‘resorption’. All that the usual drugs for osteoporosis such as oestrogen, calcitonin or etidronate (called ‘antiresorbing drugs’) do is to slow this process of turnover and renewal, preventing the hardhat osteoclasts from doing their job. Eventually, there is no further bone formation.
Some researchers argue that the presence or absence of low bone density is a meaningless indicator of risk of fractures or osteoporosis.85 In one nine-year study of 1,000 middle-aged women, the group considered at high risk of osteoporosis actually had fewer fractures than the group not considered at risk. Bone-density screening has also never been shown to be effective in preventing fractures, according to a large review of published work on bone-density screening.86
Bone scans may have a one-time use to help in diagnosing women suspected clinically of osteoporosis, but appear to be too variable to be relied upon as a general screening test for women without symptoms.
CAT SCANS
As with most other industries, the advent of the computer has taken the medical x-ray business to a new level. In the 1970s, computed axial tomography, now usually known as CAT, or CT, scans, revolutionized diagnosis, particularly of bones, blood vessels and soft tissue of the body, offering pictures with up to 20 times the detail of ordinary x-rays. It has now made it possible to scan for diseases of the abdomen, lung, heart, liver and pancreas, and even for early osteoporosis.
Adapted from an image-processing system developed for the Apollo moon landings, CAT scans take a 360-degree series of cross-sectional x-ray images from multiple angles – up to 30 shots – by passing a pencil-thin beam through a particular portion of the body, sometimes with the use of a contrast agent. An X-ray tube on a moveable ring revolves around your body, taking individual ‘slices’ of images.
This information is then passed through a computer, which reconstructs the slices into a three-dimensional image on a video screen, allowing the operator to see this portion of the body from any angle. It is also stored so that the doctor can take photographs of the video screen or call up the information in the future. Your problem is that now that your doctor has computerized diagnostic toys at his disposal, he’s more likely to want to play with them. Although doctors have attempted to claim that CT scanning reduces the need for other tests such as brain scans, arteriography or exploratory surgery, this may be a false saving.
While no doubt CAT scanning represented the height of 20th-century technology, it also poses far more risks than most other tests, blasting you with far higher doses of radiation. In 1991, the NRPB concluded that CAT scans accounted for only 2 per cent of the total UK x-ray examinations but 20 per cent of the overall collective dose, and so were the largest single source of exposure from x-rays.87 This risk is magnified if you don’t stay stock still during the half-minute or so of the test and it has to be repeated. In Japan nearly one-eighth of the population was getting CT-scanned as far back as 1979. Radiation from a single body shot is now considered comparable to that of the low-dose atomic bomb survivors from Hiroshima.88
CAT scans are particularly dangerous when used on children. Despite their reduced size, they may receive adult-sized doses of x-rays, up to five times of what is necessary, leaving them prone to cancer. In the US, where 600,000 children under 15 receive CAT scans every year, an estimated 500 die as a result.89 Furthermore, although all the early studies showed that CAT scans reduced diagnosis time, helped doctors to understand their diagnosis, reassured doctors about their diagnosis or treatment plans and avoided the need for other tests, very few demonstrated that this knowledge in any way reduced illness, shortened hospital stay or prevented death.90
There are also questions of accuracy. Despite the dangers of high-dose radiation in children, particularly of their sexual organs, it is often used to diagnose cerebral (brain) hernia after lumbar puncture for meningitis. Nevertheless, one study found that one-third of children with hernias were misdiagnosed as normal.91 As with other contrast mediums, the dyes used can permanently damage the kidneys.92
Despite any real demonstration of value, other than as a diagnostic toy, use of CT scanning has moved briskly apace. Patients who have a seizure are scanned, even before a clinical history is taken, to rule out alcohol withdrawal.93 So beloved is this gadgetry that it has even been used to research the cause of the common cold, the researchers concluding that their study patients had – wait for it – swelling of the mucous membranes.94 Besides megadoses of radiation, CT scans (indeed all x-rays) have long been known to cause cataracts and other lens opacities, such as nuclear sclerosis,95 and could affect thyroid function.96
MRI SCANS
The dangers of CAT scans and the use of computers led to the development of nuclear magnetic resonance, which developed into magnetic resonance imaging (MRI). This screening procedure was hailed as a promising alternative to x-rays for providing detailed pictures of soft body tissue, particularly the brain and spinal cord.
In MRI, you are placed inside a massive cylindrical magnet weighing up to 500 tons – large enough to envelope the entire body. While you are inside the magnet a quick pulse is applied, creating a magnetic field some 50,000 times stronger than that of the earth.97 The effect of this is to excite the nuclei of atoms within body cells. These hyped-up nuclei produce radiofrequency echoes, which get translated into images on a computer.
The MRI scan works by focusing on the water molecules, which largely make up the tissues of your body. The scan excites the hydrogen and oxygen molecules and, as they begin moving in a certain pace and direction, the scanner is able to detect and measure them and then reconstruct a picture of your body from them, displaying it in real time on a television monitor. Although it was originally believed that the good ‘pictures’ afforded by MRI would eliminate the need for injectible dyes, this hasn’t proved so. Contrast agents are needed to detect brain tumours, for example. Unlike the contrast materials used for CAT scans, which contain iodine, those used for MRI are magnetically-active substances.
Currently, the only MRI contrast materials approved by the American Food and Drug Administration are chelates, containing a rare earth element called gadolinium. When injected into a patient’s veins, this works similarly to iodine contrast agents, but is supposed to be far safer, with severe reactions occurring in about 1 in 350,000 patients.
MRI is mainly used to view the nervous system, for suspected strokes, brain tumours, multiple sclerosis, brain infections such as meningitis, epilepsy, developmental disorders of the brain such as hydrocephalus, and problems of the spinal cord or vertebrae. Its advantages over CAT scans are that it shows better tissue contrast, enables you to get images in multiple planes, has no radiation, employs a safer contrast medium, and enables you to view veins and the top and front joining of the skull. The big drawback is that you must undergo a much longer scanning time, and results can be flawed if you move at any time during the procedure. However, these days the latest MRI scanners can work faster and take in more detail in one go.98 MRI is reputed to be fairly accurate for detecting multiple sclerosis; one study of MS patients showed a 95–99 per cent accuracy in detecting the disease.99