Читать книгу What Doctors Don’t Tell You - Lynne McTaggart, Lynne McTaggart - Страница 20

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

But, again, large question marks remain about its accuracy. According to a medical textbook on CT and MRI, many initial reports that MRI gave more detailed images than CT were ‘overly optimistic’. All the initial fanfare, which came from individual cases of patients, could not be confirmed by subsequent larger studies using full scientific methods. The earlier studies turned out not to be well controlled.¹⁰⁰

Lately, MRI has shown to be less than accurate in detecting early prostate cancer¹⁰¹ or coronary artery disease.¹⁰² It is now thought that MRI is better than CT for the brain and spine, because of its ability to take shots of the top of the head and front of the skull and to detect subtle tissue changes, but CT is better for studying any sort of trauma – such as blows to a body part – or the bones or calcium.

The problem is that no one yet knows the likely long-term effects of subjecting the body to a magnetic field powerful enough to send magnetic objects flying across the room. So far, the National Radiological Protection Board has sounded a warning about the heating effects of the magnetic field and its ability to influence magnetic matter inside the body or to damage tissues.

Microbiologist Wendell Winter and colleagues at the University of Texas Health Center at San Antonio stated that exposure to these types of electromagnetic fields may not be totally harmless. They subjected a number of living things to a range of electromagnetic fields and found that they stimulated the growth rate of cancer cells.¹⁰³

Research on chick embryos has demonstrated that they are at risk with the increased temperatures; female mice chronically exposed showed changes in their white blood cell count. Other animal studies show that MRI can cause birth defects in the eyes¹⁰⁴ and damage to the ears.¹⁰⁵ In the States, several patients with pacemakers died when the magnetic forces altered them.¹⁰⁶

Another potential danger concerns any metallic substances on your body. Complications can occur if you have any metal prostheses or implants, surgical clips or artificial heart valves, you are wearing any metal object, like a watch, have any metal on your clothing, wear a shade of eye shadow that contains metallic substances or even have your ATM card in your wallet.

One of the big problems with MRI scannings is claustrophobia. Up to one-third of patients given MRI scans have felt so claustrophobic that the tests had to be abandoned.¹⁰⁷ ‘After an MRI scan for my neck, I had appalling claustrophobia (during it), with memory loss,’ writes Jill from Aberdeen. ‘I kept crying, shaking, couldn’t write, stammered, had nightmares for two weeks afterwards. It was 55 minutes of hell – worse than the two previous CAT scans. It must affect the brain cells with all that magnetism.’

Perhaps the most unsuspected problem caused by radiofrequency fields of MRI is localized heating, a risk that is magnified among babies or patients who are anaesthesized.¹⁰⁸ For instance, in one poll of 10 US American departments of radiology, the overwhelming majority of serious injuries relating to MRI imaging were burns.¹⁰⁹ This heating can also cause future fertility problems in men, since sperm are rendered sterile if heated up to body temperature. One study found that average scrotal skin temperature was significantly raised by an average of 2°C, with the highest change 4°C.¹¹⁰ Four separate studies support Jill’s contention that the technique causes memory loss.¹¹¹

The National Radiological Protection Board concludes that a magnetic field of 2.5 tesla (T) is safe for all patients. Between 2.5 and 4 T, evidence of harm is doubtful, but from 4 T upwards, likely to occur.

If you are pregnant, have a pacemaker or have a metal prosthesis such as an artificial hip, retained shrapnel or cochlear, carbon-fibre implants, you should avoid MRI. Implants in particular can either move or become foci for the heating effect of MRI, causing discomfort and local tissue damage. Besides the dangers of metal inside your body, every metallic object in the scanning room becomes a potentially lethal missile once the MRI device is turned on. The most serious reported injury with MRI occurred when an oxygen tank near the magnet started flying and struck a patient’s face.¹¹²

Doctors are also increasingly worried about the contrast agents used for all the ‘nuclear’ imaging techniques.

Of all the reports made to the UK Adverse Reaction Reporting Scheme in the six years between 1977–83, nearly half concerned methylene diphosphonate for bone imaging and one-third concerned colloids for liver scans. The majority of complaints concerned hypersensitivity to the dyes. The most conservative estimate is one in 1,000 people react – a figure far higher than originally believed.¹¹³

If your doctor wants you to undergo the procedure you should make sure he first takes your full medical history, since the protocol for using MRI differs depending on what you are investigating. According to multiple sclerosis specialist Dr Patrick Kingsley, when diagnostic toys like MRI weren’t available, any reasonably experienced neurologist could make a confident diagnosis of MS based on a patient’s symptoms and history. The only reason perhaps to proceed with an MRI scan is if the neurologist wishes to rule out a brain tumour which might be amenable to surgery.