Q:A friend of mine has suspected multiple sclerosis and has been advised by a specialist to have an MRI (magnetic resonance imaging) scan to confirm the diagnosis.
Since being advised about MRI, she has read in a Dr Robert Mendelsohn publication that the NMR (nuclear magnetic radiation) scanner has some nasty effects, one of which is that it promotes the growth of cancer cells.
Are MRI and the NMR the same thing? If they are different, how does MRI work? What are its side effects. F G, Pershore.....
A:Nuclear magnetic resonance indeed is magnetic resonance imaging. This relatively new screening procedure has been hailed by the medical profession as a promising alternative to x-rays for providing detailed pictures of soft body tissue, particularly the brain and spinal cord.
Although it was originally believed that the good "pictures" afforded by MRI would eliminate the need for contrast agents, this hasn't proved so. Contrast agents (that is, injectible dyes), are needed to detect brain tumours, for example. Unlike the contrast materials used for CAT (computerized tomography) 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 like 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 and a safer contrast medium and enables you to view veins. The big minus is that the patient must undergo much longer scanning time, and results can be flawed if patients move during the process.
In MRI, the patient is 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.
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 the computer.
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. 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 damage tissues.
Thank you for supplying us with the reference from the late Dr Mendelsohn's newsletter, The People's Doctor (vol 10 no 11), about the possible link between MRI and the promotion of cancer cells. According to the Chicago Tribune (13 May 1984), researchers at the University of Texas Health Centre at San Antonio stated that exposure to electromagnetic fields may not be totally harmless. According to Mendelsohn: "Microbiologist Wendell Winter and colleagues subjected living things to a range of electromagnetic fields and found that they stimulated the growth rate of cancer cells."
Research on chick embryos has demonstrated that they are at risk with the increased temperatures and female mice chronically exposed showed changes in their white blood cell count. In the States, several patients with pacemakers died when the magnetic forces altered them.
Up to one third of patients given MRI scanners have felt so claustrophobic that the tests had to be abandoned (The Lancet, 21 Sept 1991).
The following types of patients should never be MRI scanned: those with cardiac pacemakers or cochlear, carbon fibre or metallic implants. Pregnant women should avoid it, particularly in the first trimester. And all patients intending to undergo the procedure should make sure their doctor takes a full medical history, since the protocol for use differs, depending on what you are investigating.
MRI is supposed to be fairly accurate for detecting MS; one study of 260 MS patients showed a 95-99 per cent accuracy in detecting the disease (Radiology 1991; 178: 447-51). However, according to Drs Robert Edelman and Steven Warach of the Departments of Radiology and Neurology at New York's Beth Israel Hospital and Harvard Medical School, most diagnoses of MS are done clinically, that is, based on history (New England Journal of Medicine, 11 March 1993).
We asked our MS expert, panel member Patrick Kingsley, for his view. He echoed the views of Drs Edelman and Warach: "Until MRI is fully understood, MS patients can be confidently diagnosed clinically." Indeed, he says, when diagnostic toys like MRI weren't available, any reasonably experienced neurologist could make a confident diagnosis of MS based on patient 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 is amenable to surgery.