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Mri scans

MagazineMay 1995 (Vol. 6 Issue 2)Mri scans

Q:After an MRI scan for my neck I had an appalling claustrophobia (during it), with memory loss

Q:After an MRI scan for my neck I had an appalling claustrophobia (during it), with memory loss. 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 scan

A:The dangers of CAT scans and the use of computers led to the development of nuclear magnetic resonance, which developed into 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 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 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 and the top and front joining of the skull. 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 British Medical Journal, July 27, 1991).

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 this type of magnetic field, which is 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.

Researchers at the University of Texas Health Centre at San Antonio stated that exposure to electromagnetic fields may not be totally harmless. 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 (Chicago Tribune, May 13, 1984).

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. Other animal studies show that MRI can cause birth defects in the eyes (Oral Surgery, Oral Medicine, Oral Pathology, November 1993) and damage the ears (Acta Oto Laryngologica, July 1993). In the States, several patients with pacemakers died when the magnetic forces altered them (BMJ, July 27, 1991).

The side effects you experienced are relatively common. Up to one third of patients given MRI scanners, like you, have felt so claustrophobic that the tests had to be abandoned (The Lancet, September 21, 1991).

Four separate studies have also shown that the technique causes memory loss (J of MRI, 1992; 2(6): 721-8).

But perhaps the most unsuspected problem caused by radiofrequency fields of MRI is localized heating, if the exposed object is non-uniform, as bodies always are (IEEE Transactions on Biomedical Engineering, December 1993 and Amer J of Phys Med & Rehab, June 1993). This risk is magnified among babies or anesthesized patients. In 10 American departments of radiology reporting serious injuries relating to MR imaging, nine of 14 were burns (American Journal of Roentgenology, January 1994).

This may 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 an average two degrees centigrade, with the highest change four degrees" (Amer J of Roentgenology, 1990; 154 (6):1229-32).

The UK's 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.

The NRPB also recommends that pregnant women, patients with pacemakers and those with metal prostheses like artificial hips or retained shrapnel avoid MRI, since they can either move or become focuses 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 (Am J of Roententgenology, January 1994).

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.

According to a medical textbook on CT and MRI, many initial reports that MRI gave more detailed images than CT were "overly optimistic, and initial case reports showing the presumed ability of MRI to make a tissue specific pathologic diagnosis have not been confirmed by subsequent larger series employing appropriate scientific methods." These studies turned out to be "biased" or not "well controlled scientific studies" (Ronald G Evens, in Lee, Joseph K., ed. Computed Body Tomography with MRI Correlation. Raven Press, New York, 1989).

MRI has shown to be less than accurate in detecting early prostate cancer (New Eng J of Med, 1993; 328 (12): 879-80) or coronary artery disease (The New England Journal of Medicine, 1990; 323 (10): 621-6). They are quite good at detecting inhaled foreign bodies inhaled by children, particularly peanuts, the most common culprit (Monitor Weekly, March 1, 1995).

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, March 11, 1993).

MRI is best for brain and spine because of its ability to take shots on the top and front of the head and to detect subtle tissue changes, but CT is better for studying trauma, bone or calcium.


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