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CELPIP Practice Reading: Reading for Information ID: #63122 Hard MRI: strong magnets without X-rays

Read the following passage.

A. The science behind MRI began with atoms, not patients. In 1946, Felix Bloch and Edward Mills Purcell showed how protons, the smallest atomic nuclei, behave in a magnetic field. Atomic nuclei in a strong magnetic field spin at a frequency set by the strength of the field, and they can absorb radio waves of that same frequency. When they return to their earlier energy level, they give off radio waves of their own. Bloch and Purcell shared the Nobel Prize in Physics in 1952. For the following decades, magnetic resonance was used mainly to study the chemical structure of substances.

B. The move to medical pictures came in the early 1970s. In 1973, Paul Lauterbur described how adding gradient magnets to the main magnet made it possible to picture a cross section of tubes holding ordinary water surrounded by heavy water. Peter Mansfield developed the use of gradients further and showed how the signals could be analysed mathematically and turned into an image. He also showed that extremely fast imaging could be achieved, and this became useful in clinics a decade later. The first MRI equipment reached health care at the beginning of the 1980s, and in 2002 about twenty-two thousand scanners were in use worldwide.

C. MRI has become widely useful in medicine because water makes up about two thirds of the body's weight. The nuclei of hydrogen atoms in that water act like tiny compass needles and line up in the strong field of the main magnet. Pulses of radio waves change their energy, and after each pulse the nuclei send out a signal as they return to their earlier state. Computers turn these signals into detailed three-dimensional images. The brain and spinal cord show up far more clearly than with ordinary X-rays or CT, and unlike those methods, MRI uses no ionizing radiation.

D. Problems with MRI scans are very rare, but the machine still has hazards. Its strong, constant field pulls on magnetic objects, from keys and phones to oxygen tanks, and it is strong enough to fling a wheelchair across a room, so people and objects are screened before they enter. Patients with implants should not be scanned unless the device has been identified as MR Safe or MR Conditional. Rapidly changing fields cause loud knocking noises that can harm hearing without ear protection. In the US, the FDA receives around 300 reports of problems with MRI scanners and coils each year. Second degree burns are the patient problem reported most often.

E. Not given in any of the above paragraphs.

Decide which paragraph, A to D, has the information given in each statement below. Select E if the information is not given in any of the paragraphs.

 - 1. Small things that people carry every day are drawn toward the machine with dangerous force.

 - 2. Looking inside the head takes longer than looking at the back.

 - 3. The method's broad value to doctors comes from the large share of our bodies that is water.

 - 4. An early demonstration produced a picture of containers of liquid rather than of a human body.

 - 5. Heat injuries head the list of patient problems that get reported.

 - 6. Before it served patients, the technique was mostly a tool for learning what materials consist of.

 - 7. About two decades after the first machines appeared, more than 20,000 were in service globally.

 - 8. Lauterbur used heavy water in his test because it was cheaper than other liquids.

 - 9. Devices placed inside a person must first be confirmed as compatible before that person can be examined.

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