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.
AI explanationShows the answer. Tap to open.
Correct Answer: D
Why this is correct: Look at Paragraph D. The magnet pulls on magnetic objects, from keys and phones to oxygen tanks. It is strong enough to fling a wheelchair across a room. Keys and phones are everyday things, and that pull is dangerous.
Passage Reference: 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.
Tips: Think about small everyday things near the machine. Check what happens to them, and how strong the force is.
Why the other options are wrong:
- A: Paragraph A explains how atomic nuclei behave in a magnetic field. It does not talk about objects near a scanner.
- B: Paragraph B mentions gradient magnets added to the main magnet. Nothing is pulled or thrown in it.
- C: In Paragraph C, hydrogen nuclei line up in the strong field. Loose objects in the room are not discussed.
- E: The text gives this detail. Keys, phones and a flung wheelchair all appear in Paragraph D.
Correct Answer: E
Passage Reference: 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.
Why this is correct: Paragraph C says the brain and spinal cord show up far more clearly than with X-rays or CT. It never says how long a scan of either one takes. So this comparison is not in the text.
Tips: Clear pictures and scan time are two different things. Check which one the paragraph talks about.
Why the other options are wrong:
- A: Paragraph A is about early physics with atoms and radio waves. No body parts are scanned there.
- B: Paragraph B covers the first MRI pictures and the number of scanners. It gives no scan times.
- C: Paragraph C names the brain and spinal cord, but only to say how clear the images are. Time is never compared.
- D: Paragraph D is about hazards such as the magnet and noise. It does not time any scan.
Correct Answer: C
Passage Reference: MRI has become widely useful in medicine because water makes up about two thirds of the body's weight.
Why this is correct: The clue is at the start of Paragraph C. MRI has become widely useful because water makes up about two thirds of the body's weight. Two thirds is a large share.
Tips: Paragraph B also mentions water. Ask if the water is in a tube or in a person.
Why the other options are wrong:
- A: Paragraph A explains the physics of nuclei and radio waves. It does not mention the water in our bodies.
- B: Paragraph B mentions tubes of ordinary and heavy water in a 1973 test. That is not water inside a person.
- D: Paragraph D is about the dangers of the magnet and the noise. It does not say why MRI is so widely used.
- E: The first sentence of Paragraph C links body water to the wide use of MRI.
Correct Answer: B
Passage Reference: 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.
Why this is correct: Look at Paragraph B. In 1973, Lauterbur showed how to picture a cross section of tubes. The tubes held ordinary water surrounded by heavy water. Tubes of water are containers of liquid, not a person.
Tips: Look for a picture of something that is not a patient. Note the date too.
Why the other options are wrong:
- A: Paragraph A reports the 1946 work on protons. It does not describe any picture.
- C: Paragraph C describes images of the brain and spinal cord. Those are pictures of people.
- D: Paragraph D deals with dangers during scans. It does not describe any early image.
- E: The text includes this. The 1973 picture of water tubes is in Paragraph B.
Correct Answer: D
Passage Reference: Second degree burns are the patient problem reported most often.
Why this is correct: Read the last two sentences of Paragraph D. The FDA receives around 300 problem reports a year. Second degree burns are the patient problem reported most often. Burns are heat injuries.
Tips: Look at the patient problems that get reported. Check which kind comes top, and whether heat is behind it.
Why the other options are wrong:
- A: Paragraph A talks about energy levels in atomic nuclei. Injuries to patients are not part of it.
- B: Paragraph B counts scanners in use in 2002. It has no reports of harm.
- C: Paragraph C tells you MRI uses no ionizing radiation. It does not mention burns or reports.
- E: The reports to the FDA, with burns at the top, close Paragraph D.
Correct Answer: A
Passage Reference: For the following decades, magnetic resonance was used mainly to study the chemical structure of substances.
Why this is correct: Paragraph A ends with the decades after 1952, when magnetic resonance was used mainly to study the chemical structure of substances. That means learning what materials are made of.
Tips: Paragraph B also covers early history. Find the use that came before any pictures of patients.
Why the other options are wrong:
- B: Paragraph B tells how the medical use began in the 1970s. The earlier study of materials is not in it.
- C: Paragraph C describes how scans of people work today. It does not mention an earlier use with substances.
- D: Paragraph D covers risks from the magnet now. It says nothing about earlier uses.
- E: The text does give this. The study of chemical structure ends Paragraph A.
Correct Answer: B
Passage Reference: 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.
Why this is correct: Check the dates in Paragraph B. The first MRI equipment reached health care in the early 1980s. By 2002, about twenty-two thousand scanners were in use worldwide. That is about two decades later, and more than 20,000.
Tips: Paragraph D also has a number. Make sure you match a count of machines, not of reports.
Why the other options are wrong:
- A: Paragraph A gives the years 1946 and 1952. It does not count any machines.
- C: Paragraph C explains how scanners make images today. It gives no number of machines.
- D: Paragraph D gives about 300 problem reports a year. That is not a count of scanners.
- E: This number is in the text. The 2002 scanner count is in Paragraph B.
Correct Answer: E
Passage Reference: 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.
Why this is correct: Paragraph B tells you Lauterbur pictured tubes of ordinary water surrounded by heavy water. It does not say why he used heavy water. Cost is never mentioned.
Tips: Paragraph B tells you what Lauterbur used. Ask if it also tells you why.
Why the other options are wrong:
- A: Paragraph A covers Bloch and Purcell's 1946 work on protons. Lauterbur and his test do not appear.
- B: Lauterbur's test with ordinary and heavy water is in Paragraph B. No reason for his choice is given.
- C: Paragraph C explains why the water in our bodies makes MRI useful. It does not discuss liquids used in early tests.
- D: Paragraph D is about magnet dangers, noise and reported problems. The cost of materials is not mentioned.
Correct Answer: D
Passage Reference: Patients with implants should not be scanned unless the device has been identified as MR Safe or MR Conditional.
Why this is correct: Look at Paragraph D. Patients with implants should not be scanned unless the device is identified as MR Safe or MR Conditional. An implant is a device inside the body.
Tips: This is about devices inside the body. Check what must be confirmed before such a person can be examined.
Why the other options are wrong:
- A: Paragraph A deals with protons and radio waves. Patients with devices are not mentioned.
- B: Paragraph B tells how scanners were invented and spread. It gives no rules for particular patients.
- C: Paragraph C explains how water in the body sends a signal. Implants do not come up.
- E: The text states this rule. Implants and the MR Safe label are in Paragraph D.
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