College Physics
College Physics
2nd Edition
ISBN: 9780134601823
Author: ETKINA, Eugenia, Planinšič, G. (gorazd), Van Heuvelen, Alan
Publisher: Pearson,
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Chapter 20, Problem 52RPP

BIO Magnetic resonance imaging In magnetic resonance imaging (MRI). a patient lies in a strong uniform constant magnetic field B oriented parallel to the body. Typical magnitudes of this field are between 1.0 T and 3.0 T The field is produced by a largo superconducting solenoid. The MRI measurements depend on the magnetic dipole moment μ of a proton, the nucleus of a hydrogen atom. The proton magnetic dipoles can have only two orientations either with the field or against the field. The energy needed to reverse this orientation ("flip" the protons) from with the field to against the field is exactly Δ U = 2 μ B

(like the energy needed to turn a compass needle from north to south).

The pulse of an alternating magnetic field of frequency several tens of MHz irradiates the patient's body in the region to be imaged When this alternating field is tuned correctly so that its energy equals the Δ U = 2 μ B needed to reverse the orientation of the protons from with the external B field to against it, a reasonable number of protons will flip. When the protons return to their initial orientation and a lower energy stale, they produce an alternating magnetic field with almost exactly the same frequency as that of the original radiation. This alternating magnetic field produced by the protons is detected and provides information about the spatial distribution of the concentration of protons as well as information about the structure of the material surrounding the protons in the region irradiated by the alternating magnetic field. The proton concentration as well as the protons' characteristic interactions with their surroundings differ in fat, muscle and bone tissue, and in healthy and diseased tissue.

The MRI imago of an internal body part is made by adjusting an auxiliary magnetic field which varies the external B field over the region being examined so that the probe field energy equals the flipping energy Δ U = 2 μ B in only a thin slice of the body. A measurement is made at this slice. The external magnetic field is then adjusted to flip protons in a neighboring slice Continual shifts in the magnetic field and detection of proton concentrations at different slices produce a map of proton concentration in the body. The MRI image of the lower back in Figure 20.36 indicates an L45 disc that has partially collapsed— it has lost water and because it contains fewer protons, it produces a darker MRI image.

Chapter 20, Problem 52RPP, BIO Magnetic resonance imaging In magnetic resonance imaging (MRI). a patient lies in a strong

Why might a herniated disc projecting slightly out from between two vertebrae look different in an MRI image than a nonherniated disc? a The vertebrae adjacent to a herniated disc are closer than vertebrae beside a nonherniated disc.

b. There is a different concentration of hydrogen atoms in bone and in discs.

c. Protons in the herniation produce an image that can be seen.

d. b and c

e. a, b, and c

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Chapter 20 Solutions

College Physics

Ch. 20 - Choose all that apply. Objects that produce...Ch. 20 - 5. What is one difference between magnetic and...Ch. 20 - 6. Two parallel straight current-carrying wires...Ch. 20 - 7. Choose all of the units that are fundamental,...Ch. 20 - 8. Particles of various masses, charges, and...Ch. 20 - When a diamagnetic material Is placed in an...Ch. 20 - If you triple the speed of a particle entering a...Ch. 20 - In 1911 physicists measured a magnetic field...Ch. 20 - Describe two experiments that will allow you to...Ch. 20 - How can you determine if there is a magnetic field...Ch. 20 - You have a magnet on which the poles are not...Ch. 20 - 15. List as many ways as you can to detect a...Ch. 20 - Prob. 16CQCh. 20 - Prob. 17CQCh. 20 - An electron flies through the magnetic field shown...Ch. 20 - Prob. 19CQCh. 20 - 20. A beam of electrons is not deflected as it...Ch. 20 - 21 A beam of electrons moving toward the east is...Ch. 20 - 22. Why are residents of northern Canada less...Ch. 20 - Prob. 23CQCh. 20 - An electron enters a solenoid at a small angle...Ch. 20 - Two parallel wires carry electric current in the...Ch. 20 - Prob. 26CQCh. 20 - Describe a situation in which an electron will be...Ch. 20 - When a switch is closed a compass needle deflects...Ch. 20 - 2. You have a lightbulb connected to a battery....Ch. 20 - 3 The current through a circuit is shown in Figure...Ch. 20 - 4. Draw field lines for the magnetic field...Ch. 20 - 5. * You need to determine the direction of the ...Ch. 20 - 6.* Two compass needles are fixed at the ends of a...Ch. 20 - 7. * In Houston, Earth’s field has a magnitude of...Ch. 20 - * A 15-g 10-cm-long wire is suspended horizontally...Ch. 20 - Prob. 9PCh. 20 - * A metal rod is connected to a battery through...Ch. 20 - * After you turned on the current in the circuit...Ch. 20 - 13. ** A square coil with 30 turns has sides that...Ch. 20 - * (a) Determine the magnetic force (magnitude and...Ch. 20 - 16. * A 500-turn square coil of wire is hinged to...Ch. 20 - * Electric motor 1 An electric motor has a square...Ch. 20 - 18. ** You make a seesaw by placing a 50-g magnet...Ch. 20 - * Electric motor 2 An electric motor has a...Ch. 20 - 20. Each of the lettered dots a-d shown In Figure...Ch. 20 - Duck gets a lift A duck accumulates a positive...Ch. 20 - 22. An electron of mass kg moves horizontally...Ch. 20 - A 1000-kg car moves west along the equator. At...Ch. 20 - * BIO Magnetic force exerted by Earth on ions in...Ch. 20 - 105m/s. Design a magnetic shield that will deflect...Ch. 20 - s magnetic field.Ch. 20 - 27. * An electron and a proton, moving side by...Ch. 20 - An east-west electric power line carries a 500-A...Ch. 20 - * Pigeons A solenoid of radius 1.0 m with 750...Ch. 20 - * A horizontal current-carrying wire that is...Ch. 20 - Prob. 31PCh. 20 - field inside a long solenoid is given by the...Ch. 20 - * Electron current and magnetic field in H atom In...Ch. 20 - * Two long, parallel wires are separated by 2.0 m....Ch. 20 - * Minesweepers During World War II, explosive...Ch. 20 - 40. An electron moves at the speed of toward the...Ch. 20 - * Mass spectrometer A mass spectrometer has a...Ch. 20 - 42. * Mass spectrometer 2 One type of mass...Ch. 20 - 43. * An ion with charge C moves at speed m/s...Ch. 20 - * A box has either an electric field or a magnetic...Ch. 20 - 45. ** A piece of wire, shown in Figure P20.45 ,...Ch. 20 - 46. ** EST Particles in cosmic rays are mostly...Ch. 20 - BIO Magnetic resonance imaging In magnetic...Ch. 20 - BIO Magnetic resonance imaging In magnetic...Ch. 20 - BIO Power lines—do their magnetic fields pose a...Ch. 20 - BIO Magnetic resonance imaging In magnetic...Ch. 20 - BIO Magnetic resonance imaging In magnetic...Ch. 20 - BIO Magnetic resonance imaging In magnetic...Ch. 20 - BIO Power linesdo their magnetic fields pose a...Ch. 20 - BIO Power linesdo their magnetic fields pose a...Ch. 20 - BIO Power linesdo their magnetic fields pose a...Ch. 20 - BIO Power linesdo their magnetic fields pose a...Ch. 20 - BIO Power linesdo their magnetic fields pose a...

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