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10 - Magnetic resonance imaging

Published online by Cambridge University Press:  05 July 2011

Shahzad Ilyas ,
Tomasz Matys ,
Nasim Sheikh-Bahaei ,
Adam K. Yamamoto  and
Martin J. Graves
By
T. Matys  and
M. J. Graves
Shahzad Ilyas
Affiliation:
Addenbrooke’s Hospital, Cambridge, UK
Tomasz Matys
Affiliation:
Addenbrooke’s Hospital, Cambridge, UK
Nasim Sheikh-Bahaei
Affiliation:
Addenbrooke’s Hospital, Cambridge, UK
Adam K. Yamamoto
Affiliation:
Addenbrooke’s Hospital, Cambridge, UK
Martin J. Graves
Affiliation:
Addenbrooke’s Hospital, Cambridge, UK
T. Matys
Affiliation:
Cambridge University Hospitals NHS Foundation Trust
M. J. Graves
Affiliation:
Cambridge University Hospitals NHS Foundation Trust
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Summary

  1. Regarding nuclear magnetic resonance imaging (MRI):

  1. In an external magnetic field, more hydrogen nuclei align with their magnetic moments parallel to the external field than antiparallel

  2. Protons subject to a strong static external magnetic field start to precess in phase

  3. The frequency of precession (Larmor frequency) of protons in a static magnetic field of 1.5 T equals 42.6 MHz

  4. At 1.5 T, the precessional frequency of hydrogen nuclei in fat is 220 Hz lower than that of hydrogen nuclei in water

  5. Apart from hydrogen, other nuclei that can be polarized in an external magnetic field include carbon 12C and oxygen 16O

  1. Which of the following are true about MRI signal formation in biological tissues?

  1. A free induction decay (FID) signal can only occur after a 90° pulse

  2. After a 90° pulse, the longitudinal magnetization recovers at the same rate as the transverse magnetization decays

  3. The rate of the longitudinal magnetization recovery does not depend on the external magnetic field strength

  4. Dephasing of the transverse magnetization is mainly due to spin–lattice relaxation

  5. The FID is not usually considered in clinical MRI

  1. In spin–echo (SE) imaging:

  1. The first radiofrequency pulse in a spin–echo pulse sequence is a 180° pulse

  2. Rephasing of the transverse magnetization is caused by the 180° pulse

  3. […]

Type
Chapter
Information
Physics MCQs for the Part 1 FRCR , pp. 126 - 143
Publisher: Cambridge University Press
Print publication year: 2011

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