MRI E-Book

Brian M. Dale

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 439

Veröffentlichungsjahr: 2015

Beschreibung

This fifth edition of the most accessible introduction to MRI principles and applications from renowned teachers in the field provides an understandable yet comprehensive update.

• Accessible introductory guide from renowned teachers in the field
• Provides a concise yet thorough introduction for MRI focusing on fundamental physics, pulse sequences, and clinical applications without presenting advanced math
• Takes a practical approach, including up-to-date protocols, and supports technical concepts with thorough explanations and illustrations
• Highlights sections that are directly relevant to radiology board exams
• Presents new information on the latest scan techniques and applications including 3 Tesla whole body scanners, safety issues, and the nephrotoxic effects of gadolinium-based contrast media

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Preface

ABR study guide topics

Chapter 1: Production of net magnetization

1.1 Magnetic fields

1.2 Nuclear spin

1.3 Nuclear magnetic moments

1.4 Larmor precession

1.5 Net magnetization

1.6 Susceptibility and magnetic materials

Chapter 2: Concepts of magnetic resonance

2.1 Radiofrequency excitation

2.2 Radiofrequency signal detection

2.3 Chemical shift

Chapter 3: Relaxation

3.1

T1

relaxation and saturation

3.2

T2

relaxation,

T2

* relaxation, and spin echoes

Chapter 4: Principles of magnetic resonance imaging – 1

4.1 Gradient fields

4.2 Slice selection

4.3 Readout or frequency encoding

4.4 Phase encoding

4.5 Sequence looping

Chapter 5: Principles of magnetic resonance imaging – 2

5.1 Frequency selective excitation

5.2 Composite pulses

5.3 Raw data and image data matrices

5.4 Signal-to-noise ratio and tradeoffs

5.5 Raw data and

k

-space

5.6 Reduced

k

-space techniques

5.7 Reordered

k

-space filling techniques

5.8 Other

k

-space filling techniques

5.9 Phased-array coils

5.10 Parallel acquisition methods

Chapter 6: Pulse sequences

6.1 Spin echo sequences

6.2 Gradient echo sequences

6.3 Echo planar imaging sequences

6.4 Magnetization-prepared sequences

Chapter 7: Measurement parameters and image contrast

7.1 Intrinsic parameters

7.2 Extrinsic parameters

7.3 Parameter tradeoffs

Chapter 8: Signal suppression techniques

8.1 Spatial presaturation

8.2 Magnetization transfer suppression

8.3 Frequency-selective saturation

8.4 Nonsaturation methods

Chapter 9: Artifacts

9.1 Motion artifacts

9.2 Sequence/Protocol-related artifacts

9.3 External artifacts

Chapter 10: Motion artifact reduction techniques

10.1 Acquisition parameter modification

10.2 Triggering/Gating

10.3 Flow compensation

10.4 Radial-based motion compensation

Chapter 11: Magnetic resonance angiography

11.1 Time-of-flight MRA

11.2 Phase contrast MRA

11.3 Maximum intensity projection

Chapter 12: Advanced imaging applications

12.1 Diffusion

12.2 Perfusion

12.3 Functional brain imaging

12.4 Ultra-high field imaging

12.5 Noble gas imaging

Chapter 13: Magnetic resonance spectroscopy

13.1 Additional concepts

13.2 Localization techniques

13.3 Spectral analysis and postprocessing

13.4 Ultra-high field spectroscopy

Chapter 14: Instrumentation

14.1 Computer systems

14.2 Magnet system

14.3 Gradient system

14.4 Radiofrequency system

14.5 Data acquisition system

14.6 Summary of system components

Chapter 15: Contrast agents

15.1 Intravenous agents

15.2 Oral agents

Chapter 16: Safety

16.1 Base magnetic field

16.2 Cryogens

16.3 Gradients

16.4 RF power deposition

16.5 Contrast media

Chapter 17: Clinical applications

17.1 General principles of clinical MR imaging

17.2 Examination design considerations

17.3 Protocol considerations for anatomical regions

17.4 Recommendations for specific sequences and clinical situations

References and suggested readings

Index

End User License Agreement

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Guide

Cover

Table of Contents

Preface

Begin Reading

List of Illustrations

Chapter 1: Production of net magnetization

Figure 1.1 A rotating nucleus (spin) with a positive charge produces a magnetic field known as the magnetic moment oriented parallel to the axis of rotation (a). This arrangement is analogous to a bar magnet in which the magnetic field is considered to be oriented from the south to the north pole (b).

Figure 1.2 Microscopic and macroscopic pictures of a collection of spins in the absence of an external magnetic field. In the absence of a magnetic field, the spins have their axes oriented randomly (microscopic picture, left side of figure). The vector sum of these spin vectors is zero (macroscopic picture, right side).

Figure 1.3 Inside a magnetic field, a proton precesses or revolves about the magnetic field. The precessional axis is parallel to the main magnetic field,

B

0

. The

z

component of the spin vector (projection of the spin onto the

z

axis) is the component of interest because it does not change in magnitude or direction as the proton precesses. The

x

and

y

components vary with time at a frequency ω

0

proportional to

B

0

as expressed by equation (1.1).

Figure 1.4 Zeeman diagram. In the absence of a magnetic field (left side of figure), a collection of spins will have the configurations of

z

components equal in energy so that there is no preferential alignment between the spin-up and spin-down orientations. In the presence of a magnetic field (right side), the spin-up orientation (parallel to

B

0

) is of lower energy and its configuration contains more spins than does the higher-energy spin-down configuration. The difference in energy Δ

E

between the two levels is proportional to

B

0

.

Figure 1.5 Microscopic (a) and macroscopic (b) pictures of a collection of spins in the presence of an external magnetic field. Each spin precesses about the magnetic field. If a rotating frame of reference is used with a rotation rate of ω

0

, the collection of protons appears stationary. Whereas the

z

components are one of two values (one positive and one negative), the

x

and

y

components can be any value, positive or negative. The spins will appear to track along two cones, one with a positive

z

component and one with a negative

z

component. Because there are more spins in the upper cone, there will be a nonzero vector sum

M

0

, the net magnetization. It will be of constant magnitude and parallel to

B

0

.

Chapter 2: Concepts of magnetic resonance

Figure 2.1 Energy absorption (microscopic). The difference in energy Δ

E

between the two configurations (spin up and spin down) is proportional to the magnetic field strength

B

0

and the corresponding precessional frequency ω

0

, as expressed in Equation (2.1). When energy at this frequency is applied, a spin from the lower-energy state is excited to the upper-energy state. Also, a spin from the upper-energy state is stimulated to give up its energy and relax to the lower-energy state. Because there are more spins in the lower-energy state, there is a net absorption of energy by the spins in the sample.

Figure 2.2 Energy absorption (macroscopic). In a rotating frame of reference, the RF pulse broadcast at the resonant frequency ω

0

can be treated as an additional magnetic field

B

1

oriented perpendicular to

B

0

. When energy is applied at the appropriate frequency, the spins absorb it and

M

rotates into the transverse plane. The initial direction of rotation is perpendicular to both and . The amount of resulting rotation of is known as the pulse flip angle.