Principles of magnetic resonance imaging
- Daniel Chernoff, MD, PhD
Daniel Chernoff, MD, PhD
- Director of MRI
- Adirondack Radiology Associates
- Paul Stark, MD
Paul Stark, MD
- Professor of Radiology
- University of California San Diego
- Section Editor
- Nestor L Muller, MD, PhD
Nestor L Muller, MD, PhD
- Section Editor — Pulmonary Imaging
- Professor of Radiology
- University of British Columbia
Magnetic resonance (MR) imaging is an important tool in the diagnosis and evaluation of diseases . In the early 1970s, Paul Lauterbur and Raymond Damadian applied nuclear magnetic resonance (NMR) technology to the imaging of living organisms, generating images referred to as zeugmatographs [2-5]. Subsequent refinements in image acquisition and processing, developed by Sir Peter Mansfield and others, allowed improved visualization of anatomic detail and broader clinical application of MR imaging [1,6-8]. Lauterbur and Mansfield were awarded the 2003 Nobel Prize in Medicine and Physiology for their contributions to medical imaging.
This topic will review the principles of magnetic resonance imaging. Clinical applications of MR are discussed in individual topic reviews.
Atoms are characterized by mass, electrical charge, and a magnetic property called spin. Atomic nuclei that contain an odd number of protons or neutrons possess a magnetic moment, which describes the strength and direction of a microscopic magnetic field surrounding the nucleus. In the presence of a strong, constant external magnetic field, such as that produced inside an imaging magnet, a small excess fraction of nuclei, on average, align themselves with the magnetic field, producing a macroscopic, measurable magnetic moment (figure 1) [9-11].
In addition, the interaction between the magnetic moment of the nucleus and the external field causes each spinning nucleus to precess (ie, change the orientation of the rotation axis of the spinning nucleus). Each nucleus precesses at a characteristic (resonant) frequency that is proportional to the strength of the external field. The resonant frequency can be calculated with the Larmor equation:
Resonant frequency F = B0 x Larmor constant
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- MR PHYSICS
- MR IMAGING TECHNOLOGY AND PULSE SEQUENCES
- Magnet and coil design
- Pulse sequences
- - Spin echo
- - Gradient echo
- - Other sequences
- MAGNETIC RESONANCE CONTRAST AGENTS
- MOTION COMPENSATION TECHNIQUES
- Cardiac gating
- Respiratory compensation
- Flow compensation (gradient moment nulling)
- SPATIAL AND CHEMICAL PRESATURATION
- Suppression of signal from flowing blood
- Suppression of respiratory motion artifact
- Suppression of signal from fat
- PRACTICAL ASPECTS
- Cardiovascular devices
- - Timing of MR examination
- - Coronary artery and peripheral vascular stents
- - Aortic stent grafts
- - Mechanical cardiac valves
- - Cardiac closure and occluder devices
- - Inferior vena cava filters
- - Embolization coils
- - Loop recorder (Event monitor)
- - Hemodynamic monitoring and temporary pacing devices
- - Permanent pacemakers and implantable cardioverter-defibrillators
- - Retained transvenous pacemaker and defibrillator leads
- - Hemodynamic support devices
- Other implanted electronic devices
- Aneurysm clips
- Other foreign materials
- - Transdermal patches
- Unstable patient
- MR contrast agent
- - Kidney disease
- - Retained gadolinium