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Magnetic Resonance Imaging

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Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI...

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...

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A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.

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Updated: Jun 21, 2026

Cardiac Magnetic Resonance Imaging at 7 Tesla

Cardiac Magnetic Resonance Imaging at 7 Tesla

Published on: January 6, 2019

Understanding and manipulating the RF fields at high field MRI.

Tamer S Ibrahim¹, Yik-Kiong Hue, Lin Tang

¹Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA15213, USA. tibrahim@pitt.edu

NMR in Biomedicine

|July 22, 2009

Summary

This study analyzes MRI electromagnetics at various field strengths, focusing on transmit/receive fields and power absorption. It explores B(1) shimming and array coil techniques to improve high-field MRI performance.

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Area of Science:

Medical Physics
Electromagnetics
Magnetic Resonance Imaging

Background:

Electromagnetic phenomena are critical in Magnetic Resonance Imaging (MRI), influencing image quality and safety.
Understanding the behavior of electromagnetic fields at different static field strengths is essential for MRI advancements.

Purpose of the Study:

To provide a comprehensive overview of MRI electromagnetics at low and high fields.
To analyze the physics impacting transmit field, receive field, and power absorption in MRI.
To investigate techniques for manipulating electromagnetic quantities to enhance high-field MRI.

Main Methods:

Analytical formulations
Numerical modeling (computational electromagnetics)
Ultrahigh field imaging experiments
Phantom studies for B(1) shimming

Main Results:

Detailed analysis of electromagnetic quantities (transmit field, receive field, power absorption) across different field strengths.
Demonstration of B(1) shimming and receive array signal combination for improved MRI.
First phantom demonstration of B(1) shimming without B(1) measurements at 7 Tesla.

Conclusions:

Electromagnetic properties significantly change with static field strength in MRI.
Techniques like B(1) shimming and array coils offer viable methods to optimize high-field MRI.
Further research into electromagnetic manipulation can advance MRI capabilities.