Simulation of Gradient Magnetic Fields

Numerical Simulations of Gradient Magnetic Fields for MRI

In Magnetic Resonance Imaging (MRI) a variety of magnetic fields are applied to the human body to manipulate the hydrogen nuclei throughout the body. These fields interact with the body in a variety of ways, producing both the desired signal and favorable image contrast, but also side effects including image distortions and heating of tissues.

We develop a variety of numerical methods and tools considering anatomical models of the human body in the MRI environment and use them to characterize electromagnetic field behavior, image appearance, and temperature increase due to field/tissue interactions in MRI. Such tools are increasingly becoming an integral part of engineering and safety assurance in MRI.

In order to encode spatial information onto the signal from processing nuclei for MRI, the magnetic field strength is made a function of position and time with the application of Gradient fields throughout the imaging process. Gradient fields can be switched on and off thousands of times in in an imaging session. The switching of the gradient coils (or magnets) in the presence of the large static magnetic field, B0, creates large forces and the loud noise associated with MRI. The rapidly-changing magnetic fields during switching also induce unwanted electrical fields throughout the human body. These electric fields can simulated nerves resulting in sensory perception or in involuntary muscle contraction. Fortunately these effects tend to occur at the surface of the body and anything truly detrimental - such as induction of cardiac contraction - is extremely unlikely.

We have used a variety of methods to calculate the electric fields induced within and surrounding the human body during switching of the gradient fields (Fig. 1)(1,2). There are still a lot of questions to be answered and experiments to be performed before it is clear how well these can be used to predict peripheral nerve stimulation (PNS) in MRI (3).

 

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05/23/2017 - 14:55
05/19/2017 - 16:45

Philanthropic Support

We gratefully acknowledge generous support for radiology research at NYU Langone Medical Center from:
 
• The Big George Foundation
• Raymond and Beverly Sackler
• Bernard and Irene Schwartz

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