Magnetic Resonance Imaging System Components

Outline

Mind Map

Learning Objectives

Teaching Visuals

Online Module
(Requires Enrollment)

Text Reference

 

Outline and Learning Guide


INTRODUCTION AND OVERVIEW

Tissue Magnetization

Tissue Resonance

 

THE MAGNETIC FIELD

Field Direction

Field Strength

Homogeneity

 

MAGNETS

Superconducting

Resistive

Permanent

 

GRADIENTS

Gradient Orientation

Gradient Functions

Gradient Strength

Risetime and Slew-Rate

Eddy Currents

 

SHIMMING

 

MAGNETIC FIELD SHIELDING

Passive Shielding

Active Shielding

 

THE RADIO FREQUENCY SYSTEM

RF Coils

Transmitter

Receiver

RF Polarization

RF Shielding

 

COMPUTER FUNCTIONS

Acquisition Control

Image Reconstruction

Image Storage and Retrieval

Viewing Control and Post Processing

 

MIND MAP and SUMMARY

 

 

Learning Objectives

  • Sketch a cross-section of a super-conducting magnet showing the directional characteristics of both the internal and external magnetic field
     
  • Describe the significance of the direction of the internal field and what it is used for in MRI.
     
  • Name the two units used to express the strength of magnetic fields.
     
  • Explain a practical reason for using two different units and where each unit is generally used.
     
  • Describe the general range of magnet field strengths used for MRI.
     
  • The strength of the earth's field is often used as a general reference. Express the typical strength of the earth's field in both units.
     
  • Explain the concept of homogeneity as it applies to magnetic fields used for MRI.
     
  • Identify the three types of magnets, with respect to the type of technology used to produce fields, that are used for MRI.
     
  • Explain the concept of superconductivity and why it is used in MRI.
     
  • Describe the two conditions that are necessary for a magnet coil to operate as a superconductor.
     
  • A quench is generally an undesirable event. Describe what it is and the conditions that produce it.
     
  • Explain why certain types of magnets are classified as "resistive" and why they have limited applications for MRI.
     
  • Describe both an advantage and a limitation in using permanent magnetic technology for MRI.
     
  • Describe a gradient in a magnetic field.
     
  • Identify the component of a MR system that is used to produce a gradient in the magnetic field.
     
  • Name at least four functions that are performed by gradients during MR imaging procedures.
     
  • State the units that are used to express gradient strength and a typical gradient strength value for a contemporary MR system.
     
  • Specifications for gradients include the parameters of rise time and slew rate. Explain what these parameters describe about the gradient system.
     
  • Explain how eddy currents are produced and why they are undesirable.
     
  • Explain what the process of shimming does to a magnetic field.
     
  • Identify the type of metal used and describe it's placement to produce shielding of a magnetic field.
     
  • Explain two undesirable effects associated with a magnetic field that can be reduced by shielding.
     
  • Describe the basic difference between active and passive magnetic shielding.
     
  • Describe the general function of the radio frequency coils that are a part of a MR system.
     
  • Briefly explain the advantage of using quadrature type coils (compared to single type coils) for MR imaging.
     
  • Identify the type of medal used and it's general placement to produce radio frequency shielding.
     
  • Explain why it is generally necessary to have radio frequency shielding of a MR facility.
     
  • Briefly describe at least four functions that are performed by the digital computer that is a component of a MR system.
 

 

Text Reference

Chapter 2

Magnetic Resonance Imaging: Principles, Methods, and Techniques
Medical Physics Publishing,  http://www.medicalphysics.org

 

 

Mind Map