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MRI: Magnetic Resonance Imaging. Tyler Bradshaw University of Utah 2010. Overview. Introduction Medical imaging MRI uses History How does magnetic resonance work? Magnetic fields Atomic spin Resonance Relaxation Magnetic resonance imaging Hydrogen in the body Scanners

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slide1

MRI: Magnetic Resonance

Imaging

Tyler Bradshaw

University of Utah 2010

slide2

Overview

Introduction

Medical imaging

MRI uses

History

How does magnetic resonance work?

Magnetic fields

Atomic spin

Resonance

Relaxation

Magnetic resonance imaging

Hydrogen in the body

Scanners

Imaging

Getting an MRI scan

Why get one?

The scanner room

The scan

The future of MRI

slide3

Medical Imaging

Medical Imaging:

Creating images of the human body for clinical or scientific purposes

•Ultrasound

• Fluoroscopy

• Computed Tomography (CT)/X-ray

• Positron Emission Tomography (PET)

• Single Photon Emission Computed

Tomography (SPECT)

• Magnetic Resonance Imaging (MRI)

slide4

MRI Uses

One of the best diagnostics exams for soft-

tissue injuries, such as:

• Musculoskeletal system;

joints

• Brain; Spinal cord

• Heart; aorta; arteries

• Internal organs (liver,

kidney, lungs, etc.)

• Breasts

slide5

History

• 1946 - Felix Bloch and Edward Purcell discovered

magnetic resonance; won Nobel prize in 1952

• At first could only analyze chemical and physical

properties

• 1971 – discovered that magnetic resonance could show

differences between tissue

• 1977 – first human MRI exam (5 hours)

• 1980 – first commercial MRI scanner

• Over 20,000 MRI scanners in use today

slide6

How Does it Work?

Magnetic Resonance Imaging

Its based on how atoms react to magnetic fields

slide7

To understand magnetic resonance, we first need to understand 2 things…

1) Magnetic Fields

2) Spin

slide8

Magnetic Fields

Definition: A field surrounding a magnet that will exert a force on other magnetic material

Magnetic field

slide9

Spin

•Every particle (proton, neutron,

electron) have a spin value

• It’s a fundamental property of

the particle (like charge, or mass)

• Similar to a sphere rotating on

its axis

Spin axis

slide10

Magnetic Fields & Spin

• Spins have a random orientation

in the absence of a magnetic field

• The atom’s spin will cause it to

react to a magnetic field

• Most spins will align with the

direction of the magnetic field

slide11

Resonance

• Atoms can absorb specific radio waves

• This can cause them to change spin-directions in

the magnetic field

• This is known as resonance

Radiowave

Resonance

slide12

Relaxation

After the atom experiences resonance it will want to rotate back and realign with the magnetic field

This is called relaxation

During relaxation an atom will

release a radio wave

Radio signals can be

easily detected

Radio wave

(detectable)

slide15

Hydrogen

  • The human body is about 60% water
  • (by weight)
  • About 20% fat
  • The human body is therefore about
  • 63% hydrogen
  • -Hydrogen has spin and can experience
  • resonance

H

slide17

MRI Scanners

An MRI scanner uses a very powerful magnet to align the hydrogen in your body

Magnetic Field

MRI

MRI

slide19

MRI - Resonance

• After the hydrogen spins are aligned they are

hit with radio waves

• Resonance occurs and the spins change

Magnetic Field

MRI

slide20

MRI - Relaxation

• When the hydrogen “relaxes” they release radio waves

• These signals are detected by the MRI scanner

• Each radio wave is transmitted to a computer as data

• The computer interprets all the

data points, constructs a 3

dimensional image

slide22

MRI - Images

The images represent different densities of hydrogen in the body

slide24

A doctor will order the MRI for you in order to….

-Visualize torn ligaments

-Visualize shoulder injuries

-Diagnose multiple sclerosis (MS)

-Diagnose tumors

-Diagnose infections in the brain, spine or joints

-Diagnose tendonitis

-Evaluate masses in the soft tissues of the body

-Evaluate bone tumors, cysts and bulging or herniated discs in the

spine

-Diagnose strokes in their earliest stages

slide25

The MRI Room

  • • Constructed to isolate the scanner from outside signals
  • • No metal allowed!
    • Dress in hospital gown
    • Not even bras or hair clips
    • -Orthopedic implants usually
    • ok (except in the eye or brain)
    • Most pacemakers and
    • internal defibrillators not
    • allowed
    • Beware of unknown
    • shrapnel!
slide26

The Scan

• Closed – better image quality, but can cause claustrophobia

• Open – More comfortable, lower image quality, fit larger patients

• Can image a specific body part

• Scans usually last 30-60 minutes

• The magnets make a loud noise

• Costs $400-$3,000

slide27

Future of MRI

It’s not leaving anytime soon…

MRI and CT were ranked as most important medical innovations by physicians

MRI doesn’t harm the patient (unlike PET, CT)

The future…

Small scanners to scan specific body parts

Hyperpolarized gas (imaging lungs)

Color

slide28

References

Discovery Communications. “How MRI Works”.

<http://www.howstuffworks.com/mri.htm> (March 2010)

Aziz, Salwa and Christina Derbidge, “Magnetic Resonance Imaging”

University of Utah.

Simply Physics. “Introduction to MRI Physics”.

< http://www.simplyphysics.com/page2_1.html> (March 2010)

Hornak, Joseph, PhD. “The Basics of MRI”. 1996-2003.

<http://www.cis.rit.edu/htbooks/mri/index.html> (March 2010)