Main magnet, RF energy and Gradients

Energy sources of MRI

1. Main magnetic field

2. Gradient field

3. Radiofrequency pulse {RF}

Main Magnetic field

B0

Energy sources of MRI

1. Main magnetic field

2. Gradient field

3. Radiofrequency pulse {RF}

Main Magnetic field

B0

B0 used for

Clinically used for molecular alignment. This is the cause for projectiles flying into the magnet.

• Spatial distribution of static magnetic field

• How rapidly the magnetic field  changes is what causes pulling of ferromagnetic objects.

• The greater the differences, more pull.

• Items in the center would fall to the bottom from gravity.

B0 is responsible for

translation-projectile tork-rotation

cause for projectiles flying into the magnet

Main magnetic field

what causes pulling of ferromagnetic objects

rapidly the magnetic field change.
greater differences the greater the pull

Gradient Coils

Db/Dt

Db/Dt

Rate of change of magnetic field over time..

Db/Dt does what

Uses electricity to slope the magnetic field in a linear fashion.

dangers of Db/Dt

This can cause electrical malfunctions to internal devices and or burns. 
Can induce current into devices

where is Db/Dt most dangerous

Uses electrical charge

Greatest at ends and riskiest there.

Db/Dt is clinically used for

Spatial resolution, image formation

Radio Frequency Pulse

B1

B1 does what

Resonate protons to create the MR signal.

Dangers of B1

This can cause proximity burns where the pt may be touching the bore. Increase on sides of magnet
Large patients more susceptible
Electricity can also be induced into abandoned leads. 

how to protect against burns

Important to use manufacture pads where pts are in contact with the bore.