MRI Safety, 3

How does MRI create images?

MRI uses changing magnetic fields to create a signal emitted from the patient that is digitized into an image.

What happens to the patient inside the MRI scanner?

The patient is placed in a strong external magnetic field, causing hydrogen atoms in the body to align with the field.

What type of signal does the patient emit in MRI?

The patient emits a signal in the form of an oscillating magnetic field.

How is the MRI signal captured and processed?

The emitted signal is captured and digitized into a detailed image.

What are the two common units used to measure magnetic field strength?

Gauss (G) and Tesla (T).

How strong is a typical refrigerator magnet?

Between 100 and 400 Gauss.

What is the strength of the Earth's magnetic field?

Approximately 0.25 to 0.65 Gauss.

Which unit is preferred for measuring MRI magnet strength?

Tesla (T), a larger unit of magnetic field strength.

What is the conversion between Tesla and Gauss?

1 Tesla (T) = 10,000 Gauss (G).

What are smaller magnetic field strengths measured in?

Microtesla (μT) or millitesla (mT).

What is the conversion between Tesla, millitesla, and Gauss?

1 T = 1000 mT; 1 μT = 100 G; 1 G = 0.1 mT.

What are the two main types of MRI scanners?

Resistive and Superconducting.

How is the magnetic field produced in a resistive MRI scanner?

By two opposing electromagnets powered by an external electrical supply.

Can a resistive MRI magnet be turned off?

Yes, resistive magnets can be turned off when power is disconnected.

What is the typical field strength of a resistive MRI system?

Between 0.5 and 1.5 Tesla.

How is the magnetic field produced in a superconducting MRI scanner?

By a superconducting electromagnet that maintains current with no resistance.

Can a superconducting MRI magnet be turned off?

No, superconducting magnets cannot be turned off under normal operation.

What is the typical field strength range for a superconducting MRI system?

Between 1.5 and 7 Tesla; research magnets can reach up to 10 Tesla.

What is superconductivity?

The property of certain materials that, when cooled to nearly absolute zero, conduct electricity without resistance.

At what temperature does superconductivity occur?

Nearly absolute zero, approximately -459.67°F (0 Kelvin).

What substance is used to cool superconducting MRI magnets?

Liquid helium.

What is the temperature of liquid helium used for cooling MRI magnets?

Approximately -452.1°F (-268.9°C).

Why is liquid helium important for MRI systems?

It cools the superconducting coils to eliminate electrical resistance and maintain the strong magnetic field.