MRI 1

MRI is based on the magnetic properties of ________.

• oxygen atoms
• carbon molecules
• atomic nuclei

• nitrogen ions

The magnetism of atomic nuclei is very small, but if we have a very large number of nuclei, we can detect the ________ magnetisation.

• individual
• hydrogen

• random
• net

What does putting a patient in the strong magnetic field of an MRI scanner create?

• Ultrasound waves for treatment
• Thermal images for diagnosis
• A temporary net magnetisation that we can manipulate

• Electrical signals for monitoring

The strength and behaviour of the induced magnetisation depends on the type of ________, and the way we perform the MRI scan.

• device
• frequency
• current

• tissue

The human body contains lots of water (two hydrogen nuclei per water molecule) and, in most of us, lots of fat (many hydrogen nuclei per fat molecule).

• False

• True

The human body is about (a)   % hydrogen by number of atoms. Most is in water which has strong magnetisation.

What two factors combine to make MRI feasible?

• Prevalence of nuclei AND magnetic strength of the hydrogen nucleus magnetisation

• Static electricity AND thermal imaging

• High voltage AND light pulses

• Weak magnetic fields AND sound waves

• We can think of the hydrogen nucleus (a single proton) as a spinning blob that has mass and ______ electric charge. The moving charge generates a magnetic field.

• positive

• negative

What property does the spinning mass give the nucleus?

• Angular momentum
• Linear momentum
• Mass energy
• Centrifugal force

What does the circulating electric charge in the hydrogen nucleus create?

• A gravitational field – the nuclear gravitational dipole.

• • A sound wave – the nuclear acoustic dipole.

• An electric current – the nuclear electric dipole.

• A magnetic field – the nuclear magnetic dipole.

Answer explanation

The positive charge moving in a circle will act like an electric current flowing in a circle. This will give rise to a magnetic field oriented along the axis of rotation.

We call this tiny magnetic field the Nuclear Magnetic Dipole, and typically use an arrow or vector to represent its strength and orientation.