MRI Applications in Cardiovascular Medicine

Vulnerable Plaque Research Group

Basics of MRI

• Magnetic resonance imaging is based on the phenomenon of nuclear magnetic resonance.

• Resonance is defined as amplified response to a stimulus that has the same natural frequency.

Basics of MRI

Consider the simplest atom; hydrogen, its nucleus consists of only one proton.

Protons are positively charged.

Electrons are not involved in MR imaging.

Hydrogen atoms (protons) are the simplest and most abundant element in the body.

All current MRI techniques are based on receiving and processing signals from protons.

Protons have a rotational axis, and since they are positively charged, they create a small magnetic field an a magnetic axis.

In nature, the orientation of these axes is random.

Magnetic moment: The direction of a single hydrogen atom nucleus.

In the presence of a magnetic field, protons spin around an axis that is aligned with the main magnetic field.

The dominant axis of these spinning protons is oriented parallel to the main magnetic field.

Precession is the rotation of protons around the main Magnetic field.

Net magnetization is the sum of all magnetic moments.

Precession

The Larmor frequency: The speed of frequency of precession. It is proportional to the scanners magnetic field.

The Larmor equation: w=&.B

w= larmor frequency in MHz &=The gyromagnetic ratio in MHz/Tesla B= The magnetic strength in Tesla

Resonance only occurs if the RF frequency matches the larmor frequency of the nuclei.

In order to see the precession of the net magnetizationWe should flip the net magnetization from longitudinal to transverse plane.

Recovery of the net magnetization from the transverse plane is associated with the induction of MR signal.

Free Induction Decay (FID): First MR signal after the RF pulse.

Bffe_4c.mpgBffe_la.mpg

Bffe_l~1.mpg

Bffe_r~1.mpgBffe_sa.mpg

PD

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