MRI PRELIM 1

HISTORICAL DEVELOPMENT OF MRI

1930s

Magnetic fields associated with atoms and nuclei were

first described in the _____________.

Otto Stern and Isador Rabi

____________________ each received a Nobel Prize in physics for their work on atomic and nuclear magnetism

Isador Rabi

______________ coined the term nuclear magnetic resonance (NMR).

1946

In _______, Felix Bloch at Stanford and Edward Purcell at Harvard independently described NMR in a solid.

• They shared the 1952 Nobel Prize in physics for this work.

• Felix Bloch at Stanford and

• Edward Purcell at Harvard

In 1946, they independently described NMR in a solid. They shared the 1952 Nobel Prize in physics for this work.

1952 Nobel Prize in physics

In 1946, Felix Bloch at Stanford and Edward Purcell at Harvard independently described NMR in a solid.

• They shared the ______________ for this work.

Felix Bloch

• He continued extensive studies with the NMR of water, thereby laying the groundwork for later developments that led to MRI.

• Father of MRI

• A theoretical physicist who proposed some novel properties for the atomic nucleus, including that the nucleus behaves like a small magnet.

  • He described this nuclear magnetism by what are now called the Bloch equations.

Bloch equations

Bloch proposed some novel properties for the atomic nucleus, including that the nucleus behaves like a small magnet. He described this nuclear magnetism by what are now called the _____________.

• This explain that a nucleus, because it spins on an imaginary axis, has an associated magnetic field.

Amagnetic moment

Bloch’s equations explain that a nucleus, because it spins on an imaginary axis, has an associated magnetic field.

• This field is called _____________.

• Nucleons that have charge (e.g., protons) and that spin have even stronger magnetic fields.

Stronger magnetic fields

Bloch’s equations explain that a nucleus, because it spins on an imaginary axis, has an associated magnetic field. This field is called amagnetic moment.

• Nucleons that have charge (e.g., protons) and that spin have even _________________.

Late 1960s

In the _________,

• Engineer-physician Raymond Damadian, while working with NMR spectroscopy, showed that malignant tissue has a different NMR (relaxation time of water) spectrum from normal tissue.

Raymond Damadian

In the late 1960s, engineer-physician ____________, while working with NMR spectroscopy, showed that malignant tissue has a different NMR (relaxation time of water) spectrum from normal tissue.

• He also showed that the parameters associated with

  NMR (i.e., proton density, spinlattice relaxation time, and

  spin-spin relaxation time) differ between normal and

  malignant tissue.

Maps of relaxation rates

Raymond Damadian also showed that the parameters associated with NMR (i.e., proton density, spinlattice relaxation time, and spin-spin relaxation time) differ between normal and malignant tissue.

• This finding suggested that images of the body might be obtained by producing _________________.

Crude NMR image of a rat tumor

In 1974,

• Damadian produced a __________________.

First body image

In 1976,

• Damadian produced the ____________.

Paul Lauterbur

• An NMR chemist at State University of New York in Stony Brook

• Developed the first imaging method using NMR that is similar to what is used today.

Zeugmatography

Paul Lauterbur developed the first imaging method using NMR that is similar to what is used today.

• He called this method _______________, which was sort of Greek for saying that this imaging method requires a whole bunch of magnetic fields wheezing and buzzing around.

1973

In ________, Lauterbur published the first cross-sectional images of objects obtained with MRI techniques.

• These first images were crude, and only large objects could be distinguished.

• Since that time, MRI technology has developed so much that tiny structures can be imaged rapidly with increased resolution and contrast.

Peter Mansfield

• Meanwhile in Nottingham, England, a solid-state physicist, was engaged in similar research (to Paul Lauterbeur)

• He eventually developed the echoplanar MRI method that is used for functional MR neuroimaging today.

Lauterbur and Mansfield

In 2003,

• _____________ shared the Nobel Prize in physiology and medicine “for their discoveries concerning magnetic resonance imaging.”

• James Hutchinson and William A. Edelstein at the University of Aberdeen

• David Hoult at Oxford University

• Ian Young at EMI Laboratories, and

• Waldo Hinshaw and E. Raymond Andrew, both from University of Nottingham

In fact, a large number of scientists made significant contributions to the early development of MRI, among them:

• These gentlemen have all received numerous high scientific and engineering honors for their contributions to the field

Basic principle of MRI

Protons in certain atomic nuclei, if placed in a magnetic field, can be stimulated by (absorb energy from) radio waves of the correct frequency.

After this stimulation, the protons relax while energy is induced into a receiver antenna (the MRI signal), which is then digitized into a viewable image.

• Relaxation times represent the rates of signal decay and the return of protons to equilibrium.

Relaxation times

___________ represent the rates of signal decay and the return of protons to equilibrium.

MRI

• A non-invasive imaging technology that produces three dimensional detailed anatomical images.

• These scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body.

Magnet

The most important component of an MRI system is the __________.

• The strength of the magnet is measured in teslas (T).

Any material capable of attracting iron and producing a magnetic field outside itself.

Teslas (T)

The strength of the magnet is measured in ____________.

Shim coils

Components of MRI:

• For correcting inhomogeneities in the main magnetic field.

The gradient system

Components of MRI:

• Which is used to localize the MR signal.

RF system

Components of MRI:

• Which excites the sample and detects the resulting

  NMR signal.

One or more computers

The whole system (MRI) is controlled by ___________.

• Diamagnetism

• Paramagnetism

• Ferromagnetism

• Non-Magnetism

The magnetic behavior of materials can be classified into the following 5(?) major groups:

Diamagnetism

A magnetism that are repelled by a magnetic field;

• An applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force.

Paramagnetism

A magnetism whereby some materials are weakly attracted by an externally applied magnetic field

Ferromagnetism

The basic mechanism by which certain materials form permanent magnets, or are strongly attracted to magnets.

Non-Magnetism

Substances that do not get attracted by a magnet

Magnetic Field

A field that passes through space and which makes a magnetic force move electric charges and magnetic dipoles.

Atomic Nucleus

The small, dense region consisting of protons and neutrons at the center of an atom.

Proton spin

Protons have a constant spin that is an intrinsic particle property like mass or charge.

Larmour relationship

An MRI term for a formula for which the frequency of precession of the nuclear magnetic moment is directly proportional to the product of the magnetic field strength (Bo) and the gyromagnetic ratio (g).

• As in the equation: å = gx Bo

Radiofrequency (RF)

The oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system

Phase Coherent

A fixed relationship between the phase of waves in a beam of radiation of a single frequency.

• Two beams of light are coherent when the phase difference between their waves is constant;

• They are noncoherent if there is a random or changing phase relationship.

Free Precession

A magnetic resonance imaging (MRI) sequence which uses steady states of magnetizations.

Relaxation Time (T1 and T2)

• The T1 relaxation time, also known as the spin-lattice relaxation time, is a measure of how quickly the net magnetization vector (NMV) recovers to its ground state in the direction of B₀.

• Two other forms of relaxation are:

  • The T2 relaxation time (spin-spin relaxation)

  • and T2* relaxation.

T1 relaxation time

The ________________, also known as the spin-lattice relaxation time, is a measure of how quickly the net magnetization vector (NMV) recovers to its ground state in the direction of B₀.

Spin Density

Weighted image visualizes the number of protons per volume.

• Tissues with few protons have low signal intensity, tissues with many protons have high signal intensity.

• Fat has a relatively high signal intensity, however, not as high as in a T1 weighted image.

• Contrast resolution

• Spatial resolution

• Non-invasive, uses non-ionizing type of radiation

What are the advantages of MRI?