Radiospectroscopy

ESR: Elektron Spin Resonance

properties of the electron shells

NMR:Nuclear Magnetic Resonance

properties of nuclei

Quantum numbers name symbol orbital meaning range of values value example

principal quantum number n shell 1 ≤ n n = 1, 2, 3, …

azimuthal quantum number (angular momentum)

ℓ subshell (s orbital is listed as 0, p orbital as 1 etc.)

0 ≤ ℓ ≤ n − 1 for n = 3: ℓ = 0, 1, 2 (s, p, d)

magnetic quantum number, (projection of angular momentum)

mℓ energy shift (orientation of the subshell's shape)

−ℓ ≤ mℓ ≤ ℓ for ℓ = 2: mℓ = −2, −1, 0, 1, 2

spin projection quantum number ms

spin of the electron (−½ = counter-clockwise, ½ = clockwise)

−½, ½ for an electron, either: −½, ½

Basics

angular momentum

magnetic momentum - charge

Current in a circle

Magnet bar

Dipole strength and direction

Electron behaves as a magnetic dipole

rIL

vmI

Rotation around its own axis:

Own angular momentum

SPIN

gyroscope

Own electromagnetic momentum:

Magnet bar

SPIN: own angular momentum of electron, proton, neutron Independent

of its movement

( 1)

1

2

3

2

S s s

s

S

1

2

1 1 / -

2 2

z s

s

z

S m

m

S

0

0

: paralel

: antiparalel

B

B

It gives you the magnitude of the

spins projection in a certain direction

in a megnetic field there are two

directions:

Spin

quantumnumber: Shows you the own

electromagnetic momentum

Magnetic spin quantumnumber: ms

No magnetic field: Orientation of the bars is random

Magnetic field: Two different positions:

Precession

Energy levels split

0 0B

0 0B

DE

B0

E

B

0

0

E B

E hf

D

D

0 : resonance frequencyf

: macroscopic magnetismM

0B

0f

0fM

~

paralel

antiparalel

Precession

Larmor (precession) frequency:

0fM

B0

M

excitation Electromagnetic radiation with radiofrequency

Resonance criteria: Larmor frequency 0 0E hf BD ~

2Larmor

B

T1 Processes At equilibrium, the net magnetization vector lies along the direction of the applied magnetic field Bo and is called the equilibrium magnetization Mo. It is possible to change the net magnetization by exposing the nuclear spin system to energy of a frequency equal to the energy difference between the spin states. If enough energy is put into the system, it is possible to saturate the spin system and make MZ=0. The time constant which describes how MZ returns to its equilibrium value is called the spin lattice relaxation time (T1). The spin-lattice relaxation time (T1) is the time to reduce the difference between the longitudinal magnetization (MZ) and its equilibrium value by a factor of e.

T2 Processes In addition to the rotation, the net magnetization starts to dephase because each of the spin packets making it up is experiencing a slightly different magnetic field and rotates at its own Larmor frequency. The longer the elapsed time, the greater the phase difference. Here the net magnetization vector is initially along +Y. The time constant which describes the return to equilibrium of the transverse magnetization, MXY, is called the spin-spin relaxation time, T2. MXY =MXYo e

-t/T2 T2 is always less than or equal to T1. The net magnetization in the XY plane goes to zero and then the longitudinal magnetization grows in until we have Moalong Z.

In summary, the spin-spin relaxation time, T2, is the time to reduce the transverse magnetization by a factor of e. In the previous sequence, T2 and T1processes are shown separately for clarity. That is, the magnetization vectors are shown filling the XY plane completely before growing back up along the Z axis. Actually, both processes occur simultaneously with the only restriction being that T2 is less than or equal to T1.

NMR

Frequency range: 60 – 400 MHz

Magnetic field: 1 – 10 T

Blockdiagram of the spectrometer

Transmitter

N

S

Reciever M

Homogenous magnetic field : B0

electromagnet

EM radiation with radio frequency: f0

oscillator

Radioreciever

Detection of the signal in proportion with the absorbed energy

ESR

Frequency range : 9 – 250 GHz

Magnetic field : 0.1 – 10 T

Spectra

The extent of the absorbtion is proportional to the concentration of

the nuclei/electrones.

The ESR/NMR spectrum shows the absorbed energy by the system as a

function of the frequency of the excitation energy (ΔE) or as a function

of magnetic field (H, B).

Because of the different molecular invirement the excitation energies

of the spin of the nuclei and the spin of the electrons is different.

0 2 4 6 8 10 12

Am

pli

tud

ó

ppm

Signals of

protons in

different

environment

Reference

NMR spectrum

Relative Amplitudes of the spectrumlines

Fine structure of the

spectrumlines

~ absorbtion

~ protonconcentration

CH3-CH2-OH Am

plit

ude

ESR spectrum

H [Gauss]

Am

pli

túd

óA

mpl

itud

e

Application

NMR

× Organic material molecular structure

× Interaction between Organic material

× Macromolecules (proteins, nucleidacids) structure

× Biological and artificial membrane, liposome research

MRI: Magnetic resonance tomography

MRI=Magnetic Resonance

Imaging

Allows the clinician to see

high quality images of the

inside of the body:

• Brain

• Heart

• Lungs

• Spine

• Knees

• Wrist

• Etc.

In 1952 Felix Bloch and Edward Purcell were awarded

the Nobel Prize when they discovered the concepts

surrounding NMR/MRI.

During the time between 1950-1970, the idea was

used for chemical and physical analysis of molecules.

• In 1971, Raymond Damadian

discovered that NMR could be

used in the detection of diseases.

• In 1974, Damadian received a

patent for the design of his MRI

machine.

• In 1977, Damadian did his first

scan on a human, his assistant,

Larry Minkoff. He couldn’t go in himself due to his

enormous size.

The MRI machine picks points

in the patients body, decides

what type of tissue the points

define, then compiles the

points into 2 dimensional and

3 dimensional images.

Once the 3 dimensional image is created, the MRI

machine creates a model of the tissue. This allows

the clinician to diagnose without the use of

invasive surgery.

The largest and most important components of the MRI machine are the

magnets.

The magnet strength is measured in units of Tesla or Gauss (1 Tesla =

10,000 Gauss).

Today’s MRI machines have magnets with strengths from 5000 to 20,000

Gauss.

To give perspective on the strength of these

magnets, the earth’s magnetic field is about

.5 Gauss, making the MRI machine 10,000

to 30,000 times stronger.

MRI’s of the heart can be done to look at many different areas including: vessels,

chambers, and valves.

The MRI can detect problems associated with

different heart diseases including plaque build up

and other blockages in blood vessels due to

coronary artery disease or heart attacks.

MRI’s of the brain can evaluate how the

brain is working, whether normal or

abnormal.

Brain MRI’s can show damage resulting from different problems such as: damage

due to stroke, abnormalities associated with dementia and/or Alzheimer’s,

seizures, and tumors.

fMRI are done prior to brain surgery, to give a map of the

brain, and help plan the procedure.

MRI’s can be done on the knee to evaluate damage

to the meniscus, ligaments, and tendons.

Tears in the ligaments are given a grade 1-3

depending on their severity:

1-fluid around the ligament

2-fluid around the ligament with partial disruption of the ligament fibers

3-complete disruption of the ligament fibers

Often prior to a MRI scan, a patient would need to have a contrast dye, either

injected or taken orally, usually gadolinium as seen here.

The Procedure…

Once the contrast dye has been injected, the patient enters the bore of the MRI

machine on their back lying on a special table.

The patient will enter the machine head first or feet first, depending on the area to

be scanned.

Once the target is centered, the scan can

begin.

•The scan can last anywhere from 20-30 minutes.

•The patient has a coil that is placed in the target area, to be scanned.

•A radio frequency is passed through the coils that excites the hydrogen protons

in the target area.

•The gradient magnets are then activated in the main magnet and alter the

magnetic field in the area that is being scanned.

The patient must hold completely still in order to get a high quality

image. (This is hard for patients with claustrophobia, and often times a

sedative will be given, if appropriate.)

The radio frequency is then turned-off and the hydrogen protons slowly begin

to return to their natural state.

The magnetic field runs down the center of the patient, causing the

slowing hydrogen protons to line-up.

The protons either align themselves pointed towards the head or the

feet of the patient, and most cancel each other out.

The protons that are not cancelled create a signal and are the ones

responsible for the image.

The contrast dye is what makes the target area stand out and

show any irregularities that are present.

The dye blocks the X-Ray photons from reaching the film,

showing different densities in the tissue.

The tissue is classified as normal or abnormal based on its

response to the magnetic field.

The tissues with the help of the magnetic field send a signal to the

computer.

The different signals are sent and modified into images that the

clinician can evaluate, and label as normal or abnormal.

If the tissue is considered abnormal, the clinician can often detect the

abnormality, and monitor progress and treatment of the abnormality.

The MRI has allowed clinicians to treat, monitor, and learn about many

different diseases and problems. As well as, to learn how the body

functions, normally, without needing to resort to more invasive methods

like surgery.

MRI treatment is a wonderful option for most

patients, but there are some people who are not

candidates.

Those include:

1) Patients with pacemakers cannot have the scan

done as the magnet from the MRI interferes with

the signal sent from the pacemaker, and

deactivates it.

2) Patients who are too tall, or too obese

3) Patients who have orthopedic hardware can get

distortion in the image, and the scan quality is

not as high.

THE FUTURE OF

MRI: •The possibility of having very small machines

that scan specific parts of the body.

• The continuing improvements on seeing the

venous and arterial systems.

• Brain mapping while the patient does specific

tasks, allowing clinician’s to see what part of the

brain is responsible for that task/activity.

• Improvements on the ability to do MRI’s of the

lungs.

• ETC.