PRE-CLINICAL IMAGING
WITH FOCUS ON
NEUROLOGY
, LECTURE 1 – MRI CONTRAST PRINCIPLES
Common imaging modalities:
Projection X-ray = (electromagnetic)
Computed Tomography (CT) = (electromagnetic)
Ultrasound = (sound waves)
Positron Emission Tomography (PET) = (nuclear)
Single Photon Emission Tomography (SPET) = (nuclear)
Magnetic Resonance Imaging (MRI) = (magnetic)
MRI uses radio-waves with a longer wavelength and thus a lower amount of
energy → not enough energy to cause change in atoms - Ultrasound is the only
method of imaging that uses sound waves (in the range of MHz) when all other
methods use electromagnetic waves → this method is fast and simple, it is the
first method to be used in the emergency unit when a person has complains to
have a quick look at the situation ➔ MRI and ultrasound have no health
consequences and can be performed as many times as necessary. This is in
,contrast to CT, PET and SPECT where there is the risk of ionization = major
advantage of MRI
MRI scans work as an imaging method due to unique composition of the human
body. We are comprised entirely of cells which all contain water – principally
made of H-ions.
The magnet embedded within the MRI scanner act on these positively charged
hydrogen ions and cause them to spin in an identical manner.
By varying strength and direction of this magnetic field, we can change the
direction of spin of the protons, enabling us to build layers of details.
When the magnet is switched off, the protons will gradually return to their
original state in a process known as precession. Fundamentally, the different
tissue types within the body will return at different rates and this is what
allows us to visualise and differentiate between the different tissues.
, As hydrogen atoms are electrically charged, they can be considered as little
magnets with north and south poles. This is what makes the hydrogen protons
susceptible to external magnetic field.
Each proton rotates 360 degrees around its own axis and has a positive and
negative pole.
!!! Each proton spins with a certain speed – LARMOR FREQUENCY. Because of
its spin, the proton continually changes phase (each phase is a snapshot).
When hydrogen protons enter strong
Nucleus of Gyromagnetic
external magnetic field, most protons will
align themselves parallel to the strong
particle ratio in
MHz/Tesla
1H 42.58
Electron -27,204
13C 10.71
WITH FOCUS ON
NEUROLOGY
, LECTURE 1 – MRI CONTRAST PRINCIPLES
Common imaging modalities:
Projection X-ray = (electromagnetic)
Computed Tomography (CT) = (electromagnetic)
Ultrasound = (sound waves)
Positron Emission Tomography (PET) = (nuclear)
Single Photon Emission Tomography (SPET) = (nuclear)
Magnetic Resonance Imaging (MRI) = (magnetic)
MRI uses radio-waves with a longer wavelength and thus a lower amount of
energy → not enough energy to cause change in atoms - Ultrasound is the only
method of imaging that uses sound waves (in the range of MHz) when all other
methods use electromagnetic waves → this method is fast and simple, it is the
first method to be used in the emergency unit when a person has complains to
have a quick look at the situation ➔ MRI and ultrasound have no health
consequences and can be performed as many times as necessary. This is in
,contrast to CT, PET and SPECT where there is the risk of ionization = major
advantage of MRI
MRI scans work as an imaging method due to unique composition of the human
body. We are comprised entirely of cells which all contain water – principally
made of H-ions.
The magnet embedded within the MRI scanner act on these positively charged
hydrogen ions and cause them to spin in an identical manner.
By varying strength and direction of this magnetic field, we can change the
direction of spin of the protons, enabling us to build layers of details.
When the magnet is switched off, the protons will gradually return to their
original state in a process known as precession. Fundamentally, the different
tissue types within the body will return at different rates and this is what
allows us to visualise and differentiate between the different tissues.
, As hydrogen atoms are electrically charged, they can be considered as little
magnets with north and south poles. This is what makes the hydrogen protons
susceptible to external magnetic field.
Each proton rotates 360 degrees around its own axis and has a positive and
negative pole.
!!! Each proton spins with a certain speed – LARMOR FREQUENCY. Because of
its spin, the proton continually changes phase (each phase is a snapshot).
When hydrogen protons enter strong
Nucleus of Gyromagnetic
external magnetic field, most protons will
align themselves parallel to the strong
particle ratio in
MHz/Tesla
1H 42.58
Electron -27,204
13C 10.71
