Unit 21: Medical Physics Applications
Radiation use in medical diagnosis and treatment
Non-ionising radiation
Introduction
Non-ionising radiation is found towards the left of the electromagnetic spectrum, and it is a type of
radiation that everyone is exposed to in low levels. If abundance of direct non-ionising radiation is
exposed, then tissues can be damaged. However, it is not common to be exposed by excessive non-
ionising radiation other than when it is used for treatments such as magnetic resonance imaging
(MRI), lasers, infrared thermography (IRT), and ultrasound. Before any type of imaging technique
taking place, it is ensured that patient agreement has been achieved for any imaging to be carried on
as the patient would be exposed by different types of waves and particles in high doses, which can
be damaging to the body.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging is a non-ionising imaging technique that uses a combination of
radiofrequency waves and strong magnets to produce detailed images of soft tissues in the body
rather than ionizing radiation, which is used in X-rays and CT. In addition to this, it can be used to
examine most of the body as well as being the ideal imaging technique for imaging the central
nervous system (CNS). It also can distinguish normal and abnormal tissue as well as displaying
whether the image is showing a blood flow, cellular density, tissue stiffness due to blood
oxygenation change.
The magnetic field strength if an MRI machine is measured in Tesla, T, and the common magnetic
field strength of MRI machines that are used in hospitals and clinics are 1.5 T – 3 T. Therefore, the
magnetic field of an MRI machine is approximately 30000 times stronger than the earth.
When using an MRI machine to produce an image, the machine relies on the magnetic properties of
hydrogen atoms. The body contains about 60% - 70% water, which is made up of hydrogen and
oxygen. The magnetic properties of the hydrogen atoms that are achieved from the water are used
by the MRI machine. The nucleus of the hydrogen atom contains no neutrons but one proton, which
has a positive charge and one electron, which is a negatively charged particle. All the protons
present in the body spin randomly creating no overall magnetic field. However, when the strong
magnetic field of the MRI machine is established, all the protons align with the MRI machines field. A
radiofrequency pulse is then introduced that force the protons to turn either 90° or 180° to realign
with the static magnetic field. When the radiofrequency pulse is turned off, the protons reposition
themselves as they realign to the strong magnetic field of the MRI machine. This process leads to the
release of electromagnetic energy, which is detected by the MRI and can separate the different
tissues based on how quickly they released the energy after the radiofrequency pulse was turned
off.
The image below shows the different components of an MRI machine and how an MRI machine
looks:
[1]
The image below shows how an MRI image of the brain looks like as well as how an MRI image of a
knee looks like:
Radiation use in medical diagnosis and treatment
Non-ionising radiation
Introduction
Non-ionising radiation is found towards the left of the electromagnetic spectrum, and it is a type of
radiation that everyone is exposed to in low levels. If abundance of direct non-ionising radiation is
exposed, then tissues can be damaged. However, it is not common to be exposed by excessive non-
ionising radiation other than when it is used for treatments such as magnetic resonance imaging
(MRI), lasers, infrared thermography (IRT), and ultrasound. Before any type of imaging technique
taking place, it is ensured that patient agreement has been achieved for any imaging to be carried on
as the patient would be exposed by different types of waves and particles in high doses, which can
be damaging to the body.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging is a non-ionising imaging technique that uses a combination of
radiofrequency waves and strong magnets to produce detailed images of soft tissues in the body
rather than ionizing radiation, which is used in X-rays and CT. In addition to this, it can be used to
examine most of the body as well as being the ideal imaging technique for imaging the central
nervous system (CNS). It also can distinguish normal and abnormal tissue as well as displaying
whether the image is showing a blood flow, cellular density, tissue stiffness due to blood
oxygenation change.
The magnetic field strength if an MRI machine is measured in Tesla, T, and the common magnetic
field strength of MRI machines that are used in hospitals and clinics are 1.5 T – 3 T. Therefore, the
magnetic field of an MRI machine is approximately 30000 times stronger than the earth.
When using an MRI machine to produce an image, the machine relies on the magnetic properties of
hydrogen atoms. The body contains about 60% - 70% water, which is made up of hydrogen and
oxygen. The magnetic properties of the hydrogen atoms that are achieved from the water are used
by the MRI machine. The nucleus of the hydrogen atom contains no neutrons but one proton, which
has a positive charge and one electron, which is a negatively charged particle. All the protons
present in the body spin randomly creating no overall magnetic field. However, when the strong
magnetic field of the MRI machine is established, all the protons align with the MRI machines field. A
radiofrequency pulse is then introduced that force the protons to turn either 90° or 180° to realign
with the static magnetic field. When the radiofrequency pulse is turned off, the protons reposition
themselves as they realign to the strong magnetic field of the MRI machine. This process leads to the
release of electromagnetic energy, which is detected by the MRI and can separate the different
tissues based on how quickly they released the energy after the radiofrequency pulse was turned
off.
The image below shows the different components of an MRI machine and how an MRI machine
looks:
[1]
The image below shows how an MRI image of the brain looks like as well as how an MRI image of a
knee looks like:
