The strength of the flux density at the Earth’s surface ranges from less than 30μT in an area including most of South America and South Africa to over 60μT in northern Canada and south of Australia. Why does it vary? Comment on the strength of the magnetic field inside an MRI scanner

Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI

Precession Larmor Frequency Relaxation Time Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI What do the following terms mean? Precession Larmor Frequency Relaxation Time What does the process have to do with resonance?

Be able to describe the main components of an MRI scanner Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI http://www.mayoclinic.com/health/mri/MM00395

Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI Apparatus used in MRI http://www.simplyphysics.com/flying_objects.html

This varies the Larmor frequency at different points Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI There is a high constant magnetic field across the imaging section (Approx 90cm long) The field strength is typically 1.4 T This is produced by a super-cooled electromagnet kept at a temperature of 4.2K Additional magnets are used to alter the magnetic field strength very slightly throughout the scanner This varies the Larmor frequency at different points

An RF coil transmits the RF pulse into the body. Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI An RF coil transmits the RF pulse into the body. An RF receiver coil detects the signal emitted by the nuclei as they relax to their original orientation. This may be the same coil as the transmitter coil. A computer controls the magnetic field strength throughout the scanner and the RF pulses as well as storing and analysing the received signals. The image formed represents areas of different relaxation times as different shades / colours

At what distance from X is the Larmor frequency: Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI The magnetic field due to the main magnet in a MRI scanner is 1.400T. Using subsidiary magnets, the total field is increased linearly from 1.400T at point X to 1.440T at point Y a distance of 0.500m along the length of the patient. At what distance from X is the Larmor frequency: 59.5 MHz 61.2 MHz 60.0 MHz?

Be able to describe the main components of an MRI scanner Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI

What are the pros and cons of MRI scans? Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI What are the pros and cons of MRI scans? - Sort the statements and explain why

Does not use ionising radiation Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI Does not use ionising radiation Good distinction between types of soft tissue Radiowaves can travel through bone Metallic objects would heat up if placed in scanner Scans take around 45 minutes The receivers can detect radiowaves from any sources Machines are very expensive

Patient does not receive a dose of ionising radiation Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI The upside… Patient does not receive a dose of ionising radiation Staff are not exposed to ionising radiation High quality image with clear contrast between tissue type The brain can be imaged

Many people suffer from claustrophobia when having a scan done The downside… Patients cannot be scanned if they have a pace maker or metal pins in joints Many people suffer from claustrophobia when having a scan done Equipment must be screened to eliminate any stray fields Scanners cost millions of pounds and cannot have a fast throughput of patients because each scan takes so long Learning Objectives By the end of this lesson you should… Be able to describe the main components of an MRI scanner Be able to outline the use of MRI to obtain diagnostic information about internal organs Be able to outline the benefits and limitations of MRI