Lecture notes
Lecture Notes
- Institution
- Queen Mary, University Of London (QMUL)
Lecture notes of 6 pages for the course Techniques For Biological And Chemical Sciences at QMUL
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MRI: from lab to hospitalSummary of MRI
MRI is a scanning technique
Used in hospitals
Study internal structures of the body
Uses same technology as NMR Spectroscopy
Patient placed in a large magnet and radio waves are directed at the area of the body being
investigated.
Hydrogen nuclei in water molecules in the body absorb energy from the radio waves at
certain frequencies.
The frequency depends on the kind of tissue that the water is in, so an image of the different
tissues can be built up.
By moving the beam of radio waves, a series of images are produced, which can be added
together by a computer to build up a 3D image.
Used to diagnose and monitor:
- cancerous tumours.
- examine bones and joints for signs of injury.
- Study brain and cardiovascular system.
Advantage
no damaging radiation used like X-ray or gamma ray.
Gives high quality images of soft tissue like the brain.
Background information
Formally called NMR tomography
Patients found the word, nuclear intimidating although it is a non-invasive, harmless
technique and, therefore, the name of technique changed to MRI.
MRI is the sibling to NMR
MRI uses the same software/programme used by NMR so all the controls are the same.
The only difference is the sample used i.e. NMR uses liquid sample but MRI use parts of the
human body (head,knees..)
The image
The intensity or colour of each pixel represents the value of a measured property within a
small volume of the patient’s body
The image is an NMR signal of water in body
Certain organs are denser (concentrated) in water than other organ
-i.e. eye balls are rich in water & bones are poor in water
Can measure concentration and mobility of water
What is the MRI signal?
Measures 1H NMR of water protons
, -1H NMR is sensitive
-water is abundant in bodies
3 properties of water measured
1. Concentration- density of water (number of protons per unit volume)
2&3. Relaxation properties (T1 and T2)-related to mobility of water
- Shine radio wave light on molecule causes excitation and the electron jumps up
to a higher energy state and then relaxes down to a lower energy level and the
radio waves are emitted
- The rate at which the electrons relaxes down provides information about the
environment of the proton.
Careful waiting of these 3 properties brings into contrast internal features
of the body
Contrast water density and mobility
NMR can be used to image any part of the body in a non-invasive
manner
Typically, the images are created by differences in the
concentration and relaxation properties of water, in different part
of the body.
X-rays can only tell us if we have bone, cartilage,…etc
X-rays cannot tell the differences between soft tissue but MRI can
Different organs have different water content and relaxation
therefore, can differentiate the different type of soft tissue
This MRI image emphasises the high density of water (protons) in the
eye ball
White= water dense i.e. eye ball
Dark=not water dense i.e. skull
The contrast of water signal is due to the differences
in water mobility, which causes variation in relaxed
properties (T1 &T2)
If add relaxation properties can distinguish between
brains
X-ray image the brain will look like it’s not bone
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