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MRI
• MRI is a radiology technique
• That uses magnetism, radio waves, and a computer to
produce images of body structures.
• MRI is based on the principles of NMR
• In1997 the first MRI exam was performed on a human
being.
• It took 5 hours to produce one image.
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HISTORY
1924 - Pauli
suggests that
nuclear particles
may have
angular
momentum
(spin).
1937 – Rabi
measures magnetic
moment of nucleus.
Coins “magnetic
resonance”.
1985 – Insurance
reimbursements
for MRI exams
NMR renamed
MRI
1920 1930 1940 1950 1960 1970 1980 1990 2000
1946 – Purcell
shows that matter
absorbs energy at a
resonant frequency.
1946 – Bloch
demonstrates that
nuclear precession can
be measured in detector
coils.
1972 –
Damadian
patents idea for
large NMR
scanner to detect
malignant tissue.
1959 – Singer
measures blood
flow using NMR
(in mice).
1973 – Lauterbur
publishes method
for generating
images using
NMR gradients.
1973 –
Mansfield
independently
publishes
gradient
approach t1o9 M75R –. Ernst
develops 2D-Fourier
transform for
MR.
MRI scanners
become clinically
prevalent.
1990 – Ogawa and
colleagues create
functional images
using endogenous,
blood-oxygenation
contrast.
begin.
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NOBAL PRIZES FOR MRI
• 1944: Rabi
Physics (Measured magnetic moment of nucleus)
• 1952: Felix Bloch and Edward Mills Purcell
Physics (Basic science of NMR phenomenon)
• 1991: Richard Ernst
Chemistry (High-resolution pulsed FT-NMR)
• 2002: Kurt Wuthrich
Chemistry (3D molecular structure in solution by NMR)
• 2003: Paul Lauterbur & Peter Mansfield
Physiology or Medicine (MRI technology)
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WHAT CAN BE DIAGNOSED BY AN MRI
SCAN?
• Most ailments of the brain, including tumours
• Sport injuries
• Musculoskeletal problems
• Most spinal conditions/injuries
• Vascular abnormalities
• Female pelvic problems
• Prostate problems
• Some gastrointestinal tract conditions
• Certain ear, nose and throat (ENT) conditions
• Soft tissue and bone pathology/conditions
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WHO CAN’T HAVE AN MRI SCAN?
• A cardiac pacemaker
• Certain clips in your head from brain operations
• A cochlear implant
• A metallic foreign body in your eye
• Had surgery in the last 8 weeks
• If you are pregnant
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PRINCIPLE
• MRI makes use of the magnetic properties of certain
atomic nuclei.
• Hydrogen nucleus (single proton) present in water
molecules, and therefore in all body tissues.
• The hydrogen nuclei partially aligned by a strong
magnetic field in the scanner.
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CONTI..
• The nuclei can be rotated using radio waves, and they
subsequently oscillate in the magnetic field while returning
to equilibrium.
• Simultaneously they emit a radio signal.
• This is detected using antennas (coils)
• Very detailed images can be made of soft tissues.
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Randomly arranged
hydrogen atom
After the strong magnetic
field applied
14. MAIN COMPONENTS OF MRI
• Scanner
• Computers
• Recording hardware
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SCANNER
• An MRI scanner is a large tube that contains powerful
magnets.
• Main components of scanner
– Static magnetic field coils
– Gradient coils
– RF (radiofrequency) coils
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Static Magnetic Field Coils
• Three methods to generate magnetic field
1. Fixed magnet
2. Resistive magnet
3. Super conducting magnet
• Fixed magnets and resistive magnets are generally
restricted to field strengths below 0.4t
• High-resolution imaging systems use super conducting
magnets.
• The super-conducting magnets are large and complex
• They need the coils to be soaked in liquid helium to reduce
their temperature to a value close to absolute zero.
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GRADIENT COILS
• Gradient coils are used to produce deliberate variations in
the main magnetic field
• There are usually three sets of gradient coils, one for each
direction.
• The variation in the magnetic field permits localization of
image slices as well as phase encoding and frequency
encoding.
• The set of gradient coils for the z axis are helmholtz pairs,
and for the x and y axis paired saddle coils.
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RADIOFREQUENCY COIL
• RF coils act as transmitter and receiver
• RF coils are the "antenna" of the MRI system
• That transmit the RF signal and receives the return signal.
• They are simply a loop of wire either circular or
rectangular
• Helmholtz pair coils consist of two circular coils parallel
to each other.
• They are used as the z gradient coils in MRI scanners
• Paired saddle coils are also used for the x and y gradient
coils.
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ADVANTAGES OF MRI
• No ionizing radiation
• Variable thickness in any plane
• Better contrast resolution
• Many details without iv contrast
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DISADVANTAGES OF MRI
• Very expensive
• Dangerous for patients with metallic devices placed within
the body
• Difficult to be performed on claustrophobic patients
• Movement during scanning may cause blurry images
• RF transmitters can cause severe burns if mishandled
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FUNCTIONAL MRI
• Since the early 1990s, FMRI has come
• FMRI is based on the same technology as MRI
• FMRI looks at blood flow
• It is a technique for measuring brain activity
• It works by detecting the changes in blood oxygenation and
flow that occur in response to neural activity
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DIFFERENCE BETWEEN MRI AND FMRI
MRI
• Views anatomical
structure
• Focuses on protons in
hydrogen nuclei
• High spatial resolution
• Utilized for
experimental purposes
FMRI
• Views metabolic
function
• Calculates oxygen
levels
• Long-distance
resolution
• Utilized for diagnostic
purposes
