magnetic image resonance MRI

1. MAGNETIC RESONANCE
IMAGING
QURATULAIN MUGHAL
ISRA UNIVERSITY
BATCH IV
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2. CONTENTS
• What is MRI
• MRI equipments
• Indications
• Contraindications
• How it help in diagnosis
• Findings in MRI
• Advantages
• Disadvantages
• Functional MRI
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3. DEFINITION
“MRI IS MAGNET RADIO FREQUENCY IMAGING
TECHNIQUE USING A MAGNETIC FIELD AND
RADIOFREQUENCY.”
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4. HISTORY OF MRI
• Discovered simultaneously by two physicists:
• Felix Bloch
• Edward Mills Purcell
• First clinical images is obtained by:
• Paul Lauterbur
• Peter Mansfield
• Raymond Damadian
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5. MAGNETIC FIELD
• Magnetic flux density is measured in Tesla(T).
• Clinical MRI performed at 1.5-3T.
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6. MRI PRINCIPLE
• MRI is based on the principle of nuclear magnetic resonance (NMR)
Two basic principles of NMR
1. Atoms with an odd number of protons or neutrons have spin.
2. A moving electric charge, be it positive or negative, produces a
magnetic field.
• Human body is built of only 26 elements.
• Body has many such atoms that can act as good MR nuclei (1H, 13C,
19F, 23Na)
• Hydrogen nuclei is one of them which is not only positively
charged, but also has magnetic spin.
• MRI utilizes this magnetic spin property of protons of hydrogen to
elicit images.
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7. HYDROGEN ATOMS
• Randomly protons are orientated with no applied field.
• So there’s no overall magnetic field.
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8. MRI COMPONENTS
• Primary magnet
• Gradient magnets
• Radiofrequency (RF) coils
• Computer system
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10. PRIMARY MAGNETIC FIELD
• Superconducting magnet.
• Constant 1.5-3T.
• Hydrogen atoms align parallel or antiparallel
to the primary field (B0) = longitudinal
magnetization.
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11. PRIMARY MAGNETIC FIELD
• Transverse magnetization is orthogonal to the
magnetic field and falls in the x-y plane.
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12. PRECESSION
• Protons spin around the long axis of the
primary magnetic field= PRECESSION.
• The precession rate is termed as LARMOR
FREQUENCY.
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13. PRECESSION
• When protons process together, this is known
as in phase.
• When protons process separately, this is
known as out of phase.
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14. PRECESSION
• Frequency changes with in proportion to
magnetic field strength.
• At 1.5T=63.9MHz
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15. GRADIENT COILS
• It generate secondary magnetic filed over the
primary field.
• They are located within the boa of the primary
magnet.
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16. GRADIENT COILS
• They are arrange in opposition to each other
to produce positive and negative pulse.
• The arrangement of these gradient pulse gives
MRI the capacity to image directionally along
the x, y and z axis.
• Alter the primary magnetic field thereby
changing the precessing frequency between
slices.
• They responsible for loud noises of MRI.
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17. •Allow spatial encoding for MRI images
in the x, y & z axis i.e. localization.
• Z: axial images
• Y: coronal images
• X: sagittal images
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19. RADIOFREQUENCY (RF) COILS
• Use to transmit RF pulse (causes the net
magnetic moment of the nuclei) and receiving
signals in MRI.
• They come in many designs alter to best suits
each body part.
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20. RELAXATION
• RF coils is use to receives signals to create
images.
• When the protons returns to their prior state
this is known as relaxation.
1. Longitudinal (T1)- parallel to B0 (z axis).
2. Transverse (T2)- perpendicular to B0 (x-y axis)
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21. • Different tissues have different relaxation
times.
• These relaxation time differences is used to
generate image contrast.
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22. TR AND TE
• TE (echo time) : time interval in which signals
are measured after RF excitation.
• TR (repetition time) : the time between two
excitations is called repetition time.
By varying the TR and TE one can obtain T1WI
and T2WI.
• In general a short TR (<1000ms) and short TE
(<45 ms) scan is T1WI.
• Long TR (>2000ms) and long TE (>45ms) scan is
T2WI.
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23. T1-weighted contrast
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24. T2-weighted contrast
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26. COMPUTER SYSTEM
• RF signals covert to analog or digital
conversion mathematical conversions
will form MR images in the screen.
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27. KIND OF IMAGES
• T1WI
• T2WI
• DWI
• ADC(Apparent diffusion
coefficient)
• Functional MRI
• MRA(angiography)
• MRV( Magnetic
resonance venography)
• FLAIR
• STIR (Short TI Inversion
Recovery)
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28. MAGNETIC RESONANCE
ANGIOGRAPHY
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29. FLUID-ATTENUATED INVERSION
RECOVERY
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30. DIFFUSION WEIGHTED IMAGING
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31. ADC(APPARENT DIFFUSION
COEFFICIENT)
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32. MRV
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33. STIR (Short Tesla Inversion Recovery)
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34. HOW MRI IS DONE?
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35. In a Tunnel, of course!
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36. CONTRAINDICATIONS
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40. MRI INDICATIONS
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44. The Uses of the MRI
• Diagnosing: MS; strokes; infections of
the brain/spine/CNS; tendonitis
• Visualising: Injuries; torn ligaments –
especially in areas difficult to see like
the wrist, ankle or knee
• Evaluating: Masses in soft tissue; cysts;
bone tumours or disc problems.
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45. FINDINGS IN MRI
When contrast agent is not used an MRI can show:
• The shape, size, appearance, and location of
organs, bones, and joints
• The presence of abnormal growths
• Signs of inflammation or infection
When contrast agent is used MRI can show:
• size and location of benign or malignant growths
• enlarged lymph nodes
• changes in blood flow
• extracellular volume
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46. BENEFITS OF MRI
• MRI is non-invasive and does not use radiation
• MRI does not involve radiation
• MRI contrasting agent is less likely to produce an allergic reaction that may
occur when iodine-based substances are used for x-rays and CT scans
• MRI gives extremely clear, detailed images of soft-tissue structures that
other imaging techniques cannot achieve
• MRI can easily create hundreds of images from almost any direction and in
any orientation
• Unlike techniques that examine small parts of the body (i.e. ultrasound or
mammography) MRI exams can cover large portions of the body
• MRI can determine if a cancer has spread, and help determine the best
treatment
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47. DISADVANTAGES OF MRI
• MRI is expensive
• MRI will not be able to find all cancers (i.e. breast cancers indicated by
microcalcifications)
• MRI cannot always distinguish between malignant tumors or benign
disease (such as breast fibroadenomas), which could lead to a false
positive results
• MRI is not painful, but the patient must remain still in an enclosed
machine, which may be a problem for claustrophobic patients
• An undetected metal implant in a patient’s body may be affected by the
strong magnet of the MRI unit
• There is a small chance that a patient could develop an allergic reaction to
the contrasting agent, or that a skin infection could develop at the site of
injection
• If a patient chooses to be sedated for the scanning, there is a slight risk
associated with using the sedation medication
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48. FUNCTIONAL MAGNETIC RESONANCE
IMAGING
• Functional MRI (fmri) is a functional
neuroimaging procedure using MRI technology
that measures brain activity by detecting changes
associated with blood flow.
• This technique relies on the fact that cerebral
blood flow and neuronal activation are coupled.
• When an area of the brain is in use, blood flow to
that region also increases.
• The primary form of fMRI uses the blood-oxygen-
level dependent (BOLD) contrast.
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51. REFERENCES
• Slideshare.com
• Wikipedia
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