This document provides an overview of magnetic resonance imaging (MRI). It begins by defining MRI as a medical imaging technique that uses magnetic fields and radio waves to produce detailed images of the body. The document then covers the history, components, principles, and types of MRI images. It discusses how MRI works to detect tissue properties using relaxation times and how varying pulse sequences produces different contrasts. The document concludes by outlining the clinical applications and benefits of MRI, such as its ability to clearly image soft tissues without radiation, as well as some limitations like expense and the enclosed scanner.

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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