mri finals

• MAGNETIC RESONANCE IMAGING - A computer-based cross-sectional imaging modality
• MAGNETIC RESONANCE IMAGING -The use of magnetic field and radio waves to obtain a mathematically reconstructed image
• MAGNETIC RESONANCE IMAGING - Originally called Nuclear Magnetic Resonance
• ADVANTAGES OF MRI

   Best low contrast resolution

  o Main advantage

  o Rationale:

   X-ray attenuation coefficient in soft tissue – differ by <1% (in same tissue)

   Spin density & T1 – differ by 20-30% (in same tissue)

   T2 – differ by 40% (in same tissue)

   No ionizing radiation

   Direct multiplanar imaging

   No bone or air artifact

   Direct flow measurements

   Totally noninvasive

   Contrast media not required
• MRI CONTRAINDICATION

   Cardiac pacemaker

   Aneurysm clips

   Claustrophobia

   Metallic fragments in the eye

   Cochlear implants

   Internal drug infusion pumps

   Neurostimulators

   Bone growth stimulators
• MRI

   Provides sectional images

   No superimposition of structures

   Clearly demonstrates structures even

  without contrast media

   Can resolved relatively small contrast

  differences among tissue

   Contrast depends on the interaction of

  matter with electromagnetic forces
• CONVENTIONAL

   Provides “flat” image

   Structures are superimposed

   Contrast media is required to clearly

  distinguished one anatomic structure or

  organ from one another

   Limited in its ability to distinguish types of

  tissue

   Cannot detect small attenuation changes

   Can only distinguish air, fat, bone, soft

  tissue, and metal

   Contrast depends on differences of x-ray

  attenuation
• 1940’s

   Felix Bloch and Edward Purcell first

  discovered the properties of magnetic

  resonance

   MRI spectroscopy: technique they used for

  analysis of complex molecular structures

  and dynamic chemical processes
• 1952

   Bloch and Purcell shared a Nobel Prize in

  Physics
• 1971

   Raymond Damadian showed that the

  relaxation time of water in a tumor differed from the relaxation time of water in normal tissue

   Investigated excised rat tissue

   He reported that there were significant

  differences between normal rat tissues and

  tumors
• 1975

   Damadian obtained the first animal images
• 1970s

   MRI was progressing rapidly
• 1978

   The first human head scans were obtained

   Followed by first human body scans
• INDOMITABLE

   Original name of the first MRI machine
• ANTENNA

   Device for transmitting or receiving radio

  wave
• ARTIFACTS

   Spurious finding in or distortion of an image
• ATTENUATION

   Reduction in energy or amount of a beam of

  radiation when it passes through tissue or

  other substances
• COIL

   Single or multiple loops of wire designed to

  produce a magnetic field from current

  flowing through the wire
• CLAUSTROPHOBIA

   The fear of having no escape and being in

  closed or small spaces or rooms
• CRYOGENIC - Relating to extremely low temperature
• DIFFUSION

   Spontaneous random motion of molecules in

  a medium
• FAT SUPPRESSED IMAGES

   Fat tissue in the image is made to be of a

  lower, darker signal intensity
• FREE INDUCTION DECAY

   Signal emitted by tissue after RF excitation
• GATING

   Technique used in reducing motion artifacts
• GRADIENT ECHO

   Fast pulse sequence

   Often used with 3D imaging to generate T2-

  weighted images
• GRADIENT MAGNETIC FIELD

   A change in the intensity of a magnetic field

  in space

   Unit: mT/cm
• GYROMAGNETIC RATIO

   A constant, specific ratio for each nucleus

   Half-life in MRI

   Unit: MHz/T

   Hydrogen: 43 MHz/T

  o Most abundant element in the body

  (60%)
• INVERSE RECOVERY

   Standard pulse sequence available in most

  MRI imagers

   Used for T1-weighted images
• LARMOR FREQUENCY -  The frequency at which a nucleus precesses in the magnetic field

   Unit: MHz
• MAGNETIC MOMENT

   A force created when magnetic dipole is in a

  magnetic field

   The inherent magnetism

   Unit: T
• MAGNETIZATION

   The large-scale macroscopic magnetic

  moment resulting from many nuclear

  magnetic moments
• NET MAGNETIZATION

   Magnetic moments of individual hydrogen

  nuclei aligned in the external magnetic field
• PERFUSION

   Flow of blood through vessels of an organ or

  anatomic structure
• PRECESSION

   The wobble of the rotational axis of a

  spinning body about a stationary axis

   Describes a cone

   Rate of precision: increases as MF strength

  increase
• RADIO FREQUENCY (RF)

   Electromagnetic radiation having a

  frequencies from 0.3kHz to 300 GHz

   RF range in MRI: 1-100 MHz
• RAW DATA

   Information obtained by radio reception of

  the MRI signal as stored by a computer
• RELAXATION

   Returning to equilibrium
• RELAXATION TIME

   The time required for return
• SPECIFIC ABSORPTION RATE (SAR)

   The power absorbed during RF irradiation

   Unit: W/kg
• RESONANCE

   Transfer of vibrating energy from one

  system to another