MRIMRI

DRAFT 5-12-09DRAFT 5-12-09

Principles of MRI Principles of MRI

►Sectional AnatomySectional Anatomy

►Provides anatomic and physiologic infoProvides anatomic and physiologic info

►Non- invasiveNon- invasive

►No radiationNo radiation Magnetic fields and Radio wavesMagnetic fields and Radio waves

MRI vs. Conventional MRI vs. Conventional RadiographyRadiography

► Sectional Sectional No superimpositionNo superimposition

► Can resolve small Can resolve small contrast differencescontrast differences

► Uses magnets Uses magnets instead of x-raysinstead of x-rays

► Flat imageFlat image Superimposed Superimposed

structuresstructures

► Can only distinguish Can only distinguish air, at, soft tissue, air, at, soft tissue, bone and metalbone and metal

► Most organs can Most organs can only be seen with only be seen with contrastcontrast

► Uses radiationUses radiation

Xray vs. MRI

Signal ProductionSignal Production

►MRI depends on nucleusMRI depends on nucleus

►Hydrogen Hydrogen Most commonly usedMost commonly used Most common element in bodyMost common element in body Creates a strong signalCreates a strong signal Nucleus is a single protonNucleus is a single proton

HydrogenHydrogen

► ContainsContains

1 proton1 proton 1 orbiting electron1 orbiting electron

PrecessionPrecession► Protons in random directionsProtons in random directions

► With magnet attempt to line upWith magnet attempt to line up Do not line up preciselyDo not line up precisely They rotate about the direction of the magnetic They rotate about the direction of the magnetic

fieldfield

► ProtonsProtons Absorb energy when RF is appliedAbsorb energy when RF is applied Absorption is called resonanceAbsorption is called resonance

► Radiowaves and nuclear precession are at Radiowaves and nuclear precession are at the same frequencythe same frequency

Field Strength and FrequencyField Strength and Frequency

► 1.5 tesla1.5 tesla

► 1 telsa1 telsa

► 0.5 telsa0.5 telsa

► 0.2 telsa0.2 telsa

► 63MHz63MHz

► 42 MHz42 MHz

► 21 MHz21 MHz

► 8 MHz8 MHz

PrecessionPrecession

►http://mrsrl.stanford.edu/~brian/mri-http://mrsrl.stanford.edu/~brian/mri-movies/resonance.mpgmovies/resonance.mpg

Spin ControlSpin Control

► http://images.google.com/imgres?http://images.google.com/imgres?imgurl=http://www.magnet.fsu.edu/imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/education/tutorials/magnetacademy/mri/images/mri-scanner.jpg&imgrefurl=http://images/mri-scanner.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/magnetacademy/mri/&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h=300&w=390&sz=33&hl=en&start=1&tbnid=300&w=390&sz=33&hl=en&start=1&tbnid=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&pre=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&prev=/images%3Fq%3Dresonance%2B%252Bv=/images%3Fq%3Dresonance%2B%252B%2BMRI%26gbv%3D2%26hl%3Den%2BMRI%26gbv%3D2%26hl%3Den

The Wonder of WavesThe Wonder of Waves

► http://images.google.com/imgres?http://images.google.com/imgres?imgurl=http://www.magnet.fsu.edu/imgurl=http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/education/tutorials/magnetacademy/mri/images/mri-scanner.jpg&imgrefurl=http://images/mri-scanner.jpg&imgrefurl=http://www.magnet.fsu.edu/education/tutorials/www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/magnetacademy/mri/&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h&usg=__7QaxmAuglPxgvYqzlBDl4yatfQc=&h=300&w=390&sz=33&hl=en&start=1&tbnid=300&w=390&sz=33&hl=en&start=1&tbnid=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&pre=iCrVIzxgDH1sFM:&tbnh=95&tbnw=123&prev=/images%3Fq%3Dresonance%2B%252Bv=/images%3Fq%3Dresonance%2B%252B%2BMRI%26gbv%3D2%26hl%3Den%2BMRI%26gbv%3D2%26hl%3Den

Gradient CoilsGradient Coils

MRI Slices of BrainMRI Slices of Brain

EquipmentEquipment

ConsoleConsole

Computer RoomComputer Room

Magnet RoomMagnet Room

Console and Computer RoomConsole and Computer Room

Magnet RoomMagnet Room► Must be LG enough for magnets and antennasMust be LG enough for magnets and antennas

Coils are antennas wound up in shape of body partCoils are antennas wound up in shape of body part 3 types of magnets (strength measured in Gauss or Tesla)3 types of magnets (strength measured in Gauss or Tesla)

► RESISTIVE RESISTIVE Not to exceed 0.15 telsaNot to exceed 0.15 telsa 10 tons10 tons LG amount of current through coilsLG amount of current through coils Fringe field in all directionsFringe field in all directions

► SUPERCONDUCTIVE or CryogenicSUPERCONDUCTIVE or Cryogenic High field strengthsHigh field strengths 10 tons10 tons Cooled with liquid heliumCooled with liquid helium Fringe field in all directionsFringe field in all directions

► PERMANENTPERMANENT Not to exceed 0.3 telsaNot to exceed 0.3 telsa 100 tons100 tons Smaller fringe fieldSmaller fringe field

Body Coils…AntennasBody Coils…Antennas

Significance of SignalSignificance of Signal

► Signal strength is converted to different Signal strength is converted to different shades of grayshades of gray White is strong signalsWhite is strong signals Black is weak signalsBlack is weak signals

► Three properties affect signal strengthThree properties affect signal strength

Nuclear DensityNuclear Density

Relaxation ratesRelaxation rates

Flow phenomenaFlow phenomena

Relaxation Rates:T1 and T2

MRA and Flow Phenomena

Contrast MediaContrast Media► No Oral ContrastNo Oral Contrast

► GadoliniumGadolinium IV injectedIV injected Lower toxicityLower toxicity Low side effectsLow side effects

► Less than IV in CT Less than IV in CT and conventional and conventional radiographyradiography

Many new contrasts Many new contrasts being developed being developed but none approved but none approved for clinical use yetfor clinical use yet

Lawsuits and GadoliniumLawsuits and Gadolinium► In May 2007 FDA issued a In May 2007 FDA issued a

public warning about public warning about Gadolinium increasing the Gadolinium increasing the incidence of Nephrogenic incidence of Nephrogenic Systemic Fibrosis Systemic Fibrosis

For those with impaired kidney For those with impaired kidney functionfunction

Development of excessive scar Development of excessive scar tissue and thick, hardened and tissue and thick, hardened and tight areas of skin which often tight areas of skin which often cover the joints, resulting in cover the joints, resulting in severe limitations on severe limitations on movement. movement.

Can lead to confinement to a Can lead to confinement to a wheelchair, bed or death.wheelchair, bed or death.

ContraindicationsContraindications

►Objects containing metalObjects containing metal►Scissors, O2 tanks, and gurneysScissors, O2 tanks, and gurneys►Metallic prosthesisMetallic prosthesis►Aneurysm clipsAneurysm clips►Hearing aidsHearing aids►Slivers of metal in eyesSlivers of metal in eyes►Electronic equipmentElectronic equipment►ClaustrophobiaClaustrophobia

Imaging PlanesImaging Planes

► Images can be obtained in many planesImages can be obtained in many planes CoronalCoronal TransverseTransverse ObliqueOblique

►Equal resolution for any planeEqual resolution for any plane►Loss of detail if reconstructedLoss of detail if reconstructed►3D block of tissue can be obtained 3D block of tissue can be obtained

instead of slicesinstead of slices

Coronal Thorax

Sagittal Thorax

3D Imaging3D Imaging

Closed MRIClosed MRI

Open MRIOpen MRI

Sitting MRISitting MRI

Extremity MRIExtremity MRI