Engineering Science 167 15-Nov-2006 MRI Artifacts Learning ObjectivesDisclosuresComing Attractions …ENGG 287: Adv Med Img & CompMRI ArtifactsMRI ArtifactsArtifacts (cont.)High Resolution Spiral MRIHigh Resolution Spiral MRIHigh Resolution Spiral MRIPerfusion SeriesBasis for MRIFrom a Few Good Seeds…How Many ProtonsProton PropertiesChange in MagnetizationMRI of the Brain - AxialFrom Mxy to ImageK-SpaceK-SpaceFourier TransformMethodsStd Phantom, X≠YVibration during low KVibration during hi KBad ShimSmall FOVClipping = lose low KPoint Src – Trunc RingLower Resolution RingT2* effect of IronMRA of human legAngiogenesis-SensitiveT2*-MRI (EPI)The Problem + SolutionValidations of CX vs. CT, CX vs. mS, HistologyGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the ArtifactGuess the artifactArtifact ReductionArtifact ReductionArtifact ReductionProblem…Pulsation artifactsPulsation artifact reductionVessel ExtractionOther ideasSpatial domainRegion growingPulse Artifact in K spaceGhostGhost removal in K spaceCell TrackingSpherical HarmonicsOngoing WorkV-mode at DHMC 21Feb06REMEMBER …ConclusionsThank youMonitoring AngiogenesisMicrovessel MRIMRA of human legGhostGhost extraction in K spaceConversion of pulsation artifact to Super Resolution Super-resolutionPulmonary VesselsMicrovessel MRIEngineering Science 167Engineering Science 1671515--NovNov--20062006MRI ArtifactsMRI ArtifactsJustin D Pearlman MD ME PhD MAJustin D Pearlman MD ME PhD MADirector, Dartmouth Advanced Imaging Director, Dartmouth Advanced Imaging CenterCenter Dartmouth-Hitchcock Medical CenterLearning ObjectivesLearning Objectives••MRI ArtifactsMRI Artifacts––ExamplesExamples––CausesCauses––CorrectionsCorrections––OpportunitiesOpportunitiesMRIDisclosuresDisclosures••OffOff--label/nonlabel/non--standard standard uses of imaging systemsuses of imaging systemsComing Attractions Coming Attractions ……••ENGS 267 ENGS 267 ••ADVANCED MEDICAL ADVANCED MEDICAL IMAGING AND COMPUTINGIMAGING AND COMPUTING––Winter Term 07 Winter Term 07 ––PrePre--requisite courses: requisite courses: ENGS 167 or permission of ENGS 167 or permission of instructorinstructorENGG 287:ENGG 287:Adv Med Adv Med ImgImg& Comp& Comp••Advanced level exploration of medical imagingAdvanced level exploration of medical imaging••HandsHands--on experience with equipment in the DAICon experience with equipment in the DAIC3T MRI, 64 slice CT, micro CT, PET, 3D US, NIR3T MRI, 64 slice CT, micro CT, PET, 3D US, NIRSGI PRISM IMAGING SUPERCOMPUTERSGI PRISM IMAGING SUPERCOMPUTERTOPICS:TOPICS:Physical Principles, Practical Issues,Physical Principles, Practical Issues,Advanced challenges, DICOM image dataAdvanced challenges, DICOM image dataprocessing, processing, segmentation, 3D analysis,segmentation, 3D analysis,modeling, project developmentmodeling, project developmentMRI ArtifactsMRI Artifacts••Motion ArtifactMotion Artifact••Phase artifactPhase artifact••Pulsation artifactPulsation artifact••Susceptibility artifactSusceptibility artifact••ChemChemShift artifactShift artifact••FoldFold--over artifactover artifact••Reconstruction artifacts Reconstruction artifacts ……MRI ArtifactsMRI Artifacts••MRI model has impractical assumptions MRI model has impractical assumptions resulting in artifactsresulting in artifacts––Infinite space tiled by FOVInfinite space tiled by FOV––No motionNo motion––Single shiftSingle shift––Reproducible signalReproducible signal––KK--space covered under consistent space covered under consistent conditioncondition––Phase=verticalPhase=vertical--offsetoffsetArtifacts (cont.)Artifacts (cont.)ADC ErrorADC OverflowArcAudio-frequency ProblemsBo InhomogeneityB1 InhomogeneityChemical ShiftClippingData DropoutDC OffsetDigitizer QuantizationExtra EchoesFID in Spin EchoFilter ringingGibbs Ringing InstabilityLow Dynamic RangeLoose ConnectionMoireMotionNoiseReceiver turn-onQuadrature GhostRF InhomogeneityRadio-frequency InterferenceRandom NoiseShimming ErrorsStuck ADC BitSusceptibilityTruncation of EchoExample Study: Patient Unknown Cardiac MassMass is in pericardialspaceMass impinges onRVOTMass engulfs RCARV and LV functionWNLFour-Chamber MovieHigh Resolution Spiral MRIHigh Resolution Spiral MRIMass wraps around Aorta3mm high resolution spiral imagingshows intact tissue plane at all Levels– Aorta has not been invadedSpiral AliasArtifactsHigh Resolution Spiral MRIHigh Resolution Spiral MRIMass indents RVOTThis is likely cause of DOEHigh Resolution Spiral MRIHigh Resolution Spiral MRIRV Wall is not involvedPerfusion SeriesPerfusion SeriesTumor is highly Tumor is highly vascular, systemic vascular, systemic arterial supplyarterial supplyNote artifactual fluctuating signal outside the chest in empty space••Mass Lesion in Pericardial SpaceMass Lesion in Pericardial Space••Highly VascularHighly Vascular••Retains contrast in multiple cavities consistent with Retains contrast in multiple cavities consistent with cavernous cavernous hemangiomahemangioma••RCA is envelopedRCA is enveloped••There is a tissue plane between mass and RV, mass There is a tissue plane between mass and RV, mass and Aortaand Aorta••DX: Pericardial Cavernous DX: Pericardial Cavernous HemangiomaHemangioma, encasing , encasing RCA and impinging on RVOTRCA and impinging on RVOT••KEY PART OF DX PROCESS: RECOGNIZE, KEY PART OF DX PROCESS: RECOGNIZE, UNDERSTAND ARTIFACTS v. DESIRED INFOUNDERSTAND ARTIFACTS v. DESIRED INFOBasis for MRIBasis for MRIB0B1MzMxyFrom a Few Good SeedsFrom a Few Good Seeds……How Many ProtonsHow Many Protons••Typical Typical VoxelVoxel= 2 x 2 x 5 mm = 0.02 ml= 2 x 2 x 5 mm = 0.02 ml••1 ml water = 1 mole H1 ml water = 1 mole H22O = 1+1+16 gO = 1+1+16 g••AvagadroAvagadro: 1 mole = 6.0225 x 10: 1 mole = 6.0225 x 102323••#H/#H/VoxelVoxel= = (H/W)(W/(H/W)(W/mole)(mole/ml)(ml/Voxelmole)(mole/ml)(ml/Voxel))––=(2) (6.0225x10=(2) (6.0225x102323) (1/18) (0.02)= 1.338 x10) (1/18) (0.02)= 1.338 x102121protonsprotons––=1,338 billion =1,338 billion billionbillionprotonsprotons••Recruit 6/million/TeslaRecruit 6/million/Tesla––(H/voxel)(6/million/Tesla)(1.5 T) (H/voxel)(6/million/Tesla)(1.5 T) ––= 12,000 million billion recruited protons = 12,000 million