Diffusion

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  • Diffusion

    1. 1. 1 DIFFUSION & PERFUSIONDIFFUSION & PERFUSION MRI IMAGINGMRI IMAGING Dr. Wael DarwishDr. Wael Darwish
    2. 2. 2 DIFFUSION MRI IMAGING
    3. 3. 3 - History - • The feasibility of diffusion images was demonstrated in the middle 1980s • Demonstration on clinical studies is more recent ; it corresponds with the availability of EPI on MR system • A single shot EPI sequence can freeze the macroscopic pulsating motion of the brain or motion of the patient’s head
    4. 4. 4 Diffusion Weighted Image • Core of infarct = irreversible damage • Surrounding ischemic area  may be salvaged • DWI: open a window of opportunity during which ttt is beneficial • DWI: images the random motion of water molecules as they diffuse through the extra-cellular space • Regions of high mobility “rapid diffusion”  dark • Regions of low mobility “slow diffusion”  bright • Difficulty: DWI is highly sensitive to all of types of motion (blood flow, pulsatility, bulk patient motion, ……).
    5. 5. Diffusion gradients sensitize MR Image toDiffusion gradients sensitize MR Image to motion of water moleculesmotion of water molecules More motion = Darker imageMore motion = Darker image Freely Diffusing Water = DarkFreely Diffusing Water = Dark Restricted Diffusion = BrightRestricted Diffusion = Bright - Diffusion contrast -
    6. 6. 6 - Principles - Velocities and methods of measurement Fast Flow Arteries ~ 1000mm/ s “Phase Contrast” Slow Flow Veins ~ 100mm/ s “Phase Contrast” Perfusion Capillaries ~ 1mm/ s Contrast Wash out Diffusion Intercellular space ~ 0,001mm/ s Diffusion weighting
    7. 7. 7 - Principles - About the b factor • b is a value that include all gradients effect (imaging gradients + diffusion gradients) • The b value can be regarded as analogous to the TE for the T2 weighting
    8. 8. Low Mediu m High ““b = 5”b = 5” ““b = 500”b = 500” ““b = 1000”b = 1000”
    9. 9. 9 - Principles - About ADC The ADC value does not depend on the field strength of the magnet or on the pulse sequence used (which is different for T1 or T2) The ADC obtained at different times in a given patient or in different patients or in different hospitals can be compared
    10. 10. 10 - Principles - Isotropic and Anisotropic diffusion • Diffusion is a three dimensional process, but molecular mobility may not be the same in all directions • In brain white matter, diffusion’s value depends on the orientation of the myelin fiber tracts and on the gradient direction*
    11. 11. X Diffusion - WeightingX Diffusion - Weighting Y Diffusion - WeightingY Diffusion - Weighting Z Diffusion - WeightingZ Diffusion - Weighting Anisotropic diffusion : IndividualAnisotropic diffusion : Individual direction weighteddirection weighted
    12. 12. Individual DiffusionIndividual Diffusion DirectionsDirections Mathematical CombinationMathematical Combination (Sorensen et al., MGH)(Sorensen et al., MGH) Isotropic Diffusion-Isotropic Diffusion- Weighted ImageWeighted Image - + x /- + x / Isotropic diffusionIsotropic diffusion
    13. 13. 13 Diffusion weighted image
    14. 14. TE=100msTE=100ms SR 120SR 120 TE=75msTE=75ms SR150SR150 b = 1000 s/mmb = 1000 s/mm 22 Short TE DWI gives more SNRShort TE DWI gives more SNR Characteristics of diffusion’s contrastCharacteristics of diffusion’s contrast
    15. 15. Higher b value increases sensitivityHigher b value increases sensitivity b = 1000 b= 3000 MS Stroke Tumor Vasogenic edema Cytotoxic Edema Higher CNR helps distinguish active lesions Higher CNR Vasogenic edema Characteristics of diffusion’s contrastCharacteristics of diffusion’s contrast
    16. 16. Diffusion-weightedDiffusion-weighted ADCADC mapmap Mathematical ProcessingMathematical Processing
    17. 17. Diffusion-weightedDiffusion-weighted ADCADC mapmap Exponential ADCExponential ADC Mathematical ProcessingMathematical Processing
    18. 18. Exponential ADC (ratio of Isotropic DWI/T2)Exponential ADC (ratio of Isotropic DWI/T2) eliminates T2 shine through artifacts and mayeliminates T2 shine through artifacts and may distinguish subacute from acute strokedistinguish subacute from acute stroke Diffusion Imaging ProcessingDiffusion Imaging Processing
    19. 19. b=0b=0 eADCeADC ADCADC b=1000b=1000 Arachnoid CystArachnoid Cyst
    20. 20. 20 ClinicalClinical ApplicationApplication
    21. 21. 21 MR Images of 60-Year-Old Man with Glioblastoma Multiforme . 2. Figures 1, 2. On (1) T2-weighted fast spin-echo and (2) contrast- enhanced T1-weighted spin-echo images, the differential diagnosis between glioblastoma and abscess is impossible.
    22. 22. 22 . 3. 4. central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.
    23. 23. 23 MR Images of 57-Year-Old Woman with Cerebral Metastasis 5. 6.
    24. 24. 24 7. 8. central hypointensity on diffusion-weighted image and hyperintensity on ADC map, consistent with the diagnosis of tumor.
    25. 25. 25 1. 2. MR Images of 70-Year-Old Man with History of Recent Vertigo and Disequilibrium
    26. 26. 26 3. 4. A brain abscess with Streptococcus anginosus was found at surgery.
    27. 27. 27 5. 6. the differential diagnosis between metastasis and abscess is impossible. MR Images of 57-Year-Old Woman with Cerebral Metastasis
    28. 28. 28 7. 8. Central hypointensity is seen on the diffusion-weighted image and hyperintensity on the ADC map, consistent with the diagnosis of tumor.
    29. 29. 29 APPLICATIONS SPINE
    30. 30. 30 BENIGN VERSUS MALIGNANT FRACTURE
    31. 31. 31 • This finding indicates that the lack of signal reduction in malignant vertebral fractures is caused by tumor cell infiltration • Different diffusion effect is caused by more restriction or hindrance in densely packed tumor cells compared with more mobile water in extracellular volume fractions in fractures
    32. 32. 32 • diffusion-weighted spin-echo sequences could differentiate benign fracture edemas and fractures caused by tumor infiltration due to higher restriction of water mobility in tumor cells.
    33. 33. 33 T2-weighted MR image shows ovoid hypointense mass in spinal canal.
    34. 34. 34 T1-weighted sagittal MR image after infusion of gadolinium contrast material shows diffuse signal enhancement of mass.
    35. 35. 35 T1-weighted transverse MR image after infusion of contrast material shows extent of tumor in spinal canal and C4-C5 neural foramen
    36. 36. 36 Diffusion-weighted sagittal MR image using peripheral pulse gating and navigator correction shows signal intensity of mass (open arrows) to be intermediate, less than that of brainstem (large solid arrow) and greater than that of vertebral bodies (small solid arrows).
    37. 37. 37 ADC map shows mass (arrows) as structure of intermediate intensity.
    38. 38. 38 • In that study, tumors with high cellularity had low mean ADC values, and tumors with low cellularity had high mean ADC values. • In addition, the relatively high ADC value seen in our patient corresponded to a low degree of cellularity, such as has been reported in cerebral gliomas.
    39. 39. 39 Perfusion imagingPerfusion imaging • DefinitionsDefinitions • PrinciplesPrinciples • Some more definitionsSome more definitions • Perfusion techniquePerfusion technique • ApplicationsApplications • FutureFuture
    40. 40. 40 DefinitionsDefinitions • Perfusion is refer to the delivery of oxygenPerfusion is refer to the delivery of oxygen and nutrients to the cells via capillariesand nutrients to the cells via capillaries • Perfusion is identified with blood flowPerfusion is identified with blood flow which is measured in milliliters per minutewhich is measured in milliliters per minute per 100 g of tissueper 100 g of tissue
    41. 41. 41 PrinciplesPrinciples After injection of a contrast agentAfter injection of a contrast agent • In normal brainIn normal brain, the paramagnetic contrast agent, the paramagnetic contrast agent remains enclosed within the cerebral vasculatureremains enclosed within the cerebral vasculature because of the blood brain barrierbecause of the blood brain barrier • The difference inThe difference in magnetic susceptibilitymagnetic susceptibility between thebetween the tissue and the blood results in local magnetic fieldtissue and the blood results in local magnetic field finally to large signal lossfinally to large signal loss
    42. 42. 42 Some more DefinitionsSome more Definitions • rCBF “ the rate of supply of Gd chelate to a specifiedrCBF “ the rate of supply of Gd chelate to a specified mass ”mass ” ( ml / 100g / min)( ml / 100g / min) • rCBV - “ the volume of distribution of the Gd chelaterCBV - “ the volume of distribution of the Gd chelate during its first passage through the brain ”during its first passage through the brain ” ( % or ml /( % or ml / 100g )100g ) • MTT - “ the average time required for any givenMTT - “ the average time required for any given particle to pass through the tissue, following an idealisedparticle to pass through the tissue, following an idealised input function ”input function ” (min or s)(min or s) MTT = rCBV / rCBFMTT = rCBV / rCBF
    43. 43. 43 ► Passage of Gd. can be followed by the changesPassage of Gd. can be followed by the changes in the relaxation rates concentration of localin the relaxation rates concentration of local contrast.contrast. ► Linear relation bet. concentration and rates ofLinear relation bet. concentration and rates of signal changes can be expressed as curve.signal changes can be expressed as curve. ► Tissue contrast concentration time curve can beTissue contrast concentration time curve can be used to determine tissue micro vascularity,used to determine tissue micro vascularity, volume and flow.volume and flow.
    44. 44. slice n time intensity ~ ‘mean transit time’ Integral:= cerebral blood volume At each voxel we observe :At each voxel we observe : time
    45. 45. 45 PrinciplesPrinciples • Each one of these effects is linearly proportional toEach one of these effects is linearly proportional to the concentration of the paramagnetic agentthe concentration of the paramagnetic agent • To date, this technique results in non-quantitativeTo date, this technique results in non-quantitative perfusion parametersperfusion parameters (like rCBV,rCBF or MTT)(like rCBV,rCBF or MTT) because of the ignorance of the arterial inputbecause of the ignorance of the arterial input functionfunction
    46. 46. PrinciplesPrinciples Extract time-intensityExtract time-intensity curvescurves Perform mathematicalPerform mathematical manipulationmanipulation Generate functionalGenerate functional mapsmaps++ ++ - + x /- + x / Negative EnhancementNegative Enhancement Integral Map(NEI)Integral Map(NEI) Qualitative rCBV mapQualitative rCBV mapFirst PassFirst Pass Contrast bolusContrast bolus Mean Time toMean Time to Enhance (MTE)MapEnhance (MTE)Map Ischaemic PenumbraIschaemic Penumbra MTEMTE NEINEI Dynamic Susceptibility Contrast ImagingDynamic Susceptibility Contrast Imaging
    47. 47. 47 • Hemodynamics Bl. volume Bl. flow • Aim 1. Diagnosis 2. Monitoring management 3. Understanding intracranial lesions Dynamic MR perfusion
    48. 48. rCBVrCBV rCBV, processed with “Negative Enhancement Integral”(NEI)rCBV, processed with “Negative Enhancement Integral”(NEI) is related to area under curveis related to area under curve
    49. 49. MTTMTT MTT is related to the time to peak and to the width of the peak ; itMTT is related to the time to peak and to the width of the peak ; it is processed with “Mean Time to Enhance“(MTE)is processed with “Mean Time to Enhance“(MTE)
    50. 50. Cerebral blood perfusion by bolusCerebral blood perfusion by bolus trackingtracking power injector - Gadolium 5ml/sec Procedure :Procedure : 1 - Start Imaging1 - Start Imaging 2 - Inject Contrast*2 - Inject Contrast* 3 - Continue Imaging3 - Continue Imaging Requires very high speed imaging 10 slices - 50 images of each slice - TOTAL time 1:34 min10 slices - 50 images of each slice - TOTAL time 1:34 min ** Push Gadolinium with 20 cc of saline flushPush Gadolinium with 20 cc of saline flush
    51. 51. 51 Applications of Perfusion MRIApplications of Perfusion MRI • Neurology • Gerontology • Neuro-oncology • Neurophysiology • Neuropharmacology
    52. 52. Perfusion Imaging: Findings in InfarctionPerfusion Imaging: Findings in Infarction • CBVCBV – regional perfusion deficitregional perfusion deficit – compensatory increased volumecompensatory increased volume • MTTMTT – regional prolongation of transit timeregional prolongation of transit time StrokeStroke
    53. 53. Head TraumaHead Trauma T2 image showingT2 image showing bifrontal volume lossbifrontal volume loss FLAIR image showingFLAIR image showing bifrontal gliosis andbifrontal gliosis and encephalomalaciaencephalomalacia
    54. 54. Head trauma:Hypo-perfusionHead trauma:Hypo-perfusion rCBV MAPrCBV MAPTc-HMPAO SPECTTc-HMPAO SPECT Hypo-perfusionHypo-perfusion
    55. 55. E.g. 1 : Left hemisphere stroke, 4.5E.g. 1 : Left hemisphere stroke, 4.5 hrs after onset of symptomshrs after onset of symptoms 3D-TOF Vascular3D-TOF Vascular FSE-T2WFSE-T2W FSE-FLAIRFSE-FLAIR
    56. 56. Same patient with DWI and FLAIRSame patient with DWI and FLAIR EPIEPI FLAIRFLAIR 4.5 hrs4.5 hrs 24 hrs24 hrs Diffusion imaging showsDiffusion imaging shows lesion early.lesion early. b=0b=0 b=800b=800 FLAIR shows enhancedFLAIR shows enhanced changes after 24 hrs.changes after 24 hrs. 4.5 hrs4.5 hrs
    57. 57. Isotropic diffusion imageIsotropic diffusion image b=800b=800 ADC mapADC map Apparent diffusion coefficient ADCApparent diffusion coefficient ADC
    58. 58. Contrast enhanced perfusion imagingContrast enhanced perfusion imaging 24 slices24 slices 3 seconds/acquisition3 seconds/acquisition Time/intensity graphTime/intensity graph
    59. 59. Mean Time To EnhanceMean Time To Enhance delayeddelayed compensatorycompensatory hyperhyperperfusionperfusion delayeddelayed hypohypoperfusionperfusion
    60. 60. EPI PerfusionEPI Perfusion MTTMTT Mean Time To EnhanceMean Time To Enhance CBVCBV Negative EnhancementNegative Enhancement IntegralIntegral ADC Diffusion Coefficient* EPI Diffusion and Perfusion mappingEPI Diffusion and Perfusion mapping EPI DiffusionEPI Diffusion
    61. 61. Findings with PerfusionFindings with Perfusion Imaging for InfarctionImaging for Infarction • Changes seen almost immediately after the induction of ischemiaChanges seen almost immediately after the induction of ischemia – more sensitive than conventional MRImore sensitive than conventional MRI • Perfusion findings often more extensive than those on DW-EPI inPerfusion findings often more extensive than those on DW-EPI in early strokeearly stroke – more accurately reflects the amount of tissue under ischemicmore accurately reflects the amount of tissue under ischemic conditions in the hyperacute period than DW EPIconditions in the hyperacute period than DW EPI – Abnormal results correlate with an increased risk of strokeAbnormal results correlate with an increased risk of stroke – PerfEPI - DWEPI = tissue at riskPerfEPI - DWEPI = tissue at risk
    62. 62. Alzheimer’s diseaseAlzheimer’s disease • FDG PET – marked temporo-parietal hypometabolism • Tc-HMPAO SPECT – marked temporo-parietal hypoperfusion • DSC MRI – correlates well with SPECT Findings with Perfusion imagingFindings with Perfusion imaging for Gerontologyfor Gerontology
    63. 63. Findings with Perfusion imaging forFindings with Perfusion imaging for Neurophysiology and pharmacologyNeurophysiology and pharmacology • Traumatic brain injuryTraumatic brain injury – focal rCBV deficits that correlate withfocal rCBV deficits that correlate with cognitive impairmentcognitive impairment • SchizophreniaSchizophrenia – decreased frontal lobe rCBVdecreased frontal lobe rCBV • HIV/ AIDSHIV/ AIDS – multiple discrete foci of decreased CBVmultiple discrete foci of decreased CBV • Polysubstance abusePolysubstance abuse – multiple discrete foci of decreased CBVmultiple discrete foci of decreased CBV New Jersey Neuroscience InstituteNew Jersey Neuroscience Institute
    64. 64. Findings with Perfusion imagingFindings with Perfusion imaging for Neuro-oncologyfor Neuro-oncology • Critical imaging to BBBB imaging of neoplasmCritical imaging to BBBB imaging of neoplasm – many tumors have high rCBVmany tumors have high rCBV – regions of increased rCBV correlate with areas ofregions of increased rCBV correlate with areas of active tumor.active tumor. – heterogeneous patterns of perfusion suggest highheterogeneous patterns of perfusion suggest high gradegrade – radiation necrosis typically demonstrates low rCBVradiation necrosis typically demonstrates low rCBV • Lesion characterization may be possibleLesion characterization may be possible – meningiomas have very high CBV in contrast tomeningiomas have very high CBV in contrast to schwannomasschwannomas New Jersey Neuroscience InstituteNew Jersey Neuroscience Institute
    65. 65. 65 Clinical applications:- • Intracranial neoplasm N.B angiogenesis usually = aggressiveness Exceptions:- 1. Meningioma 2.Choroid plexus papilloma 1.Glioma Grading Biopsy D.D recurrence from radiation necrosis Dynamic MR perfusion
    66. 66. 66 2.Metastasis Can differentiate solitary metastasis from 1ry brain neoplasm (glioma) by measuring the peritumoral relative blood volume. 3.1ry cerebral lymphoma Can help in differentiating lymphoma from glioma as lymphoma is much less vascular
    67. 67. 67 4. Meningioma4. Meningioma Hypervascular Extra axialHypervascular Extra axial Has leaky and permeable capillaries causing noHas leaky and permeable capillaries causing no recovery of T2* signal to basline.recovery of T2* signal to basline. 5. Tumor mimicking lesions e.g.5. Tumor mimicking lesions e.g. cerebral infectionscerebral infections tumefactive demyelinating lesionstumefactive demyelinating lesions less commonly infarctsless commonly infarcts
    68. 68. 68 6.Tumefactive demyelinating lesions6.Tumefactive demyelinating lesions No neo-vascularization in demyelinating lesionsNo neo-vascularization in demyelinating lesions To concludeTo conclude MR perfusion should be included in routineMR perfusion should be included in routine evaluation of brain tumor as it improveevaluation of brain tumor as it improve diagnostic accuracy.diagnostic accuracy.
    69. 69. 69
    70. 70. 70
    71. 71. 71
    72. 72. 72
    73. 73. 73 Neuro-oncologyNeuro-oncology • low rCBV in tumourlow rCBV in tumour infersinfers low grade gliomalow grade glioma rCBV mapsrCBV maps
    74. 74. Eg2 Diffused tumor: Abnormal capillary density Glioblastoma multiformGlioblastoma multiform Hyper perfusionHyper perfusion ExcisedExcised regionregion Before surgery MTSE shows blood brain /Before surgery MTSE shows blood brain / barrier breakdownbarrier breakdown (bbbb)(bbbb) After surgery rCBV map shows diffuseAfter surgery rCBV map shows diffuse disease in right frontal lobedisease in right frontal lobe
    75. 75. Recurrent TumorRecurrent Tumor Eg3Eg3 tumor vs.radiation necrosistumor vs.radiation necrosis Conventional T2Conventional T2 CBVCBV Non specific changesNon specific changes

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