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ANISOTROPIC AND OPTICAL IMAGING

ANISOTROPIC AND OPTICAL IMAGING. Yelda Ozsunar , Prof. of Radiology Adnan Menderes University School of Medicine , Radiology Department , Aydin (Tralleis), Turkey. ANISOTROPIC AND OPTICAL IMAGING. New non - invasive brain imaging techniques

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ANISOTROPIC AND OPTICAL IMAGING

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  1. ANISOTROPIC AND OPTICAL IMAGING Yelda Ozsunar, Prof. of Radiology Adnan Menderes UniversitySchool of Medicine, RadiologyDepartment, Aydin (Tralleis), Turkey

  2. ANISOTROPIC AND OPTICAL IMAGING • New non-invasivebrainimagingtechniques • Bothevolvingfromresearcheratoclinicalroutine • Bothare on scale of electromagneticspectrum

  3. Electromagneticspectrum

  4. -Wavelengths and energy have an inverse relationship -The shorter the wavelengths, the higher the energy, the more harmfull effect for biological tissue

  5. Flowchart • AnisotropicImaging • Physicalprincipals • ClinicalApplications • OpticalImaging • Descriptions • MethodsandInstrumentations • Clinicalapplications

  6. Radiowaves: MagneticResonanceImaging • DiffusionWeightedImaging • IsotropicImaging: DWI, ADC • AnisotropicImaging: FA, DTI or Fiber tracking…

  7. IsotropicDiffusion (CSF, etc) H+ H+ Anisotropic Diffusion (myelin fiber, etc ) Diffusion: Directional Translational

  8. AnisotropicImaging IsotropicImaging Choiceof direction: not impotantImportant Appliedgradients: at least 3 at least 6noncolineardirection Eigenvectors: 3 principal axes of the diffusion tensor Primary eigenvector: largest Thevariance of 3 eigenvectors: A. Themean of 3 eigenvectors: ADC

  9. Technique: 1,5-3 Tesla, gradient strength 20-60 mT/m, slew rate of 120 T/m/s, TR/TE: 6000/100ms, FOV: 24cm, ax. orcor. planewith 3-5mm, b max:703-1000 (1,1,0) (1,-1,0) (0,1,1) (0,-1,1) (1,0,1) (-1,0,1)

  10. ANISOTROPIC DATA 2) TRACTOGRAPHY 1) ANISOTROPY MAPS FA: Themostsensitivetolowestanisotropy VolumeRatio: Themostsensitivetohighestanisotropy Relativeanisotropy: morelinear

  11. ANISOTROPY MAPS

  12. Projectionfibers 2D Fibertracking Up • Comissuralfibers L R Down Ant. • Associationfibers Can differentiatedirections of WM Post

  13. DTI / Anisotropy • Unlike DWI alone, DTI can distinguish white matter from gray matter • 2D or 3D anatomicalimagingfor fiber tracts • Deterministicmethods (userdefinedROIs) • Probabilisticmethods • Quantification • Measurements of A. in vivo and in formalin-fixed myelinatedwhite matter show similar values

  14. ClinicalApplications • Ischemia • TumorImaging • Trauma • DemyelinatingDiseases • AgingBrain • PsychiatricDiseases • PediatricNeuroimaging • Post-treatmentchanges

  15. DWI ADC EP T2 FA 8 hours after onset

  16. ADC DWI EP T2 FA 11 hoursafteronset

  17. A significantnegativecorrelationbetween FA and T2 signalchange (r= -0.66, p=0.00025), (Ozsunar Y, AJNR, 2004)

  18. Temporal evolution of anisotropy in ischemia Pierpaoli C,Proc. Int. Soc. Magn. Reson. Med. 1996 T2 FA

  19. Anisotropy • Increasedanisotropicdiffusionsuggestcontinuedstructuralintegrityandtissuesalvageability • Ozsunar Y, AJNR, 2004 • A potential role for anisotropy indifferentiating hyperacute stroke from acute or subacutestrokeHarris AJ MagnReson Imaging 2004 • Specificlocalization of pathwaysallow more accurate prognosis of long-term recoveryordisability

  20. Tumorimaging • Conventional MRI underestimatestumorextends • Help in preoperative planning • Benigntumors, metastasesandmeningiomasdisplacetheneighbouring fiber tracts Lowgradeglioma Inflitrativeglioma

  21. Tumor vs Peritumoralvasogenicedema • Vasogenicedema: • reduced FA, but normal color hues (Field AS, 2005, Ann. N.Y. Acad. Sci.) DTI

  22. Trauma : Diffuseaxonalinjury Normal • CT andconventionalMR imaging underestimate injury and correlate poorly with outcome • FA bettercorraletewithcliniccomparing ADC Trauma Huisman AGM, AJNR, 2004

  23. Aging • FA ofwhite matter declines and ADC values rise. young old

  24. WhiteMattermaturation Duringinfancy and childhood, anisotropy increases in developingwhite matter tracts.

  25. PediatricNeuroimaging • Decreased FA (microstructuralaxonaldamage, vasogenicedema) • Periventricularleukomalacia • Braintumors • Multiplesclerosis • Idiopathicepilepsy • Corticaldysplasia • Hypoxicischemicencephalopathy • Mostmethabolic d. (Krabbe, Adrenoleukodystrophy… ) unilateral congenital hemiparesis Mukherjee P. NeuroimagClin N Am

  26. PediatricNeuroimaging • Increased FA (dysorganisation, cytotoxicedema) • Heterotopia of graymatter • Partialagenesis of corpuscallosum • Diffusecerebraledema

  27. Limitatons • DTI is oversimplification of theproperties of waterdiffusion • DTI is morelimited in areas of complexwhitematterarchitecture, such as branchs, intersectionsetc • Can not differentiateantegradefromretrogradealong a fiber pathway • Resolution is limited • Artifacts: Eddycurrent, ghost, misregistration

  28. OpticalImaging

  29. What is OpticalImaging? • An imagingmethodthatuseslight • Light in physicsrefers to electromagnetic radiation of any wavelength, whether visible or not

  30. energy Wavelengths high frequency harmforbiologicaltissue

  31. LightversusNearInfrared

  32. What is Near Infrared?

  33. Dailyuse of nearinfrared TV'sremotecontrol.

  34. visiblelightimages Infraredimage Biologicaltissuesreflectmorenearinfraredlightcomparedtovisiblelight http://www.nasa.gov/

  35. HealthyplantUnhealthyplant http://www.nasa.gov/

  36. HealthybrainUnhealtybrain Howthisworks?

  37. Medicaluse of OpticalImaging • First reported by Jöbsis in 1977 • Pulseoxymetry • Opticnerve: OpticalCoheranceTomography • Breast: OpticalMammography (NearInfraredLaserLighttransmission ) • Brain: • NIRS • functionalimaging, not anatomical! • Howtissueinteractswith NIRS?

  38. Howtissueinteractswith NIR? • Spectroscopyis interaction between radiation and matter • NearInfraredSpectroscopy • DiffuseOpticalImaging

  39. Huppert et alAppl Opt. 2009.

  40. Whatwegetout of OpticalImaging • Noninvasivelydetect: Oxy-haemoglobin (HbO) Deoxy-haemoglobin (HHb) Total hemoglobin (CBV ) Cytochromeoxidase (tissueoxygenation) associated with neural activity

  41. Why NIRS areneeded? • Bedside assessment of neonatal brain health • EEG, US, TranscranialDoppler • PET, SPECT: Radiation, expensive • NIRS • Similarinformation as functional MagneticResonanceImaging (fMRI), but

  42. near infrared spectroscopy (NIRS) vs fMRI, • Portable, smaller, bed site application • Highertemporal resolution • Spectroscopicinformation about both oxyhemoglobin and deoxyhemoglobin • Lessexpensive, safer • No needforimmobility • Can not competewithspatialresolution MRI, US

  43. Clinicalutilities of NIRS • Tumorlocalizationandcharacterization: breast • Monitoring tumor changes during neoadjuvant chemotherapy • Measurement of normal and abnormal tissue physiologicalproperties • Functionalchanges in the visual, auditory, and somatosensory cortices, motor, prefrontal cortices, cognitive and language systems • Seizures • Alzheimer’s disease • Neonate brain status • Strokerehabilitation • Depression and schizophrenia

  44. OPTICAL IMAGING Optical Topography (2D) Optical Tomography (3D) NearInfraredlight 1-ContiniousWave 2-FrequencyDomain 3-Time Domain Instrumentation

  45. OpticalTopography -Real-time imaging modality -Imagescan be displayed at a rate of a few hertz or faster Optical tomography Hebden JC, 2003

  46. OxyHb DeoxyHb Passivemovement of the right arm.

  47. OpticalTomography (3D) transverse slice imaging full three-dimensional imaging

  48. Time domain opticaltomography Hebden et al.

  49. 1. ContinuousWave • Simple, inexpensive, portable • Usefulforadultcalvarium • Providequalitativeinformation • Measurethetransmitted intensity with fixed spacing intensity time

  50. Disadvantages CW • Quantificationis impossible in human subjects • Limiteddepthinformation (We cannot obtain an image ofbrainfunction)

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