anisotropic and optical imaging
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
ANISOTROPICAND
OPTICAL IMAGING
Yelda Ozsunar,Prof. of RadiologyAdnan Menderes University School of Medicine,Radiology Department, Aydin (Tralleis), Turkey
New non-invasive brain imaging techniques Both evolving from research era to clinical
routine Both are on scale of electromagnetic
spectrum
ANISOTROPIC AND OPTICAL IMAGING
Electromagnetic spectrum
-Wavelengths and energy have an inverse relationship
-The shorter the wavelengths, the higher the energy, the more harmfull effect for biological tissue
Flowchart
Anisotropic Imaging Physical principals Clinical Applications
Optical Imaging Descriptions Methods and Instrumentations Clinical applications
Radiowaves:
Magnetic Resonance Imaging
Diffusion Weighted Imaging
Isotropic Imaging: DWI, ADC Anisotropic Imaging: FA, DTI or Fiber tracking…
H+H+
Isotropic Diffusion (CSF, etc)
Anisotropic Diffusion (myelin fiber, etc )
TranslationalDiffusion: Directional
Isotropic Imaging Anisotropic Imaging
Choice of direction: not impotant ImportantApplied gradients: at least 3 at least 6 noncolinear direction
Eigenvectors: 3 principal axes of the diffusion tensor
Primary eigenvector: largest
The mean of 3 eigenvectors: ADC The variance of 3 eigenvectors: A.
(1,1,0) (1,-1,0) (0,1,1) (0,-1,1) (1,0,1) (-1,0,1)
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. or cor. plane with 3-5mm, b max:703-1000
ANISOTROPIC DATA2) TRACTOGRAPHY
FA: The most sensitive to lowest anisotropyVolume Ratio: The most sensitive to highest anisotropyRelative anisotropy: more linear
1) ANISOTROPY MAPS
ANISOTROPY MAPS
2D FibertrackingUp
Down
R L
Ant.
Post
Association fibers
Projection fibers
Comissural fibers
Can differentiate directions of WM
DTI / Anisotropy
2D or 3D anatomical imaging for fiber tracts Deterministic methods (user defined
ROIs) Probabilistic methods
Quantification Measurements of A. in vivo and in
formalin-fixed myelinated white matter show similar values
Unlike DWI alone, DTI can distinguish white matter from gray matter
Clinical Applications Ischemia Tumor Imaging Trauma Demyelinating Diseases Aging Brain Psychiatric Diseases Pediatric Neuroimaging Post-treatment changes
A B C D
A B C D
DWI ADC
FA EP T2
8 hours after onset
A B C DA B C D
A B C DA B C D
DWI ADC
FA EP T2
11 hours after onset
A significant negative correlation between FA and T2 signal change (r= -0.66, p=0.00025), (Ozsunar Y, AJNR, 2004)
FA vs T2 % Change
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
T2 % Change
FA %
Cha
nge
Temporal evolution of anisotropy in ischemia
FA
Pierpaoli C, Proc. Int. Soc. Magn. Reson. Med. 1996
T2
Anisotropy Increased anisotropic diffusion suggest
continued structural integrity and tissue salvageability Ozsunar Y, AJNR, 2004
A potential role for anisotropy in differentiating hyperacute stroke from acute or subacute stroke Harris AJ Magn Reson Imaging 2004
Specific localization of pathways allow more accurate prognosis of long-term recovery or disability
Tumor imaging
Conventional MRI underestimates tumor extends Help in preoperative planning Benign tumors, metastases and meningiomas
displace the neighbouring fiber tracts
Inflitrative glioma Low grade glioma
Tumor vs Peritumoral vasogenic edema
DTI
Vasogenic edema: reduced FA, but normal color hues
(Field AS, 2005, Ann. N.Y. Acad. Sci.)
Trauma : Diffuse axonal injury
CT and conventional MR imaging underestimate injury and correlate poorly with outcome
FA better corralete with clinic comparing ADC
Huisman AGM, AJNR, 2004
Normal
Trauma
Aging FA of white matter declines and ADC values
rise.
young old
White Matter maturation
During infancy and childhood, anisotropy increases in developing white matter tracts.
Pediatric Neuroimaging
Decreased FA (microstructural
axonal damage, vasogenic edema) Periventricular leukomalacia Brain tumors Multiple sclerosis Idiopathic epilepsy Cortical dysplasia Hypoxic ischemic encephalopathy Most methabolic d. (Krabbe,
Adrenoleukodystrophy… )
unilateral congenital hemiparesis
Mukherjee P. Neuroimag Clin N Am
Increased FA (dysorganisation, cytotoxic
edema) Heterotopia of gray matter Partial agenesis of corpus callosum Diffuse cerebral edema
Pediatric Neuroimaging
Limitatons
DTI is oversimplification of the properties of water diffusion
DTI is more limited in areas of complex white matter architecture, such as branchs, intersections etc
Can not differentiate antegrade from retrograde along a fiber pathway
Resolution is limited Artifacts: Eddy current, ghost, misregistration
Optical Imaging
What is Optical Imaging?
An imaging method that uses light Light in physics refers to electromagnetic
radiation of any wavelength, whether visible or not
Wavelengths energy
harm for biological tissue
high frequency
Light versus Near InfraredVisible Light Near Infrared Light (NIR)
Harm for human Little Better
Wavelength (nm) 400-700 700-900 (1300)
Frequency ( terra Hertz) 500-800 300
Penetration Good (1-3cm ?) Better
Reflection Little Better
Scattering More Less
Tissue absorbsion Nonselective Selective (Hb, Mb, cyt. Ox)
What is Near Infrared?
Daily use of near infrared
TV's remote control.
http://www.nasa.gov/
Biological tissues reflect more near infrared light compared to visible light
Infrared image
visible light images
Healthy plant Unhealthy plant
http://www.nasa.gov/
Healthy brain Unhealty brain
How this works?
Medical use of Optical Imaging
First reported by Jöbsis in 1977 Pulse oxymetry Optic nerve: Optical Coherance Tomography Breast: Optical Mammography (Near Infrared Laser Light
transmission ) Brain:
NIRS functional imaging, not anatomical!
How tissue interacts with NIRS?
Spectroscopy is interaction between radiation and matter
Near Infrared Spectroscopy Diffuse Optical Imaging
How tissue interacts with NIR?
Huppert et al Appl Opt. 2009.
What we get out of Optical Imaging
Noninvasively detect:Oxy-haemoglobin (HbO) Deoxy-haemoglobin (HHb)Total hemoglobin (CBV )Cytochrome oxidase (tissue oxygenation)
associated with neural activity
Why NIRS are needed? Bedside assessment of neonatal brain
health EEG, US, Transcranial Doppler
PET, SPECT: Radiation, expensive NIRS
Similar information as functional Magnetic Resonance Imaging (fMRI), but
near infrared spectroscopy (NIRS) vs fMRI, Portable, smaller, bed site application Higher temporal resolution Spectroscopic information about both
oxyhemoglobin and deoxyhemoglobin Less expensive, safer No need for immobility Can not compete with spatial resolution MRI, US
Clinical utilities of NIRS Tumor localization and characterization: breast Monitoring tumor changes during neoadjuvantchemotherapy Measurement of normal and abnormal tissue
physiological properties Functional changes in the visual, auditory, and somatosensory cortices,
motor, prefrontal cortices, cognitive and language systems Seizures Alzheimer’s disease Neonate brain status Stroke rehabilitation Depression and schizophrenia
OPTICAL IMAGING
Optical Topography (2D) Optical Tomography (3D)
1-Continious Wave
2-Frequency Domain
3-Time Domain
Near Infrared light
Instrumentation
Optical tomography
Optical Topography
Hebden JC, 2003
-Real-time imaging modality
-Images can be displayed at a rate of a few hertz or faster
Passive movement of the right arm.
OxyHb Deoxy Hb
Optical Tomography (3D)
transverse slice imaging full three-dimensional imaging
Time domain optical tomography
Hebden et al.
1. Continuous Wave
Simple, inexpensive, portable Useful for adult calvarium Provide qualitative information Measure the transmitted intensity with fixed
spacing
intensity
time
Disadvantages CW
Quantification is impossible in human subjects Limited depth information (We cannot obtain
an image of brain function)
2. Frequency Domain Most applicable for neonathal brain imaging Measure intensity /phase shift of light signal Quantitative measurement possible Provide very fast temporal sampling (up to 50
Hz). More complicated comparing CW, Portable, Easy to develop and use, Inexpensive compared to TD
3. Time Domain
Measure delay of light pulse at detector More complicated, more expensive Acquire information at all frequencies
simultaneously, Provide depth information Mostly are used for optical tomography
Austin T, NeuroImage 31 (2006) 1426 – 143332-channel time-resolved device
known as MONSTIR (Multi-channel Opto-electronic Near-infraredSystem for Time-resolved Image Reconstruction).
Limitations of NIRS
Incomplete knowledge of which region of the brain is sampled
Deep brain structure (diencephalon) can not be measured
Cross talk between oxyhemoglobin and deoxyhemoglobin concentrations
Artifacts (respiration, motion…)
Companies
Hitachi (ETG-100, ETG-7000) Shimadzu ISS (USA). Philips NIRx Medical Technologies (USA)
Hybrid instruments (CW+FD) are exist
Conclusion
Biomedical optics is one of the fastest growing areas of physics applied to medicine
Newborn infants are going to be one of the principal beneficiaries of optical technology
Thank you…