anisotropic and optical imaging

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

yeldaozsunar@gmail.com

Thank you…