Medical optical imaging
Medical optical imagingis the use oflightas an investigationalimagingtechnique formedicalapplications, pioneered byAmericanPhysical ChemistBritton Chance.Examples includeoptical microscopy,spectroscopy,endoscopy,scanning laser ophthalmoscopy,laser Doppler imaging,andoptical coherence tomography.Because light is anelectromagnetic wave,similar phenomena occur inX-rays,microwaves,andradio waves.
Optical imaging systems may be divided into diffusive[1][2]and ballistic imaging[3]systems. A model for photon migration in turbid biological media has been developed by Bonner et al.[2]Such a model can be applied for interpretation data obtained from laser Doppler blood-flow monitors and for designing protocols for therapeutic excitation of tissue chromophores.
Diffusive optical imaging
[edit]Diffuse optical imaging(DOI) is a method of imaging usingnear-infrared spectroscopy(NIRS)[4]or fluorescence-based methods.[5] When used to create 3D volumetric models of the imaged material DOI is referred to asdiffuse optical tomography,whereas 2D imaging methods are classified asdiffuse optical topography.
The technique has many applications to neuroscience, sports medicine, wound monitoring, and cancer detection. Typically DOI techniques monitor changes in concentrations of oxygenated and deoxygenatedhemoglobinand may additionally measure redox states of cytochromes. The technique may also be referred to as diffuseoptical tomography(DOT), near infrared optical tomography (NIROT) or fluorescence diffuse optical tomography (FDOT), depending on the usage.
In neuroscience, functional measurements made using NIR wavelengths, DOI techniques may classify asfunctional near infrared spectroscopy(fNIRS).
Ballistic optical imaging
[edit]Ballistic photonsare thelightphotonsthat travel through ascattering(turbid)mediumin a straight line. Also known asballistic light.Iflaserpulses are sent through a turbid medium such asfogorbody tissue,most of the photons are either randomly scattered or absorbed. However, across short distances, a few photons pass through the scattering medium in straight lines. These coherent photons are referred to as ballistic photons. Photons that are slightly scattered, retaining some degree ofcoherence,are referred to assnakephotons.
If efficiently detected, there are many applications for ballistic photons especially in coherent high resolutionmedical imagingsystems. Ballistic scanners (using ultrafast time gates) andoptical coherence tomography(OCT) (using theinterferometryprinciple) are just two of the popular imaging systems that rely on ballistic photon detection to creatediffraction-limitedimages. Advantages over other existing imaging modalities (e.g.,ultrasoundandmagnetic resonance imaging) is that ballistic imaging can achieve a higher resolution in the order of 1 to 10 micro-meters, however it has limited imaging depth. Furthermore, more scattered 'quasi-ballistic' photons are often measured as well to increase the signal 'strength' (i.e.,signal-to-noise ratio).
Due to the exponential reduction (with respect to distance) of ballistic photons in a scattering medium, oftenimage processingtechniques are applied to the raw captured ballistic images, to reconstruct high quality ones. Ballistic imaging modalities aim to reject non-ballistic photons and retain ballistic photons that carry useful information. To perform this task, specific characteristics of ballistic photons vs. non-ballistic photons are used, such astime of flightthrough coherence gated imaging, collimation, wavefront propagation, and polarization.[6]
See also
[edit]- Ballistic photon
- Diffuse optical imaging
- Optical coherence tomography
- Optical tomography
- Photon diffusion
- Photon diffusion equation
- Laser Doppler imaging
References
[edit]- ^Durduran T; et al. (2010)."Diffuse optics for tissue monitoring and tomography".Rep. Prog. Phys.73(7): 076701.Bibcode:2010RPPh...73g6701D.doi:10.1088/0034-4885/73/7/076701.PMC4482362.PMID26120204.
- ^abA. Gibson; J. Hebden; S. Arridge (2005)."Recent advances in diffuse optical imaging"(PDF).Phys. Med. Biol.50(4): R1–R43.doi:10.1088/0031-9155/50/4/r01.PMID15773619.S2CID23029891.[permanent dead link]
- ^S. Farsiu; J. Christofferson; B. Eriksson; P. Milanfar; B. Friedlander; A. Shakouri; R. Nowak (2007)."Statistical Detection and Imaging of Objects Hidden in Turbid Media Using Ballistic Photons"(PDF).Applied Optics.46(23): 5805–5822.Bibcode:2007ApOpt..46.5805F.doi:10.1364/ao.46.005805.PMID17694130.
- ^Durduran, T; et al. (2010)."Diffuse optics for tissue monitoring and tomography".Rep. Prog. Phys.73(7): 076701.Bibcode:2010RPPh...73g6701D.doi:10.1088/0034-4885/73/7/076701.PMC4482362.PMID26120204.
- ^"Harvard.edu Diffuse Optical Imaging".Archived fromthe originalon June 16, 2012.RetrievedAugust 20,2012.
- ^Lihong V. Wang; Hsin-i Wu (26 September 2012).Biomedical Optics: Principles and Imaging.John Wiley & Sons. pp. 3–.ISBN978-0-470-17700-6.
External links
[edit]- Medical Optics Groupat ICFO, Barcelona, Spain
- Understanding Near-Infrared Imaging– Resource to better understand the benefits of Near-Infrared imaging.
- Diffuse Optics Lab at University of Pennsylvania, Philadelphia
- DOI at Massachusetts General Hospital, Boston
- Biomedical Imaging Group at Dartmouth
- DOS/I Labat theBeckman Laser Institute,University of California, Irvine
- A review article in the field by A.P. Gibson et al.
- An article on optical breast imaging
- Illinois ECE 460 Principles of Optical ImagingCourse lecture notes
- MRRA Inc. fNIRS Systems[1]
