Medicine:Optical coherence elastography

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Optical coherence elastography (OCE) is an emerging imaging technique used in biomedical imaging to form pictures of biological tissue in micron and submicron level and maps the biomechanical property of tissue.[1][2][3]

Introduction

Elastography was first used in 1979[4] and subsequent progress in the field has been extensive, based largely on ultrasound, and magnetic resonance imaging.[5][6] Optical techniques have also been proposed for elastography to probe mechanical properties of tissues dates back to at least the 1950s.[7] In 1998, Schmitt first proposed optical coherence elastography (OCE), in employing optical coherence tomography (OCT) detect depth-resolved sample deformation induced by quasi-static compression.[8] The first OCT elastography of arteries was done by the Brezinski group in 2004[9]But the term optical coherence elastography was first coined in a 2004 paper with Brett Bouma.[10]

Requiring no injections, OCE is a non-invasive imaging method can gives more details than ultrasound or MRI. Using light source to image biological tissue, OCE is considered generally safe compared to CT scan and other radiographic imaging modalities which involve with ionizing radiation. And it is also more affordable and time efficient compared to MRI. However, OCE can also cause tissue damage in some handling. For example, surface acoustic wave OCE can cause to a tissue is primarily concentrated on temperature effects. In the focus point, the temperature of the tissue will rise locally. Therefore, it is necessary to take this into account in certain circumstances.[citation needed]

OCE is characterized by its niche in intermediate spatial resolution (10s–100s μm)[8] and degree of depth penetration and, by exploiting optical interferometry, its high sensitivity to small mechanical changes—at the microstrain level. However, it's still in the early stage of development and needs more clinical practice before enters into the market. But the term optical coherence elastography was first coined in a 2004 paper with Brett Bouma.[10]

Theory

Although optical coherence tomography (OCT) provide crucial information for the diagnosis, they often are insufficient for early diagnosis, before structural changes occur. Elastography, the display of the elastic properties of soft tissues, may be performed using ultrasound, magnetic resonance imaging (MRI) or OCT. Elastography has been proven feasible for characterization of ocular tissues.[11]

Tissue exhibits varying degrees of viscoelasticity (time-dependent response to a load), poroelasticity (presence of fluid-filled pores or channels), and anisotropy, as well as a nonlinear relationship between elasticity and the applied load. As a starting point in establishing the link between elasticity and displacement, a number of simplifying assumptions are usually made about tissue behavior and structure. Most commonly, tissue is approximated as a linear elastic solid with isotropic mechanical properties. The assumption of linearity is commonly valid for the level of strain (typically <10%) applied in elastography.[8]

Selected applications

Optical coherence elastography holds great promise for detecting and monitoring the altered mechanical properties that accompany many clinical conditions and pathologies, particularly in cancer, cardiovascular disease and eye disease.[citation needed]

Ophthalmology

In ophthalmology, OCE could be utilized to characterize the mechanical properties of the cornea in order to diagnose related ocular disease: especially to diagnose and assess the properties of keratoconus, which provides necessary information to establish adaptive biomechanical models of the cornea for the optimization of individual laser ablation procedure.[12] It also helps improve the management of collagen cross-linking therapy.[13] The methods utilizing OCE to study these properties are still under investigation and some particular ones listed below seem promising to be developed into clinical use. Methods could be divided into two main categories based on required interactions which are in-contact and non-contact detections.

Contact detection

In contact detection using a standard clinical gonioscopy,[14] direct contact with the cornea using gonioscopy creates static compression and resultant displacement amplitude inside the cornea responding to the compression indicates the heterogeneous mechanical properties of the cornea.

Non-contact detection

Non-contact detection methods including creating mechanical contrasts by pulsed laser and focused air puff stimulation[15][16] Non-contact OCE detection methods are more likely to be developed into clinical usages since they are more comfortable and applicable for patients. Pulsed laser is used to generate surface acoustic waves on the cornea and then quantitative Young's modulus measurements of the cornea could be obtained[122]. The focused air puff, described as short duration (<1ms) and low pressure (level of pascal) is capable to measure the cornea stiffness in a safe and easy-to-control stimulus.[16]

Dermatology

The elasticity of skin could indicate related pathologies such as scleroderma[17] and cancer.[18] Developing OCE technology could detect differences in stiffness of human skin layers in vivo.[19] Besides, with dynamic mechanical loading coupled to skin surface, OCE is also capable of making Young's modulus measurements from the quantification of the surface wave velocity based on phase shift of the displacement profile,[15] and thus showing the hydration and dehydration effect of the in vivo human skin.

Oncology

Imaging ex vivo excised tissues[20][21][22][23] to perform two-dimensional mapping of elastic modulus. By either applying static or dynamic compression loading, different sample regions with different stiffness could be highlighted with the mapping of displacement amplitude[20] in a 2D depth-resolved elastogram. Experiments have shown that such method could be utilized to detect tumor region in ex vivo rat mammary tissues.

Assisting intraoperative assessment[24][25] by detecting exact tumor margin. Recently, the needle OCE technique is applied whereas integrates OCE with a needle probe.[24] The needle tip works as the compression loading when inserted into tissue, and the resultant displacement amplitude of tissue is plotted over depth.[24] In this way, the relative stiffness of different regions of tissue could be shown as well as the sharp change in strains that differentiates the tumor boundary from healthy tissue.[24]

Cardiology

To improve management of atherosclerosis, monitoring the stability of plaque by mechanical characterization of the arterial wall plays an important role.[26] This task has always been done by utilizing intravascular ultrasound (IVUS) elastography[27] to characterize the elastic properties of parts within the plaque. Plaque components and stability could be analyzed based on these detected elastic properties.[28] However, detailed plaque structural detection could be limited due to IVUS elastography's relatively low spatial frequency (hundreds of microns). Intravascular OCE could perfectly complements IVUS elastography by developing high-resolution biomechanical imaging of the arterial wall.[10]

Research Tools

OCE could be utilized to determine mechanical properties of engineered tissues at their early stage of development.[29]

References

  1. ↑ "Optical coherence elastography for tissue characterization: a review". Journal of Biophotonics 8 (4): 279–302. April 2015. doi:10.1002/jbio.201400108. PMID 25412100. 
  2. ↑ "Practical obstacles and their mitigation strategies in compressional optical coherence elastography of biological tissues". Journal of Innovative Optical Health Sciences (World Scientific) 10 (6): 1742006. 2017. doi:10.1142/S1793545817420068. 
  3. ↑ "Biophotonics: Optical Coherence Elastography and Biomechanical Modeling of Developing Tissues". National Science Foundation. https://www.nsf.gov/awardsearch/showAward?AWD_ID=0519920. 
  4. ↑ "The use of elastography to assess the rheologic properties of the soft tissues of the human limb with normal and disturbed peripheral lymphatic circulation.". Bulletin of Experimental Biology and Medicine 88 (6): 1501–3. December 1979. doi:10.1007/BF00830374. 
  5. ↑ ""Sonoelasticity" images derived from ultrasound signals in mechanically vibrated tissues". Ultrasound in Medicine & Biology 16 (3): 231–9. 1990. doi:10.1016/0301-5629(90)90002-t. PMID 1694603. 
  6. ↑ "Elastography: a quantitative method for imaging the elasticity of biological tissues". Ultrasonic Imaging 13 (2): 111–34. April 1991. doi:10.1177/016173469101300201. PMID 1858217. 
  7. ↑ "Physics of vibrations in living tissues". Journal of Applied Physiology 4 (12): 886–900. June 1952. doi:10.1152/jappl.1952.4.12.886. PMID 14946086. 
  8. ↑ 8.0 8.1 8.2 "A review of optical coherence elastography: fundamentals, techniques and prospects". IEEE Journal of Selected Topics in Quantum Electronics 20 (2): 272–288. 2014. doi:10.1109/jstqe.2013.2291445. Bibcode: 2014IJSTQ..20..272K. 
  9. ↑ Rogowska, J.; Patel, N. A.; Fujimoto, J. G.; Brezinski, M. E. (2004-05-01). "Optical coherence tomographic elastography technique for measuring deformation and strain of atherosclerotic tissues" (in en). Heart 90 (5): 556–562. doi:10.1136/hrt.2003.016956. ISSN 1355-6037. PMID 15084558. 
  10. ↑ 10.0 10.1 10.2 "OCT-based arterial elastography: robust estimation exploiting tissue biomechanics". Optics Express 12 (19): 4558–72. September 2004. doi:10.1364/opex.12.004558. PMID 19484007. Bibcode: 2004OExpr..12.4558C. 
  11. ↑ "In Vivo Elasticity Mapping of Posterior Ocular Layers Using Acoustic Radiation Force Optical Coherence Elastography". Investigative Ophthalmology & Visual Science 59 (1): 455–461. January 2018. doi:10.1167/iovs.17-22971. PMID 29368002. 
  12. ↑ "Corneal elasticity and ocular rigidity in normal and keratoconic eyes". Acta Ophthalmologica 66 (2): 134–40. April 1988. doi:10.1111/j.1755-3768.1988.tb04000.x. PMID 3389085. 
  13. ↑ "Induction of cross-links in corneal tissue". Experimental Eye Research 66 (1): 97–103. January 1998. doi:10.1006/exer.1997.0410. PMID 9533835. 
  14. ↑ "Method for optical coherence elastography of the cornea". Journal of Biomedical Optics 16 (1): 016005–016005–7. 2011. doi:10.1117/1.3526701. PMID 21280911. Bibcode: 2011JBO....16a6005F. 
  15. ↑ 15.0 15.1 "Biomechanical properties of in vivo human skin from dynamic optical coherence elastography". IEEE Transactions on Bio-Medical Engineering 57 (4): 953–9. April 2010. doi:10.1109/TBME.2009.2033464. PMID 19822464. 
  16. ↑ 16.0 16.1 "A focused air-pulse system for optical-coherence-tomography-based measurements of tissue elasticity". Laser Physics Letters 10 (7): 075605. 2013-05-20. doi:10.1088/1612-2011/10/7/075605. PMID 29805349. Bibcode: 2013LaPhL..10g5605W. 
  17. ↑ "Quantification of cutaneous sclerosis with a skin elasticity meter in patients with generalized scleroderma". Journal of the American Academy of Dermatology 35 (3 Pt 1): 381–7. September 1996. doi:10.1016/s0190-9622(96)90601-5. PMID 8784273. 
  18. ↑ "Real-time tissue elastography as promising diagnostic tool for diagnosis of lymph node metastases in patients with malignant melanoma: a prospective single-center experience". Dermatology 226 (1): 81–90. 2013. doi:10.1159/000346942. PMID 23548643. 
  19. ↑ "Audio frequency in vivo optical coherence elastography". Physics in Medicine and Biology 54 (10): 3129–39. May 2009. doi:10.1088/0031-9155/54/10/011. PMID 19420415. Bibcode: 2009PMB....54.3129A. 
  20. ↑ 20.0 20.1 "Spectroscopic optical coherence elastography". Optics Express 18 (25): 25519–34. December 2010. doi:10.1364/OE.18.025519. PMID 21164898. Bibcode: 2010OExpr..1825519A. 
  21. ↑ "Optical coherence micro-elastography: mechanical-contrast imaging of tissue microstructure". Biomedical Optics Express 5 (7): 2113–24. July 2014. doi:10.1364/BOE.5.002113. PMID 25071952. 
  22. ↑ "Optical micro-scale mapping of dynamic biomechanical tissue properties". Optics Express 16 (15): 11052–65. July 2008. doi:10.1364/oe.16.011052. PMID 18648419. Bibcode: 2008OExpr..1611052L. 
  23. ↑ "Dynamic spectral-domain optical coherence elastography for tissue characterization". Optics Express 18 (13): 14183–90. June 2010. doi:10.1364/OE.18.014183. PMID 20588552. Bibcode: 2010OExpr..1814183L. 
  24. ↑ 24.0 24.1 24.2 24.3 "Needle optical coherence elastography for the measurement of microscale mechanical contrast deep within human breast tissues". Journal of Biomedical Optics 18 (12): 121510. December 2013. doi:10.1117/1.JBO.18.12.121510. PMID 24365955. Bibcode: 2013JBO....18l1510K. 
  25. ↑ "Noncontact measurement of elasticity for the detection of soft-tissue tumors using phase-sensitive optical coherence tomography combined with a focused air-puff system". Optics Letters 37 (24): 5184–6. December 2012. doi:10.1364/OL.37.005184. PMID 23258046. Bibcode: 2012OptL...37.5184W. 
  26. ↑ "Distribution of circumferential stress in ruptured and stable atherosclerotic lesions. A structural analysis with histopathological correlation". Circulation 87 (4): 1179–87. April 1993. doi:10.1161/01.cir.87.4.1179. PMID 8462145. 
  27. ↑ "Intravascular ultrasound elastography". Ultraschall in der Medizin 19 (5): 196–201. October 1998. doi:10.1055/s-2007-1000491. PMID 9842682. https://pure.eur.nl/ws/files/46566380/990623_KORTE,%20Christoffel%20Leendert%20de.pdf. 
  28. ↑ "Characterization of plaque components and vulnerability with intravascular ultrasound elastography". Physics in Medicine and Biology 45 (6): 1465–75. June 2000. doi:10.1088/0031-9155/45/6/305. PMID 10870704. Bibcode: 2000PMB....45.1465D. 
  29. ↑ "Modulation of the mechanical properties of tissue engineered cartilage". Biorheology 37 (1–2): 141–7. 2000. PMID 10912186. 



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