1. Articles from Costas Pitris

    1-20 of 20
    1. Dual-angle optical coherence tomography for index of refraction estimation using rigid registration and cross-correlation

      Dual-angle optical coherence tomography for index of refraction estimation using rigid registration and cross-correlation

      The index of refraction ( n ) of materials and/or tissues depends on their physical properties and serves as a source of optical contrast in imaging. The variations of the index of refraction have also been investigated for diagnostic purposes in various fields, such as hematology, oncology, etc., since they can signify disease and cell dynamic changes. Optical coherence tomography (OCT) has been used in the past to measure the index ex vivo . However, most methodologies described in the literature are not appropriate for in vivo imaging since they require either a mirror below the sample or a complicated imaging setup ...

      Read Full Article
    2. Comparison of tissue dispersion measurement techniques based on optical coherence tomography

      Comparison of tissue dispersion measurement techniques based on optical coherence tomography

      The effects of dispersion on optical coherence tomography (OCT) images have long been documented. The imbalance of spectral broadening, caused by dispersion mismatches in the two arms of the OCT interferometer, can result in significant resolution degradation. Efforts to correct this phenomenon have resulted in improved image quality using various techniques. However, dispersion is also present and varies in tissues. As a result, group velocity dispersion (GVD) can be used to detect changes in tissues and provide useful information for diagnosis. Several methods can be utilized to measure the GVD from OCT images: (i) the degradation of the point spread ...

      Read Full Article
    3. Automated detection of esophageal dysplasia in in vivo optical coherence tomography images of the human esophagus

      Automated detection of esophageal dysplasia in in vivo optical coherence tomography images of the human esophagus

      Catheter-based Optical Coherence Tomography (OCT) devices allow real-time and comprehensive imaging of the human esophagus. Hence, they provide the potential to overcome some of the limitations of endoscopy and biopsy, allowing earlier diagnosis and better prognosis for esophageal adenocarcinoma patients. However, the large number of images produced during every scan makes manual evaluation of the data exceedingly difficult. In this study, we propose a fully automated tissue characterization algorithm, capable of discriminating normal tissue from Barrett’s Esophagus (BE) and dysplasia through entire three-dimensional (3D) data sets, acquired in vivo. The method is based on both the estimation of the ...

      Read Full Article
    4. Using speckle to measure tissue dispersion in optical coherence tomography

      Using speckle to measure tissue dispersion in optical coherence tomography

      Tissue dispersion could be used as a marker of early disease changes to further improve the diagnostic potential of optical coherence tomography (OCT). However, most methods to measure dispersion, described in the literature, rely on the presence of distinct and strong reflectors and are, therefore, rarely applicable in vivo . A novel technique has been developed which estimates the dispersion-induced resolution degradation from the image speckle and, as such, is applicable in situ . This method was verified experimentally ex vivo and was applied to the classification of a set of normal and cancerous colon OCT images resulting in 96% correct classification.

      Read Full Article
    5. Tissue dispersion measurement techniques using optical coherence tomography

      Tissue dispersion measurement techniques using optical coherence tomography

      Dispersion, a result of wavelength-dependent index of refraction variations, causes pulse-width broadening with detrimental effects in many pulsed-laser applications. It is also considered to be one of the major causes of resolution degradation in Optical Coherence Tomography (OCT). However, dispersion is material dependent and, in tissue, Group Velocity Dispersion (GVD) could be used, for example, to detect changes associated with early cancer and result in more accurate disease diagnosis. In this summary we compare different techniques for estimating the GVD from OCT images, in order to evaluate their accuracy and applicability in highly scattering samples such as muscle and adipose ...

      Read Full Article
    6. Using speckle to measure tissue dispersion in optical coherence tomography

      Using speckle to measure tissue dispersion in optical coherence tomography

      In Optical Coherence tomography (OCT), dispersion mismatches cause degradation of the image resolution. However, dispersion is specific to the material that is causing the effect and can therefore carry useful information regarding the composition of the samples. In this summary, we propose a novel technique for estimating the dispersion in tissue which uses the image speckle to calculate the PSF degradation and is therefore applicable to any tissue and can be implemented in vivo and in situ. A Wiener-type deconvolution algorithm was used to estimate the image PSF degradation from the speckle. The proposed method was verified ex vivo resulting ...

      Read Full Article
    7. Lateral resolution improvement of oversampled OCT images using Capon estimation of weighted subvolume contribution

      Lateral resolution improvement of oversampled OCT images using Capon estimation of weighted subvolume contribution

      A novel technique for lateral resolution improvement in optical coherence tomography (OCT) is presented. The proposed method is based on lateral oversampling of the image. The locations and weights of multiple high spatial resolution sub-volumes are calculated using a Capon estimator assuming each contributes a weighted portion to the detected signal. This technique is independent of the delivery optics and the depth of field. Experimental results demonstrate that it is possible to achieve ~4x lateral resolution improvement which can be diagnostically valuable, especially in cases where the delivery optics are constrained to low numerical aperture (NA).

      Read Full Article
    8. Development of a new, robust and accurate, spectroscopic metric for scatterer size estimation in optical coherence tomography (OCT) images

      Development of a new, robust and accurate, spectroscopic metric for scatterer size estimation in optical coherence tomography (OCT) images

      The modulations appearing on the backscattering spectrum originating from a scatterer are related to its diameter as described by Mie theory for spherical particles. Many metrics for Spectroscopic Optical Coherence Tomography (SOCT) take advantage of this observation in order to enhance the contrast of Optical Coherence Tomography (OCT) images. However, none of these metrics has achieved high accuracy when calculating the scatterer size. In this work, Mie theory was used to further investigate the relationship between the degree of modulation in the spectrum and the scatterer size. From this study, a new spectroscopic metric, the bandwidth of the Correlation of ...

      Read Full Article
    9. Estimation of weighted multi-scatterer contributions for improvement of lateral resolution of optical coherence tomography images

      Estimation of weighted multi-scatterer contributions for improvement of lateral resolution of optical coherence tomography images

      A method for improvement of lateral resolution in Optical Coherence Tomography (OCT) is presented. The resolution improvement achieved with this method does not depend on the delivery optics. Moreover the depth of focus is not restricted. The method is based on the lateral oversampling of the image. The laterally oversampled signals are backscattered signals from shifted and overlapped resolution volumes. Signals from successive volumes are correlated due to the region shared by adjacent resolution volumes. By utilizing the cross correlation of signals from such overlapped volumes, resolution can be improved by various degrees depending on which pairs of signals are ...

      Read Full Article
    10. Axial resolution improvement by modulated deconvolution in Fourier domain optical coherence tomography

      Axial resolution improvement by modulated deconvolution in Fourier domain optical coherence tomography

      A novel technique for axial resolution improvement in Fourier domain optical coherence tomography (FDOCT) is presented. The technique is based on the deconvolution of modulated optical coherence tomography signals. In FDOCT, the real part of the Fourier transform of the interferogram is modulated by a frequency which depends on the position of the interferogram in k space. A slight numerical k shift results in a different modulation frequency. By adding two shifted signals, beating can appear in the A-scan. When the amount of shifting is appropriately selected, deconvolution of the resulting depth profile, using suitable modulated kernels, yields a narrower ...

      Read Full Article
    11. Lateral resolution improvement in oversampled Optical Coherence Tomography images assuming weighted oversampled multi-scatterer contributions

      Lateral resolution improvement in oversampled Optical Coherence Tomography images assuming weighted oversampled multi-scatterer contributions

      A novel method for lateral resolution improvement of Optical Coherence Tomography (OCT) images, which is independent of the focusing of the delivery optics and the depth of field, is presented. This method was inspired by radar range oversampling techniques. It is based on the lateral oversampling of the image and the estimation of the locations of the multiple scatterers which contribute to the signal. The information in the oversampled images is used to estimate the locations of multiple scatterers assuming each contributes a weighted portion to the detected signal, the weight determined by the location of the scatterer and the ...

      Read Full Article
    12. Fourier domain optical coherence tomography axial resolution improvement with modulated deconvolution

      Fourier domain optical coherence tomography axial resolution improvement with modulated deconvolution

      In this manuscript the application of a novel technique for axial resolution improvement in Fourier Domain Optical Coherence Tomography (FDOCT) is demonstrated. Axial resolution in FDOCT can be improved by ~7x without the need for a broader bandwidth light source using modulated deconvolution. In FDOCT the real part of FFT of each interferofram is modulated by a frequency which depends on the position of the interferogram. If an interferogram is shifted slightly, the frequency of the real part of the FFT changes. By adding two shifted interferograms, beating can be appeared in the OCT A-Scans. Subsequently deconvolution with suitable kernels ...

      Read Full Article
    13. Modulated deconvolution for resolution improvement in Fourier domain optical coherence tomography

      Modulated deconvolution for resolution improvement in Fourier domain optical coherence tomography

      This manuscript presents a novel technique for axial resolution improvement in Fourier Domain Optical Coherence Tomography (FDOCT). The technique is based on the modulated deconvolution of OCT signals which results in a resolution improvement by a factor of ~ 7 without the need for a broader bandwidth light source. This method relies on a combination of two basic properties: beating, which appears when adding two signals of slightly different frequencies, and the resolution improvement, achieved by deconvolution of an OCT image with the encoded source autocorrelation function. In FDOCT the real part of the FFT of the interferogram is modulated by ...

      Read Full Article
    14. Scatterer size-based analysis of optical coherence tomography images using spectral estimation techniques

      Scatterer size-based analysis of optical coherence tomography images using spectral estimation techniques

      A novel spectral analysis technique of OCT images is demonstrated in this paper for classification and scatterer size estimation. It is based on SOCT autoregressive spectral estimation techniques and statistical analysis. Two different statistical analysis methods were applied to OCT images acquired from tissue phantoms, the first method required prior information on the sample for variance analysis of the spectral content. The second method used k-means clustering without prior information for the sample. The results are very encouraging and indicate that the spectral content of OCT signals can be used to estimate scatterer size and to classify dissimilar areas in ...

      Read Full Article
    15. AM-FM techniques in the analysis of optical coherence tomography signals

      The subtle tissue changes associated with the early stages of malignancies, such as cancer, are not clearly discernible even at the current, improved, resolution of optical coherence tomography (OCT) systems. However, these changes directly affect the spectral content of the OCT image that contains information regarding these unresolvable features. Spectral analysis of OCT signals has recently been shown to provide additional information, resulting in improved contrast, directly related to scatterer size changes. Amplitude modulation-frequency modulation (AM-FM) analysis, a fast and accurate technique for the estimation of the instantaneous frequency, phase, and amplitude of a signal, can also be applied to ...

      Read Full Article
    16. In vivo ultrahigh-resolution optical coherence tomography.

      Ultrahigh-resolution optical coherence tomography (OCT) by use of state of the art broad-bandwidth femtosecond laser technology is demonstrated and applied to in vivo subcellular imaging. Imaging is performed with a Kerr-lens mode-locked Ti:sapphire laser with double-chirped mirrors that emits sub-two-cycle pulses with bandwidths of up to 350 nm, centered at 800 nm. Longitudinal resolutions of ~1mum and transverse resolution of 3mum, with a 110-dB dynamic range, are achieved in biological tissue. To overcome depth-of-field limitations we perform zone focusing and image fusion to construct a tomogram with high transverse resolution throughout the image depth. To our knowledge this is ...
      Read Full Article
    17. High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery

      High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery
      Abstract  This study demonstrates the first real-time imaging in vivo of human cartilage in normal and osteoarthritic knee joints at a resolution of micrometers, using optical coherence tomography (OCT). This recently developed high-resolution imaging technology is analogous to B-mode ultrasound except that it uses infrared light rather than sound. Real-time imaging with 11-μm resolution at four frames per second was performed on six patients using a portable OCT system with a handheld imaging probe during open knee surgery. Tissue registration was achieved by marking sites before imaging, and then histologic processing was performed. Structural changes including cartilage thinning, fissures, and ...
      Read Full Article
    18. Imaging needle for optical coherence tomography

      Imaging needle for optical coherence tomography
      We describe a miniature optical coherence tomography (OCT) imaging needle that can be inserted into solid tissues and organs to permit interstitial imaging of their internal microstructures with micrometer scale resolution and minimal trauma. A novel rotational coupler with a glass capillary tube is also presented that couples light from a rotating single-mode fiber to a stationary one. A prototype needle with a 27-gauge 410-mm outer diameter has been developed and is demonstrated for in vivo imaging. The OCT needle can be integrated with standard excisional biopsy devices and used for OCT-guided biopsy.
      Read Full Article
    19. High resolution imaging of neoplasma using optical coherence tomography (Thesis)

      High resolution imaging of neoplasma using optical coherence tomography (Thesis)
      Diagnostic imaging technologies for the detection of cancer include CT, MRI, ultrasonography, and endoscopy. However, many early neoplastic changes remain beyond their detection limits. A modality capable of imaging at or near the cellular level could detect disease at earlier stages than currently possible and thus improve patient prognosis. Optical coherence tomography (OCT) can achieve resolutions in the cellular and subcellular range (1-15 um) and could improve the diagnostic range of clinical imaging procedures.
      Read Full Article
    20. Forward-imaging instruments for optical coherence tomography

      Forward-imaging instruments for optical coherence tomography
      We discuss the design and implementation of forward-imaging instruments for optical coherence tomography (OCT), which require the delivery, scanning, and collection of single-spatial-mode optical radiation. A hand-held surgical probe for use in open surgery can provide cross-sectional images of subsurface tissue before surgical incisions are made. A rigid laparoscope for minimally invasive surgical OCT imaging provides a simultaneous enface view of the area being imaged. OCT imaging is demonstrated on in vitro human specimens.
      Read Full Article
    1-20 of 20
  1. Categories

    1. Applications:

      Art, Cardiology, Dentistry, Dermatology, Developmental Biology, Gastroenterology, Gynecology, Microscopy, NDE/NDT, Neurology, Oncology, Ophthalmology, Other Non-Medical, Otolaryngology, Pulmonology, Urology
    2. Business News:

      Acquisition, Clinical Trials, Funding, Other Business News, Partnership, Patents
    3. Technology:

      Broadband Sources, Probes, Tunable Sources
    4. Miscellaneous:

      Jobs & Studentships, Student Theses, Textbooks
  2. Topics in the News

    1. (15 articles) University of Cyprus
    2. (5 articles) Massachusetts Institute of Technology
    3. (2 articles) Harvard University
    4. (1 articles) Massachusetts General Hospital
    5. (1 articles) Brigham and Women’s Hospital
    6. (1 articles) Jichi Medical University
    7. (1 articles) Stanford University
    8. (1 articles) University of Florence
    9. (1 articles) Centre Hospitalier Intercommunal de Créteil
    10. (1 articles) University of Montreal
    11. (1 articles) Hanyang University
    12. (1 articles) University of Toronto
    13. (1 articles) Carl Zeiss Meditec
    14. (1 articles) Heidelberg Engineering
  3. Popular Articles

  4. Picture Gallery

    Forward-imaging instruments for optical coherence tomography High resolution imaging of neoplasma using optical coherence tomography (Thesis) Imaging needle for optical coherence tomography Scatterer size-based analysis of optical coherence tomography images using spectral estimation techniques Modulated deconvolution for resolution improvement in Fourier domain optical coherence tomography High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery Fourier domain optical coherence tomography axial resolution improvement with modulated deconvolution Lateral resolution improvement in oversampled Optical Coherence Tomography images assuming weighted oversampled multi-scatterer contributions The truth about invisible posterior vitreous structures The Influence of Eyelid Position and Environmental Conditions on the Corneal Changes in Early Postmortem Interval: A Prospective, Multicentric OCT Study The Use of Optical Coherence Tomography for Gross Examination and Sampling of Fixed Breast Specimens: A Pilot Study The Role of Widefield and Ultra Widefield Optical Coherence Tomography in the Diagnosis and Management of Vitreoretinal Diseases