Portrait of Dr George Dobre

Dr George Dobre

Senior Lecturer in Applied Optics

About

Dr George Dobre's background is in applied optics and particularly optical coherence tomography (OCT). His main research interests are in areas connected to coherence imaging and sensing. He is leading research into phase-sensitive optical coherence microscopy, swept source design and optical design. 

George contributed to the development of en-face OCT techniques in the 1990s; later, he embarked on further extending the functionality of en-face imaging instruments and demonstrated novel high-resolution optical configurations, devised multi-interferometer configurations and evaluated OCT imaging with adjustable depth resolution.
He was also closely involved in extending the applications of en-face OCT to the study of other tissue and outside the medical field, such as in art conservation. Support from the ARIBA Foundation of the New York Eye and Ear Infirmary enabled him to build and test in 2004 an OCT system with multiple capabilities, enabling the acquisition for the first time of simultaneous OCT and indocyanine green angiography of the living human eye. EPSRC further provided support on research (2006-2009) into broadband devices and particularly noise from broadband supercontinuum sources in OCT.

Research interests

  • Optical coherence tomography
  • Optical design
  • Interferometric sensors
  • Fibre optic sensors

Teaching

George lectures on mathematics, thermodynamics and statistical physics.

Publications

Showing 50 of 108 total publications in the Kent Academic Repository. View all publications.

Article

  • Duma, V. et al. (2015). Handheld scanning probes for optical coherence tomography. Romanian Reports in Physics 67:1346-1358.
    We report the design of two handheld scanning probes for Optical Coherence Tomography (OCT). The probes are equipped with a one-dimensional (1D) galvanometer scanner (GS), offering cross-sectional capabilities with OCT. One of the variants of the probe is tested in the lab, including in vivo on healthy volunteers.
  • Wang, J. et al. (2015). Full-Field Swept Source Master-Slave Optical Coherence Tomography. IEEE Photonics Journal [Online] 7. Available at: http://dx.doi.org/10.1109/JPHOT.2015.2461571.
    We apply the principle of master-slave (MS) interferometry to a full-field swept source optical coherence tomography (OCT) setup equipped with a fast 2-D camera. MS interferometry does not involve Fourier transformations and, therefore, eliminates the need for spectrum data resampling required by the conventional spectral domain OCT. Using this method in a full-field OCT setup, en face images are acquired in vivo from finger skin, Drosophila melanogaster larvae, and pupae, with no spectrum resampling and no mechanical scanning. The signal processing is based on a comparison operation of the shapes of channeled spectra for each camera pixel, with a set of reference signals (masks). In this way, en face OCT images can be obtained with no need for the volumetric assembly and software cutting the en face images from an image volume, which are required by the conventional spectral domain OCT method. We demonstrate that the sensitivity and axial resolution of the MS method in a full-field swept source OCT setup are similar to the values obtained using the conventional Fourier-transformation-based swept source OCT method in a full-field setup. Multiple en face images can be produced in parallel by using multiple stored shapes of channeled spectra for the depths of interest. The full-field MS-OCT method presented here opens the possibility of parallel processing for all image points in a 3-D volume of the object.
  • Nasiriavanaki, M. et al. (2013). Further study on iterative control loop for aberration correction in imaging systems with single mode fibre aperture. Journal of Optoelectronics and Advanced Materials [Online] 15:530-538. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84881304303&partnerID=40&md5=b04007b198279783c2e77620663d01e9.
    An iterative control system was designed for compensation of wavefront aberration utilizing a micromachined deformable mirror through simulated annealing algorithm. 37 elements within a deformable mirror are controlled individually in a closed-loop to maximize the output optical intensity collected in a single mode aperture. In this paper, the design of the control system is explained comprehensively. The effect of the parameters involved on the achievable accuracy, computational load and speed of the algorithm are investigated. The shape of the mirror's surface throughout the runtime of the algorithm is also monitored and analyzed.
  • Cernat, R. et al. (2012). Dual instrument for in vivo and ex vivo OCT imaging in an ENT department. Biomedical Optics Express [Online] 3:3346-3356. Available at: http://dx.doi.org/10.1364/BOE.3.003346.
    A dual instrument is assembled to investigate the usefulness of optical coherence tomography (OCT) imaging in an ear, nose and throat (ENT) department. Instrument 1 is dedicated to in vivo laryngeal investigation, based on an endoscope probe head assembled by compounding a miniature transversal flying spot scanning probe with a commercial fiber bundle endoscope. This dual probe head is used to implement a dual channel nasolaryngeal endoscopy-OCT system. The two probe heads are used to provide simultaneously OCT cross section images and en face fiber bundle endoscopic images. Instrument 2 is dedicated to either in vivo imaging of accessible surface skin and mucosal lesions of the scalp, face, neck and oral cavity or ex vivo imaging of the same excised tissues, based on a single OCT channel. This uses a better interface optics in a hand held probe. The two instruments share sequentially, the swept source at 1300 nm, the photo-detector unit and the imaging PC. An aiming red laser is permanently connected to the two instruments. This projects visible light collinearly with the 1300 nm beam and allows pixel correspondence between the en face endoscopy image and the cross section OCT image in Instrument 1, as well as surface guidance in Instrument 2 for the operator. The dual channel instrument was initially tested on phantom models and then on patients with suspect laryngeal lesions in a busy ENT practice. This feasibility study demonstrates the OCT potential of the dual imaging instrument as a useful tool in the testing and translation of OCT technology from the lab to the clinic. Instrument 1 is under investigation as a possible endoscopic screening tool for early laryngeal cancer. Larger size and better quality cross-section OCT images produced by Instrument 2 provide a reference base for comparison and continuing research on imaging freshly excised tissue, as well as in vivo interrogation of more superficial skin and mucosal lesions in the head and neck patient.
  • Clonda, C. et al. (2010). Time domain OCT in galvano-ceramic fixed partial prostheses investigations. Timisoara Medical Journal [Online] 60:82-85. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349263394&partnerID=40&md5=c7965e9437773ebb74f47e01c90ac017.
    Introduction. The technologic procedures to realise galavano-ceramic fxed partial dentures can lead to aeric inclusions, at various depths in the ceramic layers. These material defects could initiate partial or total fractures in the esthetic parts of the dentures with the detachment of these from the infrastructure. The aim of this study was to use a non-invasive method in order to analize galvano-ceramic fxed partial dentures. Method and the material. Twenty-three units galvano-ceramic fxed dentures have been used for this study (fg.1, 2). 250 slices at an interval of 20 microns each have been created for each investigation. The OCT system employed in this investigation was the one using the 1300 mm wavelength. Results. As a result of OCT investigation of the galvano-ceramic fxed partial prosthesis, various material imperfections of the ceramic mass, situated at the cervical areea, with different volumes and forms, have been identifed. 3D reconstructions were developed from bidimensional image slices. Conclusions. In conclusion, the optical coherent tomography is a non-invasive technique that permits the detection of structural imperfections in the galvano-ceramic fxed partial prosthesis.
  • Stoica, E. et al. (2010). En face optical coherence tomography investigation of pathological dental wear. Timisoara Medical Journal [Online] 60:74-77. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349269075&partnerID=40&md5=634df0c86bb5d1b78204948a797019fa.
    Aim and objectives. Excessive dental wear (pathological attrition and abfractions) is a frequent complication of occlusal overload. Pathological attrition results from mechanical wear during parafunction and is limited to the contacting surfaces of opposing teeth. Abfraction is the pathological loss of cervical hard tooth substance caused by biomechanical loading forces. The present study proposes the microstructural characterization of frontal teeth with pathological dental wear by en face optical coherence tomography (EFOCT). Materials and methods: 42 extracted frontal teeth were investigated using eFOCT. 35 teeth derived from patients with active eccentric bruxism (diagnosed by BiteStrip devices) and presented deep abfractions and variable degrees of occlusal pathological attrition. The other 7 frontal teeth, with a normal morphology of dental crowns, were not exposed to occlusal overload before extraction. The dental samples were investigated using a OCT device operating at 1300 nm (B-scan and C-scan mode). Results. The EFOCT investigation of frontal teeth with a normal morphology revealed a homogeneous structure of the occlusal and cervical enamel. The OCT images obtained from the occlusal overloaded frontal teeth visualized the wedge-shaped loss of cervical enamel and damage in the microstructure of the underlying dentin. The high occlusal forces produced also characteristic pattern of large cracks, which reached the occlusal tooth surface. Conclusions: EFOCT is a useful imaging method for the microstructural characterization of frontal teeth with pathological wear. It allows also the monitoring of the wear process.
  • Marcauteanu, C. et al. (2010). Microstructural characterization of non-carious cervical lesions by en face optical coherence tomography. Timisoara Medical Journal [Online] 60:60-63. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349260059&partnerID=40&md5=c1709628429ba063a8a329990612cee7.
    Non-carious cervical lesions (NCCL) are defned as the loss of tooth substance at the cemento-enamel junction. They are attributed to abrasion, erosion and/or eccentric occlusal overload. In order to evaluate the importance of occlusal factors in the etiology of NCCL, we investigated extracted frontal teeth by en face optical coherence tomography (eFOCT). Materials and methods. 35 frontal teeth, derived from patients with active bruxism and eccentric occlusal interferences, presented early NCCL on the labial surfaces. The other 5 frontal teeth had a normal crown morphology and were not exposed to occlusal overload before extraction. The dental samples were investigated using eFOCT operated in B-scan and C-scan mode. The eFOCT employs a low coherence source at 1300 nm. Results. Frontal teeth with normal crown morphology had a homogeneous microstructure of the cervical hard tissues on eFOCT images. The eFOCT investigation revealed a characteristic pattern of cracks in the area of NCCL of occlusal overloaded frontal teeth. Conclusions. eFOCT is an imaging technique that effectively identifes the microstructural effects of occlusal overload on the cervical hard tissues of frontal teeth.
  • Rominu, M. et al. (2010). Class V cavities diagnostic by en-face optical coherence tomography. the necessity of increasing the scattering for adhesive layer media. Timisoara Medical Journal [Online] 60:39-43. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349295244&partnerID=40&md5=1c4dfb44fbde68978bdf57f814266c94.
    Introduction. For the evaluation of marginal adaptation in class V composite restorations, several methods have been developed. Dye penetration tests, however, are to be the most widely used due to their ease of application and low costs. In previous works, the advantages of using en-face optical coherence tomography investigation in this research direction were demonstrated. The purpose of this study is to underline the need to increase the scattering of the adhesive layers in order to facilitate the imagistic interpretations. Material and Methods. En-face Optical Coherence Tomography was employed to investigate 20 class V cavities samples. Standardized class V cavities, prepared in human extracted teeth, were flled with Premise (Kerr) composite. In 10 samples a normal adhesive (OptiBond Solo Plus) was applied, while in the other 10 both the normal and the improved adhesive were used. The specimens were thermocycled. The interfaces were examined by Optical Coherence Tomography method (OCT) combined with the confocal microscopy (CM). Results. Using the normal adhesive could lead to errors in evaluation of the interfaces between the dental structures and dental fllings, when OCT is employed. However, when an adhesive with an improved scattering was used, the differences between the aeric inclusions and the adhesive layer are obvious. Conclusions. An adhesive with improved scattering properties is recommended in an OCT investigation of microleakage for class V composite restorations.
  • Sinescu, C. et al. (2010). Multiple possibilities in detection of materials defects in ceramic fixed partial prostheses. Numerical simulation and photoelasticity methods employed for evaluation and prognostic. Timisoara Medical Journal [Online] 60:50-55. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349247480&partnerID=40&md5=15302bccaa9ca771359360560eef9f96.
    Introduction. For the evaluation of marginal adaptation in class V composite restorations, several methods have been developed (bacterial penetration, fluid transport, clarification, penetration of radioisotopes, electrochemical methods and gas chromatography). Dye penetration tests (microleakage tests) however, are to be the most widely used due to their ease of application and low costs. Their main disadvantage is that the samples are sectioned. In previous works the advantages of using en face optical coherence tomography investigation in this research direction were demonstrated. The purpose of this study is to increase the scattering of the adhesive layers in order to facilitate the interpretations. Material and Methods. En Face Optical Coherence Tomography was employed to investigate 147 class V cavities samples. Standardized class V cavities, prepared in human extracted teeth, were filled with Premise (Kerr) composite. The specimens were thermo cycled. The interfaces were examined by Optical Coherence Tomography method (OCT) combined with the confocal microscopy. The optical configuration uses two single mode directional couplers with a superluminiscent diode as the source at 1300 nm. The scanning procedure is similar to that used in any confocal microscope, where the fast scanning is en-face (line rate) and the depth scanning is much slower (at the frame rate) Results. Marginal adaptation at the interfaces and gaps inside the composite resin materials were identified by means of optical coherence tomography. Exploration of the recent advances in OCT in terms of different excitation wavelengths and wider bandwidths can lead to state-of-the-art imaging systems in odontology. Conclusion. OCT has numerous advantages which justify its use in the oral cavity in comparison with conventional dental imaging. OCT can achieve the best depth resolution of all known methods (in principle one micron if the source exhibits a sufficiently wide spectrum) and is safe. It is important to use an improved adhesive in order to be spotted on the imaging investigation.
  • Negrutiu, M. et al. (2010). Imaging of defects at the interface of fiber posts restored endodontically treated teeth. Timisoara Medical Journal [Online] 60:29-33. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349247482&partnerID=40&md5=1d0fd363561075a23a47d9687d80073e.
    Clinically, the necessity of placing posts arises when tooth structure is insuffcient to sustain a coronal restoration. The aim of this study was to analyze the adaptation and gap width between fber posts, adhesive luting cement and root canal wall using en face optical coherence tomography (efOCT). Materials and Method: Twenty four extracted single-root canal human teeth were horizontally sectioned at the cemento-enamel junction and instrumented up to a no. 40 master apical fle, 1 mm from the anatomical apex. After the instrumentation was completed, standardized post spaces in all root canals were prepared to a depth of 8 mm, using the manufacturers' corresponding post drill system, and then the posts were cemented, applying a primer/adhesive system and using a dual-cured resin based cement system. After 15 minutes, the specimens were placed in a high-humidity environment at 37°C for 48 hours before the investigation. The interfaces fber posts/adhesive luting cement/root canal wall were investigated using en face optical coherence tomography. Results, Discussions and Conclusions: The efOCT scanning reveals material defects in the adhesive cement between the fber posts and the root canal wall. Those gaps could lead to line fractures in the mentioned interface, with failure of the prosthetic treatment.
  • Meadway, A. et al. (2009). A rapid method of measuring dispersion in low coherence interferometry and optical coherence tomography systems. Journal of Optics A: Pure and Applied Optics [Online] 12:0-0. Available at: http://dx.doi.org/10.1088/2040-8978/12/1/015302.
    A method of using multiple spectral channels to measure dispersion mismatch in optical coherence tomography (OCT) and low coherence interferometry systems is presented. The method is tested on a time domain OCT system in comparison to the measurement of the auto-correlation profile. The method is quicker to implement and is more sensitive than the measurement of the auto-correlation profile.
  • Rosen, R. et al. (2009). Simultaneous OCT/SLO/ICG Imaging. Investigative Ophthalmology and Visual Science [Online] 50:851-860. Available at: http://dx.doi.org/10.1167/iovs.08-1855.
    PURPOSE. To evaluate how information from combined coronal optical coherence tomography (OCT) and confocal laser scanning ophthalmoscopy (SLO) with integrated simultaneous indocyanine green (ICG) dye angiography can be used in the diagnosis of a variety of macular diseases. METHODS. A compact chin-rest-based OCT/confocal imaging system was used to produce the OCT image and excite the fluorescence in the ICG dye. The same eye fundus area can be visualized with coronal (C-scans, en face) OCT and ICG angiography simultaneously. Fast T scanning (transverse scanning, en face) was used to build B- or C-scan OCT images along with confocal SLO views, with and without ICG filtration. The OCT, confocal SLO and ICG fluorescence images were simultaneously presented in a three-screen format. A live mixing channel overlaid the ICG sequence on the coronal OCT slices in a fourth panel for immediate comparison. RESULTS. Thirty eyes were imaged. The pathologic conditions studied included classic and occult neovascular membranes, vascularized RPE detachments, polypoidal choroidal vasculopathy, traumatic choroidal rupture, diabetic maculopathy, central serous retinopathy, and macular drusen. Images were evaluated with special attention toward identifying novel relationships between morphology and function revealed by the superimposition of the studies. CONCLUSIONS. Simultaneous visualization of an en face (coronal, C-scan) OCT image and of an ICG angiogram, displayed side by side and superimposed, permits more precise correlations between late fluorescence accumulation with structures deep to the retinal surface at the retina-choroid interface. The multiplanar scanning also permits immediate B-scan OCT cross-sectional views of regions of abnormal fluorescence. The paper demonstrates the synergy between the two types of studies, functional and anatomic, in providing a more complete view of the pathologic condition.
  • Cernat, R. et al. (2009). Evaluation of effective noise bandwidth for broadband optical coherence tomography operation. Journal of the Optical Society of America A: Optics and Image Science, and Vision [Online] 26:723-731. Available at: http://dx.doi.org/10.1364/JOSAA.26.000723.
    Key noise parameters in optical coherence tomography (OCT) systems employing splitters with a nonflat spectral response are evaluated using a supercontinuum fiber laser source with a spectrum of 450 nm-1700 nm and a time domain OCT architecture based on 1300 nm fiber splitters. The spectral behavior of the splitter leading to balanced detection is measured over a range of 300 nm. Because of spectrally different signals at the balanced detector input a residual excess photon noise term results. A rigorous treatment of this noise term [Appl. Opt. 43, 4802 (2004)] introduced two new quantities that take into account the spectral properties of the coupler. In this report, we have evaluated these two noise bandwidth quantities and comparatively assessed the noise behavior predicted by the classical theory with the theory based on the two new noise bandwidths. We show that under certain operating parameters, the additional excess photon noise is twice that predicted for a coupler with a flat spectral response. © 2009 Optical Society of America.
  • Cernat, R., Dobre, G. and Podoleanu, A. (2009). Two spectral shaping methods of a broadband fibre source for biomedical OCT imaging. Scientific Bulletin- Politehnica University of Bucharest Series a Applied Mathematics and Physics [Online] 71:51-60. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84887679847&partnerID=40&md5=77b5edff143e811ab0d0a836ea142025.
    The authors report two investigation methods into the spectral shaping of an optical broadband source (BBS) to be used in Optical Coherence Tomography (OCT). The BBS spectrum extends from 450 nm to 1750 nm and is selectively used in multiple spectral wavebands. Spectral shaping is performed with: (i) an optical filter unit (a combination of dichroic and bandpass filters at different incident angles) and (ii) a double-pass prism sequence (a cube beam splitter, two equilateral prisms and a metallic mirror) which allow the freedom to select the characteristics of the spectrum (central wavelength, spectral bandwidth). BBS can allow imaging with a depth resolution of 2 μm or better. Such a high depth resolution makes BBS suitable for OCT imaging in embryology, cells culture and eye imaging, investigations which will complement the more traditional fluorescence labelling and confocal imaging.
  • Rosen, R. et al. (2009). Multidimensional en-Face OCT imaging of the retina. Optics Express [Online] 17:4112-4133. Available at: http://dx.doi.org/10.1364/OE.17.004112.
    Fast T-scanning (transverse scanning, en-face) was used to build B-scan or C-scan optical coherence tomography (OCT) images of the retina. Several unique signature patterns of en-face (coronal) are reviewed in conjunction with associated confocal images of the fundus and B-scan OCT images. Benefits in combining T-scan OCT with confocal imaging to generate pairs of OCT and confocal images similar to those generated by scanning laser ophthalmoscopy (SLO) are discussed in comparison with the spectral OCT systems. The multichannel potential of the OCT/SLO system is demonstrated with the addition of a third hardware channel which acquires and generates indocyanine green (ICG) fluorescence images. The OCT, confocal SLO and ICG fluorescence images are simultaneously presented in a two or a three screen format. A fourth channel which displays a live mix of frames of the ICG sequence superimposed on the corresponding coronal OCT slices for immediate multidimensional comparison, is also included. OSA ISP software is employed to illustrate the synergy between the simultaneously provided perspectives. This synergy promotes interpretation of information by enhancing diagnostic comparisons and facilitates internal correction of movement artifacts within C-scan and B-scan OCT images using information provided by the SLO channel. © 2009 Optical Society of America.

Conference or workshop item

  • Dobre, G. (2018). Design considerations for ease of access and maneuverability of OCT imaging platforms in the oral cavity. in: Todea, C., Podoleanu, A. G. H. and Duma, V. -F. eds. Seventh International Conference on Lasers in Medicine. SPIE. Available at: https://doi.org/10.1117/12.2282646.
    With the advent of instruments incorporating elements of confocal microscopy and Optical Coherence Tomography (OCT), optical technologies are steadily gaining usage in a variety of biomedical applications. They offer tissue visualization both at the superficial level and in depth, they operate using non-ionizing radiation at a relatively low cost, and the procedures are easily tolerated by patients. One area of growth for optical imaging is in the oral cavity, which has excellent optical accessibility both for dental tissue and oral mucosa. The need to image features accurately (both as part of oral mapping and as part of investigating the underlying tooth structure) requires producing 3-D volumes with sufficiently good lateral and vertical resolution to allow identification of features of interest. Although a few types of intraoral optical scanners are already successfully commercialized for surface mapping, the examination of optical design considerations that are particular to scanned beam imaging in the oral cavity does highlight particular challenges of interest to both clinicians and optical engineers engaged in designing the next generation of optical instruments.
  • Dobre, G., Duma, V. and Everson, M. (2018). Optimisation of a polygon mirror-based spectral filter for swept source optical coherence tomography (SS-OCT). in: Podoleanu, A. G. H. and Bang, O. eds. Second Canterbury Conference on Optical Coherence Tomography, 2017, Canterbury, United Kingdom. SPIE, p. . Available at: https://doi.org/10.1117/12.2283034.
    Medical imaging using Optical Coherence Tomography (OCT) provides clinicians with 3D, high resolution reconstructions of microscopic structures, in depth. It has been initially developed for ophthalmology, in order to scan the retinas of patients to diagnose illness. The quality of the images depends upon their axial and lateral resolutions and the properties of the light being used. Research using a polygon mirror (PM) as a spectral filter in Swept Source OCT (SS-OCT) has resulted in a variety of different experimental arrangements. Although the application of PM-based SS-OCT sources has been successfully demonstrated, the combination of their components’ fundamental properties and the overall impact they have on imaging performance is rarely reported. A more detailed examination of these properties would lead to a full description of their operation and to the best methods to employ if system performance is to be maximised. This work presents our current findings of on-going research into the optimisation of PM-based SS-OCT systems. A swept source spectral filter, consisting of a collimator, a transmission grating, a two-lens telescope and an off-axis PM with an end reflector mirror has been evaluated experimentally and compared with theoretical predictions. The system’s performance has been compared for two different fibre collimators. Although the beam width on the grating is different for each of the two collimators, the spot size at the PM facet is made the same by selecting appropriate focal lengths. An improvement in the signal roll-off at the interferometer output of ~1.0 dB/mm was obtained when using a 3.4 mm collimator compared to a 1.5 mm collimator.
  • Everson, M., Duma, V. and Dobre, G. (2018). Aspects of vignetting in a polygon mirror-based spectral filter for swept source optical coherence tomography (SS-OCT). in: Todea, C., Podoleanu, A. G. H. and Duma, V. -F. eds. Seventh International Conference on Lasers in Medicine. SPIE. Available at: https://doi.org/10.1117/12.2282284.
    Optical Coherence Tomography (OCT) is a technology capable of producing 3-D volumes of microscopic structures
    with micron-scale resolution. Its main area of application remains ophthalmology and in particular retinal imaging. The
    quality and usability of the images depends upon the frame rate and the properties of the light being used. Swept source
    OCT (SS-OCT) can offer a speed advantage; variants using polygon mirrors (PMs) as spectral filters in SS-OCT have
    resulted in a variety of different arrangements. Although their application has been successfully demonstrated, a more
    detailed study of the particular aspects and requirements of beam propagation through the filter and their overall impact
    on the system performance have not been reported. Examining aspects related to vignetting at the PM facet leads to
    maximizing light throughput and system performance, which is the aim of this work. A swept source spectral filter
    consisting of a transmission grating, a two-lens telescope, an off-axis PM, and an end reflector mirror has been evaluated
    in terms of the beam width at the PM facet and how this parameter varies across the entire width of the spectrum at the
    input of the spectral filter.
  • Everson, M., Duma, V. and Dobre, G. (2017). Geometric & Radiometric Vignetting Associated with a 72-Facet, Off-Axis, Polygon Mirror for Swept Source Optical Coherence Tomography (SS-OCT). in: TIM15-16 Physics Conference. IOP Institute of Physics. Available at: http://dx.doi.org/10.1063/1.4972382.
    Optical Coherence Tomography (OCT) has a broad range of applications in 2D and volumetric imaging of micron scale structures typically used on inaccessible objects such as the retina of the eye. This report focuses on Swept Source OCT (SS-OCT), favoured for its faster scanning speeds and therefore faster data acquisition (highly favourable when imaging live patients). SS-OCT relies on the scanning of a narrow laser line at speeds typically in excess of 100 kHz. We have employed ZemaxTM ray tracing software to simulate one method of splitting the spectrum of a broadband, near-infrared source, into its component wavelengths by reflecting the spectrum from an off-axis, 72-facet polygon mirror at a frequency of 48 kHz. We specifically addressed the geometric and radiometric vignetting associated with the reflected spectrum off an individual mirrored facet and how this may impose limitations to the incident beam size and hence lead to a loss in the power available from the source. It was found that for certain configurations up to 44% of the light was lost at the edges of the spectrum due to both radiometric and geometric vignetting, which may result in an effective swept range of <50 nm from an initial bandwidth of 100 nm. Our simulations account for real refractive errors and losses in the beam caused by lens aberrations, and produce a model of the sampling function of wavelength against time.
  • Everson, M., Duma, V. and Dobre, G. (2017). Optical power transmission in a polygon mirror-based swept source optical coherence tomography system. in: Digital Optical Technologies 2017 Bernard C. Kress; Wolfgang Osten; H. Paul Urbach. Bellingham, USA, pp. 1033520-1033520. Available at: http://dx.doi.org/10.1117/12.2270256.
    Swept Source Optical Coherence Tomography (SS-OCT) relies on the rapid tuning of a broadband light source to produce narrow laser linewidths. Imaging speed is governed by the sweeping frequency of the source and the axial resolution is given by the total bandwidth generated. Mechanical, free space methods, employing rotating polygonal mirrors with a pair of telescopically arranged lenses, can achieve tuning speeds in excess of 100 kHz. Their success relies upon maximising the light throughput of the swept spectrum by reducing the effects of aberration and vignetting caused by the lens design and the geometrical properties of the polygon respectively. However, these properties impose constrictions on the spectral filter’s design and care must be taken when building the filter to avoid unnecessarily limiting the performance of the system. This paper presents some of the initial stages of a much larger study into the optimisation of such systems. Theoretical work has been confirmed by experimental observations and compared with ideal simulations for a spectral filter consisting of a dispersive element, a double lens telescope, arranged in a Littman configuration, and a 72-facet, offaxis polygon mirror with end reflector. A non-linear relationship between the linewidth’s location on the telescope in time with the rotation of the polygon was observed and a first approximation for the tuned wavelength with respect to the polygon rotation angle was found. These observations, coupled with ongoing research, will lead to a complete description of polygon based scanners and how their performance can be optimised in future designs
  • Kress, B. et al. (2017). Optical power transmission in a polygon mirror-based swept source optical coherence tomography system. in: World of photonics congress, digital optical technologies. Society of Photo-optical Instrumentation Engineers, p. . Available at: https://doi.org/10.1117/12.2270256.
    Swept Source Optical Coherence Tomography (SS-OCT) relies on the rapid tuning of a broadband light source to produce narrow laser linewidths. Imaging speed is governed by the sweeping frequency of the source and the axial resolution is given by the total bandwidth generated. Mechanical, free space methods, employing rotating polygonal mirrors with a pair of telescopically arranged lenses, can achieve tuning speeds in excess of 100 kHz. Their success relies upon maximising the light throughput of the swept spectrum by reducing the effects of aberration and vignetting caused by the lens design and the geometrical properties of the polygon respectively. However, these properties impose constrictions on the spectral filter’s design and care must be taken when building the filter to avoid unnecessarily limiting the performance of the system. This paper presents some of the initial stages of a much larger study into the optimisation of such systems.
    Theoretical work has been confirmed by experimental observations and compared with ideal simulations for a spectral filter consisting of a dispersive element, a double lens telescope, arranged in a Littman configuration, and a 72-facet, off-axis polygon mirror with end reflector. A non-linear relationship between the linewidth’s location on the telescope in time with the rotation of the polygon was observed and a first approximation for the tuned wavelength with respect to the polygon rotation angle was found. These observations, coupled with ongoing research, will lead to a complete description of polygon based scanners and how their performance can be optimised in future designs
  • Hu, Y. and Dobre, G. (2017). Performance comparison of spectrometer based and swept source based phase sensitive optical coherence tomography. in: Optical Coherence Imaging Techniques and Imaging in Scattering Media II. Bellingham, USA: SPIE. Available at: http://dx.doi.org/10.1117/12.2279879.
    Spectrometer based and swept source based phase sensitive Fourier Domain OCT systems are compared in terms of the stability of the retrieved signal phase. The spectrometer based system performs with a significantly better phase stability with less uncertainty in the output, whereas the output of the swept source based system is influenced by the jitter noise that creates jumps to the retrieved phase. The experimentally obtained phase traces from the spectrometer based system match well to relevant mathematics.
  • Duma, V. et al. (2016). Handheld scanning probes for Optical Coherence Tomography: Developments, applications and perspectives. in: Todea, C. C., Podoleanu, A. G. H. and Duma, V. -F. eds. Fifth Congress of the World Federation for Laser Dentistry and Sixth International Conference on Lasers in Medicine. Bellingham, Washington, United States: SPIE Society of Photo-Optical Instrumentation Engineers. Available at: http://dx.doi.org/10.1117/12.2178590.
    We present the handheld scanning probes that we have recently developed in our current project for biomedical imaging in general and for Optical Coherence Tomography (OCT) in particular. OCT is an established, but dynamic imagistic technique based on laser interferometry, which offers micrometer resolutions and millimeters penetration depths. With regard to existing devices, the newly developed handheld probes are simple, light and relatively low cost. Their design is described in detail to allow for the reproduction in any lab, including for educational purposes. Two probes are constructed almost entirely from off-the-shelf components, while a third, final variant is constructed with dedicated components, in an ergonomic design. The handheld probes have uni-dimensional (1D) galvanometer scanners therefore they achieve transversal sections through the biological sample investigated - in contrast to handheld probes equipped with bi-dimensional (2D) scanners that can also achieve volumetric (3D) reconstructions of the samples. These latter handheld probes are therefore also discussed, as well as the possibility to equip them with galvanometer 2D scanners or with Risley prisms. For galvanometer scanners the optimal scanning functions studied in a series of previous works are pointed out; these functions offer a higher temporal efficiency/duty cycle of the scanning process, as well as artifact-free OCT images. The testing of the handheld scanning probes in dental applications is presented, for metal ceramic prosthesis and for teeth. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
  • Sinescu, C. et al. (2016). Dentistry investigations of teeth and dental prostheses using OCT. in: Popp, J. et al. eds. Biophotonics: Photonic Solutions for Better Health Care V. Bellingham, Washington, United States: SPIE Society of Photo-Optical Instrumentation Engineers, p. 98870B. Available at: http://doi.org/10.1117/12.2227443.
    We present some of our recent investigations in Dental Medicine using Optical Coherence Tomography (OCT). Time Domain (TD), Spectral Domain (SD), and Swept Source (SS) OCT in-house developed systems are being used, for both ex vivo and in vivo investigations in the oral cavity. We study ex vivo the interface between the tooth and the dental sealant and demonstrate the limitations of the X-rays investigations that are now the gold standard for such procedures. Using OCT, defects in the interface that cannot be identified in radiographs can be determined both as position and magnitude. The drilling process of teeth can also be characterized in real time using OCT, to monitor the remaining dentin thickness (RDT) in order to avoid opening the pulp chamber. We demonstrate in this respect that an RDT of 0.5 mm is the minimum value to assure the integrity of the dentin wall between the drilled cavity and the pulp chamber; at an RDT of 0.3 mm or less a fracture is initiated, the dentin is punctured and endodontic treatment must follow. In vivo OCT investigations in the oral cavity were also performed (i.e., for metalloceramic prostheses and for ceramic inlay tooth interfaces), with the low cost, light weight and versatile handheld probes with 1D galvoscanners that we have developed and applied for a range of in-house developed OCT systems, in various clinical applications. They are briefly discussed, as well as some of our current and future work in the field, including for studies of soft tissue in the mouth. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
  • Duma, V. et al. (2015). Handheld probes and galvanometer scanning for optical coherence tomography. in: Optical Systems Design 2015.. Available at: http://dx.doi.org/10.1117/12.2191130.
    As part of the ongoing effort of the biomedical imaging community to move Optical Coherence Tomography (OCT) systems from the lab to the clinical environment and produce OCT systems appropriate for multiple types of investigations in a medical department, handheld probes equipped with different types of scanners need to be developed. These allow different areas of a patient’s body to be investigated using OCT with the same system and even without changing the patient’s position. This paper reviews first the state of the art regarding OCT handheld probes. Novel probes with a uni-dimensional (1D) galvanometer-based scanner (GS) developed in our groups are presented. Their advantages and limitations are discussed. Aspects regarding the use of galvoscanners with regard to Micro-Electro- Mechanical Systems (MEMS) are pointed out, in relationship with our studies on optimal scanning functions of galvanometer devices in OCT. These scanning functions are briefly discussed with regard to their main parameters: profile, theoretical duty cycle, scan frequency, and scan amplitude. The optical design of the galvoscanner and refractive optics combination in the probe head, optimized for various applications, is considered. Perspectives of the field are pointed out in the final part of the paper. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
  • Duma, V. et al. (2015). Constructive solutions of handheld probes with galvanometer scanners for biomedical and industrial imaging: applications in OCT. in: Optifab.. Available at: http://dx.doi.org/10.1117/12.2195839.
  • Galloway, M., Gabriel, K. and Dobre, G. (2014). Confocal imaging through an endoscopic rod. in: Fifth International Conference on Lasers in Medicine: Biotechnologies Integrated in Daily Medicine. IEEE. Available at: http://www.dx.doi.org/10.1117/12.2045582.
    Endoscopic rods (such as the Hopkins variety) are based on a tubular design containing a sequence of refractive optical structures1. They are intended to offer a wide angle of view but often at the expense of performance in terms of field curvature. They are used in areas of biomedicine that require visualisation of live tissue at the distal end, enabling clinicians to perform a variety of endoscopy procedures including biopsy.

    Here we demonstrate a scanning confocal arrangement with the endoscopic rod used as an optical conduit, guiding the investigation beam to a resolution target placed at the distal end and guiding the backscattered light back to the detector.

    The data presented in this study highlights the possible new contributions of this method to aid Optical Coherence Tomography (OCT) measurements in vivo and what could be expected of its application in terms of scanangle (field of view) and transmission performance
  • Rees, S. and Dobre, G. (2014). Maximum permissible exposure of the retina in the human eye in optical coherence tomography systems using a confocal scanning laser ophthalmoscopy platform. in: Fifth International Conference on Lasers in Medicine: Biotechnologies Integrated in Daily Medicine. IEEE. Available at: http://www.dx.doi.org/10.1117/12.2044819.
    When using scanning laser ophthalmoscopy to produce images of the eye fundus, maximum permissible exposure (MPE) limits must be considered. These limits are set out in international standards such as the National Standards Institute ANSI Z136.1 Safe Use of Lasers (USA) and BS EN 60825-1: 1994 (UK) and corresponding Euro norms but these documents do not explicitly consider the case of scanned beams. Our study aims to show how MPE values can be calculated for the specific case of retinal scanning by taking into account an array of parameters, such as wavelength, exposure duration, type of scanning, line rate and field size, and how each set of initial parameters results in MPE values that correspond to thermal or photochemical damage to the retina. © 2014 Copyright SPIE.
  • Zhou, X. et al. (2013). Effects of fiber bundle on the performance of full-field swept source OCT. in: 5th International Symposium on Photoelectronic Detection and Imaging. SPIE. Available at: http://dx.doi.org/10.1117/12.2035199.
    This paper investigates the effects of fiber bundle on the performance of Full-field swept source OCT (FFSS-OCT) in terms of depth range, depth resolution and transversal resolution. A superfast CMOS camera with full sensor resolution 1024 x 1024 pixels and 60 kHz in maximum frame rate is employed in the testing system. A fiber bundle which contains 18000 single fibers is used to transmit images from interference beam to the camera. Depth range and resolution are assessed by varying optical path difference (OPD) between object arm and reference arm. The operation is repeated under a set of frame rates from 1 kHz to 3 kHz. In addition, an USAF plate is used as a planar object to test transversal resolution. For comparison, above parameters are tested as well with a bulk-optic setup which is built under the same system configuration but without bundle. The results show that the difference between performances of bundle and Bulkoptic setups is not remarkable. As a practical example, 3D profile of a coin is measured using two setups. In sum, this investigation shows that the performance of bundle setup can compete with that of bulk-optic setup in implementing FFSS-OCT. The quantitative results are helpful for researchers to incorporate bundles to FFSS-OCT systems in future. © 2013 SPIE.
  • Tatla, T. et al. (2012). Phantom testing of a novel endoscopic OCT probe: A prelude to clinical in-vivo laryngeal use. in: Optics in Health Care and Biomedical Optics V. Spie-Int Soc Optical Engineering. Available at: http://dx.doi.org/10.1117/12.981713.
    Optical coherence tomography is a novel imaging technique providing potentially high resolution tri-dimensional images of tissue microstructure up to 2-3mm deep. We present pre-clinical data from a novel miniaturised OCT probe utilised for endoscopic imaging of laryngeal mucosa. A 1300nm SS-OCT probe was passed in tandem with a flexible fibreoptic nasoendoscope into the larynx of a manikin. Ex vivo OCT images were acquired using a desktop 1300nm TD-OCT imaging system. The feasibility, robustness and safety of this set-up was demonstrated as a preliminary step to extending the use of this assembly to a clinical patient cohort with varying laryngeal pathologies. © Copyright SPIE.
  • Marcauteanu, C. et al. (2011). Early characterization of occlusal overloaded cervical dental hard tissues by en face optical coherence tomography. in: Optical Coherence Tomography and Coherence Techniques V.. Available at: http://dx.doi.org/10.1117/12.889711.
    Early diagnosis of occlusal overload is an important issue in dental medicine. The high occlusal forces can cause irreversible damage to the dental hard tissues. Our study proposes the early microstructural characterization of occlusal overloaded bicuspids, with abnormal crown morphology, by en face optical coherence tomography (eFOCT). The dental samples were investigated using an eFOCT system operating at 1300 nm in B-scan and C-scan mode. The eFOCT images obtained from these teeth visualized cracks, which didn't reach the tooth surface. The μCT and histological images confirmed the microstructural defects identified on eFOCT images. In conclusion, eFOCT is a promising imaging method for the early diagnosis of occlusal overload on bicuspids with normal crown morphology and for the prophylaxis of dental wear. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
  • Sinescu, C. et al. (2011). Ceramic and Polymeric Dental Onlays Evaluated by Photo elasticity, Optical Coherence Tomography and Micro Computed Tomography. in: Optical Complex Systems. Spie-Int Soc Optical Engineering. Available at: http://dx.doi.org/10.1117/12.896717.
    Dental onlays are restorations used to repair rear teeth that have a mild to moderate amount of decay. They can also be used to restore teeth that are cracked or fractured if the damage is not severe enough to require a dental crown. The use of onlays requires less tooth reduction than does the use of metal fillings. This allows dentists to conserve more of a patient's natural tooth structure in the treatment process. The aims of this study are to evaluate the biomechanical comportment of the dental onlays, by using the 3D photo elasticity method and to investigate the integrity of the structures and their fitting to the dental support. For this optical coherence tomography and micro-computed tomography were employed. Both methods were used to investigate 37 dental onlays, 17 integral polymeric and 20 integral ceramic. The results permit to observe materials defects inside the ceramic or polymeric onlays situate in the biomechanically tensioned areas that could lead to fracture of the prosthetic structure. Marginal fitting problems of the onlays related to the teeth preparations were presented in order to observe the possibility of secondary cavities. The resulted images from the optical coherence tomography were verified by the micro-computed tomography. In conclusion, the optical coherence tomography can be used as a clinical method in order to evaluate the integrity of the dental ceramic and polymeric onlays and to investigate the quality of the marginal fitting to the teeth preparations. © 2011 SPIE.
  • Petrescu, E. et al. (2011). OCT and RX Validation of metal-ceramic crowns repaired with ceramic material. in: Optical Complex Systems. Spie-Int Soc Optical Engineering. Available at: http://dx.doi.org/10.1117/12.896770.
    Objective: Study's objectives are focused on non-invasive OCT and RX investigations, of interfaces obtained after repairing a metal-ceramic crown with ceramic materials. Material and method: In this study 40 metal-ceramic crowns were involved. Each crown is restoring the first central incisor 1.1. Metallic infrastructure was performed from nickel-chrome WIRON 99 BEGO alloy, and Kiss Ceramic. The defects of 3x3mm were created into ceramic material in the buccal-incisal area with a grinding instrument. The samples were divided into two groups and the defects were reconstructed with two different types of ceramic materials: Kiss and Vita Omega. The interfaces between crown and ceramic material used for reparation were Rx and OCT investigated which are both non-invasive, imagistic investigation techniques. For better investigation three-dimensional reconstructions were performed. Results: The interfaces showed defects for both systems used. Major defects such as gaps could be identified at the ceramic-ceramic interface. Also material defects could be observed at the areas of congruence between the two ceramic materials and smaller defects along the interfaces. The defects were present into the deep and superficial layers of interface. The OCT system used a length wave of 1300nm and worked in B-scan mode along the interfaces to be studied while the C-scan mode was only used at the defect areas. Rx investigation detected the macro defects. Conclusions: Time Domain OCT and RX systems were identifying the faulty areas after repairing artificially created defects, of metal-ceramic crowns with ceramic material, hereby enabling us to establish recommendations for the clinical use. © 2011 SPIE.
  • Sinescu, C. et al. (2010). Ceramic veneers integrity investigation by opical coherence tomography and Micro Computer Tomography. in: Applied Computing Conference 2010, ACC'10. pp. 97-101. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-79958758638&partnerID=40&md5=7e464788b39006b663730ca99a0a3341.
    The aim of this study was to analyze the integrity of the ceramic veneers using a noninvasive method like the optical coherence tomography working in Time Domain. The obtained results were validated by Micro Computer Tomography. The conclusions point out the importance of investigation the integrity of every veneer before bonding in into the oral cavity.
  • Marcauteanu, C. et al. (2010). Preliminary optical coherence tomography investigation of the temporo-mandibular joint disc. in: Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XIV.. Available at: http://www.dx.doi.org/10.1117/12.842783.
    Aim and objectives. The morphology and position of the temporo-mandibular disc are key issues in the diagnosis and treatment of arthrogenous temporo-mandibular disorders. Magnetic resonance imaging and arthroscopy are used today to identify: flattening of the pars posterior of the disc, perforation and/or adhesions in the pars intermedia of the disc and disc displacements. The present study proposes the investigation of the temporo-mandibular joint disc by optical coherence tomography (OCT). Material and methods. 8 human temporo-mandibular joint discs were harvested from dead subjects, under 40 year of age, and conserved in formalin. They had a normal morphology, with a thicker pars posterior (2,6 mm on the average) and a thinner pars intermedia (1mm on the average). We investigated the disc samples using two different OCT systems: an en-face OCT (time domain (TD)-OCT) system, working at 1300 nm (C-scan and B-scan mode) and a spectral OCT system (a Fourier domain (FD)-OCT) system , working at 840 nm (B-scan mode). Results. The OCT investigation of the temporo-mandibular joint discs revealed a homogeneous microstructure. The longer wavelength of the TD-OCT offers a higher penetration depth (2,5 mm in air), which is important for the analysis of the pars posterior, while the FD-OCT is much faster. Conclusions: OCT is a promising imaging method for the microstructural characterization of the temporo-mandibular disc. © 2010 Copyright SPIE - The International Society for Optical Engineering.
  • Demjan, E. et al. (2010). Analysis of dental abfractions by optical coherence tomography. in: Lasers in Dentistry XVI; San Francisco.. Available at: http://dx.doi.org/10.1007/978-1-4020-8387-7_145.
    Aim and objectives. Abfraction is the pathological loss of cervical hard tooth substance caused by biomechanical overload. High horizontal occlusal forces result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause microfractures in the dental hard tissues, eventually resulting in the loss of cervical enamel and dentin. The present study proposes the microstructural characterization of these cervical lesions by en face optical coherence tomography (eFOCT). Material and methods: 31 extracted bicuspids were investigated using eFOCT. 24 teeth derived from patients with active bruxism and occlusal interferences; they presented deep buccal abfractions and variable degrees of occlusal pathological attrition. The other 7 bicuspids were not exposed to occlusal overload and had a normal morphology of the dental crowns. The dental samples were investigated using an eFOCT system operating at 1300 nm (B-scan at 1 Hz and C-scan mode at 2 Hz). The system has a lateral resolution better than 5 μm and a depth resolution of 9 μm in tissue. OCT images were further compared with micro - computer tomography images. Results. The eFOCT investigation of bicuspids with a normal morphology revealed a homogeneous structure of the buccal cervical enamel. The C-scan and B-scan images obtained from the occlusal overloaded bicuspids visualized the wedge-shaped loss of cervical enamel and damage in the microstructure of the underlaying dentin. The high occlusal forces produced a characteristic pattern of large cracks, which reached the tooth surface. Conclusions: eFOCT is a promising imaging method for dental abfractions and it may offer some insight on the etiological mechanism of these noncarious cervical lesions.
  • Enescu, M. et al. (2010). Amalgam and composite resin interface investigation by opical coherence tomography. in: European Conference of Systems, ECS'10, European Conference of Circuits Technology and Devices. pp. 316-322. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-79959899201&partnerID=40&md5=1aa1593e9152062da0d6be434574a100.
    The aim of this study was to analyze the interface between the amalgam and composite resin restorations using a noninvasive method like the optical coherence tomography working in Time Domain. The conclusions point out the importance of investigation the integrity of every interface after every direct restoration into the oral cavity.
  • Negrutiu, M. et al. (2010). Root canal filling evaluation using optical coherence tomography. in: Biophotonics: Photonic Solutions for Better Health Care II.. Available at: http://dx.doi.org/10.1117/12.854842.
    Endodontic therapy consists in cleaning and shaping the root canal system, removing organic debris and sealing the intra-canal space with permanent filling materials. The purpose of this study was to evaluate various root canal fillings in order to detect material defects, the marginal adaptation at the root canal walls and to assess the quality of the apical sealing. 21 extracted single-root canal human teeth were selected for this study. We instrumented all roots using NiTi rotary instruments. All canals were enlarged with a 6% taper size 30 GT instrument, 0,5 mm from the anatomical apex. The root canals were irrigated with 5% sodium hypochlorite, followed by 17% ethylenediaminetetraacetic acid (EDTA). After the instrumentation was completed, the root canals were obturated using a thermoplasticizable polymer of polyesters. In order to assess the defects inside the filling material and the marginal fit to the root canal walls, the cone-beam micro-computed tomography (CBμCT) was used first. After the CBμCT investigation, time domain optical coherence tomography working in en face mode (TDefOCT) was employed to evaluate the previous samples. The TDefOCT system was working at 1300 nm and was doubled by a confocal channel at 970 nm. The results obtained by CBμCT revealed no visible defects inside the root-canal fillings and at the interfaces with the root-canal walls. TDefOCT investigations permit to visualize a more complex stratificated structure at the interface filling material/dental hard tissue and in the apical region.
  • Rominu, M. et al. (2010). Adhesive improvement in optical coherence tomography combined with confocal microscopy for class V cavities investigations. in: Medical Imaging 2010: Biomedical Applications in Molecular, Structural, and Functional Imaging.. Available at: http://www.dx.doi.org/10.1117/12.844538.
    The purpose of this study is to present a non invasive method for the marginal adaptation evaluation in class V composite restorations. Standardized class V cavities prepared in human extracted teeth were filled with composite resin (Premise, Kerr). The specimens were thermocycled. The interfaces were examined by Optical Coherence Tomography (OCT) combined with confocal microscopy and fluorescence. The optical configuration uses two single mode directional couplers with a superluminiscent diode as the source at 1300 nm. The scanning procedure is similar to that used in any confocal microscope, where the fast scanning is en-face (line rate) and the depth scanning is much slower (at the frame rate). Gaps at the interfaces as well as on the inside of the composite resin were identified. OCT has numerous advantages that justify its in vivo and in vitro use compared to conventional techniques. One of the main concerns was the fact that at the adhesive layer site it was very hard to tell the adhesive apart from material defects. For this reason the adhesive was optimized in order to be more scattering. This way we could make a difference between the adhesive layer and the material defects that could lead to microleakages. © 2010 Copyright SPIE - The International Society for Optical Engineering.
  • Rominu, M. et al. (2009). A qualitative approach on marginal adaptation of conditioned dental infrastructures using optical coherence tomography. in: 1st International Conference on Manufacturing Engineering, Quality and Production Systems, MEQAPS '09. pp. 255-259. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-75149148219&partnerID=40&md5=af75155d394a36f298f3284786a850d4.
    Ceramic prosthesis performed through additive and subtractive technologies, lead to superior esthetic results towards metal-ceramic prosthesis. Ceramic veneers can be bonded to dental preparations with different types of cement. 100 ceramic veneers were performed on a preparation at the central maxilar incisor. The veneers were treated with different methods for obtaining a superior adhesion to dental structures. The veneers were devided into five groups and treated by (1) sandblasting, (2) sandblasting and then conditioned with HFA 9, 6% (hidrofluoric acid), (3)sandblasting with HFA (hidrofluoric acid) 5, 5%, (4) HFA 9, 6% (hidrofluoric acid), (5) HFA 5, 5% (hidrofluoric acid). After conditioning, the surfaces were investigated by Scanning Electronic Microscopy technology (SEM). The aim of this study was to analyze the quality of marginal adaptation and gap width of Empress veneers using en-face optical coherence tomography. The results prove the importance of investigation the marginal adaptation after every veneer bonding.
  • Sinescu, C. et al. (2009). Marginal adaptation of ceramic veneers investigated with en-face optical coherence tomography. in: European Conference on Biomedical Optics. Optical Society of America. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84898013943&partnerID=40&md5=ff9cf3c646d073e83f48efc376f9cec7.
    The aim of this study was to analyze the quality of marginal adaptation and gap width of Empress veneers using en-face optical coherence tomography. The results prove the necessity of investigating the marginal adaptation after each veneer bonding process.
  • Rominu, M. et al. (2009). Optical coherence tomography combined with confocal microscopy for investigation of interfaces in Class V cavities. in: ARRAY(0x7f1293d270f0).. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-77953308463&partnerID=40&md5=08d2284b189703a798fe9deb6adc66f9.
    Standardized class V cavities, prepared in human extracted teeth, were filled with Premise (Kerr) composite. The specimens were thermo cycled. The interfaces were examined using a system employing two simultaneous imaging channels, an en-face Optical Coherence Tomography channel and a confocal microscopy channel. © 2009 SPIE-OSA.
  • MÇ�rcÇ�uÅ£eanu, C. et al. (2009). Occlusal overload investigations by non invasive technology: Fluorescence microscopy and en - Face optical coherence tomography. in: Education and Training in Optics and Photonics.. Available at: http://dx.doi.org/10.1117/12.831797.
    The aim of this study is the early detection and monitoring of occlusal overload in bruxing patients. En-Face Optical coherence tomography (eF-OCT) and fluorescence microscopy (FM) were used for the imaging of several anterior teeth extracted from patients with light active bruxism. We found a characteristic pattern of enamel cracks, that reached the tooth surface. We concluded that the combination of the en-Face OCT and FM is a promising non-invasive alternative technique for reliable monitoring of occlusal overload. © 2009 SPIE-OSA.
  • Sinescu, C. et al. (2009). Time domain and spectral optical coherence tomography investigations of integral ceramic fixed partial dentures. in: 2nd International Conference on Maritime and Naval Science and Engineering. pp. 77-81. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-74549118895&partnerID=40&md5=13ed1ec843c73aa22487d0a7bbe36059.
    The common investigations methods of fixed partial dentures imply sectioning and metallographic microscopic analysis. These methods could lead to damage of the small dimension material defects. Also these methods are limited to the dimensions of the cutting devices. The method used in this paper is the optical coherent tomography, a non-invasive method, which permits the determinations of materials defects in the ceramic layers depth. Both time domain and spectral methods were used in order to investigate the possibility of materials defects detection. For this study 237 integral ceramic fixed partial dentures were used. For each investigate area 500 slices were obtain and a 3D reconstruction was perform from each stuck. As a conclusion the optical coherent tomography, as a non-invasive method, can be used as a control technique in metalceramic technology. Combining the optical coherence tomography with the confocal microscopy allow to investigate in details the dental structure with a high resolution.
  • Mǎrcǎuţeanu, C. et al. (2009). Early detection of tooth wear by en- face optical coherence tomography. in: ARRAY(0x7f1293d27c18).. Available at: http://www.dx.doi.org/10.1117/12.809828.
    Excessive dental wear (pathological attrition and/or abfractions) is a frequent complication in bruxing patients. The parafunction causes heavy occlusal loads. The aim of this study is the early detection and monitoring of occlusal overload in bruxing patients. En-face optical coherence tomography was used for investigating and imaging of several extracted tooth, with a normal morphology, derived from patients with active bruxism and from subjects without parafunction. We found a characteristic pattern of enamel cracks in patients with first degree bruxism and with a normal tooth morphology. We conclude that the en-face optical coherence tomography is a promising non-invasive alternative technique for the early detection of occlusal overload, before it becomes clinically evident as tooth wear. © 2009 SPIE.
  • Marcauteanu, C. et al. (2009). Occlusal overload investigations by non invasive technology: Fluorescence microscopy and en-face optical coherence tomography. in: European Conference on Biomedical Optics. Optical Society of America. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84897969076&partnerID=40&md5=736f9b4ac75d6de7fe55538b9973800e.
    The aim of this study is the early detection and monitoring of occlusal overload in bruxing patients. En-Face Optical coherence tomography (eF-OCT) and fluorescence microscopy (FM) were used for the imaging of several anterior teeth extracted from patients with light active bruxism. We found a characteristic pattern of enamel cracks, that reached the tooth surface. We concluded that the combination of the en-Face OCT and FM is a promising non-invasive alternative technique for reliable monitoring of occlusal overload.
  • Sinescu, C. et al. (2009). Marginal adaptation of ceramic veneers investigated with en-face optical coherence tomography. in: ARRAY(0x7f1293d2ec80).. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78349301048&partnerID=40&md5=a13b94b0d0316fba8d8880e1e2ad7e39.
    The aim of this study was to analyze the quality of marginal adaptation and gap width of Empress veneers using en-face optical coherence tomography. The results prove the necessity of investigating the marginal adaptation after each veneer bonding process. © 2009 SPIE-OSA.
  • Rominu, M. et al. (2009). Optical coherence tom ography combined with confocal microscopy for investigation of interfaces in class V cavities. in: European Conference on Biomedical Optics. Optical Society of America. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84897977168&partnerID=40&md5=738d98b2e8a2a79ecc22736a53442884.
    Standardized class V cavities, prepared in human extracted teeth, were filled with Premise (Kerr) composite. The specimens were thermo cycled. The interfaces were examined using a system employing two simultaneous imaging channels, an en-face Optical Coherence Tomography channel and a confocal microscopy channel.
  • NegruÅ£iu, M. et al. (2009). En face optical coherence tomography investigation of interface fiber posts/adhesive cement/root canal wall. in: ARRAY(0x7f1293d2c290).. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-78751621879&partnerID=40&md5=d23b6564a1b210859d2a110a99ab6f09.
    This study analyzes the adaptation and gap width between fiber posts, adhesive luting cement and root canal wall using optical coherence tomography. The results prove the importance of assessing the quality of the interface after each process of fiber post luting. © 2009 SPIE-OSA.

Monograph

  • Rosen, R. et al. (2015). En-face Flying Spot {OCT}/Ophthalmoscope. Springer International Publishing. Available at: http://dx.doi.org/10.1007/978-3-319-06419-2_61.
    This is a review of a technique for high-resolution imaging of the eye that allows multiple sample sectioning perspectives with different axial resolutions. The technique involves the flying spot approach employed in confocal scanning laser ophthalmoscopy which is extended to OCT imaging via time domain en face fast lateral scanning. The ability of imaging with multiple axial resolutions stimulated the development of the dual en face OCT–confocal imaging technology. Dual imaging also allows various other imaging combinations, such as OCT with confocal microscopy for imaging the eye anterior segment and OCT with fluorescence angiography imaging.