@inproceedings{10.1117/12.3005413,
author = {Noah Heldt and Cornelia Holzhausen and Martin Ahrens and Mario Pieper and Peter K{\"o}nig and Gereon H{\"u}ttmann},
title = {{Improved image quality in dynamic OCT imaging by reduced imaging time and machine learning based data evaluation}},
volume = {PC12830},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVIII},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {PC128302A},
abstract = {Dynamic Optical Coherence Tomography combines high resolution tomographic imagery with a cell specific contrast by Fourier analysis. However, the conversion from frequency space into RGB images by binning requires a priori knowledge and artifacts due to global movements provide another obstacle for in vivo application.
We could show that an automated binning based on the Neural Gas algorithm can yield the highest spectral contrast without a priori knowledge and that motion artifacts can be reduced with shorter sequence lengths. Imaging murine airways, we observed that even just 6 frames are enough to generate dOCT images without losing important image information.},
keywords = {Dynamic OCT, Optical Coherence Tomography, Airways, Artificial Intelligence},
year = {2024},
doi = {10.1117/12.3005413},
URL = {https://doi.org/10.1117/12.3005413}
}

@article{Singh:24,
author = {Awanish Pratap Singh and Madita G\"{o}b and Martin Ahrens and Tim Eixmann and Berenice Schulte and Hinnerk Schulz-Hildebrandt and Gereon H\"{u}ttmann and Mark Ellrichmann and Robert Huber and Maik Rahlves},
journal = {Opt. Express},
keywords = {Biomedical imaging; Endoscopic imaging; Imaging systems; Optical coherence tomography; Real time imaging; Vertical cavity surface emitting lasers},
number = {4},
pages = {5809--5825},
publisher = {Optica Publishing Group},
title = {Virtual Hall sensor triggered multi-MHz endoscopic OCT imaging for stable real-time visualization},
volume = {32},
month = {Feb},
year = {2024},
url = {https://opg.optica.org/oe/abstract.cfm?URI=oe-32-4-5809},
doi = {10.1364/OE.514636},
abstract = {Circumferential scanning in endoscopic imaging is crucial across various disciplines, and optical coherence tomography (OCT) is often the preferred choice due to its high-speed, high-resolution, and micron-scale imaging capabilities. Moreover, real-time and high-speed 3D endoscopy is a pivotal technology for medical screening and precise surgical guidance, among other applications. However, challenges such as image jitter and non-uniform rotational distortion (NURD) are persistent obstacles that hinder real-time visualization during high-speed OCT procedures. To address this issue, we developed an innovative, low-cost endoscope that employs a brushless DC motor for scanning, and a sensorless technique for triggering and synchronizing OCT imaging with the scanning motor. This sensorless approach uses the motor\&\#x2019;s electrical feedback (back electromotive force, BEMF) as a virtual Hall sensor to initiate OCT image acquisition and synchronize it with a Fourier Domain Mode-Locked (FDML)-based Megahertz OCT system. Notably, the implementation of BEMF-triggered OCT has led to a substantial reduction in image jitter and NURD (\<4 mrad), thereby opening up a new window for real-time visualization capabilities. This approach suggests potential benefits across various applications, aiming to provide a more accurate, deployable, and cost-effective solution. Subsequent studies can explore the adaptability of this system to specific clinical scenarios and its performance under practical endoscopic conditions.},
}

@Article{photonics10060685,
AUTHOR = {Leichtle, Anke and Penxova, Zuzana and Kempin, Thorge and Leffers, David and Ahrens, Martin and König, Peter and Brinkmann, Ralf and Hüttmann, Gereon and Bruchhage, Karl-Ludwig and Schulz-Hildebrandt, Hinnerk},
TITLE = {Dynamic Microscopic Optical Coherence Tomography as a New Diagnostic Tool for Otitis Media},
JOURNAL = {Photonics},
VOLUME = {10},
YEAR = {2023},
NUMBER = {6},
ARTICLE-NUMBER = {685},
URL = {https://www.mdpi.com/2304-6732/10/6/685},
ISSN = {2304-6732},
ABSTRACT = {Hypothesis: Otitis media (OM) can be successfully visualized and diagnosed by dynamic microscopic optical coherence tomography (dmOCT). Background: OM is one of the most common infectious diseases and, according to the WHO, one of the leading health problems with high mortality in developing countries. Despite intensive research, the only definitive treatment of therapy-refractory OM for decades has been the surgical removal of inflamed tissue. Thereby, the intra-operative diagnosis is limited to the surgeon’s visual impression. Supportive imaging modalities have been little explored and have not found their way into clinical application. Finding imaging techniques capable of identifying inflamed tissue intraoperatively, therefore, is of significant clinical relevance. Methods: This work investigated a modified version of optical coherence tomography with a microscopic resolution (mOCT) regarding its ability to differentiate between healthy and inflamed tissue. Despite its high resolution, the differentiation of single cells with mOCT is often impossible. A new form of mOCT termed dynamic mOCT (dmOCT) achieves cellular contrast using micro-movements within cells based on their metabolism. It was used in this study to establish correlative measurements with histology. Results: Using dmOCT, images with microscopic resolution were acquired on ex vivo tissue samples of chronic otitis media and cholesteatoma. Imaging with dmOCT allowed the visualization of specific and characteristic cellular and subcellular structures in the cross-sectional images, which can be identified only to a limited extent in native mOCT. Conclusion: We demonstrated for the first time a new marker-free visualization in otitis media based on intracellular motion using dmOCT.},
DOI = {10.3390/photonics10060685}
}

@inproceedings{10.1117/12.2652955,
author = {Awanish Pratap Singh and Madita G{\"o}b and Martin Ahrens and Tim Eixmann and Hinnerk Schulz-Hildebrandt and Gereon H{\"u}ttmann and Robert Huber and Maik Rahlves},
title = {{Synchronous high-speed OCT imaging with sensor less brushless DC motor and FDML laser in a phase-locked loop}},
volume = {12367},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXVII},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1236703},
abstract = {High-speed endoscopic optical coherence tomography (OCT) imaging in the MHz range has shown great potential in various medical applications ranging from cancer screening to vascular disease monitoring. High-speed imaging always suffers from non-uniform rotational distortion (NURD) due to asynchronous motor rotation with the OCT system. Several research groups have previously attempted to solve this problem, using either an expensive motor with a sensor or numerical correction after data acquisition. However, both techniques pose challenges for practical use. Therefore, in this study, we use an inexpensive sensorless brushless DC motor with a Fourier domain mode-locked (FDML) laser-based MHz OCT system and try to resolve the problem of synchronization using three different modalities, (i) Slave-mode: The FDML frequency serves as a master frequency for the motor, which is phase-locked to the FDML frequency, (ii) Master-mode: The revolution trigger obtained from the motor’s back electromotive force (BEMF) signal serves as a trigger signal for the OCT imaging system, (iii) Both: Fully synchronized setup, where the motor rotation is synchronized with the laser and the imaging system is synchronized with the motor to achieve phase-stable OCT imaging. The first case slightly fluctuates in live preview and imaging due to the absence of a revolution trigger, while the second has varying motor speeds. Therefore, we use the third case to phase-lock the motor with FDML and get a distortion-free live preview and image acquisition. Finally, we demonstrate high-speed SS-OCT structural imaging (at 3.3 MHz A-scan rates) of a finger with a 16 mm diameter probe (at 40,000 rpm).},
keywords = {Optical Coherence Tomography, Endoscopy, FDML , Closed Loop Motor Control, NURD compensation, Brushless DC Motor, Back Electromotive Force},
year = {2023},
doi = {10.1117/12.2652955},
URL = {https://doi.org/10.1117/12.2652955}
}

@article{Musial-2022,
   author = {Musial, G;Kohlfaerber, T;Ahrens, M;Schulz-Hildebrandt, H;Steven, P and Hüttmann, G},
   title = {Dynamic Contrast Microscopic Optical Coherence Tomography As a Novel Method for Assessing Corneal Epithelium During Exposure to Benzalkonium Chloride},
   journal = {Translational Vision Science & Technology},
keywords = {toxicity; optical coherence tomography; benzalkonium chloride},
   volume = {11(5)},

   pages = {28-28},
   ISSN = {2164-2591},
   DOI = {10.1167/tvst.11.5.28},
   url = {https://doi.org/10.1167/tvst.11.5.28},
   year = {2022},
   type = {Journal Article}
}

@article{Kohlfarber2022,
   author = {Kohlfaerber, T;Pieper, M;Münter, M;Holzhausen, C;Ahrens, M;Idel, C;Bruchhage, K-L;Leichtle, A;König, P;Hüttmann, G and Schulz-Hildebrandt, H},
   title = {Dynamic microscopic optical coherence tomography to visualize the morphological and functional micro-anatomy of the airways},
   journal = {Biomedical Optics Express},
   volume = {13 (6)},
   pages = {3211-3223},
   DOI = {10.1364/BOE.456104},
  
   year = {2022},
   type = {Journal Article}
}

@inproceedings{10.1117/12.2578787,

title = {Voice coil based endomicroscopic optical coherence tomography probe for in vivo mucosa examination},

author = {Martin Ahrens and Christian Idel and Peter K\"{o}nig and Gereon H\"{u}ttmann and Hinnerk Schulz-Hildebrandt},

editor = {Guillermo Tearney J M.D. and Thomas D Wang and Melissa J Suter},

url = {https://doi.org/10.1117/12.2578787},

doi = {10.1117/12.2578787},

year  = {2021},

date = {2021-01-01},

booktitle = {Endoscopic Microscopy XVI},

volume = {11620},

publisher = {SPIE},

organization = {International Society for Optics and Photonics},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{10.1117/12.2575733,

title = {Endo-microscopic optical coherence tomography (emOCT) with dynamic contrast},

author = {Hinnerk Schulz-Hildebrandt and Martin Ahrens and Michael M\"{u}nter and Elisa Wilken and Tabea Kohlf\"{a}rber and Cornelia Holzhausen and Peter K\"{o}nig and Gereon H\"{u}ttmann},

editor = {Guillermo Tearney J M.D. and Thomas D Wang and Melissa J Suter},

url = {https://doi.org/10.1117/12.2575733},

doi = {10.1117/12.2575733},

year  = {2021},

date = {2021-01-01},

booktitle = {Endoscopic Microscopy XVI},

volume = {11620},

publisher = {SPIE},

organization = {International Society for Optics and Photonics},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@article{Münter2021,
   author = {M. Münter, M. Pieper, T. Kohlfaerber, E. Bodenstorfer, M. Ahrens, C. Winter, R. Huber, P. König, G. Hüttmann and H. Schulz-Hildebrandt},
   title = {Microscopic optical coherence tomography (mOCT) at 600 kHz for 4D volumetric imaging and dynamic contrast},
   journal = {BiomedOptE},
   volume = {12(10)},
   Keywords = {CMOS cameras,Full field optical coherence tomography,High numerical aperture optics, Image processing,In vivo imaging,Medical imaging,Ag-Huber},
   pages = {6024-6039},
   DOI = {10.1364/BOE.425001},
  
   year = {2021},
   type = {Journal Article}
}

@article{schneider2020,
   author = {Schneider, H.;Ahrens, M.;Strumpski, M.;Ruger, C.;Hafer, M.;Huettmann, G.;Theisen-Kunde, D.;Schulz-Hildebrandt, H. and Haak, R.},
   title = {An Intraoral OCT Probe to Enhanced Detection of Approximal Carious Lesions and Assessment of Restorations},
   journal = {J Clin Med},
   volume = {9(10)},
   keywords = {OCT; intraoral probe; carious lesions; caries diagnosis; dental restorations},
   ISSN = {2077-0383 (Print)
2077-0383 (Linking)},
   DOI = {10.3390/jcm9103257},
   
   year = {2020},
   type = {Journal Article}
}

@article{Münter2020,
   author = {Münter, M;Endt, M v;Pieper, M;Casper, M;Ahrens, M;Kohlfaerber, T;Rahmanzadeh, R;König, P;Hüttmann, G and Schulz-Hildebrandt, H},
   title = {Dynamic contrast in scanning microscopic OCT},
   journal = {Optic Letters},
url = {https://arxiv.org/abs/2003.00006},
   year = {2020},
   type = {Journal Article}
}

@inproceedings{Haak2019,
author = {Haak, Rainer and Ahrens, Martin and Schneider, Hartmut and Strumpski, Michaela and Rueger, Claudia and Haefer, Matthias and H{\"{u}}ttmann, Gereon and Theisen-Kunde, Dirk and Schulz-Hildebrandt, Hinnerk},
booktitle = {Proc. SPIE 11073, Clinical and Preclinical Optical Diagnostics II},
doi = {10.1117/12.2527185},
isbn = {9781510628397},
number = {110730W},
pages = {1--4},
title = {{Handheld OCT probe for intraoral diagnosis on teeth}},
keywords = {OCT,Endoskope},
year = {2019},
}

@article{Schulz-Hildebrandt:18,
author = {Hinnerk Schulz-Hildebrandt and Tom Pfeiffer and Tim Eixmann and Sabrina Lohmann and Martin Ahrens and Joshua Rehra and Wolfgang Draxinger and Peter K\"{o}nig and Robert Huber and Gereon H\"{u}ttmann},
journal = {Opt. Lett.},
keywords = {Fiber optics imaging; Endoscopic imaging; Medical and biological imaging; Optical coherence tomography; Fourier domain mode locking; Image quality; Optical coherence tomography; Single mode fibers; Step index fibers; Three dimensional imaging},
number = {18},
pages = {4386--4389},
publisher = {Optica Publishing Group},
title = {High-speed fiber scanning endoscope for volumetric multi-megahertz optical coherence tomography},
volume = {43},
month = {Sep},
year = {2018},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-43-18-4386},
doi = {10.1364/OL.43.004386},
abstract = {We present a forward-viewing fiber scanning endoscope (FSE) for high-speed volumetric optical coherence tomography (OCT). The reduction in size of the probe was achieved by substituting the focusing optics by an all-fiber-based imaging system which consists of a combination of scanning single-mode fibers, a glass spacer, made from a step-index multi-mode fiber, and a gradient-index fiber. A lateral resolution of 11 $\mu$m was achieved at a working distance of 1.2 mm. The newly designed piezo-based FSE has an outer diameter of 1.6 mm and a rigid length of 13.5 mm. By moving the whole imaging optic in spirals for scanning the sample, the beam quality remains constant over the entire field of view with a diameter of 0.8 mm. The scanning frequency was adjusted to 1.22 kHz for use with a 3.28 MHz Fourier domain mode locked OCT system. Densely sampled volumes have been imaged at a rate of 6 volumes per second.},
}

@inproceedings{Schulz-Hildebrandt2018a,
title = {Coherence and diffraction limited resolution in microscopic OCT by a unified approach for the correction of dispersion and aberrations},
author = {Schulz-Hildebrandt,H; M\"{u}nter, M; Ahrens,M; Spahr, H; Hillmann, D; K\"{o}nig, P and  H\"{u}ttmann, G},
doi = {10.1117/12.2303755},
isbn = {9781510616745},
year = {2018},
date = {2018-03-05},
booktitle = {2nd Canterbury Conference on OCT with Emphasis on Broadband Optical Sources},
volume = {10591},
pages = {105910O},
abstract = {Optical coherence tomography (OCT) images scattering tissues with 5 to 15 μm resolution. This is usually not sufficient for a distinction of cellular and subcellular structures. Increasing axial and lateral resolution and compensation of artifacts caused by dispersion and aberrations is required to achieve cellular and subcellular resolution. This includes defocus which limit the usable depth of field at high lateral resolution. OCT gives access the phase of the scattered light and hence correction of dispersion and aberrations is possible by numerical algorithms. Here we present a unified dispersion/aberration correction which is based on a polynomial parameterization of the phase error and an optimization of the image quality using Shannon’s entropy. For validation, a supercontinuum light sources and a costume-made spectrometer with 400 nm bandwidth were combined with a high NA microscope objective in a setup for tissue and small animal imaging. Using this setup and computation corrections, volumetric imaging at 1.5 μm resolution is possible. Cellular and near cellular resolution is demonstrated in porcine cornea and the drosophila larva, when computational correction of dispersion and aberrations is used. Due to the excellent correction of the used microscope objective, defocus was the main contribution to the aberrations. In addition, higher aberrations caused by the sample itself were successfully corrected. Dispersion and aberrations are closely related artifacts in microscopic OCT imaging. Hence they can be corrected in the same way by optimization of the image quality. This way microscopic resolution is easily achieved in OCT imaging of static biological tissues.},
keywords = {OCM},
pubstate = {published},
tppubtype = {inproceedings}
}

@article{schulz2018novel,
title = {Novel endoscope with increased depth of field for imaging human nasal tissue by microscopic optical coherence tomography},
author = {Schulz-Hildebrandt, H; Pieper, M; Stehmar,C; Ahrens, M; Idel, C; Wollenberg,B; K\"{o}nig,P and Gereon H\"{u}ttmann},
editor = {Optic Socie Amer},
url = {https://www.osapublishing.org/abstract.cfm?URI=boe-9-2-636
https://www.osapublishing.org/boe/viewmedia.cfm?uri=boe-9-2-636&seq=0},
doi = {10.1364/BOE.9.000636},
isbn = {10.1364/BOE.9.000636},
year = {2018},
date = {2018-01-16},
journal = {Biomedical Optics Express},

pages = {636-647},
abstract = {Intravital microscopy (IVM) offers the opportunity to visualize static and dynamic changes of tissue on a cellular level. It is a valuable tool in research and may considerably improve clinical diagnosis. In contrast to confocal and non-linear microscopy, optical coherence tomography (OCT) with microscopic resolution (mOCT) provides intrinsically cross-sectional imaging. Changing focus position is not needed, which simplifies especially endoscopic imaging. For in-vivo imaging, here we are presenting endo-microscopic OCT (emOCT). A graded-index-lens (GRIN) based 2.75 mm outer diameter rigid endoscope is providing 1.5 \textendash 2 μm nearly isotropic resolution over an extended field of depth. Spherical and chromatic aberrations are used to elongate the focus length. Simulation of the OCT image formation, suggests overall a better image quality in this range compared to a focused Gaussian beam. Total imaging depth at a reduced sensitivity and lateral resolution is more than 200 μm. Using a frame rate of 80 Hz cross-sectional images of concha nasalis were demonstrated in humans, which could resolve cilial motion, cellular structures of the epithelium, vessels and blood cells. Mucus transport velocity was determined successfully. The endoscope may be used for diagnosis and treatment control of different lung diseases like cystic fibrosis or primary ciliary dyskinesia, which manifest already at the nasal mucosa.},
keywords = {Endoskope, OCM},
pubstate = {published},
tppubtype = {article}
}