@inproceedings{10.1117/12.3046222,
author = {Sazgar Burhan and Berenice Schulte and Madita G{\"o}b and Awanish Pratap Singh and Bayan Mustafa and Simon Lotz and Wolfgang Draxinger and Philipp Lamminger and Yasmeine Saker and Tim Eixmann and Martin Ahrens and Marvin Heimke and Tillmann Heinze and Thilo Wedel and Maik Rahlves and Mark Ellrichmann and Robert Huber},
title = {{Switchable lateral resolution real-time MHz-OCT rectoscopy for enhanced colorectal disease diagnosis}},
volume = {13305},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIX},
editor = {Rainer A. Leitgeb and Yoshiaki Yasuno},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1330512},
abstract = {Endoscopic optical coherence tomography (OCT) offers in vivo live visualization of transmural structures with histological resolution, making it a valuable tool in medical imaging. In gastroenterology, OCT endoscopy is particularly advantageous for assessing rectal wall layers, providing superior axial and lateral resolution compared to conventional rectal endoscopic ultrasound. However, the large diameter and uneven colon surface present challenges for comprehensive imaging. Extending the OCT imaging range addresses this issue by enabling a thorough examination of the entire colon, facilitating the detection of surface polyps, tumors, and their infiltration depth. Once these regions of interest are identified, high-resolution imaging becomes essential for detailed evaluation. To meet these demands, this study integrates two different imaging modes, an extended-range mode, and a high-detail mode, within a rigid rectoscope. The extended-range mode enables visualization of deeper structures, while the high-detail mode enhances image quality for precise, contact-based assessments. The system allows seamless, real-time transitions between the modes using a 3.2MHz-OCT system and a fiber‑optic MEMS switch.},
keywords = {Optical Coherence Tomography, Megahertz OCT, Fourier Domain Mode Locking, Three-dimensional image acquisition, Rectal Imaging, Long-Range Imaging, Non-Invasive Diagnostic Imaging, Tumor Assessment},
year = {2025},
doi = {10.1117/12.3046222},
URL = {https://doi.org/10.1117/12.3046222}
}

@article{10.1117/1.JBO.30.3.035002,
author = {Hinnerk Schulz-Hildebrandt and Michael Wang-Evers and Naja Meyer-Schell and Daniel Karasik and Malte J. Casper and Tim Eixmann and Felix Hilge and Reginald Birngruber and Dieter Manstein and Gereon H{\"u}ttmann},
title = {{Optical coherence tomography needle probe for real-time visualization of temperature-induced phase changes within subcutaneous fatty tissue}},
volume = {30},
journal = {Journal of Biomedical Optics},
number = {3},
publisher = {SPIE},
pages = {035002},
abstract = {Significance: Selective cryolipolysis is a widely used aesthetic procedure that cools subcutaneous adipose tissue to temperatures as low as −11°C to induce fat cell destruction. However, real-time monitoring techniques are lacking, limiting the ability to optimize safety and efficacy. Traditional imaging methods either fail to provide adequate penetration depth or lack the resolution necessary for visualizing subcutaneous fatty tissue dynamics.Aim: This paper aims to demonstrate that an optical coherence tomography (OCT) needle probe can be used for real-time observation of temperature-induced changes in subcutaneous fatty tissue, potentially enhancing the assessment and optimization of cryolipolysis procedures.Approach: We developed a side-viewing OCT-based needle probe designed for subcutaneous imaging. The probe consists of a fiber-optic system encased in a transparent, biocompatible polymer catheter with an outer diameter of 900 μm. A 49-degree angled fiber enables imaging, while a piezoelectric scanning system moves the fiber transversely within the catheter. The probe achieves a lateral resolution of <15 μm, a working distance of 600 μm, and a lateral field of view dictated by the scanning system length. OCT imaging was performed on porcine skin with a subcutaneous fat layer >3 cm thick during controlled heating and cooling.Results: OCT imaging revealed increased optical scattering in subcutaneous fatty tissue during cooling, corresponding to the phase transition from liquid to solid. This effect was reversible upon warming, indicating that OCT can dynamically monitor adipocyte crystallization in real time. The observed transition temperatures varied, likely due to differences in lipid composition.Conclusions: OCT-based needle imaging enables direct, high-resolution visualization of adipocyte crystallization, offering a potential tool for optimizing selective cryolipolysis treatments. This technology could improve safety and efficacy by providing real-time feedback on tissue response, facilitating a better understanding of the cooling-induced fat reduction process.},
keywords = {optical coherence tomography, endoscope, fiber probe, cryolipolysis, Optical coherence tomography, Adipose tissue, Tissues, Visualization, Crystallization, Skin, Tissue optics, Scattering, Monochromatic aberrations, Refractive index},
year = {2025},
doi = {10.1117/1.JBO.30.3.035002},
URL = {https://doi.org/10.1117/1.JBO.30.3.035002}
}

@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{10122996,

  author={Latus, Sarah and Grube, Sarah and Eixmann, Tim and Neidhardt, Maximilian and Gerlach, Stefan and Mieling, Robin and Hüttmann, Gereon and Lutz, Matthias and Schlaefer, Alexander},

  journal={IEEE Transactions on Biomedical Engineering}, 

  title={A Miniature Dual-Fiber Probe for Quantitative Optical Coherence Elastography}, 

  year={2023},

  volume={},

  number={},

  pages={1-9},

  doi={10.1109/TBME.2023.3275539}}

@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{Jaeckle2021c,
author = {J{\"{a}}ckle, Sonja and Eixmann, Tim and Matysiak, Florian and Sieren, Malte Maria and Horn, Marco and Schulz-Hildebrandt, Hinnerk and H{\"{u}}ttmann, Gereon and P{\"{a}}tz, Torben},
doi = {doi:10.1515/cdbme-2021-1004},
journal = {Current Directions in Biomedical Engineering},
year = {2021},
number = {1},
pages = {17--20},
title = {{3D Stent Graft Guidance based on Tracking Systems for Endovascular Aneurysm Repair:}},
url = {https://doi.org/10.1515/cdbme-2021-1004},
volume = {7},
}

@article{Cereda-2021,
   author = {Cereda, M G;Parrulli, S;Douven, Y. G. M.;Faridpooya, K;van Romunde, S;Hüttmann, G;Eixmann, T;Schulz-Hildebrandt, H;Kronreif, G;Beelen, M and de Smet, M D.},
   title = {Clinical Evaluation of an Instrument-Integrated OCT-Based Distance Sensor for Robotic Vitreoretinal Surgery},
   journal = {Ophthalmology Science},
   volume = {1(4)},
  
   pages = {100085},
   ISSN = {2666-9145},
   DOI = {https://doi.org/10.1016/j.xops.2021.100085},
  
   year = {2021},
   type = {Journal Article}
}

@article{Jackle2021,
abstract = {Background: In endovascular aneuysm repair (EVAR) procedures, medical instruments are currently navigated with a two-dimensional imaging based guidance requiring X-rays and contrast agent. Methods: Novel approaches for obtaining the three-dimensional instrument positions are introduced. Firstly, a method based on fibre optical shape sensing, one electromagnetic sensor and a preoperative computed tomography (CT) scan is described. Secondly, an approach based on image processing using one 2D fluoroscopic image and a preoperative CT scan is introduced. Results: For the tracking based method, average errors from 1.81 to 3.13 mm and maximum errors from 3.21 to 5.46 mm were measured. For the image-based approach, average errors from 3.07 to 6.02 mm and maximum errors from 8.05 to 15.75 mm were measured. Conclusion: The tracking based method is promising for usage in EVAR procedures. For the image-based approach are applications in smaller vessels more suitable, since its errors increase with the vessel diameter.},
author = {J{\"{a}}ckle, Sonja and Lange, Annkristin and Garcia-Vazquez, Veronica and Eixmann, Tim and Matysiak, Florian and Sieren, Malte Maria and Horn, Marco and Schulz-Hildebrandt, Hinnerk and H{\"{u}}ttmann, Gereon and Ernst, Floris and Heldmann, Stefan and P{\"{a}}tz, Torben and Preusser, Tobias},
doi = {10.1002/rcs.2327},
file = {:Users/schulz-hildebrandt/Documents/Mendeley Desktop/J{\"{a}}ckle et al/International Journal of Medical Robotics and Computer Assisted Surgery/J{\"{a}}ckle et al. - 2021 - Instrument localisation for endovascular aneurysm repair Comparison of two methods based on tracking systems or.pdf:pdf},
issn = {1478596X},
journal = {International Journal of Medical Robotics and Computer Assisted Surgery},
keywords = {2D/3D registration,3D localisation,computer-assisted surgery,electromagnetic tracking system,endovascular procedures,fibre optical shape sensing},
number = {6},
pages = {e2327},
year = {2021},
title = {{Instrument localisation for endovascular aneurysm repair: Comparison of two methods based on tracking systems or using imaging}},
volume = {17}
}

@article{jackle2020,
title = {Three-dimensional guidance including shape sensing of a stentgraft system for endovascular aneurysm repair},
author = {Jäckle,S; Garcia-Vazquez,V; Eixmann, T; Matysiak, F; von Haxthausen,F; Sieren; M m; Schulz-Hildebrandt, H;  H\"{u}ttmann, G; Ernst, F; Kleemann, M and P\"{a}tz, T},
url = {https://doi.org/10.1007/s11548-020-02167-2},

isbn = {1861-6429},
year = {2020},
date = {2020-04-06},
journal = {Int J  Comp Assis Radiology and Surgery},
abstract = {During endovascular aneurysm repair (EVAR) procedures, medical instruments are guided with two-dimensional (2D) fluoroscopy and conventional digital subtraction angiography. However, this requires X-ray exposure and contrast agent is used, and the depth information is missing. To overcome these drawbacks, a three-dimensional (3D) guidance approach based on tracking systems is introduced and evaluated.},
keywords = {HSH},
pubstate = {published},
tppubtype = {article}
}

@proceedings{Horn2019b,
title = {First Steps into Catheter Guidance Including Shape Sensing for Endovascular Aneurysm Repair Procedures},
author = {Marco Horn and Sonja J\"{a}ckle and Felix von Haxthausen and Tim Eixmann and Hinnerk Schulz-Hildebrandt and Gereon H\"{u}ttmann and Juljan Bouchagiar and Florian Matysiak and Mark Kaschwich and Markus Kleemann and Floris Ernst and Ver\'{o}nica Garc\'{i}a-V\'{a}zquez and Torben P\"{a}tz},
doi = {10.1016/J.EJVS.2019.09.091},
issn = {1078-5884},
year  = {2019},
date = {2019-12-13},
journal = {European Journal of Vascular and Endovascular Surgery},
volume = {58},
number = {6},
pages = {e610--e611},
publisher = {W.B. Saunders},
keywords = {Sensing, Fiber},
pubstate = {published},
tppubtype = {proceedings}
}

@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.},
}