Stefan Ploner

Stefan Ploner, M. Sc.

Researcher

Department of Computer Science
Chair of Computer Science 5 (Pattern Recognition)

Room: Room 09.130
Martensstr. 3
91058 Erlangen
VISTA showing neovascularization having slow flow in PDR case
VISTA revealing slower blood flow in neovascularization (top-left of FAZ) in a motion-corrected OCTA scan of a 30 y/o PDR patient.

Measurement of blood flow speeds in retinal capillaries

In 2015, when OCT angiography was just being commercialized to map the structure of the retinal vasculature, I developed the first method for plexus-specific visualization of blood flow speed accross full-size enface OCT angiography images, Variable Interscan Time Analysis (VISTA) visualization [1]. The method was patented, orally presented at the ARVO annual meeting 2016 in front of an audience of ~1000 experts, and has attracted the attention of several research groups worldwide.

Setting out for new frontiers in high resolution OCT image analysis based on the
Motion Correction and Volume Reconstruction in OCT framework (MoReOCT)

Especially OCT images from elderly subjects suffer from low SNR, as well as image artifacts like opacities, eye motion, and optical distortions. I developed a unique framework for automatic artifact correction and image enhancement. Multiple OCT scans are seamlessly fused within seconds, reaching unprecedented image qualities. Longitudinal data can be compared at the pixel scale. Working together with collaboration partners and students, my method set the basis for the first in-vivo topograhpic mapping and quantification of basal laminar deposits [2], a potential early biomarker in age-related macular degeneration, the most widespread blinding eye disease among the elderly. Furthermore, the framework unvealed a subband below the external limiting membrane, which was not imaged in-vivo before, and allowed its association with age-related ocular alterations [3].

Collaborations with pioneering international experts

MoReOCT-based volume fusion unvealed a new retinal subband below the ELM.

I’m in close collaboration with the Biomedical Optical Imaging and Biophotonics Group at the Massachusetts Institute of Technology, the group who built the first and continues to develop most advanced ophthalmic OCT systems to date. Our joint developments are transferred to clinical application at the New England Eye Center, the first clinic that used OCT technology in patient care. Together with researchers at the Center for Ophthalmic Optics & Lasers at the Oregon Health and Science University, joint investigations are performed in new imaging technologies.

My work is extensively evaluated on clinical data, was presented at international conferences like MICCAI, ISBI, and the ARVO annual meeting [4-6], including multiple oral presentations, and was awarded with an Editor’s Pick from the Editors of Biomedical Optics Express, a journal curated by leading OCT experts. Furthermore, I contributed a chapter on motion correction and volume fusion to the upcoming third edition of the book Optical Coherence Tomography.

Selected references:
[1] Retina, 2016. [2] IOVS, 2024. [3] TVST, 2025. [4] MICCAI, 2022. [5] ISBI, 2023. [6] ARVO, 2024.

Academic CV

Since 07/2017: PhD Student, Pattern Recognition Lab, Friedrich-Alexander University Erlangen-Nürnberg

  • Research focus on motion correction and enhanced signal reconstruction in the field
    of Optical Coherence Tomography (OCT) and OCT angiography (OCTA)
  • In collaboration with the Biomedical Optical Imaging and Biophotonics Group, MIT
  • Published first-authored articles at MICCAI, ISBI and in Biomedical Optics Express
  • Developed the image processing methods that enabled clinical studies published in IOVS and TVST
  • Journal reviewer for BOE, OE, IOVS, TVST, MedPhys, JBio, JBO, Optics Letters, and others

10/2014 – 05/2017: Master of Science with distinction in Computer Science, Friedrich-Alexander University Erlangen-Nürnberg

  • Focus on medical image processing, pattern recognition and high-performance computing
  • Master thesis: Improving 3D OCT motion correction (oral presentation at the ARVO annual meeting)

10/2015 – 05/2016: Visiting student, Massachusetts Institute of Technology, Cambridge, USA

04/2011 – 03/2015: Bachelor of Science in Computer Science, Friedrich-Alexander University Erlangen-Nürnberg

  • Focus on pattern recognition, computer architecture, discrete optimization and computer graphics
  • Student research assistant at the Pattern Recognition Lab, research on false
    color visualization in the multispectral imaging software framework Gerbil

Teaching Experience

  • 10/2014 – 01/2015: Student teaching assistant, Friedrich-Alexander University Erlangen-Nürnberg
    • Exercises in Theory of Computation and Formal Languages
  • 10/2011 – 09/2012: Student teaching assistant, Friedrich-Alexander University Erlangen-Nürnberg
    • Exercises in Algorithms and Data Structures

Awards

  • Article among the ~5% featured as Editor’s pick in the journal Biomedical Optics Express
  • ARVO international travel grant 2021
  • Recognized as “exceptional reviewer” by the journals IOVS and TVST
  • Graduation price from the German Physical Society for exceptional results in the high school final exam (Abitur)

International talks & invited lectures

  • Advanced 3D image fusion for volumetric analysis of subtle features in retinal OCT
    2024, Casey Eye Institute, Oregon Health and Science University, Portland, OR
  • A Spatiotemporal Illumination Model for 3D Image Fusion in Optical Coherence Tomography
    IEEE International Symposium on Biomedical Imaging 2023, Cartagena, Colombia
  • A Spatiotemporal Model for Precise and Efficient Fully-automatic 3D Motion Correction in OCT
    MICCAI main conference contribution presented at the Workshop on Biomedical Image Registration 2022, Singapore
  • 3-D OCT Motion Correction Efficiently Enhanced with OCT Angiography
    ARVO annual meeting 2018, Honolulu, Hawaii
  • Toward quantitative OCT angiography: Visualizing flow impairment using variable interscan time analysis (VISTA)
    ARVO annual meeting 2016, Ballroom A, B & C, Washington State Convention Center, Seattle, WA

Projects

2022

  • Temporally resolved 3-D retinal blood flow quantification using advanced motion correction and signal reconstruction in optical coherence tomography angiography

    (Third Party Funds Single)

    Term: since November 15, 2022
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    Abstract

    Die optische Kohärenztomographie (OCT) erzeugt volumetrische 3-D-Bilder von Gewebe mit Mikrometerauflösung, indem sie einen Laserstrahl zum Scannen verwendet und die Amplitude und Zeitverzögerung von zurückgestreutem Licht misst. Die OCT hat einen großen Einfluss auf die Augenheilkunde und wurde zu einer Standard-Bildgebungsmodalität für die Diagnose, die Überwachung des Krankheitsverlaufs und das Ansprechen auf die Behandlung sowie für die Untersuchung der Pathogenese von Krankheiten wie diabetischer Retinopathie, altersbedingter Makuladegeneration und Glaukom. Die jüngste Entwicklung der OCT-Angiographie (OCTA) hat die grundlegende und klinische Forschung dramatisch beschleunigt. OCTA führt eine tiefenaufgelöste (3-D) Bildgebung der retinalen Mikrovaskulatur durch, indem es wiederholt die gleiche Netzhautposition abbildet und den Bewegungskontrast von sich bewegenden Blutzellen erkennt. Im Vergleich zu herkömmlichen Ansätzen, die auf injizierten Kontrastmitteln basieren, hat OCTA den Vorteil, dass es nicht invasiv ist, sodass die Bildgebung bei jedem Patientenbesuch durchgeführt werden kann, was Längsschnittstudien ermöglicht. Allerdings hat OCTA auch einige Einschränkungen. Da eine wiederholte Bildgebung erforderlich ist, um den Blutfluss zu erkennen, sind die Aufnahmezeiten lang und die Daten können durch Augenbewegungen und Bildartefakte verzerrt werden, was eine quantitative Längsschnittanalyse erschwert. OCTA-Algorithmen können das Vorhandensein eines Blutflusses erkennen, sind jedoch nur begrenzt in der Lage, subtile Veränderungen des Flusses aufzulösen, die frühe Anzeichen einer Krankheit sein können. Zeitliche Schwankungen des Flusses, die durch den Herzzyklus oder die funktionelle Reaktion der Netzhaut verursacht werden, sind schwer zu untersuchen. Wir schlagen vor, ein neues Framework für OCTA zu entwickeln, das eine Bewegungskorrektur auf Kapillarebene ermöglicht, Blutflussgeschwindigkeiten differenziert und eine Analyse auf mehreren Zeitskalen ermöglicht (4-D OCTA). Die Fähigkeit, über die Visualisierung der Mikrovaskulatur hinauszugehen und den Fluss und seine zeitlichen Schwankungen zu beurteilen, ermöglicht die Beurteilung subtiler Beeinträchtigungen der mikrovaskulären Perfusion sowie des Herzzyklus und der Reaktion auf funktionelle Stimulation. In Kombination mit der vaskulären strukturellen Bildgebung versprechen diese Fortschritte, neue Krankheitsmarker in früheren Krankheitsstadien bereitzustellen, eine genauere Messung des Krankheitsverlaufs und des Ansprechens auf die Therapie in pharmazeutischen Studien zu ermöglichen und zur Aufklärung der Pathogenese bei Netzhauterkrankungen beizutragen.

2017

  • Joint Iterative Reconstruction and Motion Compensation for Optical Coherence Tomography Angiography

    (Third Party Funds Single)

    Term: August 1, 2017 - July 31, 2019
    Funding source: DFG-Einzelförderung / Sachbeihilfe (EIN-SBH)
    Abstract

    Optical coherence tomography (OCT) is a non-invasive 3-D optical imagingmodality that is a standard of care in ophthalmology [1,2]. Since the introduction of Fourier-domain OCT [3], dramatic increases in imaging speedbecame possible, enabling 3-D volumetric data to be acquired. Typically, aregion of the retina is scanned line by line, where each scanned lineacquires a cross-sectional image or a B-scan. Since B-scans are acquiredin milliseconds, slices extracted along a scan line, or the fast scanaxis, are barely affected by motion. In contrast, slices extractedorthogonally to scan lines, i. e. in slow scan direction, areaffected by various types of eye motion occurring throughout the full,multi-second volume acquisition time. The most relevant types of eyemovements during acquisition are (micro-)saccades, which can introducediscontinuities or gaps between B-scans, and slow drifts, which causesmall, slowly changing distortion [4]. Additional eye motion is caused by pulsatile blood flow,respiration and head motion. Despite ongoing advances in instrumentscanning speed [5,6] typical volume acquisition times havenot decreased. Instead, the additional scanning speed is used for densevolumetric scanning or wider fields of view [7]. OCT angiography (OCTA) [8–11] multiplies therequired number of scans by at least two, and even more scans are neededto accommodate recent developments in blood flow speed estimation whichare based on multiple interscan times [12,13]. As a consequence,there is an ongoing need for improvement in motion compensation especiallyin pathology [14–16].

    We develop novel methods for retrospective motion correction of OCT volume scans of the anterior and posterior eye, and widefield imaging. Our algorithms are clinically usable due to their suitability for patients with limited fixation capabilities and increased amount of motion, due to their fast processing speed, and their high accuracy, both in terms of alignment and motion correction. By merging multiple accurately aligned scans, image quality can be increased substantially, enabling the inspection of novel features.

Publications

2024

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2023

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2022

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2021

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2020

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2019

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2018

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2017

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2016

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