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Al-Hafeez Z Dhalla

Al-Hafeez Z Dhalla

Assistant Research Professor in the Department of Biomedical Engineering
Biomedical Engineering
PO Box 90281, Durham, NC 27708-0281
101 Science Drive, Fciemas 2574A, Durham, NC 27708-0281

Selected Publications

New Directions for Ophthalmic OCT - Handhelds, Surgery, and Robotics.

Journal Article Transl Vis Sci Technol · January 2, 2025 The introduction of optical coherence tomography (OCT) in the 1990s revolutionized diagnostic ophthalmic imaging. Initially, OCT's role was primarily in the adult ambulatory ophthalmic clinics. Subsequent advances in handheld form factors, integration into ... Full text Link to item Cite

Optical clearing with tartrazine enables deep transscleral imaging with optical coherence tomography.

Journal Article J Biomed Opt · December 2024 SIGNIFICANCE: Imaging deep structures with optical coherence tomography (OCT) is difficult in highly scattering biological tissue, such as the sclera. There is a need to visualize the suprachoroidal space and choroid through the sclera to study suprachoroi ... Full text Link to item Cite

Line-scan phase-resolved synthetic wavelength LiDAR using an off-axis holographic approach.

Journal Article Optics letters · October 2024 We demonstrate a novel, to our knowledge, approach for phase-resolved coherent 3D surface imaging that utilizes synthetic wavelength phase-based ranging and line-scan off-axis holography. Our proof-of-concept system employs an akinetic tunable laser to per ... Full text Cite

Spiral scanning improves subject fixation in widefield retinal imaging.

Journal Article Opt Lett · May 1, 2024 Point scanning retinal imaging modalities, including confocal scanning light ophthalmoscopy (cSLO) and optical coherence tomography, suffer from fixational motion artifacts. Fixation targets, though effective at reducing eye motion, are infeasible in some ... Full text Link to item Cite

Shot-noise limited optical hybrid based on fused fiber couplers.

Journal Article Optics letters · January 2024 We describe a fiber-based coherent receiver topology which utilizes intrinsic phase shifts from fiber couplers to enable instantaneous quadrature projection with shot-noise limited signal-to-noise ratio (SNR). Fused 3 × 3 fiber couplers generate three phas ... Full text Cite

Hybrid spiral scanning in a double-clad fiber-based handheld confocal scanning light ophthalmoscope.

Journal Article Biomed Opt Express · October 1, 2023 High-speed, accessible, and robust in vivo imaging of the human retina is critical for screening of retinal pathologies, such as diabetic retinopathy, age-related macular degeneration, and others. Scanning light ophthalmoscopy (SLO) is a retinal imaging mo ... Full text Link to item Cite

Methods for real-time feature-guided image fusion of intrasurgical volumetric optical coherence tomography with digital microscopy.

Journal Article Biomed Opt Express · July 1, 2023 4D-microscope-integrated optical coherence tomography (4D-MIOCT) is an emergent multimodal imaging technology in which live volumetric OCT (4D-OCT) is implemented in tandem with standard stereo color microscopy. 4D-OCT provides ophthalmic surgeons with man ... Full text Link to item Cite

Visualization of surgical maneuvers using intraoperative real-time volumetric optical coherence tomography.

Journal Article Biomed Opt Express · July 1, 2023 Ophthalmic microsurgery is traditionally performed using stereomicroscopes and requires visualization and manipulation of sub-millimeter tissue structures with limited contrast. Optical coherence tomography (OCT) is a non-invasive imaging modality that can ... Full text Link to item Cite

Quantitative measurements of intraocular structures and microinjection bleb volumes using intraoperative optical coherence tomography.

Journal Article Biomed Opt Express · January 1, 2023 Intraoperative optical coherence tomography (OCT) systems provide high-resolution, real-time visualization and/or guidance of microsurgical procedures. While the use of intraoperative OCT in ophthalmology has significantly improved qualitative visualizatio ... Full text Link to item Cite

Dual modality handheld adaptive optics optical coherence tomography probe for in vivo 3-D photoreceptor imaging

Conference Progress in Biomedical Optics and Imaging - Proceedings of SPIE · January 1, 2023 Adaptive optics optical coherence tomography (AO-OCT) has allowed for the reliable 3-D imaging of individual retinal cells. The current AO-OCT systems are limited to tabletop implementation due to their size and complexity. This work describes the design a ... Full text Cite

Real-time wide-field spectral-scanning FMCW coherent 3D imaging and velocimetry

Journal Article Optics Letters · August 15, 2022 We present a real-time spectral-scanning frequencymodulated continuous wave (FMCW) 3D imaging and velocimetry system that can produce 3D depth maps at 33 Hz, with 48°×68° field of view (FOV) and 32.8-cm depth range. Each depth map consists of 507×500 pixel ... Full text Cite

Computational 3D microscopy with optical coherence refraction tomography.

Journal Article Optica · June 20, 2022 Optical coherence tomography (OCT) has seen widespread success as an in vivo clinical diagnostic 3D imaging modality, impacting areas including ophthalmology, cardiology, and gastroenterology. Despite its many advantages, such as high sensitivity, speed, a ... Full text Link to item Cite

Video-rate high-precision time-frequency multiplexed 3D coherent ranging.

Journal Article Nature communications · March 2022 Frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) is an emerging 3D ranging technology that offers high sensitivity and ranging precision. Due to the limited bandwidth of digitizers and the speed limitations of beam steering us ... Full text Cite

Real-time wide-FOV spectral-scanning FMCW 3D imaging and velocimetry

Conference Optics InfoBase Conference Papers · January 1, 2022 We present a novel spectral-scanning FMCW 3D imaging and velocimetry system that can produce 3D depth maps of 507 × 500 pixels at 33 Hz, with 48° × 68° FOV and 32.8 cm depth range. ... Cite

High-speed multiview imaging approaching 4pi steradians using conic section mirrors: Theoretical and practical considerations

Journal Article Journal of the Optical Society of America A: Optics and Image Science, and Vision · December 1, 2021 Illuminating or imaging samples from a broad angular range is essential in a wide variety of computational 3D imaging and resolution-enhancement techniques, such as optical projection tomography, optical diffraction tomography, synthetic aperture microscop ... Full text Cite

Development of a Preclinical Laser Speckle Contrast Imaging Instrument for Assessing Systemic and Retinal Vascular Function in Small Rodents.

Journal Article Translational vision science & technology · August 2021 PurposeTo develop and test a non-contact, contrast-free, retinal laser speckle contrast imaging (LSCI) instrument for use in small rodents to assess vascular anatomy, quantify hemodynamics, and measure physiological changes in response to retinal ... Full text Cite

Unified k-space theory of optical coherence tomography

Journal Article Advances in Optics and Photonics · January 1, 2021 We present a general theory of optical coherence tomography (OCT), which synthesizes the fundamental concepts and implementations of OCT under a common 3D k-space framework. At the heart of this analysis is the Fourier diffraction theorem, which relates th ... Full text Cite

Incoherent 3D k-space synthesis with volumetric optical coherence refraction tomography

Conference Optics InfoBase Conference Papers · January 1, 2021 We present 3D optical coherence refraction tomography (OCRT), which incoherently synthesizes an extended 3D transfer function using multi-view OCT volumes spanning two angular dimensions. Our setup features a novel use of parabolic mirrors, achieving milli ... Cite

Theory of optical coherence tomography

Chapter · January 1, 2015 Several previous publications have addressed the theory of optical coherence tomography (OCT) imaging. These have included original articles, reviews, and books/book chapters. Many of these publications were authored before the major revolution that Fourie ... Full text Cite

Coherence revival multiplexed, buffered swept source optical coherence tomography: 400 kHz imaging with a 100 kHz source.

Journal Article Optics letters · July 2014 The effective speed of a swept source optical coherence tomography (SSOCT) imaging system was quadrupled using efficient sweep buffering along with coherence revival and spatial multiplexing. A polarizing beam splitter and fold mirror assembly were used to ... Full text Cite

Enhanced vitreous imaging in healthy eyes using swept source optical coherence tomography.

Journal Article PloS one · January 2014 PurposeTo describe enhanced vitreous imaging for visualization of anatomic features and microstructures within the posterior vitreous and vitreoretinal interface in healthy eyes using swept-source optical coherence tomography (SS-OCT). The study h ... Full text Cite

Optimization of confocal scanning laser ophthalmoscope design.

Journal Article Journal of biomedical optics · July 2013 Confocal scanning laser ophthalmoscopy (cSLO) enables high-resolution and high-contrast imaging of the retina by employing spatial filtering for scattered light rejection. However, to obtain optimized image quality, one must design the cSLO around scanner ... Full text Cite

Blood flow velocity quantification using splitspectrum amplitude-decorrelation angiography with optical coherence tomography

Journal Article Biomedical Optics Express · January 1, 2013 The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was recently developed as a method for imaging blood flow in the human retina without the use of phase information. In order to enable absolute blood velocity quantification, in vitro ... Full text Cite

Simultaneous swept source optical coherence tomography of the anterior segment and retina

Journal Article Biomedical Optics, BIOMED 2012 · December 1, 2012 We report on the implementation of swept source optical coherence tomography for simultaneous imaging of the anterior segment and retina. The system achieves depth-encoding by coherence revival heterodyning and a polarization-encoded sample arm. © OSA 2012 ... Cite

Efficient sweep buffering in swept source optical coherence tomography using a fast optical switch.

Journal Article Biomedical optics express · December 2012 We describe a novel buffering technique for increasing the A-scan rate of swept source optical coherence tomography (SSOCT) systems employing low duty cycle swept source lasers. This technique differs from previously reported buffering techniques in that i ... Full text Cite

Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival.

Journal Article Opt Lett · June 1, 2012 We report on an implementation of coherence revival-based heterodyne swept source optical coherence tomography that is capable of simultaneously imaging the anterior and posterior eye. A polarization-encoded sample arm was used to efficiently focus orthogo ... Full text Link to item Cite

Complex conjugate resolved heterodyne swept source optical coherence tomography using coherence revival.

Journal Article Biomedical optics express · March 2012 We describe a simple and low-cost technique for resolving the complex conjugate ambiguity in Fourier domain optical coherence tomography (OCT) that is applicable to many swept source OCT (SSOCT) systems. First, we review the principles of coherence revival ... Full text Cite

Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography.

Journal Article Biomed Opt Express · August 1, 2011 Recent advances in Doppler techniques have enabled high sensitivity imaging of biological flow to measure blood velocities and vascular perfusion. Here we compare spectrometer-based and wavelength-swept Doppler OCT implementations theoretically and experim ... Full text Link to item Cite

Doppler velocity detection limitations in spectrometer and swept-source Fourier-domain optical coherence tomography

Journal Article Progress in Biomedical Optics and Imaging - Proceedings of SPIE · April 12, 2011 Recent advances in Doppler and variance techniques have enabled high sensitivity imaging in regions of biological flow to measure blood velocities and vascular perfusion. In recent years, the sensitivity and imaging speed benefits of Fourier domain OCT hav ... Full text Cite

Crosstalk rejection in parallel optical coherence tomography using spatially incoherent illumination with partially coherent sources.

Journal Article Optics letters · July 2010 The continuing improvement of high-speed area-scan cameras has made possible the construction of parallel optical coherence tomography (OCT) systems that are competitive with the fastest demonstrated swept-source OCT systems. Unfortunately, when imaging th ... Full text Open Access Cite

Crosstalk rejection in full-field optical coherence tomography using spatially incoherent illumination with a partially coherent source

Journal Article Progress in Biomedical Optics and Imaging - Proceedings of SPIE · May 3, 2010 The recent advent of ultra high frame rate cameras gives rise to the possibility of constructing swept source full-field OCT systems with achievable volume rates approaching 10Hz and net A-scan rates approaching 10MHz. Unfortunately, when illuminated with ... Full text Cite

Feasibility of near-infrared diffuse optical spectroscopy on patients undergoing imageguided core-needle biopsy.

Journal Article Optics express · June 2007 We describe a side-firing fiber optic sensor based on near-infrared spectroscopy for guiding core needle biopsy diagnosis of breast cancer. The sensor is composed of three side firing optical fibers (two source fibers and one detection fiber), providing tw ... Full text Cite