Time-domain Optical Coherence Tomography System Research Articles

Direct Numerical Modeling as a Tool for Optical Coherence Tomography Development: SNR (Sensitivity) and Lateral Resolution Test Target Interpretation

Optical Coherence Tomography (OCT) is a growing family of biophotonic imaging techniques, but in the literature there is a lack of easy-to-use tools to universally directly evaluate a device’s theoretical performance for a given metric. Modern computing tools mean that direct numerical modeling can, from first principles, simulate the performance metrics of a specific device directly without relying on analytical approximations and/or complexities. Here, we present two different direct numerical models, along with the example MATLAB code for the reader to adapt to their own systems. The first model is of photo-electron shot noise at the detector, the primary noise source for OCT. We use this firstly to evaluate the amount of additional noise present (1.5 dB) for an experimental setup. Secondly, we demonstrate how to use it to precisely quantify the expected shot noise SNR limit difference between time-domain and Fourier-domain OCT systems in a given hypothetical experiment. The second model is used to demonstrate how USAF 1951 test chart images should be interpreted for a given lateral PSF shape. Direct numerical modeling is an easy and powerful basic tool for researchers and developers, the wider use of which may improve the rigor of the OCT literature.

Evaluation of Signal Degradation Due to Birefringence in a Multiple Reference Optical Coherence Tomography System With Polarization-Based Balanced Detection

Although time-domain optical coherence tomography (TD-OCT) systems are straightforward to realize, the imaging speed, sensitivity, and imaging depth limit their range of applications. Multiple reference optical coherence tomography (MR-OCT) based on TD-OCT increases imaging range by about tenfold while providing sensitivity to image highly scattering biological samples. The multiple path-delays and free-space construction make MR-OCT also interesting for hybrid and compact systems, filling the gap between fibre-based and wafer-level integrated optical systems. We describe an optical configuration using a balanced detection scheme and the resulting signal properties due to the required use of polarizing optical components. We numerically simulate the signal properties using Jones calculus and compare the results with measurements. We discuss the origin of signal degradation due to birefringence of the sample in OCT and show that the quarter-wave plate in the sample arm of the Michelson interferometer can be adjusted to optimize the signal returning from a birefringent sample thereby improving the visibility of structures of interest. The theory discussed will be useful to understand and minimize signal degradation due to birefringence in Time-Domain and Fourier-Domain OCT systems.

Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Optical Coherence Tomography (OCT) is a non-invasive, non-destructive optical imaging technique that uses a low coherence interferometer to obtain real-time cross-sectional images of samples. OCT is notably used in biomedical applications including ophthalmology and dermatology. Aside from generating cross-sectional images, axial scans can also provide additional information about its optical properties such as extinction coefficient and refractive index. This study determines the extinction coefficients and group refractive indices of gelatin-based skin phantoms using a portable time-domain (TD) – OCT system. The gelatin-based skin phantoms were fabricated with varying concentrations of titanium dioxide (TiO2), while keeping the amount of both gelatin and water constant. By changing the proportion of the gelatin powder and TiO2, skin phantoms can then be fabricated to mimic various skin conditions, both pathologic and non-pathologic. Results of the study found a positive correlation of extinction coefficient and refractive index with TiO2 concentration. Thus, increasing TiO2 concentration also increases both extinction coefficient and group refractive index. The median extinction coefficient values of the phantoms ranged from 4.29 mm−1 to 8.48 mm−1. Literature showed that the epidermis can have extinction coefficients of 1.64-7.3 mm−1. For refractive indices of the fabricated phantoms, values ranged from 1.32 to 1.48, while studies on human participants showed that human skin has refractive index values of 1.34-1.56. Based on these properties, it is feasible to fabricate phantoms simulating the optical properties of human skin.

Jitter Correction and SNR Improvement of A-Scan Signal Using Wavelet Denoising and Signal Averaging for a Portable Time-Domain Optical Coherence Tomography System

<p class='IJASEITAbtract'>Optical coherence tomography (OCT) is used to probe surface cross-sections of various materials in manufacturing, anatomy, and agriculture, among others. In any OCT system, signals have embedded noise in various forms, such as electrical noise and Jitter, which affect the depth profile (A-scan) and image quality. A signal processing method for correcting the Jitter and improving the signal-to-noise ratios (SNR) and image quality was developed in this study for a portable time-domain (TD) OCT system that utilizes a pc-based oscilloscope for data acquisition. A stack of five glass coverslips was used as a sample. Each signal from the oscilloscope consists of an A-scan coupled with a trigger signal. Jitter correction was done by first denoising the trigger signal using a combination of moving average and wavelet denoising. A reference trigger was selected, and all other trigger signals were adjusted, including the A-scans. Once jitter was corrected, the denoising method on the OCT A-scans was employed. The signal averaging method and various wavelet denoising methods were applied to the A-scans of the sample to identify which will give the highest SNR and improved image quality. Combining averaging of fifty signals and Daubechies 7 (Db7) with hard thresholding reduced the acquisition time and storage space by 50%, improved the SNR by 18 dB, improved the depth profile and image quality of a stack of five glass coverslips. This signal processing method will allow us to characterize and properly visualize cross-sectional images of other samples in the future using our TD-OCT system.

Time-domain optical coherence tomography and gelatin-based skin phantom as training tools for venipuncture

Optical coherence tomography (OCT) is a non-invasive imaging modality developed in the early 1990’s for retinal imaging. Further modifications allowed OCT’s to be used on other parts of the human body, and non-medical areas as well. Time-domain OCT (TD-OCT) basically is a Michelson interferometer with a low-coherence light source which enables non-invasive, cross-sectional visualization of the sample. In this paper, the researchers used the TD-OCT system, which uses a rotating reference mirror. Using this system in conjunction with fabricated skin phantoms, students of venipuncture can hone their skills on skin phantoms before practicing on actual persons. This helps in mitigating the potential risks inherent to the performance of invasive procedures such as venipuncture. Furthermore, the skin phantom is chiefly composed of gelatin with latex tubing used to imitate the veins. Such materials are cheap and readily available, allowing multiple phantoms to be fabricated easily. Preliminary results showed that OCT is a promising tool in imaging the tissue phantom and thus can be utilized for venipuncture training.

Time-domain optical coherence tomography system based on moving-optical-wedge interferometer

In this work we present a time-domain optical coherence tomography system based on moving-optical-wedge interferometer. This device has the advantage of suppressing motion artifact. The major problem with such a system is dispersion in the wedge material. We propose an algorithm for compensation of such dispersion. Moreover, we investigate the effect of dispersion in resolution. So, we introduced artificial high dispersion in the wedge material to clarify this effect. Resolution is improved from 10 μm to 5 μm. Thus we can consider dispersion is a bless in improving resolution.

Image-guided vibrometry system integrated with spectral- and time-domain optical coherence tomography.

Vibrometry using optical coherence tomography (OCT) can provide valuable information for investigating either the mechanical properties or the physiological function of biological tissues, especially the hearing organs. Real-time imaging of the measured tissues provides structure imaging and spatial guidance for and is thus highly demanded by such vibrometry. However, the traditional time-domain OCT (TD-OCT) systems, although capable of subnanometric vibrometry at large ranges of frequencies, are unable to offer an imaging speed that is high enough to acquire depth-resolved images for guidance. The spectral-domain OCT (SD-OCT) systems, although allowing image-guided vibrometry, are challenged in measuring vibration at high frequencies, particularly for scattering tissue specimens that require longer exposure time to ensure imaging and vibrometry performance. This is because of their limit in the line-scan rate of the CCD, in which the maximum resolvable frequency measured by the SD-OCT is about 1/4 of the CCD line-scan rate in practice. In the present study, we have developed a dual-mode OCT system combining both SD-OCT and TD-OCT modalities for image-guided vibrometry, as the SD-OCT can provide guiding structural images in real-time and, moreover, the TD-OCT can guarantee vibrometry at large ranges of frequencies, including high frequencies. The efficacy of the developed system in image-guided vibrometry has been experimentally demonstrated using both piezoelectric ceramic transducer (PZT) and ex vivo middle-ear samples from guinea pigs. For the vibrometry of PZT, the minimum detectable vibration amplitude was reached at ∼0.01 nm. For the vibrometry of the sound-evoked biological samples, both real-time two-dimensional imaging and subnanometric vibrometry were performed at the frequency ranging from 1 to 40kHz. These results indicate that our dual-mode OCT system is able to act as an excellent vibrometer enabling image-guided high-frequency measurement.

Gabor fusion master slave optical coherence tomography

This paper describes the application of the Gabor filtering protocol to a Master/Slave (MS) swept source optical coherence tomography (SS)-OCT system at 1300 nm. The MS-OCT system delivers information from selected depths, a property that allows operation similar to that of a time domain OCT system, where dynamic focusing is possible. The Gabor filtering processing following collection of multiple data from different focus positions is different from that utilized by a conventional swept source OCT system using a Fast Fourier transform (FFT) to produce an A-scan. Instead of selecting the bright parts of A-scans for each focus position, to be placed in a final B-scan image (or in a final volume), and discarding the rest, the MS principle can be employed to advantageously deliver signal from the depths within each focus range only. The MS procedure is illustrated on creating volumes of data of constant transversal resolution from a cucumber and from an insect by repeating data acquisition for 4 different focus positions. In addition, advantage is taken from the tolerance to dispersion of the MS principle that allows automatic compensation for dispersion created by layers above the object of interest. By combining the two techniques, Gabor filtering and Master/Slave, a powerful imaging instrument is demonstrated. The master/slave technique allows simultaneous display of three categories of images in one frame: multiple depth en-face OCT images, two cross-sectional OCT images and a confocal like image obtained by averaging the en-face ones. We also demonstrate the superiority of MS-OCT over its FFT based counterpart when used with a Gabor filtering OCT instrument in terms of the speed of assembling the fused volume. For our case, we show that when more than 4 focus positions are required to produce the final volume, MS is faster than the conventional FFT based procedure.

Acousto-optic tunable filter for dispersion characterization of time-domain optical coherence tomography systems.

A broadband supercontinuum light source with an acousto-optic tunable filter (AOTF) are used to characterize dispersion in two time-domain OCT systems, at 850 and 1300 nm. The filter is designed to sweep across two spectral ranges, which are restricted here from 800 to 900 nm and from 1200 to 1500 nm, respectively. Dispersion compensation for 850 nm was achieved with a spectral delay line. Dispersion compensation for 1300 nm was achieved using BK 7 rod glasses in the reference arm. The AOTF allows evaluation of dispersion in under as well as overcompensated systems. The AOTF method is based on wavelength dependence of the optical path difference corresponding to the maximum strength of the interference signal recorded using a mirror as object. Comparison is made between the AOTF method and the more usual method based on measurement of the full width at half-maximum of the autocorrelation peak. This comparison shows that the AOTF method is more accurate in terms of evaluation of the dispersion left uncompensated after each adjustment. The AOTF method additionally provides information on the direction of dispersion compensation.

Optical identification based on time domain optical coherence tomography.

We present a novel method for optical identification, i.e., authenticating valuable documents such as a passport, credit cards, and bank notes, using optical coherence tomography (OCT). An OCT system can capture three-dimensional (3D) images and visualize the internal structure of an object. In our work, as an object, we consider a multilayered optical identification tag composed of a limited number of thin layers (10-100μm thick). The thickness, width, and location of the layers in the tag encode a unique identification information. Reading of the tag is done using a time domain OCT (TD-OCT) system. Typically, a TD-OCT system requires continuous mechanical scanning in one or more directions to get a 3D volume image of an object. The continuous scanning implies a complicated optical setup, which makes an OCT system fragile and expensive. We propose to avoid the conventional scanning by (1)not requiring 3D imaging, and (2)utilizing the motion of the optical tag itself. The motion is introduced to the tag reader, for example, by a user, which replaces the need for conventional scanning. The absence of a conventional scanning mechanism makes the proposed OCT method very simple and suited for identification purposes; however, it also puts some constraints to the construction of the optical tag, which we discuss in this paper in detail.

3D nondestructive testing system with an affordable multiple reference optical-delay-based optical coherence tomography.

Optical coherence tomography (OCT) is emerging as a powerful noncontact imaging technique, allowing high-quality cross-sectional imaging of scattering specimens nondestructively. However, the complexity and cost of current embodiments of an OCT system limit its use in various nondestructive testing (NDT) applications at resource-limited settings. In this paper, we demonstrate the feasibility of a novel low-cost OCT system for a range of nondestructive testing (NDT) applications. The proposed imaging system is based on an enhanced time-domain OCT system with a low cost and small form factor reference arm optical delay, called multiple reference OCT (MR-OCT), which uses a miniature voice coil actuator and a partial mirror for extending the axial scan range. The proposed approach is potentially a low-cost, compact, and unique optical imaging modality for a range of NDT applications in a low-resource setting. Using this method, we demonstrated the capability of MR-OCT to perform cross-sectional and volumetric imaging at 1200 A-scans per second.

Time-domain optical coherence tomography system based on stationary wavelet transform

Time-domain optical coherence tomography system based on stationary wavelet transform

Modeling and Simulation of Optical Coherence Tomography on Virtual OCT

Optical Coherence Tomography (OCT) is noninvasive emerging medical imaging technique for acquiring depth resolved information from human tissues. Some of the commercially available OCT systems have found their applications in ophthalmology, where one can acquire detailed images from within the retina. Recently OCT has found its applications in blood flow estimation, cancer diagnosis, dermatology, dentistry, gastroenterology and other non-biomedical applications. For this purpose simulation of OCT has been done using Lab VIEW and Matlab scripts. Spectral domain OCT (SD-OCT) which is recent modification to traditional time domain OCT systems and has advantage of faster signal acquisition rates and higher signal to noise ratio. The basic principle of OCT, its types, modeling and its simulation on Virtual OCT GUI and various results obtained from it have been discussed.

TCT-657 Calibration of Intravascular Optical Coherence Tomography As Presented In Peer Reviewed Publications

Intravascular optical coherence tomography (OCT) is a new imaging modality in interventional cardiology providing highresolution intracoronary images. The modality is already established as an efficient and precise research tool and is increasingly used for guiding coronary intervention. The quantitative capabilities of marketed OCT systems have been validated and measurements are found accurate and precise in bench testing [1]. When using OCT it is important to carefully calibrate the system for accuratemeasurements [2,3]. Present standard in marketed systems is automated calibration. Still the calibration can be incorrect due to failed automated calibration, wrong manual adjustment, or changes to the length of the optic fiber due to altered bending of the imaging wire. Correct calibration and the identification of incorrect calibration can be challenging due to mirror artifacts, blood in the imaging wire and proximity to the vessel wall. Looking for guidance on calibration of intravascular OCT in published peer reviewed papers led to the identification of some inconsistencies similar to our own experience. Still we do not have a database of wrong calibrations owing to immediate corrections. Therefore we aimed at identifying patterns of failed calibration as presented in images in peerreviewed papers. Using the PubMed internet database, we built a search containing following MESH-terms: “Tomography, Optical Coherence” AND (“Percutaneous Coronary Intervention”OR “Coronary Occlusion”OR “Coronary Stenosis” OR “Coronary Restenosis” OR “Coronary Vessels” OR “Coronary Disease”OR “Coronary Circulation”OR “Coronary Thrombosis” OR “Coronary Artery Disease” OR “Myocardial Reperfusion”). With this search more than 300 articles published since 1 January 2011 were identified. Of these, 222 were included in the analysis giving a total of 1164 OCT images with the information needed for evaluating the calibration. Articles which were excluded from the analysis are due to lack of images (N = 57), lack of fiduciaries (N = 38) or no full-text subscription by the local university library (N = 27). Calibration errors were divided into 8 groups, ranging from slightly incorrect through errors with potentially clinical relevant impact on quantitative measurements. Errors in classes that may likely affect stent sizing if applied in clinical practice were termed serious calibration errors (Classes 3, 4 and 6). Frames which we were unable to classify were not counted and if a frame appearedmore than once or in more articles (e.g. editorials), it was only counted once. Our findings (shown in Table 1) were 1) 640 images produced by time domain OCT systems. Of these 15% were in-assessable. Worse than slightly incorrect calibration, was found in 35% of assessable cases. Serious calibration incorrectness was seen in 16% of images. 2) A total of 524 images had been obtained bymarketed frequency domain systems (482 by C7 system and 42 images by Illumien—both St. Jude Medical, USA). In images acquired by the C7 system serious calibration incorrectness was detected in 16% of cases. In images acquired by the Illumien system (42) only a single acquisition with 3 images was severely incorrect calibrated due to inverted calibration. Inverted calibration may cause the depicted catheter to resemble a correct calibrated OCT catheter. This is an occasional finding termed “inverted calibration” (Class 4 error). A related finding due to inverted calibration is the distortion of the image and appearance of vessel wall or wires inside the apparent imaging wire (Fig. 1 error Class 4). We propose the term “inverted calibration artifacts” for such findings. The “slightly incorrect”-group was expanded to contain also the Class 1 categorized images, as the error in these groups only result in minimal error of the measurements. For the C7 system 43% of images in articles presenting quantitative measurements showed any degree of incorrect calibration. For the M2 system, this was 40%. We are aware, that images shown in articles are chosen for illustrative purpose. This is a process different from the systematic core lab evaluation, andwe assume that all results derivedweremade from correctly calibrated images. Still, systematic errors inmany or all images in a paper might induce a slight uncertainty about derived quantitative results. Incorrect calibration in images presented for tissue characterization or similar could be seen as unimportant. Still, when presented in high impact journals, in expert reviews or consensus reports some users might potentially adopt this as the gold standard of calibration. In conclusion, a high incidence of incorrect calibrated images was found in systematic review of peer reviewed publications. Improved calibration facilities by newer generation OCT systems seems to reduce errors though not alleviating the risk associated with not identifying inverted calibration.

Probe alignment and design issues of microelectromechanical system based optical coherence tomography endoscopic imaging

Endoscopic optical coherence tomography (OCT) imaging has been demonstrated using microelectromechanical system (MEMS) technology by several research groups. The focus of this work is to study how the OCT imaging performance is affected by the radius of curvature of MEMS mirrors as well as the optical alignment accuracy inside small imaging probes. The goal of this study is to provide guidance for assembly tolerance and design optimization of OCT endoscopic probes. Gaussian beam propagation is used for theoretical analysis which is confirmed by optical simulation and verified experimentally with a time-domain OCT system as well. It has been found that the OCT imaging is very sensitive to the distance from the fiber end to the gradient-index (GRIN) lens, which needs to be controlled within 0.1 mm to achieve working distance (WD) longer than 3.5 mm and lateral resolution around 25 μm. The impact on image quality of the MEMS mirror is negligible if the radius of curvature of the mirror surface is greater than 200 mm. In addition, we studied the astigmatism introduced by cylindrical plastic tubing; the maximum astigmatism ratio is 1.1 when the WD is around 2.5 mm.

Combined Optical Coherence Tomography and Endobronchial Ultrasonography for Laser-Assisted Treatment of Postintubation Laryngotracheal Stenosis

We describe the use of combined optical coherence tomography (OCT) and endobronchial ultrasonography (EBUS) to identify the residual hypertrophic tissues and persistent inflammation that are known contributors to stricture recurrence after laser-assisted mechanical dilation (LAMD) oflaryngotracheal stenosis (LTS). Commercially available high-frequency EBUS (approximately 100-microm resolution) and time-domain OCT (approximately 10- to 20-microm resolution) systems were used to visualize airway wall microstructures in the area of hypertrophic tissue formation before and after LAMD in 2 patients with complex circumferential postintubation LTS. Before LAMD, EBUS revealed a homogeneous layer consistent with hypertrophic tissue overlying a hyperechogenic layer corresponding to tracheal cartilage. OCT revealed a homogeneous light backscattering layer and an absence of layered microstructures within hypertrophic tissue. Immediately after LAMD, OCT of the laser-charred tissue showed high backscattering and shadowing artifacts; OCT of noncharred tissue showed bright light backscattering regions that suggested acute inflammation. EBUS revealed thinner but persistent hypertrophic tissue overlying the cartilage. Stenosis recurred in both patients. Intraoperative use of EBUS and OCT could potentially identify residual hypertrophic tissues and persistent inflammation during or after LAMD. It might help physicians predict stricture recurrence, prompting alternative therapeutic strategies and avoidance of repeated endoscopic treatments for LTS.

Depth‐sensitive Raman spectroscopy combined with optical coherence tomography for layered tissue analysis

Complete characterization of a layered tissue requires probing both the biochemical and the morphological information from its different layers at various depths. We report the development of a combined Raman spectroscopy (RS) and optical coherence tomography (OCT) system that is capable of measuring depth-sensitive Raman signal from the tissue layers imaged by the OCT. The sample arm of a real-time time-domain OCT system was modified to allow for co-alignment of the OCT with the Raman probe beam. The depth sensitivity of Raman was obtained by incorporating confocal Raman configuration that minimized out-of-focus Raman scattered light. The system was first validated using a layered phantom prepared by depositing a thin layer of paraffin over acetaminophen. A good correlation was observed between the OCT images and the Raman signal. The system was also used to record OCT and Raman images of a resected mucosal tissue sample. While OCT image showed the presence of epithelial and stromal layers, Raman spectra measured from these layers confirmed the biochemical difference between the two.

Anterior Chamber Cell Grading by Optical Coherence Tomography

To quantify cells in the ocular anterior chamber (AC) by optical coherence tomography (OCT). A time-domain anterior segment OCT system was used to image latex microsphere suspensions in vitro and the AC of uveitis and normal subjects in vivo. The OCT scan pattern, consisting of 2- and 4-mm-diameter concentric circular scans, was divided into central, superior, and inferior regions. A computer algorithm was developed to automatically identify particles in OCT images. A uveitis specialist used slit-lamp biomicroscopy to grade the AC cells on a scale of 0 to 4+. Latex microspheres and ac cells were visualized as reflective spots in oct images. OCT latex microsphere concentration measurements were highly correlated to known particle concentrations (r = 1.000) and had an efficiency of 0.72. in 30 nongranulomatous and 12 granulomatous eyes, the OCT cell counts correlated well with slit-lamp grades in all three regions (Spearman's rho coefficient: >0.63). The average OCT cell count was 3.7 cells/grade in nongranulomatous eyes and 2.0 cells/grade in granulomatous eyes. OCT revealed significant amounts of inferior AC cells in 5 of 16 quiescent uveitis eyes (mean ± SD: 19.9 ± 7.4 cells). OCT captured rare cells in normal eyes (1.1 ± 1.1 cells centrally). OCT provided quantitative information on AC inflammatory cells. The OCT cell counts correlated well with clinical grading, and particles in the inferior AC that were missed by slit-lamp examination were detected by OCT. OCT could be a valuable tool for the diagnosis and management of anterior uveitis.

A 2.8-mm Imaging Probe Based On a High-Fill-Factor MEMS Mirror and Wire-Bonding-Free Packaging for Endoscopic Optical Coherence Tomography

This paper reports a miniature optical coherence tomography (OCT) probe and high-resolution 3-D OCT imaging results obtained with this side-view probe. The probe is only 2.8 mm in diameter, enabled by a unique high-fill-factor electrothermal MEMS mirror with hidden actuators and a novel wire-bonding-free packaging technique. The MEMS mirror has a large mirror aperture of 1 mm with a chip size of only 1.55 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\times$</tex></formula> 1.7 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\times$</tex></formula> 0.5 mm. The fabricated device achieves large 2-D scan optical angles up to 46 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> at only 4.8 V. The specific time-domain OCT system utilized is detailed, and the assembled side-view probe demonstrates multiple high-resolution 3-D OCT imaging results that demonstrate detailed images of a mouse ear and images detecting the presence of tumor cells, and the contrast with a normal tissue is qualitatively analyzed. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$</tex></formula> [2011-0369]

Distortion Correction of OCT Images of the Crystalline Lens

To propose a method to correct optical coherence tomography (OCT) images of posterior surface of the crystalline lens incorporating its gradient index (GRIN) distribution and explore its possibilities for posterior surface shape reconstruction in comparison to existing methods of correction. Two-dimensional images of nine human lenses were obtained with a time-domain OCT system. The shape of the posterior lens surface was corrected using the proposed iterative correction method. The parameters defining the GRIN distribution used for the correction were taken from a previous publication. The results of correction were evaluated relative to the nominal surface shape (accessible in vitro) and compared with the performance of two other existing methods (simple division, refraction correction: assuming a homogeneous index). Comparisons were made in terms of posterior surface radius, conic constant, root mean square, peak to valley, and lens thickness shifts from the nominal data. Differences in the retrieved radius and conic constant were not statistically significant across methods. However, GRIN distortion correction with optimal shape GRIN parameters provided more accurate estimates of the posterior lens surface in terms of root mean square and peak values, with errors <6 and 13 μm, respectively, on average. Thickness was also more accurately estimated with the new method, with a mean discrepancy of 8 μm. The posterior surface of the crystalline lens and lens thickness can be accurately reconstructed from OCT images, with the accuracy improving with an accurate model of the GRIN distribution. The algorithm can be used to improve quantitative knowledge of the crystalline lens from OCT imaging in vivo. Although the improvements over other methods are modest in two dimension, it is expected that three-dimensional imaging will fully exploit the potential of the technique. The method will also benefit from increasing experimental data of GRIN distribution in the lens of larger populations.