Optical coherence tomography with or without enhanced depth imaging for peripapillary retinal nerve fiber layer and choroidal thickness

AIM：To assess peripapillary retinal nerve fiber layer（RNFL）and choroidal thickness obtained with enhanced depth imaging（EDI）mode compared with those obtained without EDI mode using Heidelberg Spectralis optical coherence tomography（OCT）.METHODS：Fifty eyes of 25 normal healthy subjects and32 eyes of 20 patients with different eye diseases were included in the study.All subjects underwent 3.4 mm diameter peripapillary circular OCT scan centered on the optic disc using both the conventional and the EDI OCT protocols.The visualization of RNFL and choroidoscleral junction was assessed using an ordinal scoring scale.The paired t-test,intraclass correlation coefficient（ICC）,95%limits of agreement（LoA）,and Bland and Altman plots were used to test the agreement of measurements.RESULTS：The visibility score of RNFL obtained with and without EDI was of no significant difference（P=0.532）,the visualization of choroidoscleral junction was better using EDI protocol than conventional protocol（P〈0.001）.Peripapillary RNFL thickness obtained with EDI was slightly thicker than that obtained without EDI（103.25±9.42μm vs 101.87±8.78μm,P=0.010）.The ICC of the two protocols was excellent with the value of 0.867 to 0.924,the 95%LoA of global RNFL thickness was between-10.0 to 7.4μm.Peripapillary choroidal thickness obtained with EDI was slightly thinner than that obtained without EDI（147.23±51.04μm vs 150.90±51.84μm,P〈0.001）.The ICC was also excellent with the value of 0.960 to 0.987,the 95%LoA of global choroidal thickness was between-12.5 to 19.8μm.CONCLUSION：Peripapillary circular OCT scan with or without EDI mode shows comparable results in the measurement of peripapillary RNFL and choroidal thickness.

Standardization of choroidal thickness measurements using enhanced depth imaging optical coherence tomography

AIM: To describe and evaluate a standardized protocol for measuring the choroidal thickness(Ch T) using enhanced depth imaging optical coherence tomography(EDI OCT).METHODS: Single 9 mm EDI OCT line scans across the fovea were used for this study. The protocol used in this study classified the EDI OCT images into four groups based on the appearance of the choroidal-scleral interface and suprachoroidal space. Two evaluation iterations of experiments were performed: first, the protocol was validated in a pilot study of 12 healthy eyes. Afterwards, the applicability of the protocol was tested in 82 eyes of patients with diabetes. Inter-observer and intra-observer agreements on image classifications were performed using Cohen’s kappa coefficient(κ). Intraclass correlation coefficient(ICC) and Bland-Altman’s methodology were used for the measurement of the Ch T.RESULTS: There was a moderate(κ=0.42) and perfect(κ =1) inter- and intra-observer agreements on image classifications from healthy eyes images and substantial(κ =0.66) and almost perfect(κ =0.86) agreements from diabetic eyes images. The proposed protocol showed excellent inter- and intra-observer agreements for the Ch T measurements on both, healthy eyes and diabetic eyes(ICC 】0.90 in all image categories). The Bland-Altman plot showed a relatively large Ch T measurement agreement in the scans that contained less visible choroidal outer boundary. CONCLUSION: A protocol to standardize Ch T measurements in EDI OCT images has been developed;the results obtained using this protocol show that the technique is accurate and reliable for routine clinical practice and research.

Peripapillary choroidal thickness in Chinese children using enhanced depth imaging optical coherence tomography

AIM：To evaluate the peripapillary choroidal thickness（PPCT） in Chinese children,and to analyze the influencing factors.METHODS： PPCT was measured with enhanced depth imaging optical coherence tomography（EDI-OCT） in 70children（53 myopes and 17 non-myopes） aged 7 to 18 y,with spherical equivalent refractive errors between 0.50and-5.87 diopters（D）.Peripapillary choroidal imaging was performed using circular scans of a diameter of 3.4 mm around the optic disc.PPCT was measured by EDI-OCT in six sectors： nasal（N）,superonasal（SN）,superotemporal（ST）,temporal（T）,inferotemporal（IT）and inferonasal（IN）,as well as global RNFL thickness（G）.RESULTS： The mean global PPCT was 165.49±33.76 μm.The temporal,inferonasal,inferotemporal PPCT were significantly thinner than the nasal,superonasal,superotemporal segments PPCT were significantly thinner in the myopic group at temporal,superotemporal and inferotemporal segments.The axial length was significantly associated with the average global（β=-0.419,P =0.014）,superonasal（β=-2.009,P=0.049） and inferonasal（β=-2.000,P=0.049） PPCT.The other factors（gender,age,SE） were not significantly associated with PPCT.CONCLUSION： PPCT was thinner in the myopic group at temporal,superotemporal and inferotemporal segments.The axial length was found to be negatively correlated to PPCT.We need more further studies about the relationship between PPCT and myopia.

Optical coherence tomography enhanced depth imaging of chorioretinal folds in patients with orbital tumors

AIM:To characterize spectral-domain optical coherence tomography(SD-OCT)features of chorioretinal folds in orbital mass imaged using enhanced depth imaging(EDI).METHODS:Prospective observational case-control study was conducted in 20 eyes of 20 patients,the uninvolved eye served as a control.All the patients underwent clinical fundus photography,computed tomography,EDI SDOCT imaging before and after surgery.Two patients with cavernous hemangiomas underwent intratumoral injection of bleomycin A5;the remaining patients underwent tumor excision.Patients were followed 1 to 14mo following surgery(average follow up,5.8mo).RESULTS:Visual acuity prior to surgery ranged from 20/20 to 20/200.Following surgery,5 patients’visual acuity remained unchanged while the remaining 15 patients had a mean letter improvement of 10(range 4 to 26 letters).Photoreceptor inner/outer segment defects were found in 10 of 15 patients prior to surgery.Following surgical excision,photoreceptor inner/outer segment defects fully resolved in 8 of these 10 patients.CONCLUSION:Persistence of photoreceptor inner/outer segment defects caused by compression of the globe by an orbital mass can be associated with reduced visual prognosis.Our findings suggest that photoreceptor inner/outer segment defects on EDI SD-OCT could be an indicator for immediate surgical excision of an orbital mass causing choroidal compression.

Assessment of posterior vitreous detachment on enhanced high density line optical coherence tomography

The state of the vitreo-retinal interface affects various retinal diseases, and the presence or absence of a posterior vitreous detachment （PVD） is one of the most important factors. As such, various studies studying PVD in relation to retinal disease have been performed.

Detecting early changes in choroidal vascularity and thickness using optical coherence tomography in patients with corneal crosslinking for keratoconus

AIM:To investigate changes in choroidal thickness and vascularity in keratoconus patients treated with corneal crosslinking.METHODS:This study evaluated 28 eyes of 22 patients with keratoconus who underwent corneal crosslinking.The choroidal thicknesses were evaluated on enhanced depth imaging optical coherence tomography at the preoperative and postoperative 3d,1,and 3mo.Choroidal thickness in the four cardinal quadrants and the fovea were evaluated.The choroidal vascularity index was also calculated.RESULTS:There was no significant difference in central choroidal thickness between the preoperative and postoperative 3d,1mo(P>0.05).There was a significant increase in the 3mo(P=0.034)and a significant decrease in the horizontal choroidal vascularity index on the postoperative 3d(P=0.014),there was no statistically significant change in vertical axes and other visits in horizontal sections(P>0.05).CONCLUSION:This study sheds light on choroidal changes in postoperative corneal crosslinking for keratoconus.While it suggests the procedure’s relative safety for submacular choroid,more extensive research is necessary to confirm these findings and their clinical significance.

3D automatic segmentation method for retinal optical coherence tomography volume data using boundary surface enhancement

With the introduction of spectral-domain optical coherence tomography(SD-OCT),much larger image datasets are routinely acquired compared to what was possible using the previous generation of time-domain OCT.Thus,there is a critical need for the development of three-dimensional(3D)segmentation methods for processing these data.We present here a novel 3D automatic segmentation method for retinal OCT volume data.Brie°y,to segment a boundary surface,two OCT volume datasets are obtained by using a 3D smoothingfilter and a 3D differentialfilter.Their linear combination is then calculated to generate new volume data with an enhanced boundary surface,where pixel intensity,boundary position information,and intensity changes on both sides of the boundary surface are used simultaneously.Next,preliminary discrete boundary points are detected from the A-Scans of the volume data.Finally,surface smoothness constraints and a dynamic threshold are applied to obtain a smoothed boundary surface by correcting a small number of error points.Our method can extract retinal layer boundary surfaces sequentially with a decreasing search region of volume data.We performed automatic segmentation on eight human OCT volume datasets acquired from a commercial Spectralis OCT system,where each volume of datasets contains 97 OCT B-Scan images with a resolution of 496
512(each B-Scan comprising 512 A-Scans containing 496 pixels);experimental results show that this method can accurately segment seven layer boundary surfaces in normal as well as some abnormal eyes.

ULTRASOUND ENHANCED SKIN OPTICAL CLEARING:MICROSTRUCTURAL CHANGES

Our previous studies demonstrated the ultrasound-induced skin optical clearing enhancement with topical application of optical clearing agents on in vitro porcine skin and in vivo human skin.The objective of this study was to investigate the possible mechanisms of the enhanced skin optical clearing by ultrasound medications.Optical clearing effects of ex vivo guinea pig abdomen skin topically applied with 60% glycerol or the combination of 60% glycerol and ultrasound were studied by optical coherence tomography(OCT).Microstructure of skin surface was examined by scanning electron microscopy(SEM).Ultrasound with a frequency of 1MHz and a power of 0.75W over a 3-cm probe was simultaneously applied with glycerol solution for 15min.The combination of 60% glycerol and ultrasound results in a 19% increase in OCT 1/e light penetration depth after 30min,which is much better than 60% glycerol alone.SEM images demonstrated that changes in skin microstructure due to the tight order of the lipid bilayers in the stratum corneum disrupted and the separation of keratinocytes by the application of ultrasound contribute to the ultrasound-enhanced intact skin optical clearing effects.

IMAGE IMPROVEMENT IN THE WAVELET DOMAIN FOR OPTICAL COHERENCE TOMOGRAMS

In this paper,an image processing method for improving the quality of optical coherence tomography(OCT)images is proposed.Wavelet denoising based on context modeling and contrast enhancement by means of the contrast measure in the wavelet domain is carried out on the OCT images in succession.Three parameters are selected to assess the effectiveness of the method.It is shown from the results that the proposed method can not only enhance the contrast of images,but also improve signal-to-noise ratio.Compared with two other typical algorithms,it has the best visual effect.

Welding depth measurement for different mode lasers using optical coherence tomography

Optical coherence tomography(OCT)allows a direct and precise measurement of laser welding depth by coaxially measuring the keyhole depth and can be used for process monitoring and control.When OCT measurement was taken during single-beam laser welding,the keyhole instability of aluminum welding resulted in highly scattered OCT data and complicated the welding depth extraction methods.As a combination of an inner core beam and an outer ring beam,a novel adjustable ring mode(ARM)laser for producing a stable keyhole was applied to the OCT measurement.Different ARM laser power arrangements were conducted on aluminum and copper.The results indicated that the ring beam greatly improved the stability of the core beam-induced keyhole,and smooth welding depth can be extracted from the concentrated OCT data.

1.3μm broadband swept sources with enhanced nonlinear effects

In this work,a new structure is used to enhance the nonlinear effect in the cavity,which improvesthe performance of the 1.3μm broadband swept source.The swept source adopts a semiconductoroptical amplifier(SOA),a circulator,a coupler,and a tunable filter.In the structure,the lightpasses through the nonlinear medium(SOA)twice in two opposite directions,which excites thenonlinear ffect and increases the performance of the swept source.The tunable filter is based on apolygon rotating mirror and gratings.Traditionally,multiple SOAs are adopted to improve thesweep range and the optical power,which increases the cost and complexity of the swept source.The method proposed in this paper can improve the spectral range and optical power of the sweptsources without additional accessories.For the short-cavity swept source,the power increasesfrom 6 mW to 7.7 mW,and the sweep range increases from 98 nm to 120 nm.The broadband swept sources could have wide applications in biomedical imaging,sensor system,measurementand so on.

Numerical Optimization of Sensitivity in Fourier Domain Optical Coherence Tomography

The details of crosssectional images based on Fourier domain optical coherence tomography play an important role that is limited to nonuniform sampling,spectral dispersion,inverse discrete Fourier transform(IDFT),and noise.In this section,we propose a method for emphasizing axial details to the greatest extent possible.After removing spectral dispersion,uniform discretization in the wavenumber domain is performed based on two interferograms via a specified offset in depth,with no spectrum calibration.The sampling number in IDFT is optimized to improve axial sensitivity up to 1.62 dB.The proposed process has the advantage of being based on numerical computation rather than hardware calibration,which benefits cost,accuracy,and efficiency.

Measurement of the depths at different regions of the anterior chamber in healthy Chinese adults

AIM: To measure the depths of different regions of the anterior chamber(AC) in healthy Chinese adults, and to explore possible correlations with age or gender.METHODS: The AC was imaged by swept-source optical coherence tomography in healthy Chinese adults. The horizontal scan of the right eye was used to measure the anterior chamber depth(ACD) at 199 points.RESULTS: A total of 309 images from 309 subjects were analyzed. The ACD values at nearly all locations were negatively correlated with age(all P<0.05), except for ACD1, 2, 198, and 199(correspond to the iris roots). The mean annual decrease 0.013±0.005 mm/y for all ACDs combined, 0.008±0.004 mm/y for the peripheral region, 0.017±0.003 mm/y for the middle peripheral region, and 0.014±0.001 mm/y for the central region. The mean annual decrease was significantly different among these three regions(P<0.001). The ACD was greater in males than in females(P<0.05). The mean difference in ACD between males and females was 0.081±0.025 mm.CONCLUSION: This study showed that optical coherence tomography can be used to measure the ACD of different regions of the AC. We found reductions in ACD with age, although the reduction varied among different points, in healthy Chinese adults.

谱域光学相干层析系统深度扩展技术研究

对谱域光学相干层析系统(SD-OCT)进行成像深度扩展,能清晰地探测到更深层次的样品信息。提出结合去除复共轭镜像和焦平面叠加的方法来提高探测深度。首先通过光束偏移振镜中心,对样品添加载波频率,基于希尔伯特变换滤除负频信号,去除复共轭镜像,再对样品不同深度聚焦成像,实现聚焦平面的叠加,最终扩展成像深度。基于去复共轭成像系统测量不同样品的图像,验证了该方法的有效性和可靠性。针对透明片材料,系统有效成像范围扩大一倍,从1.97 mm达到3.94 mm,针对结肠组织,有效成像深度从0.51 mm扩展到0.65 mm。结果表明,深度扩展技术能够提升成像范围,同时也突破了焦深限制,样品深层结构信息也清晰可见。

激光焊OCT熔深测量去噪及数据拟合方法研究

为了解决激光焊接熔深在线检测及光学相干光层析成像(OCT)熔深检测信号噪声多的问题,采用了一种百分位滤波加移动平均算法的熔深曲线拟合方法。通过光学相干光层析成像系统对304不锈钢匙孔焊过程进行了熔深在线检测,在使用百分位滤波从原始散点数据中提取出百分位熔深曲线过程中,发现该方法提取的百分位熔深曲线存在尖峰干扰噪声,通过移动平均算法对百分位熔深曲线进行低通滤波处理,最终从原始散点数据中提取拟合出OCT熔深测量曲线。结果表明,将OCT熔深测量曲线与焊缝纵抛面的实际熔深曲线进行对比,该方法获取OCT熔深测量曲线的测量精度最大提升了15%。该方法能从OCT原始散点数据中有效提取拟合出更为准确的OCT熔深测量曲线。

计算增强光学相干层析成像技术研究进展

光学相干层析成像(Optical coherence tomography,OCT)作为一种重要的无损断层三维成像技术,应用场景广泛。不断发展的场景需求对OCT技术的性能提出了新的要求,包括分辨率提升、焦深解耦、像差校正及分辨率各向异性改善等。在过去的十几年内,一系列基于计算成像的方法被证明能有效实现上述性能提升。本文围绕上述OCT成像4个性能提升需求,总结综述了代表性的计算成像方法。分析对比了相应计算成像方法之间的优劣,并对未来发展趋势进行展望,旨在为计算成像方法在OCT领域的进一步研究与应用提供参考。

成年高度近视患者脉络膜厚度及其相关影响因素分析

背景 高度近视的多种眼底并发症均与眼轴增长引起的眼球壁厚度改变有关,但成年人高度近视眼脉络膜厚度与眼轴长度的量化分析研究较少见. 目的 观察成年高度近视患者脉络膜厚度的改变,并分析脉络膜厚度与眼轴长度、年龄及屈光度的关系.方法 采用前瞻性队列研究方法,纳入2012年12月至2013年5月在武汉大学人民医院就诊的成年高度近视患者75例75眼作为高度近视组,纳入同期年龄和性别相匹配的健康志愿者70例70眼作为正常对照组.采用频域光学相干断层扫描（SD-OCT）的加强深度扫描（EDI）技术,以6 mm的扫描线对黄斑部进行0±176;扫描,测量黄斑中心凹下及由中心凹向鼻侧和颞侧2 500 μm的脉络膜厚度值,共测量11个子午线,每个子午线间隔500 μm,比较两个组间脉络膜厚度和眼轴长度的差异,分析脉络膜厚度与眼轴长度、年龄及屈光度的关系.结果 高度近视组受检眼中心凹下脉络膜厚度值和平均黄斑部脉络膜厚度值分别为（146±177;52） μm和（142±177;63） μm,正常对照组分别为（306±177;60） μm和（271 ±177;71） μm,两个组间差异均有统计学意义（t=-17.130,P=0.000;t=-15.890,P=0.000）.高度近视组颞侧脉络膜最厚,中心凹下厚度次之,鼻侧最薄,而正常对照组以中心凹旁脉络膜最厚,其次为颞侧,鼻侧最薄.高度近视组受检眼各检测点脉络膜均薄于正常对照组.高度近视组患者脉络膜厚度值与眼轴长度呈明显负相关（r=-0.580,P=0.000）,眼轴长度每增加l mm,脉络膜厚度值平均减少17.943 μm. 结论 SD-OCT检测显示,成年高度近视患者脉络膜厚度较健康人明显变薄,且与眼轴长度的变化关系密切,提示脉络膜的病理改变可能在高度近视眼并发症的发生过程中发挥作用.

视网膜脱离成功复位1年以上患眼低视力与黄斑区脉络膜厚度的关系

目的使用深部增强成像频域光学相干断层扫描(enhanced depth imaging spectral domain optical coherence tomography,EDI SD-OCT)观察孔源性视网膜脱离成功复位1 a以上低视力患眼黄斑中心凹下脉络膜厚度(subfoveal choroidal thickness,SFCT),分析其与低视力的关系。方法将南昌爱尔眼科医院2010年1月到2014年3月孔源性视网膜脱离成功复位术后1 a以上最佳矫正视力(best corrected visual acuity,BCVA)<0.3的患者72例(72眼)纳入研究。行双眼BCVA及EDI SD-OCT扫描SFCT检查。分析患眼与对侧健眼术后末次随访的BCVA与SFCT的相关性。结果患眼术后末次随访SD-OCT检查显示,72眼中,黄斑中心凹正常者3眼(4.2%);外层视网膜微结构异常者69眼(95.8%)。患眼术后末次随访BCVA,转换为5分记录视力为3.59±0.51,同期健眼为4.94±0.11;患眼术后末次随访SFCT为(164.47±62.95)μm,对侧健眼SFCT为(235.47±42.40)μm;患眼与对侧健眼术后末次随访BCVA、SFCT差异均有统计学意义(均为P<0.05)。患眼术后末次随访BCVA与SFCT有相关性(P<0.05)。患眼黄斑区外层视网膜微结构异常眼与正常眼的BCVA、SFCT差异均无统计学意义(均为P>0.05)。结论孔源性视网膜脱离成功复位术后1 a以上低视力眼的SFCT薄,且与BCVA存在相关性;其视力的恢复可能要晚于EDI SD-OCT下观察到的外层视网膜微结构的恢复。

OCT系统对单层散射组织的有效探测深度

为了研究光学相干层析术(OCT)系统在细直光束下对高散射生物组织的深度探测能力,介绍并应用了一种基于蒙特卡罗仿真方法的OCT模型.通过对蒙特卡罗仿真结果的统计分析,提出了OCT系统有效探测深度的评估方法,并分析了生物组织的光学特性参数对有效探测深度的影响.研究表明,生物组织的散射系数越小,越有利于提高OCT系统的有效探测深度.

应用多级维纳滤波的OCT图像除噪方法

设计了基于维纳滤波和对比度增强的OCT图像处理方法。对OCT图像的噪声进行了分析，通过多尺度维纳滤波器对图像进行滤波处理来去除噪声干扰，然后根据区域特性采用对比度增强方法提高图像对比度。实验结果表明：经该方法处理后图像的背景方差（BV）较原始图像降低了2～6倍，细节方差和背景方差之比（DV／BV）提高了2～5倍。该方法不仅有效地去除了OCT图像的噪声，而且视觉效果良好，是一种有效的图像后处理方法。