提高全场光学相干层析系统成像质量的方法

A Method of Improving Imaging Quality of Full-Field Optical Coherence Tomography

报道了一套具有活体光学断层成像能力的全场相干层析系统(FF-OCT)。该系统基于Linnik白光干涉显微结构,使用非相干光卤钨灯照明,参考臂与样品臂采用完全相同数值孔径的显微物镜成像,实验测得的轴向分辨率为1.3μm,横向分辨率为0.89μm,640 pixel×480 pixel的CCD采集干涉信号得到的成像深度为80μm。描述了基于单片机控制的相位调制方式,采用该方法可提高成像速度(从60 s/frame提高到1 s/frame断层图)和图像信噪比(SNR),并用所获得的洋葱表皮细胞的断层图(SNR从18.36 d B提高到23.30 d B)和三维图像验证其有效性。探究了由于大数值孔径显微物镜和折射率不匹配产生球差的原因并给出补偿方法,实验结果表明,补偿后的断层图像呈现了更多的细节(SNR从25.41 d B提高到29.54 d B)。利用该系统还实现了人体手指皮肤在体细胞水平的细微结构断层成像。对人体肝组织进行成像表明,所研制的FF-OCT系统有分辨正常组织与肝癌组织的能力,从而证明了研制的全场光学相干层析系统在癌症诊断领域的价值。该系统的研制为取代冰冻切片检测的快速辅助诊断手段奠定基础。

A full-field optical coherence tomography（FF-OCT） system is reported, which has the capability of generating in vivo optical sectional images. The system is based on a Linnik white light interference microscope illuminated by tungsten halogen lamps, in which identical microscope objectives are used for both illumination and detection in reference and sample arms. Measured axial and lateral resolution of the developed system is 1.3 μmand 0.89 μm respectively. A 640 pixel × 480 pixel CCD camera is used to capture interference signals with imaging depth of 80 μm. A single chip-based control system is developed to modulate phase between both arms with the intention of higher signal-to-noise ratio（SNR） and faster acquisition speed, en face and 3D images of onion cells are presented, acquisition time is reduced from 60 s to 4 s per en face image and the SNR is improved from18.36 d B to 23.30 d B compared with the system without it. The spherical aberration introduced by high-numerical aperture objectives and refractive index mismatch is considered theoretically and a compensation method is proposed. After compensating the spherical aberration experimentally, more details are shown in the en face images of onion cells（SNR is improved from 25.41 d B to 29.54 d B）. Cell-level in vivo images of human finger skin are also presented. The imaging of liver tissue is performed, which demonstrates the potential value of FF-OCT in the early diagnosis of cancer. The apparatus proposed and developed will be helpful for the design of the practical device as a fast diagnostic means instead of the traditional frozen-section method.