Agrawal Anant, Chen Chao-Wei, Baxi Jigesh, Chen Yu, Pfefer T Joshua
Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD, USA.
Biomed Opt Express. 2013 Jun 14;4(7):1166-75. doi: 10.1364/BOE.4.001166. Print 2013 Jul 1.
In optical coherence tomography (OCT), axial resolution is one of the most critical parameters impacting image quality. It is commonly measured by determining the point spread function (PSF) based on a specular surface reflection. The contrast transfer function (CTF) provides more insights into an imaging system's resolving characteristics and can be readily generated in a system-independent manner, without consideration for image pixel size. In this study, we developed a test method for determination of CTF based on multi-layer, thin-film phantoms, evaluated using spectral- and time-domain OCT platforms with different axial resolution values. Phantoms representing six spatial frequencies were fabricated and imaged. The fabrication process involved spin coating silicone films with precise thicknesses in the 8-40 μm range. Alternating layers were doped with a specified concentration of scattering particles. Validation of layer optical properties and thicknesses were achieved with spectrophotometry and stylus profilometry, respectively. OCT B-scans were used to calculate CTFs and results were compared with convetional PSF measurements based on specular reflections. Testing of these phantoms indicated that our approach can provide direct access to axial resolution characteristics highly relevant to image quality. Furthermore, tissue phantoms based on our thin-film fabrication approach may have a wide range of additional applications in optical imaging and spectroscopy.
在光学相干断层扫描（OCT）中，轴向分辨率是影响图像质量的最关键参数之一。它通常通过基于镜面表面反射确定点扩散函数（PSF）来测量。对比度传递函数（CTF）能更深入地了解成像系统的分辨特性，并且可以以与系统无关的方式轻松生成，无需考虑图像像素大小。在本研究中，我们开发了一种基于多层薄膜体模测定CTF的测试方法，并使用具有不同轴向分辨率值的光谱域和时域OCT平台进行评估。制作了代表六个空间频率的体模并进行成像。制作过程包括旋涂厚度精确在8 - 40μm范围内的硅树脂薄膜。交替层中掺杂有特定浓度的散射颗粒。分别使用分光光度法和触针轮廓仪对层的光学性质和厚度进行了验证。使用OCT B扫描来计算CTF，并将结果与基于镜面反射的传统PSF测量结果进行比较。对这些体模的测试表明，我们的方法可以直接获取与图像质量高度相关的轴向分辨率特性。此外，基于我们的薄膜制作方法的组织体模在光学成像和光谱学中可能有广泛的其他应用。
