Improving the Resolution of Chromosome Imaging by High Numerical Aperture Fourier Ptychography Microscopy

Metaphase chromosome karyotyping plays an important role in the diagnosis of certain cancers and some genetic diseases by detecting chromosome abnormalities. For this technique, high magnification objective lens is used to ensure the chromosome's band pattern sharpness, but the small field of view (FOV) of the lens makes the imaging of chromosomes very tedious and time consuming. The purpose of this study is to verify the use of the Fourier ptychography microscopy (FPM) system in high-resolution karyotyping. Based on our former study, we further expanded the theoretical NA of the FPM system to 1.11 with a 20x/0.4 NA objective lens and higher illumination angles. To evaluate the resolving power of the FPM system, a 1951 USAF resolution target was imaged to create the modulation transfer function (MTF) curves. The performance of the FPM system was also assessed by imaging chromosomes acquired from blood and bone marrow pathological samples. The results were compared with a conventional 100x/1.45 NA oil immersion objective lens. The MTF curves demonstrate that the contrast of the FPM system is inferior but close to the 100x objective lens (1.45 NA). As compared to the images acquired by the 100x/1.45 NA oil immersion objective lens, the chromosome images recovered by the FPM system contain all the band patterns, despite the loss of some fine details. This study initially verified that the high NA FPM system can guarantee the sharpness of chromosome band patterns as the conventional high magnification oil immersion objective lens, while enabling a large FOV without the utilization of oil immersion medium.