Abstract
Quantitative phase imaging (QPI) offers high optical path length sensitivity, probing nanoscale features of live cells, but it is typically limited to imaging just few static cells at a time. To enable utility as a biomedical diagnostic modality, higher throughput is needed. To meet this need, methods for imaging cells in flow using QPI are in development. An important need for this application is to enable accurate quantitative analysis. However, this can be complicated when cells shift focal planes during flow. QPI permits digital refocusing since the complex optical field is measured. Here we analyze QPI images of moving red blood cells with an emphasis on choosing a quantitative criterion for digitally refocusing cell images. Of particular interest is the influence of optical absorption which can skew refocusing algorithms. Examples of refocusing of holographic images of flowing red blood cells using different approaches are presented and analyzed.
Highlights
Quantitative phase imaging (QPI) has been developed as a means to visualize the structure, dynamics, and function of biological cells without exogenous contrast agents
One criterion that is needed for cell based diagnostic applications is high throughput, which seems to be achievable by imaging flowing cells in a microfluidic device
The range of optical volume (OV) of red blood cells (RBCs) at different orientations varies over the propagation distances
Summary
Quantitative phase imaging (QPI) has been developed as a means to visualize the structure, dynamics, and function of biological cells without exogenous contrast agents. A more recent device from this group showed a common path interferometer implemented using a diffractive element.[6] The approach allows QPI in a microfluidic chip, suggesting a robust platform that could enable high throughput, but experiments with this platform have not extended to the analysis of biomedically relevant cells. Another compelling approach is the use of transport of intensity equations to reconstruct the phase profile. The results showed cell images with limited spatial and phase resolution and required 10 exposures for each cell; throughput can still be regarded as limited
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