Measuring methamphetamine induced morphology changes in apoptotic glial cells using the transport of intensity equation, digital holographic microscopy, and diffraction tomography

Programmed cell death, or apoptosis, can be triggered in C6 glial cells through exposure to the drug methamphetamine. Non-invasive, quantitative tracking of apoptotic glial cell morphology can be difficult, as many cellular samples are weakly scattering, and therefore traditional bright field images may be of low contrast. Higher contrast images may be found through incorporation of the quantitative phase delay a beam can undergo due to transmission through a sample. In addition, quantitative phase information can be used, non-invasively, to track meaningful morphological quantities over time. Digital holographic microscopy (DHM) and utilization of the transport of intensity equation (TIE) are two label-free, high-resolution phase imaging techniques. DHM quantitatively retrieves phase through measurement of a hologram, or the interference pattern created when combining object and reference beams. The TIE quantifies the relationship between a field's phase and intensity upon propagation. Solving the TIE requires measurement of an in-focus intensity, and images in symmetric planes about focus. On a setup capable of simultaneous data collection for both techniques, phase reconstructions were retrieved of C6 rat glial cells undergoing methamphetamine induced apoptosis. The two techniques' measurements of total optical volume of cell clusters were compared over time. Additionally, the behavior of cells' index of refraction during apoptosis was explored through optical diffraction tomography (ODT) retrieved reconstructions. Through these reconstructions, both cell volume and cell optical volume were tracked. The average relative refractive index behavior measured by ODT was extended to extrapolate volume from the TIE/DHM optical volume measurements.