Dual-wavelength oblique back-illumination microscopy for the non-invasive imaging and quantification of blood in collection and storage bags.

There is currently no low-cost method to quantitatively assess the contents of a blood bag without breaching the bag and potentially damaging the sample. Towards this end, we adapt oblique back-illumination microscopy (OBM) to rapidly, inexpensively, and non-invasively screen blood bags for red blood cell (RBC) morphology and white blood cell (WBC) count. OBM has been recently introduced as a tomographic technique that produces high-resolution wide-field images based on phase-gradient and transmission. Here we modify this technique to include illumination at dual wavelengths to facilitate spectral analysis for cell classification. Further, we apply a modified 2D Hilbert transform to recover the phase information from the phase-gradient images for facile cell segmentation. Blood cells are classified as WBCs and RBCs, and counted based on shape, absorption spectrum, and phase profile using an automated algorithm. This work has important implications for the non-invasive assessment of (1) cell viability in storage bags for transfusion applications and (2) suitability of a cord blood collection bag for stem cell therapy applications.