  A low-cost device for registration-free quantitative phase microscopy (QPM)
based on the transport of intensity equation (TIE) of cells in continuous flow
is presented. The method uses acoustic focusing to align cells into a single
plane where all cells move at a constant speed. The acoustic focusing plane is
tilted with respect to the microscope's focal plane in order to obtain cell
images at multiple focal positions. As the cells are displaced at constant
speed, phase maps can be generated without the need to segment and register
individual objects. The proposed inclined geometry allows for the acquisition
of a vertical stack without the need for any moving part, and it enables a
cost-effective and robust implementation of QPM. The suitability of the
solution for biological imaging is tested on blood samples, demonstrating the
ability to recover the phase map of single red blood cells flowing through the
microchip.
