  We present a simple and effective method to eliminate system aberrations and
speckle noise in quantitative phase imaging. Using spiral integration, complete
information about system aberration is calculated from three laterally shifted
phase images. The present method is especially useful when measuring confluent
samples in which acquisition of background area is challenging. To demonstrate
validity and applicability, we present measurements of various types of samples
including microspheres, HeLa cells, and mouse brain tissue. Working conditions
and limitations are systematically analyzed and discussed.
