This paper presents the development of a radiographic characterization method for microshells. In the Laser MegaJoule (LMJ) framework, microshells are tiny plastic spheres used in inertial fusion laser experiments. For this work, these microshells were characterized using low-energy radiography. In the microshell radiographs, phase contrast was noted at the edges of the microshells. The origin of this phenomenon has been identified as sharp variation of gray-scale amplitude due to refraction. Our theoretical model links pixel information with microshell geometry and is used for contour detection and characterization. Finally, an estimation of surface defects described by spherical harmonics is calculated.