The PICASSO (Phase Imaging for Clinical Application with Silicon detector and Synchrotron radiation) project aims at supplying a digital detector tailored for the clinical trials in mammography with synchrotron radiation that are being performed at the SYRMEP beamline of ELETTRA (Trieste, Italy). The final detector system will comprise four linear array silicon microstrip sensors in "edge-on" configuration, each 210 mm wide (4224 channels with 50 μm pitch), equipped with a fast single photon counting electronics based on the Mythen-H application-specific integrated circuit. Different prototypes have been tested at the SYRMEP beamline, proving high rate single photon counting capabilities (with negligible losses up to 1.2×l0⁶ incident photons per pixel per second), good mechanical characteristics, and remarkable imaging performances on test-objects.