Hologic Inc. of Bedford, a developer of technology for digital radiography and breast imaging, and Cytyc Corp. of Marlborough, both in Massachusetts, a manufacturer of imaging systems for cervical cancer screening, have completed their merger. Under the terms of the agreement, the latter company’s shareholders received 0.52 shares of the former’s stock and $16.50 for each share of Cytyc stock they held. The total consideration paid to the shareholders was approximately $6.2 billion. The Marlborough-based company is now a wholly owned subsidiary of Hologic.