Exhibit 24.3

                                POWER OF ATTORNEY

        Each individual whose signature appears below constitutes and appoints
Michael E. Prevoznik and Leo C. Farrenkopf, Jr., and each of them singly, his or
her true and lawful attorneys-in-fact and agents with full power of
substitution, for him or her and in his or her name, place and stead, in any and
all capacities, to sign this registration statement and any and all amendments
thereto, including post-effective amendments, and to file the same, with all
exhibits thereto, any related registration filed pursuant to Rule 462(b) under
the Securities Act of 1933, as amended, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them full power and authority to do
and perform each and every act and thing requisite and necessary to be done in
and about the premises, as fully to all intents and purposes as he or she might
or could do in person, hereby ratifying and confirming all the said
attorneys-in-fact and agents or any of them or their or his or her substitute or
substitutes, may lawfully do or cause to be done by virtue hereof.

Dated:  September 23, 2003

By:        /s/ Mary A. Cirillo
        -------------------------
        Name:  Mary A. Cirillo
        Title: Director