The board, the department or a workers' compensation judge, if it or he deem it necessary, may, of its or his own motion, either before, during, or after any hearing, make or cause to be made an investigation of the facts set forth in the petition or answer or facts pertinent in any injury under this act. The board, department or workers' compensation judge may appoint one or more impartial physicians or surgeons to examine the injuries of the plaintiff and report thereon, or may employ the services of such other experts as shall appear necessary to ascertain the facts. The workers' compensation judge when necessary or appropriate or upon request of a party in order to rule on requests for review filed under section 306(f.1),¹ or under other provisions of this act, may ask for an opinion from peer review about the necessity or frequency of treatment under section 306(f.1). The peer review report or the peer report of any physician, surgeon, or expert appointed by the department or by a workers' compensation judge, including the report of a peer review organization, shall be filed with the board or workers' compensation judge, as the case may be, and shall be a part of the record and open to inspection as such. The workers' compensation judge shall consider the report as evidence but shall not be bound by such report.