A 43-year-old Dedham man and his 36-year-old female passenger were involved in a near-fatal motorcycle crash Sunday night in Canton, according to State Police. Troopers responded to the single-vehicle accident on Interstate 93 southbound at Exit 2B just before 8 p.m. Sunday. According to State Police, a preliminary investigation found that the operator lost control of the motorcycle and sustained life-threatening injuries in the ensuing crash. He was taken by medical helicopter to Brigham and Women’s Hospital. The passenger, also of Dedham, sustained serious but not-life-threatening injuries and was taken to Norwood Hospital. The cause of the crash remains under investigation, State Police said.