A 59 modifier is used when two different exams that are normally bundled are done on the same day.
For example, a 2 view chest includes a 1 view chest so you wouldn't separately report the 1 view chest unless it was done during a different encounter then the 2view chest.
i.e. patient presented with a cough and a 2view chest was performed. A couple hours later the patient started getting a fever and worsening cough so they did a 1 view.
This would be reported as 71020 and 71010-59. The 59 modifier goes on the component code.
The 79 modifier is for surgical CPT® codes, not diagnostic procedures.