Question: The inside cover of my CPT® manual shows modifier A1 (letter A, number 1) for principal physician. I thought this was supposed to be modifier AI (letter A, letter I). Which is correct? Utah Subscriber Answer: Modifier AI (letter A, letter I) is appropriate for "Principal physician of record." Printing A1 was an error, as indicated in the AMA's "Corrections in CPT® 2011" document at http://www.ama-assn.org/ama/pub/physician-resources/solutions-managing-your-practice/coding-billing-insurance/cpt/about-cpt/errata.page. The most recent update, as of printing time, was April 12, 2011. You should also take note of the correction to the note under 36215, which should read, "For catheter placement for coronary angiography, see 93454-93461." Furthermore, the second instruction above 75557 (Cardiac magnetic resonance imaging for morphology and function without contrast material) should read, "For cardiac catheterization procedures, see 93451-93572." Check the Corrections document regularly for updates. You also can read more about CPT® errata in Radiology Coding Alert, vol. 13, no. 5, "93922 Typo Alert: Beware Miscoding Complete Bilateral Physiologic Studies."