As part of its patient care mission, the U.S. Veterans Health Administration performs diagnostic imaging procedures at 141 medical centers and 850 outpatient clinics. VHA's VistA Imaging Package provides a full archival, display, and communications infrastructure and interfaces to radiology and other HIS modules as well as modalities and a worklist provider In addition, various medical center entities within VHA have elected to install commercial picture archiving and communications systems to enable image organization and interpretation. To evaluate interfaces between commercial PACS, the VistA hospital information system, and imaging modalities, VHA has built a fully constrained specification that is based on the Radiology Technical Framework (Rad-TF) Integrating the Healthcare Enterprise. The Health Level Seven normative conformance mechanism was applied to the IHE Rad-TF and agency requirements to arrive at a baseline set of message specifications. VHA provides a thorough implementation and testing process to promote the adoption of standards-based interoperability by all PACS vendors that want to interface with VistA Imaging.