Nashville-based Saint Thomas Health Services and two radiology groups are partnering to create what is being dubbed the largest network of imaging centers in Middle Tennessee. Beginning April 1, the joint venture called Saint Thomas Outpatient Imaging will provide services at eight Nashville-area locations with more than 40 radiologists. It's the latest in moves by the five-hospital system to expand its geographic reach in specific services even as providers are being told to collaborate more and offer care in lower-cost settings near where patients live and work."We're going to bring more affordable services to the market," said Tom Blankenship, vice president for business development with the Catholic-owned Saint Thomas Health. Six of the eight imaging centers — four in Nashville and one each in Cool Springs and Mt. Juliet — are part of Premier Radiology, a 30-member radiology group that is a partner in the new joint venture.