A merger between two big medical imaging groups announced last week will create one of the largest imaging chains in the country, according to the companies involved.

On Friday, Insight Imaging Inc., a Lake Forest, Calif. provider, said it was merging with Center for Diagnostic Imaging Inc., based in Minneapolis. Terms of the deal weren't disclosed.

Private equity firm Black Diamond Capital Management L.L.C., which owns a controlling stake in Insight through investment funds, said it will buy CDI from its owners, including Onex Corp., a Toronto-based investor which has had a controlling interest in the company for seven years. According to a March financial statement, Onex and its partners own about 81 percent of CDI. (Onex said its economic ownership is 19 percent.)

The merger, which should wrap up next month, will result in "one of the nation's largest medical imaging and related services organizations," according to the press release about the merger. Together, the chains will have more than 116 fixed centers in 25 states and 90 mobile MRI and PET/CT vehicles.

The combined group will be headquartered at CDI's Minneapolis offices and will be led by Tom Tomlinson, CDI's current CEO. Kip Hallman, Insight's CEO, will stay with the company at least until the deal finishes in July.

For those keeping score, the title of the "biggest U.S. outpatient imaging chain" is still held by RadNet, a publicly traded, Los Angeles-based outfit that runs 233 fixed site centers.

The combined Insight-CDI chain's new majority stakeholder, Black Diamond, manages $10 billion in investment funds, and has offices in Greenwich, Conn. and Lake Forest, Ill.

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