One of the nation’s leading brain imaging centers at Columbia University has be temporarily shut down after F.D.A. investigators found that the center “injected mental patients with drugs that contained potentially dangerous impurities.” The Kreitchman PET Center came under fire from the F.D.A. in December 2008 for violating federal regulations, and the agency raided the labs in January 2010 when the center failed to fix its lax quality control and sloppy procedures for formulating drug injections. To perform certain scans, doctors must first inject patients with a radiotracer, but if the tracer contains too many unknown chemicals, the injection may have harmful affects on the body. The F.D.A investigation found that “at least 10 batches of drugs had been released and injected into human subjects with impurities” above federal regulatory levels since 2007.