Eli Lilly & Co. says it will push ahead with a first-of-a-kind imaging chemical designed to help screen for Alzheimer's disease, despite a negative ruling by Medicare officials.

The Centers for Medicare and Medicaid Services said it will not cover the chemical, called Amyvid, which highlights brain plaque in medical imaging scans. The government program provides health coverage to more than 47 million seniors.

Medicare officials say more trials are needed to prove the tool works. The government will pay for patients enrolled in future studies, but not for general use.

The ruling is an unexpected setback for Indianapolis-based Lilly, after European Union regulators endorsed the drug in January. The company says it will continue to seek Medicare coverage.