Pharmaceutical company Bristol-Myers Squibb Co., of New York City, today announced its plans to close more than half of its manufacturing plants, including its medical imaging unit, as part of a broad restructuring plan.

According to Bristol-Myers, its strategic plan, which also involves laying off about 4,300 employees, or 10 percent of its workforce, would generate pretax cost savings and save the company $1.5 billion by 2010.

The elimination of its medical imaging business, based in North Billerica, Mass., will allow Bristol-Myers to concentrate on "key growth products," including specialty and biologic medicines and cardiovascular and metabolic drugs, company execs said.

"It is difficult to see our valued colleagues leave the company, but right-sizing our workforce across all areas is critical to achieving our productivity goals and enhancing the competitive position of the company," CEO James Cornelius said in a statement.

The company produces Cardiolite, a technetium-based radiopharmaceutical for nuclear cardiology imaging, in addition to the Definity ultrasound contrast agent, Neurolite, TechneLite and Miraluma, among others.