VisEn Medical, a medical imaging technology company, has closed a $5 million tranche of Series B financing.

Merck Capital Ventures and Flagship Ventures co-led the expansion of the venture capital (VC) round, which initially raised $7 million in November 2007, bringing the total VC financing round to $12 million.

The Woburn, Mass.-based VisEn said it would use the additional financing to further advance its proprietary fluorescence in vivo imaging product pipelines, and to expand its commercial applications.

VisEn was initially founded in 2000 based on fluorescence in vivo imaging technologies developed at Massachusetts General Hospital and Harvard Medical School; both located in Boston.