London-based health-care company BTG has agreed to buy medical-device maker Ekos of Bothell for $180 million or more, the companies said Friday.

Ekos developed an ultrasound-enhanced system for breaking up blood clots, marketed since 2006 and now used in 490 U.S. hospitals and another 100 elsewhere.

It had $28 million in revenue last year and a $ 2 million operating profit, compared with $20 million in sales and a $1 million loss the year before, according to a BTG statement.

The company’s 150 employees are expected to remain with BTG, the statement said.

In addition to the $180 million purchase price, the deal has provisions for up to $40 million in future milestone payments.