OSI Systems Inc. on Thursday said improving sales in its long-struggling health care diagnostics unit helped it achieve a fiscal fourth quarter profit that beat analysts’ forecasts, although revenue was less than expected.

The Hawthorne company, which makes medical imaging systems, airport security screening machines and electronic components, reported net income of $12 million (61 cents a share) for the quarter ended June 30, compared with $8 million (42 cents) in the same period a year earlier.

Revenue rose 11 percent to more than $183 million, with healthcare revenue up 10 percent to $56.6 million. Sales in the security division rose 17 percent to $75.7 million.

Excluding one-time items, the company earned 66 cents a share. Analysts surveyed by Thomson Reuters on average expected per-share profit of 65 cents on revenue of $188 million.

OSI forecast fiscal 2012 revenue above analysts’ forecasts, based on an order backlog of $304 million that was 27 percent higher than at the end of fiscal 2010. “This momentum … positions us well for continued top line growth and earnings expansion in fiscal 2012,” Chief Executive Deepak Chopra said in a statement.

The company expects net income of $2.21 to $2.32 a share on revenue of $722 to $740 million. The Wall Street consensus has been for per-share profit of $2.24 on revenue of $713 million.

Shares were down 50 cents, or 1.4 percent, to $35.75 in midday trading on the Nasdaq.