Mistras Group Inc, a provider of technology to evaluate the structural integrity of infrastructure, rose slightly in its first session following an initial public offering that priced below expectations.

Mistras shares starting trading at $12.30, or 1.6 percent below the IPO price, before recovering. In early trading, they were at $12.75, on the New York Stock Exchange, or 2 percent above the IPO price of $12.50.

Mistras sold 8.7 million shares in the IPO and raised $108.75 million, as shares priced below the expected range of $14 and $16 apiece.

The company, whose clients include Pfizer Inc and ExxonMobil Corp, saw revenue rise 37.3 percent to $209.1 million in fiscal 2009, with net income of $5.5 million.

Biotech company Omeros Corp which makes central nervous system anti-inflammation products, priced at $10 per share, at the bottom of the estimate range. It is set to begin trade on Nasdaq later on Thursday morning under the symbol OMER.

(Reporting by Phil Wahba, editing by Gerald E. McCormick)