The top after-market NASDAQ Stock Market gainers are: Vital Images, LoopNet, InfoSpace, NutriSystem, Newport, Cubist Pharmaceuticals, Fortinet, Encore Wire, Citrix Systems, and Sino Clean Energy.

Vital Images Inc. (VTAL) stock jumped 31.31 percent to $18.62 in the after-market trading, as it agreed to be acquired by a subsidiary of Toshiba Medical Systems for $18.75 a share, or about $273 million in the aggregate, through a cash tender offer followed by a merger. It is anticipated that Toshiba Medical subsidiary will commence a tender offer for all of the outstanding shares of Vital Images by May 11. It is expected that the transaction will close in the second or third quarter of 2011.

On a preliminary basis, Vital Images' revenue for the first quarter of 2011 was better than expected for its non-Toshiba Medical business, although revenues pertaining to Toshiba Medical were negatively affected by Toshiba Medical's business. While overall first quarter 2011 revenue was better than first quarter of 2010, it will be slightly below analyst expectations. Earnings were largely in-line with expectations. Vital Images expects to report full first quarter financial results on May 2; however, in light of the pending transaction, the first quarter earnings conference call on May 5 has been cancelled.

LoopNet, Inc. (LOOP) stock climbed 26.03 percent to $18.11 in the after-market trading, as it agreed to be acquired by CoStar Group, Inc. (CSGP). LoopNet shareholders will receive $16.50 in cash and 0.03702 shares of CoStar common stock for each share of LoopNet common stock, representing a total equity value of about $860 million and an enterprise value of $762 million. The boards of both companies have unanimously approved the transaction which is expected to close by the end of 2011.

Separately, LoopNet reported first quarter earnings of $1.76 million or 4 cents a share, down from $2.32 million or 5 cents a share last year. Adjusted earnings were $4.018 million or 10 cents a share, compared to $4.017 million or 9 cents a share last year. Revenue rose to $20.71 million from $18.82 million. Analysts had expected profit of 5 cents a share on revenue of $20.38 million.

InfoSpace Inc. (INSP) stock advanced 19.59 percent to $10.50 in the after-market trading, as its first quarter earnings and revenue exceeded Street view. Profit was $2.1 million or 6 cents a share, up from $1.5 million or 4 cents a share last year. Adjusted profit rose to $3.2 million or 9 cents a share from $2.1 million or 6 cents a share. Revenue was $61.63 million, compared to $61.77 million last year. Analysts had expected profit of 5 cents a share on revenue of $58.99 million.

InfoSpace expects second quarter earnings of $1.5 million to $2.5 million or 4 cents to 7 cents a share and revenue of $59 million to $62 million, while Street predicts profit of 4 cents a share on revenue of $58.43 million.

NutriSystem Inc. (NTRI) stock surged 13.35 percent to $16.30 in the after-market trading. Loss from continuing operations for the first quarter were $3.42 million or 12 cents a share, compared to a profit of $4.9 million or 16 cents a share last year. Revenue declined to $132.67 million from $158.83 million. Analysts had expected a loss of 30 cents a share on revenue of $126.33 million.

NutriSystem expects second quarter earnings of 25 cents to 30 cents a share, while Street predicts 30 cents a share. For the full year 2011, the company raised its earnings guidance to range of 55 cents to 65 cents a share from previous forecast of 40 cents to 50 cents a share, while Street analysts predict 46 cents a share. The company also said its board of directors has declared a quarterly dividend of $0.175 a share, payable May 19, to shareholders of record as of May 9.

Newport Corp. (NEWP) stock soared 11.54 percent to $20 in the after-market trading, as its first quarter earnings and revenue exceeded Street view. Profit was $20.8 million or 53 cents a share, up from $5.1 million or 14 cents a share last year. Results for the latest quarter included a gain of $7.2 million or 18 cents a share, resulting from a non-recurring currency translation adjustment. Revenue grew 19.8 percent to $128.4 million. Analysts had expected profit of 28 cents a share on revenue of $123.7 million.

In the second quarter of 2011, we anticipate increasing our sales 12 percent to 15 percent over the $114.6 million recorded in the second quarter of 2010 and leveraging that revenue growth into operating income that is more than 50 percent higher than the year ago period, Newport's chief executive officer Robert Phillippy said.

For the full year, Newport expects to increase earnings per share by more than 50 percent compared with the $1.09 recorded in 2010. Excluding the non-recurring currency translation gain of 18 cents a share, adjusted earnings for the full year are expected to be more than 35 percent higher than the 2010 level.

Cubist Pharmaceuticals Inc. (CBST) stock improved 8.19 percent to $37.40 in the after-market trading. The stock reached a new 52-week high of $34.57 on Wednesday.

Fortinet Inc. (FTNT) stock grew 7.79 percent to $44.98 in the after-market trading, as its first quarter earnings and revenue exceeded Street view. Adjusted profit was $13.9 million or 17 cents a share, up from $5.8 million or 8 cents a share last year. Revenue grew 34 percent to $93.3 million. Analysts had expected profit of 14 cents a share on revenue of $86.86 million.

In addition, Fortinet said its board has approved a two-for-one stock split of the company's shares, to be effected in the form of a stock dividend. The stock split will entitle each stockholder of record at the close of business on May 9, to receive one additional share for every one share owned as of that date. The additional shares resulting from the stock split are expected to be distributed by the company's transfer agent on or about June 1. Upon the completion of the stock split, Fortinet will have about 153 million shares of common stock outstanding.

Encore Wire Corp. (WIRE) stock increased 7.36 percent to $27 in the after-market trading, as its first quarter earnings exceeded Street view. Profit was $10.7 million or 46 cents a share, compared to a loss of $2.5 million or 11 cents a share last year. Sales rose to $303.4 million from $175.2 million. Analysts had expected profit of 20 cents a share on revenue of $254 million. The company said unit volumes, measured in pounds of copper contained in the wire, sold during the quarter increased 28.9 percent from last year.

Citrix Systems, Inc. (CTXS) stock gained 6.33 percent to $82.76 in the after-market trading, as its first quarter earnings and revenue exceeded Street view. Adjusted profit was $96.64 million or 50 cents a share, up from $75.05 million or 40 cents a share last year. Revenue grew 18 percent to $490.89 million. Analysts had expected profit of 42 cents a share on revenue of $475.30 million.

Citrix expects second quarter adjusted earnings of 54 cents to 55 cents a share and revenue of $515 million to $525 million, while Street predicts profit of 54 cents a share on revenue of $516.67 million. For the full year 2011, the company expects adjusted earnings of $2.38 to $2.41 a share and revenue of $2.14 billion to $2.17 billion, while Street analysts predict profit of $2.32 a share on revenue of $2.13 billion.

Sino Clean Energy Inc. (SCEI) stock rose 3.91 percent to $2.92 in the after-market trading. The company said its board of directors has appointed Joseph Levinson as an independent director and a member and Chairman of the Board's Audit committee, effective April 27.