At September 30, 2015, we have instruments outstanding under two stock-based compensation plans; the Amended and Restated 2002 Stock Incentive Plan (the 2002 Plan) and the Amended and Restated 2014 Stock Incentive Plan (the 2014 Plan).  Total shares authorized under each plan are 12 million shares and 5 million shares, respectively.  In addition, we have stock options outstanding that were awarded as an employment inducement in connection with the appointment of our new CEO in October 2014.  Currently, under the 2014 Plan, we may grant incentive stock options, nonqualified stock options, and restricted stock awards to full-time employees and directors, and nonqualified stock options and restricted stock awards may be granted to our consultants and agents.  Although instruments are still outstanding under the 2002 Plan, the plan has expired and no new grants may be made from it.  Under both plans, the exercise price of each option is greater than or equal to the closing market price of our common stock on the date of the grant.

Stock options granted under the 2002 Plan and the 2014 Plan generally vest on an annual basis over one to four years.  The stock options that were awarded as an employment inducement in connection with the appointment of our CEO will vest in three tranches based on certain service and market conditions as defined in the agreement.  Outstanding stock options under the plans, if not exercised, generally expire ten years from their date of grant or up to 90 days following the date of an optionee’s separation from employment with the Company.  We issue new shares of our common stock upon exercise of stock options.

Stock-based payments to employees and directors, including grants of stock options, are recognized in the consolidated statements of operations based on their estimated fair values.  The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model.  Expected volatilities are based on the Company’s historical volatility, which management believes represents the most accurate basis for estimating expected future volatility under the current circumstances.  Navidea uses historical data to estimate forfeiture rates.  The expected term of stock options granted is based on the vesting period and the contractual life of the options.  The risk-free rate is based on the U.S. Treasury yield in effect at the time of the grant.

The portion of the fair value of stock-based awards that is ultimately expected to vest is recognized as compensation expense over either (1) the requisite service period or (2) the estimated performance period.  Restricted stock awards are valued based on the closing stock price on the date of grant and amortized ratably over the estimated life of the award.  Restricted stock may vest based on the passage of time, or upon occurrence of a specific event or achievement of goals as defined in the grant agreements.  In such cases, we record compensation expense related to grants of restricted stock based on management’s estimates of the probable dates of the vesting events.  Stock-based awards that do not vest because the requisite service period is not met prior to termination result in reversal of previously recognized compensation cost.

For the three-month periods ended September 30, 2015 and 2014, our total stock-based compensation expense, which includes reversals of expense for certain forfeited or cancelled awards, was approximately $397,000 and $(528,000), respectively.  For the nine-month periods ended September 30, 2015 and 2014, our total stock-based compensation expense was approximately $1.9 million and $1.0 million, respectively.  We have not recorded any income tax benefit related to stock-based compensation in either of the three-month and nine-month periods ended September 30, 2015 and 2014.

A summary of the status of our stock options as of September 30, 2015, and changes during the nine-month period then ended, is presented below:

A summary of the status of our unvested restricted stock as of September 30, 2015, and changes during the nine-month period then ended, is presented below:

In February 2015, 120,000 shares of restricted stock held by non-employee directors with an aggregate fair value of $193,000 vested as scheduled according to the terms of the restricted stock agreements.  In March 2015, 20,000 shares of restricted stock held by an employee with an aggregate fair value of $33,000 vested as scheduled according to the terms of a restricted stock agreement.  In May 2015, 100,750 shares of restricted stock held by employees with an aggregate fair value of $130,000 vested as scheduled according to the terms of the restricted stock agreements.

As of September 30, 2015, there was approximately $1.5 million of total unrecognized compensation expense related to unvested stock-based awards, which we expect to recognize over the remaining weighted average vesting term of 1.7 years.