Stock-based compensation expense included in the Company's consolidated financial statements for the three months ended March 31, 2019 and April 1, 2018 was as follows (in thousands):

	Three Months Ended
	March 31, 2019		April 1, 2018
Cost of revenue	$	26	$	34
Research and development		655		183
Selling, general and administrative		270		215
Total costs and expenses	$	951	$	432

No stock options were granted during the three-month periods ended March 31, 2019 and April 1, 2018. As of March 31, 2019 and April 1, 2018, the fair value of unvested stock options, net of expected forfeitures, was approximately $124,000 and $230,000, respectively. The remaining unrecognized stock-based compensation expense relating to stock options is expected to be recognized over a weighted average period of 1.4 years as of March 31, 2019.

The following table summarizes the activity in the shares available for grant under the 2009 Stock Plan during the three months ended March 31, 2019:

	Shares Available for Grant
	(in thousands)
Balance at December 30, 2018		6,760
Authorized		-
RSUs granted		(3,144	)
RSUs forfeited or expired		158
Options forfeited		20
Balance at March 31, 2019		3,794

The following table summarizes stock options outstanding and stock option activity under the 2009 Plan, and the related weighted average exercise price, for the three months ended March 31, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Term		Aggregate Intrinsic Value
	(in thousands)					(in years)		(in thousands)
Balance outstanding at December 30, 2018		3,201		$	2.18
Forfeited or expired		(20	)		3.12
Exercised		(4	)		0.78
Balance outstanding at March 31, 2019		3,177		$	2.18		3.48	$	-
Exercisable at March 31, 2019		2,894		$	2.30		3.09	$	-
Vested and expected to vest at March 31, 2019		3,144		$	2.19		3.44	$	-

The aggregate intrinsic value in the table above represents the total pretax intrinsic value, based on the Company's closing stock price of $0.61 as of March 31, 2019, which would have been received by the option holders had all option holders exercised their options as of that date.

The total intrinsic value of options exercised during the three months ended March 31, 2019 and April 1, 2018 was $0 as the stock price was lower than exercise price. Total cash received from employees as a result of employee stock option exercises during the three months ended March 31, 2019 and April 1, 2018 was approximately $3,600 and $0, respectively. The Company settles employee stock option exercises with newly issued common shares. In connection with these exercises, there was no tax benefit realized by the Company due to the Company's current loss position. Total stock-based compensation related to stock options was $25,000 and $38,000 for the three months ended March 31, 2019 and April 1, 2018, respectively.

The Company grants restricted stock units or RSUs, to employees and board of directors with various vesting terms. RSUs entitle the holder to receive, at no cost, one common share for each RSU as it vests. In general, the Company's policy is to withhold shares in settlement of employee tax withholding obligations upon the vesting of RSUs. The stock-based compensation related to RSUs was $877,000 and $295,000 for three months ended March 31, 2019 and April 1, 2018, respectively. As of March 31, 2019 and April 1, 2018, there was $3.2 million and $2.4 million, respectively, in unrecognized compensation expense related to RSUs. The remaining unrecognized stock-based compensation expense is expected to be recorded over a weighted average period of 1.75 years.

A summary of activity for the Company's RSUs for the three months ended March 31, 2019 and information regarding RSUs outstanding and expected to vest as of March 31, 2019 is as follows:

	RSUs & PRSUs Outstanding
	Number of Shares			Weighted Average Grant Date Fair Value
	(in thousands)
Nonvested at December 30, 2018		2,570		$	1.23
Granted		3,143			0.87
Vested		(697	)		1.06
Forfeited		(158	)		—
Nonvested at March 31, 2019		4,858		$	1.09

The weighted average estimated fair value, as defined by the amended authoritative guidance, of rights issued pursuant to the Company's 2009 ESPP during the quarters ended March 31, 2019 and April 1, 2018, was $0.31 and $0.46 per right, respectively.

As of March 31, 2019, 1.2 million shares remained available for issuance under the 2009 ESPP. For the three months ended March 31, 2019 and April 1, 2018, the Company recorded stock-based compensation expense related to the 2009 ESPP of $49,000 and $54,000 respectively.

The fair value of rights issued pursuant to the Company's 2009 ESPP was estimated on the commencement date of each offering period using the following weighted average assumptions:

	Three Months Ended
	March 31, 2019			April 1, 2018
Expected term (months)		6.0			6.0
Risk-free interest rate		2.37	%		1.39	%
Volatility		53.77	%		54.87	%
Dividend yield		—			—

As of March 31, 2019, the unrecognized stock-based compensation expense relating to the Company's 2009 ESPP was $24,000 and is expected to be recognized over a weighted average period of approximately 1.5 months.