Note 10 - Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Schedule of Share-based Compensation, Expense [Table Text Block]

	Years ended
	December 31,
	2021		2020
Research and development	$	795	$	1,369
Selling, general and administrative		866		1,583
Total share-based compensation	$	1,661	$	2,952

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Options outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining contractual term (years)		Aggregate intrinsic value (in thousands)
Balance, December 31, 2020		1,114,306		$	5.89		7.5	$	177.1
Stock options granted		772,435			3.56
Stock options exercised		(1,580	)		2.49
Stock options forfeited		(235,350	)		4.49
Stock options expired		(125	)		5.32
Balance, December 31, 2021		1,649,686		$	5.00		7.6	$	—
Exercisable, December 31, 2021		762,867		$	6.62		6.0	$	—
Options vested and expected to vest		1,649,686		$	5.00		7.6	$	—

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

				Weighted
				average
				grant date
	Number of			fair value
	shares			per share
Balance, December 31, 2020		224,311		$	4.12
RSUs granted		131,375			3.61
RSUs released		(118,472	)		3.73
RSUs forfeited		(36,943	)		3.49
Balance, December 31, 2021		200,271		$	4.13

Share-based Payment Arrangement, Option [Member]

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Years ended
	December 31,
	2021			2020
Risk-free interest rate	0.6	-	1.6%	0.4	-	1.6%
Volatility	110	-	120%	107	-	112%
Dividend yield	None			None
Expected term (in years)	6.25	-	10.0	6.25	-	10.0