Note 4 - Warrants (Tables)

3 Months Ended

Mar. 31, 2022

Notes Tables

Schedule of Warrants or Rights, Assumptions Used [Table Text Block]

	March 31, 2022	December 31, 2021
Risk-free interest rate	1.5% to 2.4%	0.1% to 1.1%
Volatility	50.0% to 112.2%	71.8% to 114.5%
Expected life (years)	0.9 to 3.4	0.1 to 3.6
Dividend yield	—%	—%

Schedule of Warrant Activity [Table Text Block]

	Number of Shares			Range of Warrant Exercise				Weighted Average		Weighted Average Remaining Contractual
	Under Warrant			Price per Share				Exercise Price		Life (Years)
Balance at January 1, 2022		2,723,645		$	6.30	$	16.80	$	9.46		2.6
Expired		(67,349	)		8.10		9.00		—		—
Balance at March 31, 2022		2,656,296		$	6.30	$	16.80	$	9.49		2.4
Exercisable at March 31, 2022		2,656,296		$	6.30	$	16.80	$	9.49		2.4