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Note 6 - Equity - Stock Option Activity (Details) - USD ($)
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Outstanding, number of shares (in shares) 1,438,352  
Outstanding, weighted average grant date fair value (in dollars per share) $ 6.35  
Outstanding, weighted average exercise price (in dollars per share) $ 8.45  
Outstanding, weighted average remaining contractual term (Year) 7 years 9 months 18 days 7 years 9 months 18 days
Outstanding, aggregate intrinsic value $ 0 $ 0
Granted, number of shares (in shares) 842,832  
Granted, weighted average grant date fair value (in dollars per share) $ 1.26  
Granted, weighted average exercise price (in dollars per share) $ 1.49  
Exercised, number of shares (in shares) 0  
Exercised, weighted average grant date fair value (in dollars per share) $ 0  
Exercised, weighted average exercise price (in dollars per share) $ 0  
Forfeited, number of shares (in shares) (5,834)  
Forfeited, weighted average grant date fair value (in dollars per share) $ 15.57  
Forfeited, weighted average exercise price (in dollars per share) $ 24.39  
Outstanding, number of shares (in shares) 2,275,350 1,438,352
Outstanding, weighted average grant date fair value (in dollars per share) $ 4.44 $ 6.35
Outstanding, weighted average exercise price (in dollars per share) $ 5.83 $ 8.45
Exercisable, number of shares (in shares) 927,723  
Exercisable, weighted average grant date fair value (in dollars per share) $ 7.53  
Exercisable, weighted average exercise price (in dollars per share) $ 10.38  
Exercisable, weighted average remaining contractual term (Year) 6 years 3 months 18 days  
Exercisable, aggregate intrinsic value $ 0