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Note 9 - Stockholders' Equity (Tables)
12 Months Ended
Dec. 31, 2021
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
  

Outstanding Warrants to Purchase Shares

  

Exercise Price

 

Expiration date

May 2018 warrants

  762  $4.05 

May 30, 2022

December 2020 warrants

  6,490  $1.00 

December 11 2024-June 21, 2025

January 2021 warrants

  4,500  $1.055 

July 8, 2025

March 2021 warrants

  10,525  $2.88 

September 22, 2025

   22,277      
Warrant [Member]  
Notes Tables  
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]

Initial Valuation

    

Common stock price

 $0.87-0.89 

Exercise price

 $1.00 

Risk-free interest rate

  0.28

%

Expected term

 

4.0 years

 

Dividend yield

  - 

Expected volatility

  107%-124%

December 31, 2020 Valuation

    

Common stock price

 $0.95 

Exercise price

 $1.00 

Risk-free interest rate

  0.27

%

Expected term

 

4.0 years

 

Dividend yield

  - 

Expected volatility

  127

%