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Note 1 - Summary of Significant Accounting Policies (Tables)
6 Months Ended
Jun. 30, 2020
Notes Tables  
Property Plant and Equipment Useful Life [Table Text Block]
   
Years
Computers and office equipment
 
3
-
7
Leasehold improvements (1)
 
 
5
 
Manufacturing tooling
 
3
-
7
Laboratory equipment
 
4
-
6
Demo equipment
 
 
3
 
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]
    Six Months Ended June 30,
    2020   2019
    Stock Options
Expected dividend yield  
 
0.0%
 
 
 
0.0%
 
Expected stock price volatility  
82.6%
-
86.8%
 
78.6%
-
79.8%
Risk-free interest rate  
0.62%
-
1.78%
 
2.00%
-
2.76%
Expected life (yeas)  
 
10
 
 
 
10
 
    Warrants
Expected dividend yield  
 
0.0%
 
 
 
0.0%
 
Expected stock price volatility  
82.6%
-
86.8%
 
78.6%
-
79.8%
Risk-free interest rate  
0.33%
-
0.79%
 
1.93%
-
2.58%
Expected life (years)  
2
5.5
 
 
5