Note 6 - Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued expenses	$ 240	$ 87
Accrued salaries and employee benefits	851	961
Accrued clinical trial costs	457	452
Grant liability	610	615
Customer deposits	90	90
Total	$ 2,248	$ 2,205