Note 7 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Net operating loss carryforwards	$ 17,309	$ 19,230
Research and development credit carryforwards	2,302	2,747
Capitalized research and development	(31)	0
Stock-based compensation	377	382
Accrued expenses and reserves	38	58
Depreciation and amortization	37	0
Deferred revenue	53	107
Lease liability	289	318
Other	46	7
Gross deferred tax assets	20,420	22,849
Less: valuation allowance	(20,161)	(22,544)
Net deferred tax assets	259	305
Depreciation and amortization	0	(16)
Right-of-use asset	(259)	(289)
Net deferred tax assets	0	0
Deferred tax assets, non-current	0	0
Deferred tax liability, non-current	$ 0	$ 0