Note 2 - Summary of Significant Accounting Policies - Revenue Disaggregated by Type and Geography (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue	$ 814	$ 2,024	$ 2,068	$ 7,844
Systems [Member]
Revenue	232	1,276	433	5,341
Instruments and Accessories [Member]
Revenue	204	373	559	1,479
Service [Member]
Revenue	378	375	1,076	1,024
UNITED STATES
Revenue	289	142	603	427
UNITED STATES | Systems [Member]
Revenue	101	0	176	0
UNITED STATES | Instruments and Accessories [Member]
Revenue	82	43	149	68
UNITED STATES | Service [Member]
Revenue	106	99	278	359
Non-US [Member]
Revenue	525	1,882	1,465	7,417
Non-US [Member] | Systems [Member]
Revenue	131	1,276	257	5,341
Non-US [Member] | Instruments and Accessories [Member]
Revenue	122	330	410	1,411
Non-US [Member] | Service [Member]
Revenue	$ 272	$ 276	$ 798	$ 665