Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net loss	$ (3,584)	$ (2,876)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	22	13
Share-based compensation	615	622
Changes in operating assets and liabilities:
Accounts receivable	(32)	(47)
Inventory	43	(9)
Prepaid expenses	63	104
Accounts payable	(164)	(249)
Accrued liabilities	34	157
Deferred revenue	(35)	1
Deferred rent	2	6
Net cash used in operating activities	(3,036)	(2,278)
Investing activities:
Purchase of property and equipment	(5)	(64)
Net used in in investing activities	(5)	(64)
Financing activities:
Proceeds from the exercise of common stock options	5	22
Net cash provided by financing activities	5	22
Net decrease in cash and cash equivalents	(3,036)	(2,320)
Cash and cash equivalents at beginning of period	12,689	21,352
Cash and cash equivalents at end of period	9,653	19,032
Supplemental disclosure of noncash investing activity:
Accounts payable recognized for the purchase of equipment		$ 15