Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (6,801)	$ (5,821)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	44	36
Share-based compensation	1,353	1,298
Changes in operating assets and liabilities:
Accounts receivable	(96)	(68)
Inventory	55	(58)
Prepaid expenses	58	74
Accounts payable	(390)	60
Accrued liabilities	25	16
Deferred revenue	(65)	82
Deferred rent	3	12
Net cash used in operating activities	(5,814)	(4,369)
Investing activities:
Purchase of property and equipment	(46)	(100)
Purchase of short-term investments		(1,796)
Net used in in investing activities	(46)	(1,896)
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	(5,855)	(6,243)
Cash and cash equivalents at beginning of period	12,689	21,352
Cash and cash equivalents at end of period	$ 6,834	$ 15,109