Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (3,617,000)	$ (3,134,000)
Adjustments required to reconcile net loss to net cash used in operating activities:
Change in fair value of derivative liabilities	11,000	79,000
Stock-based compensation	99,000	122,000
Depreciation	100,000	89,000
Amortization of patents	8,000	8,000
Changes in operating assets and liabilities:
Accounts payable and accrued expenses	453,000	(61,000)
Accrued compensation	482,000	(355,000)
Prepaid expenses and other current assets	(156,000)	(284,000)
Net cash used in operating activities	(2,620,000)	(3,536,000)
Investing activities:
Purchases of property and equipment	(7,000)
Net cash used in investing activities	(7,000)
Financing activities:
Proceeds from sale of common stock, net of offering costs		6,409,000
Proceeds from exercises of warrants	5,000	198,000
Proceeds from stock issuance under employee stock purchase plan		3,000
Net cash provided by financing activities	5,000	6,610,000
Net increase (decrease) in cash and cash equivalents	(2,622,000)	3,074,000
Cash and cash equivalents, beginning of period	8,157,000
Cash and cash equivalents, end of period	$ 5,535,000	8,206,000
Supplemental schedule of non-cash financing activities:
Offering costs included in accounts payable		$ 223,000