CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 28, 2019	Sep. 30, 2020	Sep. 28, 2019
Income Statement [Abstract]
Net revenue	$ 7,091	$ 7,205	$ 18,012	$ 17,547
Cost of revenue	2,053	2,989	6,205	7,425
Gross profit	5,038	4,216	11,807	10,122
Operating expenses:
Research, development and clinical trials	4,155	4,939	14,283	13,608
Selling, general and administrative	5,493	6,519	18,012	17,423
Total operating expenses	9,648	11,458	32,295	31,031
Loss from operations	(4,610)	(7,242)	(20,488)	(20,909)
Other income (expense):
Interest expense	(971)	(1,084)	(3,014)	(3,290)
Change in fair value of preferred stock warrant liability	0			(341)
Other income (expense), net	499	56	1,087	200
Total other expense, net	(472)	(1,028)	(1,927)	(3,431)
Loss before income taxes	(5,082)	(8,270)	(22,415)	(24,340)
Provision for income taxes	(6)	(10)	(22)	(30)
Net loss	$ (5,088)	$ (8,280)	$ (22,437)	$ (24,370)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.19)	$ (0.39)	$ (0.94)	$ (2.05)
Weighted average common shares outstanding, basic and diluted	27,156,135	21,131,618	23,885,517	11,882,626