The reconciliation of intangible assets for the six months ended June 30, 2019 and 2018 was as follows (in thousands):

	June 30,			June 30,
	2019			2018
Patented technologies
Gross carrying cost at beginning of period	$	68,322		$	36,349
Acquisition of Icon Bioscience Inc.		—			31,973
Gross carrying cost at end of period		68,322			68,322
Accumulated amortization at beginning of period		(38,193	)		(36,349	)
Amortization expense		(1,230	)		(615	)
Accumulated amortization at end of period		(39,423	)		(36,964	)
Net book value at end of period	$	28,899		$	31,358

The Company amortizes intangible assets with finite lives on a straight-line basis over their respective estimated useful lives. Amortization of intangible assets totaled $615,000 and $1.2 million for the three and six months ended June 30, 2019, respectively, and $615,000 for each of the three and six month periods ended June 30, 2018. The Company’s previously acquired finite-lived intangible assets were fully amortized as of December 31, 2017.

In connection with the Icon Acquisition (see Note 3), the initial purchase price was attributed to the DEXYCU product intangible asset. This finite-lived intangible asset is being amortized on a straight-line basis over its expected remaining useful life of 11.75 years at the rate of approximately $2.5 million per year. Amortization expense was reported as a component of cost of sales for the three and six months ended June 30, 2019, and was included in research and development for the three and six months ended June 30, 2018 in the condensed consolidated statement of comprehensive loss. In each of the next five years, the amortization expense is expected to be $2.5 million, respectively.