The reconciliation of intangible assets for the nine months ended September 30, 2022 and 2021 (in thousands) was as follows:


	September 30,			September 30,
	2022			2021
Patented technologies
Gross carrying amount at beginning of period	$	68,322		$	68,322
Gross carrying amount at end of period		68,322			68,322
Accumulated amortization at beginning of period		(45,573	)		(43,113	)
Amortization expense		(1,845	)		(1,845	)
Accumulated amortization at end of period		(47,418	)		(44,958	)
Net book value at end of period	$	20,904		$	23,364

The Company amortizes intangible assets with finite lives on a straight-line basis over their respective estimated useful lives of 13 years. Amortization of intangible assets totaled $615,000 and $1.8 million for each of the three and nine months ended September 30, 2022 and 2021, respectively.

In connection with the Company’s acquisition of Icon Bioscience, Inc., 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 8.5 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 nine months ended September 30, 2022 and 2021, respectively.

On November 1, 2022, the Center for Medicare & Medicaid Services (“CMS”) published in the Federal Register the calendar year (CY) 2023 Medicare Hospital Outpatient Prospective Payment System and ASC Payment System Final Rule (“Final Rule”). The Final Rule terminated the pass-through related separate payment for DEXYCU, which will no longer be separately reimbursed by Medicare as of January 1, 2023, when furnished in hospital outpatient departments and ASC settings. The Final Rule will reduce the amount of Medicare reimbursement provided to the Company’s DEXYCU customers and may result in a significant reduction in the Company’s DEXYCU product revenues (see Note 3). Furthermore, the reduction in the Company’s DEXYCU product revenues is expected to result in a material impairment of the Company’s net intangible asset related to DEXYCU which has a carrying value of $20.9 million at September 30, 2022.

The Company is evaluating the impact of the Final Rule on its operations, cash flows, intangible asset and its DEXYCU inventory balances. The Company expects that it will record a charge in the fourth quarter related to the impairment of the DEXYCU intangible asset and for excess inventory as a result of the Final Rule. No adjustments have been made to the Company’s September 30, 2022 financial statements as a result of the Final Rule.