GOODWILL AND OTHER INTANGIBLE ASSETS

In 2018, the Company recorded a $116.2 million impairment charge related to certain of its developed technology and IPR&D assets. See Note 4 for further information. In December 2017, the Company acquired Harpoon Medical, Inc. This transaction resulted in an increase to goodwill of $142.1 million and IPR&D of $53.1 million. In January 2017, the Company acquired Valtech. This transaction resulted in an increase to goodwill of $316.5 million, developed technology of $109.2 million and IPR&D of $87.9 million. For further information, see Note 7.

The changes in the carrying amount of goodwill, by segment, during the years ended December 31, 2018 and 2017 were as follows:



	United States		Europe			Rest of World			Total
	(in millions)
Goodwill at December 31, 2016	$	567.2	$	58.9		$	—		$	626.1
Goodwill acquired during the year	142.1		—			316.5			458.6
Currency translation adjustment	—		8.3			33.5			41.8
Goodwill at December 31, 2017	709.3		67.2			350.0			1,126.5
Currency translation adjustment	—		(3.0		)	(11.3		)	(14.3		)
Goodwill at December 31, 2018	$	709.3	$	64.2		$	338.7		$	1,112.2

Other intangible assets consist of the following (in millions):



		December 31,
	Weighted-Average Useful Life (in years)	2018							2017
	Weighted-Average Useful Life (in years)	Cost		Accumulated Amortization			Net Carrying Value		Cost		Accumulated Amortization			Net Carrying Value
Amortizable intangible assets
Patents	7.4	$	185.8	$	(181.2	)	$	4.6	$	186.1	$	(180.4	)	$	5.7
Developed technology	12.3	119.8		(44.2		)	75.6		190.8		(43.8		)	147.0
	11.9	305.6		(225.4		)	80.2		376.9		(224.2		)	152.7
Unamortizable intangible assets
IPR&D		263.0		—			263.0		315.3		—			315.3
		$	568.6	$	(225.4	)	$	343.2	$	692.2	$	(224.2	)	$	468.0

Goodwill and IPR&D resulting from purchase business combinations are not subject to amortization. Other acquired intangible assets with finite lives are amortized over their expected useful lives on a straight-line basis, or if reliably determinable, based on the pattern in which the economic benefit of the asset is expected to be used. The Company expenses costs incurred to renew or extend the term of acquired intangible assets.

Amortization expense related to other intangible assets for the years ended December 31, 2018, 2017, and 2016 was $2.5 million, $7.8 million, and $7.6 million, respectively. Estimated amortization expense for each of the years ending December 31 is as follows (in millions):



2019	$	2.4
2020	2.9
2021	4.7
2022	7.2
2023	10.7