Reply to: Contrast-enhanced ultrasonography for intrahepatic cholangiocarcinoma: A cost-effective alternative for low-resource settings

Shu-Yun Tin ,Guo Tin ,Tin-An Jing ,∗

a Department of Ultrasonography, Tongde Hospital of Zhejiang Province, Hangzhou 320012, China

b Department of Ultrasound Medicine, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310 0 03, China

TheAuthorReply:

We thank Pitcairn et al.[1]for their discussion of our study recently published inHepatobiliary＆PancreaticDiseasesInternational[2].They highlighted the added value that contrast-enhanced ultrasonography (CEUS) can present in low-resource settings,where other diagnostic modalities may be neither cost-effective nor readily available.We agree with their point.In addition,we also would like to highlight that CEUS is safer for human body than computed tomography (CT) and magnetic resonance imaging(MRI).

CEUS is an effective and low-cost tool for the qualitative diagnosis of focal liver lesions.With the accumulation of experience,CEUS has been proved to be effective in the diagnosis of intrahepatic cholangiocarcinoma (ICC).For economic reasons,CEUS are easier to be obtained than CT and MRI.The ultrasound machine(average cost about RMB 1.5 million per machine in China) used for CEUS is cheaper than that of CT (about RMB 5 million per machine) and MRI (about RMB 10 million per machine),and the room used for CEUS occupies a smaller area and does not need to be specially constructed for radiation protection and anti-magnetic interference.In addition,in most countries or regions,the price of ultrasound contrast agents also is lower than that of CT and MRI.

As the ultrasound contrast agents (UCAs) are harmless to the liver and kidneys,CEUS is safer than CT and MRI.UCAs consist of gaseous microbubbles suspended in an aqueous solution that is injected into the human venous vascular system.They are composed of an inert inner gas bubble surrounded by a stabilizing outer shell.Different UCA manufacturers use various gas/shell combinations.As the microbubbles are "blood pool" agents,they remain intravascular at all times and do not permeate into adjacent tissues.As such,they act effectively as red blood cell tracers [3].Finally,the ultrasound contrast agents dissolved in the blood are finally exhaled out of the body through breathing,which are harmless to the liver and kidneys.While the contrast agent for enhanced-CT is usually composed of iodine,which diffuses slowly between the fibrous stroma and the blood vessels after entering the body through the venous vessels for a period of time,and then it is slowly removed from the fibrous interstitial vessels [4].The contrast agents for MRI composed of gadolinium,which is the same as iodine,could cause renal function damage in the process of human metabolism,and leads to “contrast induced nephropathy” [5,6].

Based on the low cost and higher safety,CEUS will be widely used in more and more countries.With the increasing role of CEUS in the diagnosis of focal liver diseases,it may be superior to CT or MRI in the future.