Hojun Yu, Presenter: Nothing to Disclose

Hyun-Jung Jang MD, Abstract Co-Author: Advisory Board, Lantheus Medical Imaging, Inc

Tae Kyoung Kim MD, Abstract Co-Author: Advisory Board, Lantheus Medical Imaging, Inc

Korosh Khalili MD, Abstract Co-Author: Nothing to Disclose

Peter N. Burns BSc, PhD, Abstract Co-Author: Nothing to Disclose

Artifactual pseudo-enhancement can occur in deep, avascular echogenic tissue on contrast-enhanced ultrasound (CEUS) due to nonlieanr propagation of ultrasound through microbubble-filled tissue between the transducer and the target lesion with no true vascularity. The purpose of this study was to describe the imaging features of pseudo-enhancement within the post radiofrequency ablation (RFA) zones of liver tumors on CEUS and explain its origin as nonlinear ultrasound propagation.

Twenty-six patients who showed confirmed diagnosis of no tumor recurrence within the RFA zones on CEUS were included in this study. Three radiologists assessed findings on CEUS in the arterial- (<30 seconds), portal- (30 – 90 seconds) and late phases (>90seconds) including: the presence, degree (1 = minimal, 2 = between 1 and 3, 3 = equal to the parenchyma), time to first appearance, progression in degree over time, and location of pseudo-enhancement (marginal or non-marginal) as well as corresponding gray-scale echo (hypo-, iso-, or hyperechoic) and the depth from the skin to the center of the lesion.

Fourteen (14/26, 54%) lesions showed pseudo-enhancement on CEUS. All (14/14) of them corresponded to the hyperechoic area within the RFA zone on gray-scale US and were non-marginal in location. Pseudo-enhancement more frequently occurred in deep lesions (≥5cm) than superficial lesions (<5 cm) (p = 0.002). Pseudo-enhancement was most frequently initiated in the portal phase (9/14, 64%), followed by arterial- (4/14, 29%) and late phase (1/14, 7%). Progression in degree of pseudo-enhancement was demonstrated in most cases (12/14, 86%) and no washout was seen.

Pseudo-enhancement is frequently seen within post RFA zones on CEUS, particularly in deep echogenic lesions. This is consistent with nonlinear propagation of the US beam, which increases with bubble concentration. However, pseudo-enhancement has distinctive imaging features including late initiation, progression over time, and non-marginal location from tumor recurrence which typically shows early enhancement, later washout, and marginal location.

Awareness of pseudo-enhancement phenomenon and its imaging features is important for radiologists to differentiate it from real vascularity in recurrence after ablation therapy of malignant tumors.

Yu, H, Jang, H, Kim, T, Khalili, K, Burns, P, Pseudo-enhancement within Local Ablation Zone of Hepatic Tumors due to Nonlinear Artifact on Contrast-enhanced Ultrasound.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8015655.html