Intra-operative freehand real-time elastography for small focal liver lesions: "visual palpation" for non-palpable tumors

Freehand real-time elastography (RTE) has seldom been used to visualize abdominal organs due to their complicated structure and difficulty in freehand compression. We describe a novel, intra-operative imaging system for performing freehand RTE of the liver.

An RTE system was designed using a spatial, cross-correlation method equipped with a feedback function that checks the quality and quantity of the external compression. Intra-operative freehand RTE was performed for 27 adenocarcinomas, 18 hepatocellular carcinomas (HCCs), and 11 benign lesions after routine B-mode intra-operative ultrasonography (IOUS). Elasticity images were classified into 4 types, from type A (more or comparable strain relative to the background) to type D (no strain), according to the degree of strain contrast with the surrounding liver. We then evaluated the compliance of the RTE findings with the pathologic diagnosis.

RTE images were obtained for all the lesions except for 1 metastatic adenocarcinoma. Fourteen of the 18 HCCs were classified as type B or C, with a sensitivity of 83%, a specificity of 76%, and an accuracy of 61%, while 22 of the 26 adenocarcinomas were classified as type D, with a sensitivity of 85%, a specificity of 86%, and an accuracy of 86%. For 15 lesions, clear images were difficult to obtain using B-mode IOUS, whereas RTE visualized clearly the differences in elasticity.

Our new RTE system facilitated the successful freehand RTE of liver lesions in an intra-operative setting, enabling "visual palpation" during liver surgery and serving as a supportive modality for B mode IOUS.