Editorial [Hot topic: Elasticity Imaging Part I (Guest Editors: Armen Sarvazyan and Timothy J. Hall)]

From times immemorial, medical practitioners have used palpation for detection and characterization of pathologies. Recently, a new diagnostic imaging modality has emerged, called elasticity imaging (EI), which is an extension of the ancient art of palpation. Various imaging modalities may be used for EI, including ultrasound, MRI or even X-ray, to visualize the elasticity (stiffness) of soft tissue structures. Elasticity imaging is a cutting-edge diagnostic modality that can be adapted for a very wide range of medical applications. Because many diseases are accompanied by significant changes in tissue mechanical properties and various tumors, especially malignancies, have elastic properties that are often markedly different from surrounding tissues, EI could provide a significant adjunct to current diagnostic methods. Lesions in the breast, liver, thyroid, prostate, pancreas, and lymph nodes have been successfully imaged using EI. Elasticity imaging has the potential to differentiate benign and malignant lesions, to detect steatohepatitis in patients with fatty liver disease, to monitor ablation and other therapeutic lesion treatments. EI has demonstrated its effectiveness in assessing the progress of ablation therapy. In this two-volume special issue on hot topics, some of the world's leading research groups present reviews of many different approaches to EI. The first issue begins with an overview of the historical and theoretical basis of EI. A review of ultrasound methods for elasticity imaging using external vibrators is then presented. That article is followed by two articles where the ultrasound transducer is used as the source of deformation. The first volume of this two-issue series closes with three articles that involve acoustic radiation force techniques for EI. The second issue begins with three more articles that involve acoustic radiation force in EI. The final ultrasound-based EI approach described here uses physiological motion as the source of deformation to image the elastic properties of vasculature. Two papers then review the developments and status of elasticity imaging based on magnetic resonance imaging methods. The final paper of the second volume of this special issue reviews a method for elasticity imaging based on measurements of the surface stress distribution - a method that closely approximates manual palpation by humans. This is a rapidly developing field and, despite efforts to provide a comprehensive review, inevitably some new developments have been left out. We apologize in advance for this and suppose that there will be future reviews where recent meritorious work will be included. We take this opportunity to provide special thanks to the authors of these review articles. Each group has made important contributions to the field of elasticity imaging, has provided their expertise in reporting the current state of affairs and provided enthusiastic support for this project. We are deeply grateful.