Shear wave elastography (SWE) of the liver is a new technology that has been shown to be useful for distinguishing early from advanced liver fibrosis. At present, interobserver variability limits the use of shear wave elastography for precise staging and serial monitoring of the progression of diffuse liver disease. The broad research goal of this proposal is to reduce shear wave elastography variability. The research has two specific aims. [Aim 1 is to create a new system - hardware and algorithms - by (1) integrating two previously developed systems: (a) a force-measurement (FM) ultrasound probe system, which measures and displays applied transducer force (preload) in real-time, permitting the operator to precisely control applied preload, and (b) an optical tracking system (OTS), which precisely localizes a transducer relative to skin markings, facilitating precise software-based co-registration of shear wave elastograms, and (2) creating new algorithms to process data generated by the integrated FM/OTS device.] In Aim 2 Dr. Samir will perform a clinical trial in thirty human subjects testing the performance of FM/OTS enhanced SWE against the reference standard of histopathologically staged liver fibrosis. Career development goals: Immediate and long-term. Dr. Samir's short-term goal is to acquire additional technical skills and advanced clinical trial skills through the combination of device design, fabrication, and software development under the guidance of MED- RC faculty, particularly Dr. Brian Anthony, and advanced clinical trial skills under the supervision of Raymond Chung MD, who is an expert in Hepatology research. Dr. Ralph Weissleder MD PhD and Dr. Bruce Rosen MD PhD, both well-known experts in Radiology research, will mentor Dr. Samir throughout his training program in order to facilitate his long-term objective, which is to become an independently funded investigator leading a laboratory focused on rapid development and translation of medical ultrasound technology.