May the force be with you : a medical ultrasound system with integrated force measurement

Abstract

Ultrasound is a commonly used medical imaging modality for non-invasive examination of soft tissue. Clinical ultrasound scanning requires significant contact of the transducer face with the patient, and the contact force exerted by the sonographer can vary widely throughout a scan or from scan to scan. This thesis explores the design and development of an electromechanical system to measure the contact force during ultrasound scanning. The device is a handheld ultrasound probe with force sensors integrated into its housing such that the force distribution across the ultrasound transducer face can be measured. The device was used to perform shear wave elastography on tissue-mimicking phantoms and ex vivo tissue at varying force distributions. A gradient in applied pressure introduced a gradient in elasticity across the image for ex vivo tissue but not for phantoms. To consider how the device integrates into the overall system, a human factors study was done to compare feedback modalities provided to the human operator during ultrasound scanning. Visual feedback was more effective than haptic feedback for force tracking, but at expense of ultrasound path tracking. Lastly, two methods of data synchronization of the acquired force data and ultrasound images are considered. A three tap software synchronization method is a feasible alternative when hardware synchronization is unavailable. As a whole, this system will improve the repeatability and capabilities of ultrasound imaging.