An ergonomic, instrumented ultrasound probe has been developed for medical imaging applications. The device, which fits compactly in the hand of sonographers and permits rapid attachment & removal of the ultrasound probe, measures ultrasound probe-to-patient contact forces and torques in all six axes. The device was used to measure contact forces and torques applied by ten professional sonographers on five patients during thirty-six abdominal exams. Of the three contact forces, those applied along the probe axis were found to be largest, averaging 7.0N. Measurement noise was quantified for each axis, and found to be small compared with the axial force. Understanding the range of forces applied during ultrasound imaging enables the design of more accurate robotic imaging systems and could also improve understanding of the correlation between contact force and sonographer fatigue and injury.

A hand-held force-controlled ultrasound probe has been developed for medical imaging applications. The probepatient contact force can be held constant to improve image stability, swept through a range, or cycled. The mechanical portion of the device consists of a ball screw linear actuator driven by a servo motor, along with a load cell, accelerometer, and limit switches. The performance of the system was assessed in terms of the frequency response to simulated sonographer hand motion and in hand-held image feature tracking during simulated patient motion. The system was found to attenuate contact force variation by 97% at 0.1 Hz, 83% at 1 Hz, and 33% 10 Hz, a range that spans the typical human hand tremor frequency spectrum. In studies with 15 human operators, the device applied the target contact force with ten times less variation than in conventional ultrasound imaging. An ergonomic, human-in-the-loop, imaging-workflow enhancing control scheme, which combines both force-and positioncontrol, permits smooth making and breaking of probe-patient contact, and helps the operator keep the probe centered within its range of motion. By controlling ultrasound probe contact force and consequently the amount of tissue deformation, the system enhances the repeatability, usability, and diagnostic capabilities of ultrasound imaging.

It is feasible to directly measure forces applied by sonographers using a high-resolution force measurement system. Forces applied during abdominal imaging vary widely, are significantly higher when scanning subjects with high BMI, and are not related to sonographer years of experience. This force measurement system has the potential to provide an additional quantitative data point to explore the impact of applied forces on sonographer related musculoskeletal injury, particularly in conjunction with various body positions, exam types and force durations.

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Tissue deformation in ultrasound imaging poses a challenge to the development of many image registration techniques, including multimodal image fusion, multi-angle compound image and freehand three-dimensional ultrasound. Although deformation correction methods are desired to provide images of uncompressed tissue structure, they have not been well-studied. A novel trajectory-based method to correct a wide range of tissue deformation in ultrasound imaging was developed. In order to characterize tissue deformation under different contact forces, a force sensor provides contact force measurement. Template based image-flow techniques were applied to RF A-lines under different contact forces. A two-dimensional displacement trajectory field was constructed, where pixel coordinates in each scan were plotted against the corresponding contact force. Nonlinear extrapolation algorithms are applied to each trajectory to relocate the corresponding pixel to where it would have been had there been no contact, thereby correcting tissue deformation in the images. This method was validated by using a combination of FEM deformation and ultrasound simulation. It was shown that deformation of the simulated pathological tissue could be corrected. Furthermore, nonlinear polynomial regression was found to give better estimates, than linear regression, when large deformation was present. Estimation accuracy was not improved significantly for a polynomial regression larger than second order.