Flexible ultrasound transceiver array for non-invasive surface-conformable imaging enabled by geometric phase correction.

Ultrasound imaging provides the means for non-invasive real-time diagnostics of the internal structure of soft tissue in living organisms. However, the majority of commercially available ultrasonic transducers have rigid interfaces which cannot conform to highly-curved surfaces. These geometric limitations can introduce a signal-quenching air gap for certain topographies, rendering accurate imaging difficult or impractical. Here, we demonstrate a 256-element flexible two-dimensional (2D) ultrasound piezoelectric transducer array with geometric phase correction. We show surface-conformable real-time B-mode imaging, down to an extreme radius of curvature of 1.5 cm, while maintaining desirable performance metrics such as high signal-to-noise ratio (SNR) and minimal elemental cross-talk at all stages of bending. We benchmark the array capabilities by resolving reflectors buried at known locations in a medical-grade tissue phantom, and demonstrate how phase correction can improve image reconstruction on curved surfaces. With the current array design, we achieve an axial resolution of ≈ 2 mm at clinically-relevant depths in tissue, while operating the array at 1.4 MHz with a bandwidth of ≈ 41%. We use our prototype to image the surface of the human humerus at different positions along the arm, demonstrating proof-of-concept applicability for real-time diagnostics using phase-corrected flexible ultrasound probes.

On the Temperature Dependence of the Piezoelectric Response of Prepoled Poly(vinylidene fluoride) Films.

There is growing interest in integrating piezoelectric materials with complementary metal-oxide-semiconductor (CMOS) technology to enable expanded applications. A promising material for ultrasound transducer applications is polyvinylidene fluoride (PVDF), a piezoelectric polymer. One of the challenges with PVDF is that its piezoelectric properties can deteriorate when exposed to temperatures in excess of 70 °C for extended periods of time during fabrication. Here, we report on the effects of both shortening annealing times and providing this heating non-uniformly, as is characteristic of some processing conditions, on the piezoelectric coefficient (d 33) of PVDF films for various thicknesses. In this case, no degradation in the d 33 was observed at temperatures below 100 °C for anneal times of under one minute when this heating is applied through one side of the film, making PVDF compatible with many bonding and photolithographic processing steps required for CMOS integration. More surprisingly, for one-sided heating to temperatures between 90 °C and 110 °C, we observed a transient enhancement of the d 33 by nearly 40% that lasted for several hours after these anneals. We attribute this effect to induced strain in these films.

Cardiopulmonary Response to Videogaming: Slaying Monsters Using Motion Sensor Versus Joystick Devices.

OBJECTIVE: Replacing physical activity with videogaming has been implicated in causing obesity. Studies have shown that using motion-sensing controllers with activity-promoting videogames expends energy comparable to aerobic exercise; however, effects of motion-sensing controllers have not been examined with traditional (non-exercise-promoting) videogames. MATERIALS AND METHODS: We measured indirect calorimetry and heart rate in 14 subjects during rest and traditional videogaming using motion sensor and joystick controllers. RESULTS: Energy expenditure was higher while subjects were playing with the motion sensor (1.30±0.32 kcal/kg/hour) than with the joystick (1.07±0.26 kcal/kg/hour; P<0.01) or resting (0.91±0.24 kcal/kg/hour; P<0.01). Oxygen consumption during videogaming averaged 15.7 percent of predicted maximum for the motion sensor and 11.8 percent of maximum for the joystick. Minute ventilation was higher playing with the motion sensor (10.7±3.5 L/minute) than with the joystick (8.6±1.8 L/minute; P<0.02) or resting (6.7±1.4 L/minute; P<0.001), predominantly because of higher respiratory rates (15.2±4.3 versus 20.3±2.8 versus 20.4±4.2 beats/minute for resting, the joystick, and the motion sensor, respectively; P<0.001); tidal volume did not change significantly. Peak heart rate during gaming was 16.4 percent higher than resting (78.0±12.0) for joystick (90.1±15.0; P=0.002) and 17.4 percent higher for the motion sensor (91.6±14.1; P=0.002); mean heart rate did not differ significantly. CONCLUSIONS: Playing with a motion sensor burned significantly more calories than with a joystick, but the energy expended was modest. With both consoles, the increased respiratory rate without increasing tidal volume and the increased peak heart rate without increasing mean heart rate are consistent with psychological stimulation from videogaming, rather than a result of exercise. We conclude that using a motion sensor with traditional videogames does not provide adequate energy expenditure to provide cardiovascular conditioning.