Brain-mimicking phantom for biomechanical validation of motion sensitive MR imaging techniques.

Motion sensitive MR imaging techniques allow for the non-invasive evaluation of biological tissues by using different excitation schemes, including physiological/intrinsic motions caused by cardiac pulsation or respiration, and vibrations caused by an external actuator. The mechanical biomarkers extracted through these imaging techniques have been shown to hold diagnostic value for various neurological disorders and conditions. Amplified MRI (aMRI), a cardiac gated imaging technique, can help track and quantify low frequency intrinsic motion of the brain. As for high frequency actuation, the mechanical response of brain tissue can be measured by applying external high frequency actuation in combination with a motion sensitive MR imaging sequence called Magnetic Resonance Elastography (MRE). Due to the frequency-dependent behavior of brain mechanics, there is a need to develop brain phantom models that can mimic the broadband mechanical response of the brain in order to validate motion-sensitive MR imaging techniques. Here, we have designed a novel phantom test setup that enables both the low and high frequency responses of a brain-mimicking phantom to be captured, allowing for both aMRI and MRE imaging techniques to be applied on the same phantom model. This setup combines two different vibration sources: a pneumatic actuator, for low frequency/intrinsic motion (1 Hz) for use in aMRI, and a piezoelectric actuator for high frequency actuation (30-60 Hz) for use in MRE. Our results show that in MRE experiments performed from 30 Hz through 60 Hz, propagating shear waves attenuate faster at higher driving frequencies, consistent with results in the literature. Furthermore, actuator coupling has a substantial effect on wave amplitude, with weaker coupling causing lower amplitude wave field images, specifically shown in the top-surface shear loading configuration. For intrinsic actuation, our results indicate that aMRI linearly amplifies motion up to at least an amplification factor of 9 for instances of both visible and sub-voxel motion, validated by varying power levels of pneumatic actuation (40%-80% power) under MR, and through video analysis outside the MRI scanner room. While this investigation used a homogeneous brain-mimicking phantom, our setup can be used to study the mechanics of non-homogeneous phantom configurations with bio-interfaces in the future.

A force augmenting exoskeleton for the human hand designed for pinching and grasping.

Almost 1 million Americans suffer from debilitative disorders or injuries to the hand, which result in decreased grip strength and/or impaired ability to hold objects. The objective of this study was to design and test the functioning of a fivedigit exoskeleton for the human hand that augments pinching and grasping efforts. The exoskeleton digits and the wrist and forearm structure was computer designed and 3-D printed using ABS plastic, while the housing for the control system, motors, and batteries was constructed from laser-cut acrylic. The user's finger movement efforts were monitored with force sensing resistors (FSR) located within the fingertips of the exoskeleton. A microcomputer-based control system monitored the FSRs and commanded linear actuators that augmented the wearer's force production. The exoskeleton device was tested on six healthy individuals. Using the device for grasping efforts significantly decreased the muscle activity necessary to maintain a constant force $( \mathrm {p}<0.001)$; however, no significant benefit was identified during pinching efforts. In conclusion, a novel 5-digit exoskeleton was designed, and functional testing identified a significant benefit of using the device during grasping efforts.