Functional electrical stimulation (FES) is used to restore movements in paretic limbs after severe paralyses resulting from neurological injuries such as spinal cord injury (SCI). Most chronic FES systems utilize an implantable electrical stimulator to deliver a small electric current to the targeted muscle or nerve to stimulate muscle contractions. These implanted stimulators are generally bulky, mainly due to the size of the batteries. Furthermore, these battery-powered stimulators are required to be explanted every few years for battery replacement which may result in surgical failures or infections. Hence, a wireless power transfer technique is desirable to power these implantable stimulators.
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Conventional wireless power transduction faces significant challenges for safe and efficient energy transfer through the skin and deep into the body. Inductive and electromagnetic power transduction is generally used for very short distances and may also interfere with other medical measurements such as X-ray and MRI. To address these issues, we have developed a wireless, ultrasonically powered, implantable piezoelectric stimulator. The stimulator is encapsulated with biocompatible materials.
The objective of this study was to develop a wirelessly powered miniature neuromuscular stimulator that can be implanted deep inside the human body for FES-induced movement restorations after paralysis. In the present work, preference was given to acoustic power transfer over other power transduction modalities such as electrical and electromagnetic transfer, based on the efficiency, energy absorption by the skin and depth of transmission into the body. A number of recent studies have shown the efficacy of successful power transmission to biomedical implants via ultrasound energy [21]. To develop an ultrasonically powered FES system, we first tested a number of piezoelectric materials and selected the best material with the highest output power. Next, we determined the best conditioning circuit to convert piezoelectric signals into stimulation pulses. After that, we prototyped the stimulator, and coated it with biocompatible materials. The size of the implant has been greatly reduced as the battery is absent from the device. Finally, we implanted the stimulator in paralyzed rats and tested the stimulation-induced muscle contraction and leg movements in the anaesthetized condition.
Electroceuticals, i.e., treating disease or anomalies with electrical impulses, is immerging and may be the future of modern medicine [55]. But delivering power to these electrical implants, deep inside the body, remains a critical challenge [1]. To address this, different wireless powering modalities have been investigated. Wireless powering of implantable devices utilizes an energy transduction method to generate electrical energy from vibrational, electromagnetic, electrostatic, infrared radiant and/or ultrasound energy, through specific conversion [23]. Recent developments of implantable medical devices suggest that it might be more feasible to utilize wireless power transfer for electrical stimulation therapy compared to the classical power supply methods, such as battery implants [20]. The method of using harvested energy from external sources to stimulate nerve or muscle would be more endurable and could help to avoid multiple surgeries for replacing the battery or wire as the power can be wirelessly delivered to the implant [47]. There are several energy transduction methods which can possibly be implemented to power implantable devices such as optical [49], thermal gradient [68], vibrational energy [50], mid to far field radio energy [30], inductive power transfer [16], near-field capacitive coupling [34], and acoustic/ultrasound power transfer [11]. Table 2 summarizes recent developments of implantable medical devices based on these technologies. Our developed PolyUStimulator is one of the devices among them.
The present study successfully demonstrated the feasibility of using external ultrasound signals to power an implanted piezoelectric stimulator to induce movements in spinal cord injured rats using functional electrical stimulation. The stimulator uses a PZT disc, a voltage doubler circuit and a pair of stimulating electrodes. Presently, this prototype is able to generate sufficient voltage to induce muscle contraction in anaesthetized rats. However, more piezoelectric materials should be tested in the future to discover even better ones with higher efficiency to generate a higher stimulation voltage with less transferred power. Apart from this, the parameter which affects the generated output voltage should first be determined in order to select the best material. In the current study, it appears that the dielectric loss and mechanical quality factor contributed a lot to the output voltage of the stimulator. Further study of the piezoelectric parameters may be needed to improve the design of our stimulator.
Many customers are planning to purchase or already own a generator. Generators must be installed properly or they can back-feed through the service line to the distribution lines, causing a serious safety hazard for the crews restoring power, and your neighbors who may think the power lines are dead. Generators should be connected to the building's electrical system using an approved transfer switch. The alternative is to plug selected appliances and equipment directly into the generator.
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3D cardiac MRI has long held promise for improved heart coverage, higher resolution, and reduced sensitivity to poor breath-hold reproducibility. However, its use has been limited by reduced blood pool to myocardium contrast for spoiled and balanced steady-state free precession (bSSFP) implementations. T2-preparation techniques [1] are capable of increasing contrast but are unfortunately limited by lengthy preparation periods and resulting scan inefficiencies. In this work, we develop a paradigm for high contrast 3D cardiac function that relies on the alternative use of magnetization transfer (MT) preparation [2] combined with accelerated 3D spoiled gradient echo imaging (SPGR).
An off-resonance RF pulse was interleaved with whole-heart, respiratory gated 3D radial SPGR sampling [3]. Simulations and phantom scans were performed to optimize MT saturation (power, off-resonance, and frequency). Phantom scans utilized 4% agar, fat, and doped water. After optimization, initial volunteer images were collected on a clinical 1.5T system (HDx, GE, Waukesha, WI) using: FOV = 64 32 32 cm3, 2.0 mm isotropic spatial resolution, TR/TE1/TE2 = 5.6/1.32/3.32 ms, α = 4, free-breathing: scan time = 10 min, 50% acceptance window (bellows), number of projections = 39,000. In-vivo experiments utilized a 1600, 20 ms Hamming-windowed Sinc pulse applied every 10 TRs. This pulse was applied at 210 Hz off-resonance providing some fat-saturation. In addition, two full echoes (TE1 and TE2) at 62.5 kHz were added to further remove fat signal while increasing SNR of water images. Twenty cardiac time frames were reconstructed using iterative soft thresholding of temporal differences with a spatial wavelet transform. 2ff7e9595c
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