Yihe Hua

Bio: Yihe Hua is an academic researcher from General Electric. The author has contributed to research in topics: Electromagnetic coil & Magnet. The author has an hindex of 7, co-authored 18 publications receiving 181 citations.

Lightweight, compact, and high-performance 3T MR system for imaging the brain and extremities

Abstract: Purpose To build and evaluate a small-footprint, lightweight, high-performance 3T MRI scanner for advanced brain imaging with image quality that is equal to or better than conventional whole-body clinical 3T MRI scanners, while achieving substantial reductions in installation costs. Methods A conduction-cooled magnet was developed that uses less than 12 liters of liquid helium in a gas-charged sealed system, and standard NbTi wire, and weighs approximately 2000 kg. A 42-cm inner-diameter gradient coil with asymmetric transverse axes was developed to provide patient access for head and extremity exams, while minimizing magnet-gradient interactions that adversely affect image quality. The gradient coil was designed to achieve simultaneous operation of 80-mT/m peak gradient amplitude at a slew rate of 700 T/m/s on each gradient axis using readily available 1-MVA gradient drivers. Results In a comparison of anatomical imaging in 16 patients using T2 -weighted 3D fluid-attenuated inversion recovery (FLAIR) between the compact 3T and whole-body 3T, image quality was assessed as equivalent to or better across several metrics. The ability to fully use a high slew rate of 700 T/m/s simultaneously with 80-mT/m maximum gradient amplitude resulted in improvements in image quality across EPI, DWI, and anatomical imaging of the brain. Conclusions The compact 3T MRI system has been in continuous operation at the Mayo Clinic since March 2016. To date, over 200 patient studies have been completed, including 96 comparison studies with a clinical 3T whole-body MRI. The increased gradient performance has reliably resulted in consistently improved image quality.

Thermal controlling method, magnetic field generator and mri apparatus

Abstract: With a view toward implementing a thermal controlling method for making reversible a temperature characteristic of a magnetic field generator using permanent magnets small in Hcj, a magnetic field generator whose temperature characteristic is reversible, using permanent magnets small in Hcj, and an MRI apparatus provided with such a magnetic field generator, there is provided a method for controlling the temperature of a magnetic field generator having a pair of disc-shaped permanent magnets whose magnetic poles opposite in polarity to each other are opposed to each other with spacing defined therebetween, and a yoke that forms return passes for magnetic fluxes of the permanent magnets, comprising the steps of raising the temperature from room temperature to a temperature higher than the room temperature, maintaining the temperature higher than the room temperature, and lowering the temperature from the temperature higher than the room temperature to the room temperature, whereby the temperature characteristics of the permanent magnets are made reversible.

Highly efficient head-only magnetic field insert gradient coil for achieving simultaneous high gradient amplitude and slew rate at 3.0T (MAGNUS) for brain microstructure imaging.

Abstract: Purpose To develop a highly efficient magnetic field gradient coil for head imaging that achieves 200 mT/m and 500 T/m/s on each axis using a standard 1 MVA gradient driver in clinical whole-body 3.0T MR magnet. Methods A 42-cm inner diameter head-gradient used the available 89- to 91-cm warm bore space in a whole-body 3.0T magnet by increasing the radial separation between the primary and the shield coil windings to 18.6 cm. This required the removal of the standard whole-body gradient and radiofrequency coils. To achieve a coil efficiency ~4× that of whole-body gradients, a double-layer primary coil design with asymmetric x-y axes, and symmetric z-axis was used. The use of all-hollow conductor with direct fluid cooling of the gradient coil enabled ≥50 kW of total heat dissipation. Results This design achieved a coil efficiency of 0.32 mT/m/A, allowing 200 mT/m and 500 T/m/s for a 620 A/1500 V driver. The gradient coil yielded substantially reduced echo spacing, and minimum repetition time and echo time. In high b = 10,000 s/mm2 diffusion, echo time (TE) 50% reduction compared with whole-body gradients). The gradient coil passed the American College of Radiology tests for gradient linearity and distortion, and met acoustic requirements for nonsignificant risk operation. Conclusions Ultra-high gradient coil performance was achieved for head imaging without substantial increases in gradient driver power in a whole-body 3.0T magnet after removing the standard gradient coil. As such, any clinical whole-body 3.0T MR system could be upgraded with 3-4× improvement in gradient performance for brain imaging.

Peripheral nerve stimulation limits of a high amplitude and slew rate magnetic field gradient coil for neuroimaging.

Abstract: Purpose To establish peripheral nerve stimulation (PNS) thresholds for an ultra-high performance magnetic field gradient subsystem (simultaneous 200-mT/m gradient amplitude and 500-T/m/s gradient slew rate; 1 MVA per axis [MAGNUS]) designed for neuroimaging with asymmetric transverse gradients and 42-cm inner diameter, and to determine PNS threshold dependencies on gender, age, patient positioning within the gradient subsystem, and anatomical landmarks. Methods The MAGNUS head gradient was installed in a whole-body 3T scanner with a custom 16-rung bird-cage transmit/receive RF coil compatible with phased-array receiver brain coils. Twenty adult subjects (10 male, mean ± SD age = 40.4 ± 11.1 years) underwent the imaging and PNS study. The tests were repeated by displacing subject positions by 2-4 cm in the superior-inferior and anterior-posterior directions. Results The x-axis (left-right) yielded mostly facial stimulation, with mean ΔGmin = 111 ± 6 mT/m, chronaxie = 766 ± 76 µsec. The z-axis (superior-inferior) yielded mostly chest/shoulder stimulation (123 ± 7 mT/m, 620 ± 62 µsec). Y-axis (anterior-posterior) stimulation was negligible. X-axis and z-axis thresholds tended to increase with age, and there was negligible dependency with gender. Translation in the inferior and posterior directions tended to increase the x-axis and z-axis thresholds, respectively. Electric field simulations showed good agreement with the PNS results. Imaging at MAGNUS gradient performance with increased PNS threshold provided a 35% reduction in noise-to-diffusion contrast as compared with whole-body performance (80 mT/m gradient amplitude, 200 T/m/sec gradient slew rate). Conclusion The PNS threshold of MAGNUS is significantly higher than that for whole-body gradients, which allows for diffusion gradients with short rise times (under 1 msec), important for interrogating brain microstructure length scales.

Electrical properties tomography: Available contrast and reconstruction capabilities.

Abstract: MR-based electrical properties tomography converts the MRI transmit/receive RF field measurements to tissue electrical property maps through dedicated reconstruction algorithms. Recent reports showed that despite limitations, electrical properties tomography holds promise for generating additional contrast for tumor detection and patient-specific modeling of tissue-RF field interactions. This review summarizes the available tissue electrical property contrasts and compares them with the capabilities of the most commonly used electrical properties tomography reconstruction method. Future directions and prospects of clinical translation are discussed.

Prosthetic Valve For Transluminal Delivery

Abstract: A prosthetic valve assembly for use in replacing a deficient native valve comprises a replacement valve supported on an expandable valve support. If desired, one or more anchor may be used. The valve support, which entirely supports the valve annulus, valve leaflets, and valve commissure points, is configured to be collapsible for transluminal delivery and expandable to contact the anatomical annulus of the native valve when the assembly is properly positioned. The anchor engages the lumen wall when expanded and prevents substantial migration of the valve assembly when positioned in place. The prosthetic valve assembly is compressible about a catheter, and restrained from expanding by an outer sheath. The catheter may be inserted inside a lumen within the body, such as the femoral artery, and delivered to a desired location, such as the heart. When the outer sheath is retracted, the prosthetic valve assembly expands to an expanded position such that the valve and valve support expand within the deficient native valve, and the anchor engages the lumen wall.

Heart Valve Prosthesis and Methods of Manufacture and Use

Abstract: A heart valve prosthesis is provided having a self-expanding multi-level frame that supports a valve body comprising a skirt and plurality of coapting leaflets. The frame transitions between a contracted delivery configuration that enables percutaneous transluminal delivery, and an expanded deployed configuration having an asymmetric hourglass shape. The valve body skirt and leaflets are constructed so that the center of coaptation may be selected to reduce horizontal forces applied to the commissures of the valve, and to efficiently distribute and transmit forces along the leaflets and to the frame. Alternatively, the valve body may be used as a surgically implantable replacement valve prosthesis.

Cardiac valve prosthesis

Abstract: A cardiac-valve prosthesis which can be used, for example, as a valve for percutaneous implantation. The prosthesis includes an armature for anchorage of the valve prosthesis in the implantation site. The armature defines a lumen for passage of the blood flow and supports a set of prosthetic valve leaflets, which, under the action of the blood flow, are able to move into a radially divaricated condition to enable the flow of the blood through the lumen in a first direction and a radially contracted condition, in which the valve leaflets co-operate with one another and block the flow of the blood through the prosthesis in the opposite direction. The armature includes, in one embodiment, two annular elements connected by anchor members having the capacity of projecting radially with respect to the prosthesis, and support members for the set of leaflets, the support members being carried by at least one of the annular elements so as to leave substantially disengaged the aforesaid lumen for passage of the blood.

A non-cylindrical prosthetic valve system for transluminal delivery

Abstract: A prosthetic valve assembly (820) for use in replacing a deficient native valve comprises a replacement valve supported on an expandable prosthesis frame (822) . The prosthesis frame has a non-cylindrical configuration with a preset maximum expansion diameter region about the valve opening to maintain the preferred valve geometry. The prosthesis frame may also have other regions having a preset maximum expansion diameter to avoid blockage of adjacent structures such as the coronary ostia. The prosthesis valve may be inserted into a existing artificial valve.

Method for guiding a medical device

Abstract: A device and method for valve replacement or valve repair is disclosed comprising the steps of acquiring an anatomical image of a patient, correlating the image to the patient, guiding a valve replacement delivery member or a valve repair delivery member within the patient while tracking the position of the delivery member in the patient, positioning the valve replacement member or valve repair member in a desired position to place a valve or repair valve and removing the delivery member from the patient. In one aspect of the invention, a delivery system is provided for percutaneous delivery of a heart valve to a predetermined position in the heart of a patient, where the delivery system itself includes features that allow it to be accurately positioned in the heart. In another aspect of the invention, a delivery system is provided for percutaneous repair of a heart valve in the heart of a patient, where the repair system itself includes features that allow it to be accurately positioned in the heart. In another aspect of the invention, a method and device are provided that involve imaging a native root using an interoperative technique, then introducing a device that is easily visualized in a chosen imaging modality.