Purpose:
In radiotherapy (RT) based on magnetic resonance imaging
(MRI) as
the only modality, the information on electron density must be derived from the
MRI
scan by creating a so-called pseudo computed tomography (pCT). This is a nontrivial
task, since the voxel-intensities in an MRI scan are not uniquely related to electron
density. To solve the task, voxel-based or atlas-based models have typically been
used. The voxel-based models require a specialized dual ultrashort echo time
MRI
sequence for bone visualization and the atlas-based models require deformable
registrations of conventional MRI scans. In this study, we investigate the
potential of a patch-based method for creating a pCT based on conventional
T
1-weighted MRI scans without
using deformable registrations. We compare this method against two
state-of-the-art methods within the voxel-based and atlas-based categories.
Methods:
The data consisted of CT and MRI scans of five
cranial RT patients. To compare the performance of the different methods, a nested
cross validation was done to find optimal model parameters for all the methods.
Voxel-wise and geometric evaluations of the pCTs were done. Furthermore, a
radiologic evaluation based on water equivalent path lengths was carried out,
comparing the upper hemisphere of the head in the pCT and the real CT. Finally,
the dosimetric accuracy was tested and compared for a
photon
treatment plan.
Results:
The pCTs produced with the patch-based method had the best voxel-wise, geometric,
and radiologic agreement with the real CT, closely followed by the atlas-based
method. In terms of the dosimetric accuracy, the patch-based method had average
deviations of less than 0.5% in measures related to target coverage.
Conclusions:
We showed that a patch-based method could generate an accurate pCT based on
conventional T
1-weighted MRI sequences and
without deformable registrations. In our evaluations, the method performed better
than existing voxel-based and atlas-based methods and showed a promising potential
for RT of the brain based only on MRI.

/pdf/patch-based-generation-of-a-pseudo-ct-from-conventional-mri-1opw1pr1n8.pdf

Patch-based generation of a pseudo CT from conventional MRI sequences for MRI-only radiotherapy of the brain.

Increasing the switching frequency for switch mode power supplies is one of methods to achieve smaller, lighter weight and cheaper power converters. This work investigates the opportunity of using two layer circular spiral inductors implemented in a 150 µm finished thickness printed circuit board for a high frequency DC-DC converter. The inductor was tested in a 5 W buck converter switching at 10 MHz. The converter achieved 84.7% peak efficiency converting 12 V to 5 V and 78% efficiency converting 24 V to 5 V.

/pdf/design-and-implementation-of-high-frequency-buck-converter-3idzi27vue.pdf

Design and implementation of high frequency buck converter using multi-layer PCB inductor

With the increasing demand for volume reduction and efficiency improvement, very high frequency (VHF) power converters (30–300 MHz) have attracted great interest. Under such high operating frequency conditions, the value and volume of passive components can be greatly reduced, and the power density can be improved. However, many concerns and challenges accompany the increasing operating frequency, such as high switching loss, high magnetic components loss and high driving circuit loss. Including various topologies of the VHF converter, this study reviews the state-of-the-art technology involved in the VHF power converter, also encompassing the inverter stage and matching network stage. Secondly, different magnetic components and semiconductor devices were evaluated under the VHF operating condition. Thirdly, the high-efficiency driving methods, such as the resonant driving method and self-resonant driving method, were demonstrated. A guideline for converter design and system optimisation of the VHF converter and related technologies, including all components and systems, is illustrated in this study. Finally, the future research hot spots and challenges have been pointed out as guidance for further advanced VHF power conversion techniques.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2019.1301

Review of very high frequency power converters and related technologies

with the fast development of power electronics, very high frequency (VHF) power converters (30-300 MHz) gradually become research focus, which can greatly reduce the value, volume of passive components and help to improve the system power density. However, at such high operating frequency, many challenges have been proposed, such as switching characteristics, topologies characteristics and control methods. This paper starts from the development background of VHF power converters, and an overview of VHF development is described. Different topologies adopted in VHF condition are introduced and compared. At the same time, the resonant driving strategies and control methods for very high frequency converters are discussed and analyzed, which can provide guidance for further research of VHF converters.

/pdf/topologies-and-control-strategies-of-very-high-frequency-1468rnjcyz.pdf

Topologies and control strategies of very high frequency converters: A survey

This paper describes the design and evaluation of high current toroidal Printed Circuit Board (PCB) embedded inductor applicable for high frequency DC/AC converters (lower than 10MHz). The equivalent circuit model of the inductor is presented and the filtering effectiveness is verified by testing three different geometries with its own characteristics and function through a GaN converter. Besides, the temperature rise analysis is provided for all the prototypes by using finite element methods, and the obtained results are also verified by experiments. The reason behind asymmetric trend of temperature rise for the toroidal PCB embedded inductor is also discussed through both simulation and experiment, and the capability of using a heat sink to lower the temperature increment for different geometries is explained.

Design and evaluation of high current PCB embedded inductor for high frequency inverters

A new printed circuit board embedded air-core transformer/coupled inductor is proposed and presented The transformer is intended for use in power converter applications operating at very high frequency between 30 MHz to 300 MHz The transformer is based on two or more solenoid structures in different configurations The different configurations are compared for usefulness as a transformer solution, and an analytical model of the inductive parameters for the most suitable configuration is derived for design purpose The analytical model is verified by comparing calculations and measurements of prototypes The analytical model shows good agreement with the measured results The model can predict the inductive parameters of the transformer with a deviation range of approximately 3% to 22% Lastly a prototype is used in a VHF converter to achieve a rise of 22% points in efficiency

Investigation, development and verification of printed circuit board embedded air-core solenoid transformers

The present invention relates in a first aspect to a galvanically isolated power converter assembly comprising a first set of electrically interconnected resonant power inverters configured for generating respective output voltages and output currents. The galvanically isolated power converter assembly further a first positive summing node and a first negative summing node configured to combining the output voltages and output currents of the first set of resonant power inverters and a first common load circuit comprising a positive load input and a negative load input. A galvanic isolation barrier comprises first and second common isolation capacitors electrically insulating the common load circuit. Each of the first and second common isolation capacitors possesses an official safety rating.

A galvanically isolated resonant power converter assembly

This paper presents a new way of rearranging the input and output of isolated converters. The new arrangement posses several advantages, as increased voltage range, higher power handling capabilities, reduced voltage stress and improved efficiency, for applications where galvanic isolation is not a requirement. The proposed technique is particularly valuable in power conversion at very high frequencies, and may be combined with other stress reduction methods. Finally, the new arrangements are experimentally verified both on off the shelf converters and on a VHF resonant SEPIC converter. All results are in good agreement with the theory and twice the power handling capabilities and 5–10% higher efficiencies are shown.

Input-output rearrangement of isolated converters

A resonant power converter for operation in the radio frequency range, preferably in the VHF, comprises at least one PCB-embedded transformer. The transformer is configured for radio frequency operation and comprises a printed circuit board defining a horizontal plane, the printed circuit board comprising at least two horizontal conductive layers separated by an isolating layer, a first embedded solenoid forming a primary winding of the transformer and a second embedded solenoid being arranged parallel to the first solenoid and forming a secondary winding of the transformer, wherein the first and second embedded solenoids are formed in the conductive layers of the printed circuit board, wherein each full turn of an embedded solenoid has a horizontal top portion formed in an upper conductive layer, a horizontal bottom portion formed in a lower conductive layer, and two vertical side portions formed by vias extending between the upper and the lower conducting layers.

Embedded solenoid transformer for power conversion

This paper investigates a hybrid winding concept for a toroidal inductor by simulating the winding resistance as a function of frequency. The problem of predicting the resistance of a non-uniform and complex winding shape is solved using 3D Finite Element Modeling. A prototype is built and tested experimentally to verify the simulation results. Finally COMSOL LiveLink to CAD is utilized to highlight a bottleneck for this kind of winding scheme.

/pdf/investigation-of-a-hybrid-winding-concept-for-toroidal-41zmtjdxs6.pdf

Investigation of a Hybrid Winding Concept for Toroidal Inductors using 3D Finite Element Modeling

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