Project Details
Projekt
Homogenizing the B1+ field with fast online-customized (FOCUS) parallel transmission (pTx)
Applicant
Professor Armin Nagel, Ph.D.
Subject Area
Medical Physics, Biomedical Technology
Nuclear Medicine, Radiotherapy, Radiobiology
Nuclear Medicine, Radiotherapy, Radiobiology
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 500888779
This project is part of the research unit (RU) “Fast Mapping of Quantitative MR biosignatures at Ultra-high Magnetic Field”. It focuses on the development of radiofrequency (RF) pulses for magnetic resonance imaging (MRI) that enable homogeneous excitation/ saturation at ultra-high magnetic field strengths such as 7 T. At these field strengths, there are substantial technical challenges that must be overcome to enable the acquisition of high-quality MRI data. In particular, the spatial inhomogeneity of the transmit magnetic field (B1+) results in spatially varying flip angles (FAs), leading to spatially varying signal intensity and image contrast. In addition, inhomogeneities of the main magnetic field (B0) can result in image artifacts. To improve data quality in proton (1H) MRI, we will make use of a parallel transmission (pTx) system that enables the simultaneous transmission of different B1+ fields by different RF coil elements. We will develop and evaluate specially tailored pTx excitation, inversion and saturation pulses for the diffusion weighted imaging (DWI) and chemical exchange saturation transfer (CEST) projects, as well as for the clinical projects of the RU. For CEST MRI, we plan to develop a comprehensive CEST saturation pulse design that provides high-quality CEST data so that typically required B0 and B1+ correction methods can be omitted. The designed pulses shall improve the overall data quality, repeatability, and quantitative accuracy of the applied imaging techniques, while limiting additional time requirements for calibration procedures to a minimum (< 1 min). To achieve these goals, we will make use of our previously published concept of fast online-customized (FOCUS) pTx pulses that combines precalculated universal pulses with a fast subject-specific calculation of the pTx pulses. The pulses will be designed for brain and breast imaging. For the latter, a new 4-channel transmit/ 16-channel receive breast RF coil will be used. In close collaboration with another subproject of the RU working on the development of advanced RF coil technology, validation of RF field simulations will be performed to ensure safe operation in pTx mode. In addition, the concept of FOCUS pulse design will also be applied to sodium (23Na) MRI to tackle limitations caused by specific absorption rate (SAR) restrictions and B0 inhomogeneities. In line with the other methods and developments of the RU aiming to accelerate image acquisition, we will combine 23Na MRI and 23Na inversion recovery MRI into one pulse sequence. To achieve this goal, we will split the 180° inversion pulse into two 90° pulses. The duration of the second pulse will be increased to reduce SAR. To compensate for dephasing effects and to achieve high data quality, information about B0 inhomogeneities will be integrated into the pulse design.
DFG Programme
Research Units
