Biomedical subjects

Ulrich Katscher

Publications and source records attributed to Ulrich Katscher.

3 recordsLinked to original sources

PubMed2006

Parallel RF transmission in MRI.

Following the development of parallel imaging, parallel transmission describes the use of multiple RF transmit coils. Parallel transmission can be applied to improve RF excitation, in particular, multidimensional, spatially selective RF excitation. For instance, parallel transmission is able to shorten spatially selective RF pulses in two or three dimensions, or to minimize the occurring SAR. One potential major application might be the compensation of patient-induced B(1) inhomogeneities, particularly at high main fields. This paper provides an overview of selected aspects of this new transmission approach. The basic principles of parallel transmission are discussed, initial experimental proofs are described, and the impact of error propagation on coil design for parallel transmission is outlined.

Algorithms↗

PubMed2004

Theoretical and numerical aspects of transmit SENSE.

The ideas of parallel imaging techniques, designed to shorten the acquisition time by the simultaneous use of multiple receive coils, can be adapted for parallel transmission of a spatially selective multidimensional RF pulse. In analogy to data acquisition, a multidimensional RF pulse follows a certain trajectory in k-space. Shortening this trajectory shortens the pulse duration. The use of multiple transmit coils, each with its own time-dependent waveform and spatial sensitivity, compensates for the missing parts of k-space. This results in a maintained spatial definition of the pulse profile while its duration is reduced. This paper describes the basic equations of parallel transmission with arbitrarily shaped transmit coils ("Transmit SENSE") focusing on two-dimensional RF pulses. Results of numerical studies are presented demonstrating the theoretical feasibility of the approach.

Computer Simulation↗

PubMed2003

Transmit SENSE.

The idea of using parallel imaging to shorten the acquisition time by the simultaneous use of multiple receive coils can be adapted for the parallel transmission of a spatially-selective multidimensional RF pulse. As in data acquisition, a multidimensional RF pulse follows a certain k-space trajectory. Shortening this trajectory shortens the pulse duration. The use of multiple transmit coils, each with its own time-dependent waveform and spatial sensitivity, can compensate for the missing parts of the excitation k-space. This results in a maintained spatial definition of the pulse profile, while its duration is reduced. This work introduces the concept of parallel transmission with arbitrarily shaped transmit coils (termed "Transmit SENSE"). Results of numerical studies demonstrate the theoretical feasibility of the approach. The experimental proof of principle is provided on a commercial MR scanner. The lack of multiple independent transmit channels was addressed by combining the excitation patterns from two separate subexperiments with different transmit setups. Shortening multidimensional RF pulses could be an interesting means of making 3D RF pulses feasible even for fast T(2)(*) relaxing species or strong main field inhomogeneities. Other applications might benefit from the ability of Transmit SENSE to improve the spatial resolution of the pulse profile while maintaining the transmit duration.

Computer Simulation↗