2026-09-29T09:58:48Zhttps://publikationen.uni-tuebingen.de/oai/requestoai:publikationen.uni-tuebingen.de:10900/1275672022-06-02T01:02:05Zcom_10900_42126col_10900_42133
Publikationssystem UB Tuebingen
advisor
Henning, Anke (Prof. Dr.)
author
Geldschläger, Ole
2022-06-01T09:41:31Z
2022-06-01
http://hdl.handle.net/10900/127567
Magnetic resonance imaging is a powerful, non-invasive technology to acquire
anatomical images from the human body. Operating at a magnetic field strength of 7T
or higher (i.e. ultrahigh field (UHF)) provides a higher signal-to-noise ratio, facilitates
higher spatial resolutions, and potentially improves diagnostic sensitivity and
specificity compared to clinical field strength, such as 1.5T or 3T.
Unfortunately, UHF is accompanied with technical hurdles, from which the most
problematic is the inhomogeneity in the radiofrequency transmit field. That can lead to
spatially varying flip angles and, thus, to signal dropouts, local brightening or spatially
altering imaging contrast.
The most flexible approach to address this issue is the parallel transmission (pTx)
technique, which itself has the disadvantage of a lengthy calibration procedure. To
overcome the calibration procedure the ‘universal pTx pulse’ (UP) concept was
introduced. It is a radiofrequency pulse design concept that relies on a pre-collected
design database. The resulting pulses then work on a wide cohort of subjects without
recalibration.
As a first step, in this PhD project the advantages of imaging the human spinal cord at
UHF were exploited. It was possible to acquire the first images from the human spinal
cord at an ultrahigh in-plane resolution of 0.15x0.15mm2 at 9.4T. The images showed
the tiny structures of the spinal cord in great detail. The signal-to-noise ratio and T2
*-
times in the human spinal cord at 9.4T were presented.
Furthermore, in this thesis the UP concept was further developed, in order to use UHF
and the pTx technique more widely.
While UPs were originally introduced for whole-brain or slice selective excitation, in
this work a feasibility study for UPs for local excitation in the human brain (i.e. exciting
only specific regions of the brain, while others should experience no excitation) was
performed. UPs that locally excite the visual cortex area were calculated. The
underlying transmit k-space trajectory for these radiofrequency pulses were ‘spiral’
trajectories. These local excitation UPs were successfully tested in vivo on nondatabase
subjects at 9.4T.
In a next step, the UP performance was further improved by optimizing the underlying
transmit k-space trajectory to match the excitation target. The trajectory optimization
and the UP design algorithms have been implemented into an open source software
package (called OTUP) and demonstrated using simulations and in vivo experiments
at 9.4T. The code was tested for three different target excitation pattern with varying
complexity.
en
ubt-podok
Universal parallel transmission pulse design for the human brain and spinal cord MRI at 9.4T
PhDThesis
URL
https://publikationen.uni-tuebingen.de/xmlui/bitstream/10900/127567/1/diss_printed_with_defenseDate_forBib.pdf
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