GSTF-based pre-emphasis to investigate the possibilities of a perfectly balanced steady state-free precession sequence
Nuclear Medicine, Radiotherapy, Radiobiology
Final Report Abstract
The aim of this project was the implementation of a GSTF-based pre-emphasis for balanced SSFP measurements. Such a pre-emphasis allows a perfectly balanced gradient scheme and a phase correction during the measurement, to avoid disruptions of the steady-state. This improvement of the sequence renders the acquired signal independent of hardware imperfections and measurement settings. Furthermore, it can then provide high quality bSSFP-images independent of the read out trajectory. Here, special focus is put on non-linear cartesian and non-cartesian readouts. Traditionally, the combination of such readout designs and bSSFP results in image artefacts, which limit the diagnostic usability. The zeroth and first order GSTF were used to calculate the necessary corrections. Effects of gradient switching on the gradients themselves and on the B0-field were compensated for a time period on 5*TR following the switching event. All corrections were directly implemented within the sequence source code as additional steps and do not require further user interaction. The evaluation of the correction in phantom measurements yields promising results. Although not all artefacts were completely eliminated, the intensity was significantly reduced using the implemented GSTF-based correction. In vivo evaluation of the implementation clearly showed that different types of artefacts, like flow or banding artefacts, have significantly higher impact on image quality. Future work should therefore focus on a combination of strategies for the avoidance of diverse artefacts. Or, where strategies are in direct contrast (e.g. perfect balance and partial dephasing), should investigate the benefits of each strategy in a definite setup.
