| Autor: |
Egger, Nico, Nagelstraßer, Sophia, Wildenberg, Saskia, Bitz, Andreas, Ruck, Laurent, Herrler, Jürgen, Meixner, Christian Rainer, Kimmlingen, Ralph, Lanz, Titus, Schmitter, Sebastian, Uder, Michael, Nagel, Armin Michael |
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| Zdroj: |
Magnetic Resonance in Medicine; Nov2024, Vol. 92 Issue 5, p1933-1951, 19p |
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Purpose: To investigate the impact of reduced k‐space sampling on B1+$$ {\mathrm{B}}_1^{+} $$ mapping and the resulting impact on phase shimming and dynamic/universal parallel transmit (pTx) RF pulse design. Methods: Channel‐wise 3D B1+$$ {\mathrm{B}}_1^{+} $$ maps were measured at 7 T in 35 and 23 healthy subjects for the heart and prostate region, respectively. With these B1+$$ {\mathrm{B}}_1^{+} $$ maps, universal phase shims optimizing homogeneity and B1+$$ {\mathrm{B}}_1^{+} $$ efficiency were designed for heart and prostate imaging. In addition, universal 4kT‐point pulses were designed for the heart. Subsequently, individual phase shims and individual 4kT‐pulses were designed based on B1+$$ {\mathrm{B}}_1^{+} $$ maps with different acceleration factors and tested on the original maps. The performance of the pulses was compared by evaluating their coefficients of variation (CoV), B1+$$ {\mathrm{B}}_1^{+} $$ efficiencies and specific energy doses (SED). Furthermore, validation measurements were carried out for one heart and one prostate subject. Results: For both organs, the universal phase shims showed significantly higher B1+$$ {\mathrm{B}}_1^{+} $$ efficiencies and lower CoVs compared to the vendor provided default shim, but could still be improved with individual phase shims based on accelerated B1+$$ {\mathrm{B}}_1^{+} $$ maps (acquisition time = 30 s). In the heart, the universal 4kT‐pulse achieved significantly lower CoVs than tailored phase shims. Tailored 4kT‐pulses based on accelerated B1+$$ {\mathrm{B}}_1^{+} $$ maps resulted in even further reduced CoVs or a 2.5‐fold reduction in SED at the same CoVs as the universal 4kT‐pulse. Conclusion: Accelerated B1+$$ {\mathrm{B}}_1^{+} $$ maps can be used for the design of tailored pTx pulses for prostate and cardiac imaging at 7 T, which further improve homogeneity, B1+$$ {\mathrm{B}}_1^{+} $$ efficiency, or SED compared to universal pulses. [ABSTRACT FROM AUTHOR] |
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Complementary Index |
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