Respiration induced B1+ changes and their impact on universal and tailored 3D kT‐point parallel transmission pulses for 7T cardiac imaging

Abstract

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Tailored and universal parallel transmit broadband pulses for homogeneous 3D excitation of the human heart at 7T

“…5 Tailored pTx in the human body can be challenging and time-consuming, particularly for the excitation of different respiration states or multiple resonance frequencies, due to increased computational demands and potential motion between B + 1 -mapping and pTx data acquisition. 8,12,30 The proposed broadband UP BB provides a robust alternative to TP BB for a 1307 Hz frequency range, including all six primary fat and the water peak, acceptable FA homogeneity. On average, the broadband UP approach saves roughly 10-15 min of adjustment times for B + 1 -acquisition (3:35 min), non-Cartesian reconstruction (1 min), manual ROI drawing (3 min), and pulse design and quality checks (up to 5 min).…”

“…The safety limits were meticulously executed following established protocols and consistent with previous studies conducted in this field. 5,11,12,30,31,38…”

“…This issue has been successfully addressed using universal pulses (UP) in the human brain [27][28][29] and the human body targeting the heart. 30,31 However, such UPs cannot be applied straightforwardly for fat/water separation techniques at 7T, 5 since the resonant frequencies of fat span a range of approximately 1300 Hz at 7T. Since both UP and TP are designed to excite a single frequency, typically water, they might result in reduced excitation fidelity for other frequencies, such as those within the fat spectrum.…”

“…A fundamental problem with designing such tailored pulses in the human body is the adjustment time of 10–15 min required to acquire volunteer specific $$$ {\mathrm{B}}_1^{+} $$$/∆B 0 information, design, and apply the tailored pTx pulses. This issue has been successfully addressed using universal pulses (UP) in the human brain 27–29 and the human body targeting the heart 30,31 . However, such UPs cannot be applied straightforwardly for fat/water separation techniques at 7T, 5 since the resonant frequencies of fat span a range of approximately 1300 Hz at 7T.…”

Whole‐liver flip‐angle shimming at 7 T using parallel‐transmit kT‐point pulses and Fourier phase‐encoded DREAMB1+ mapping

“…Another patient‐friendly option would be to add respiratory binning, 69 allowing free breathing and therefore $$$ {\mathrm{B}}_1^{+} $$$ mapping flexibility. Calculating respiration‐robust k T ‐points, possibly universal, pulses based on these respiration‐resolved $$$ {\mathrm{B}}_1^{+} $$$ maps as in Aigner et al 70 would make the proposed method suitable for numerous other abdominal applications such as Dixon, 71 dynamic contrast enhancement, 72 and 4D Flow 73 …”